AMMONIUM REMOVAL FROM MUNICIPAL WASTEWATER WITH ...697261/FULLTEXT01.pdf · Nitrogen removal from...

TRITA-LWR LIC-2014:01

ISSN 1650-8629

ISBN 978-91-7595-010-5

AMMONIUM REMOVAL FROM MUNICIPAL

WASTEWATER WITH APPLICATION OF ION

EXCHANGE AND PARTIAL

NITRITATION/ANAMMOX PROCESS

Andriy Malovanyy

February 2014

Andriy Malovanyy TRITA-LWR LIC-2014:01

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© Andriy Malovanyy 2014 Licentiate thesis Division of Land and Water Resources Engineering Department of Sustainable development, Environmental science and Engineering Royal Institute of Technology (KTH) SE-100 44 STOCKHOLM, Sweden Reference should be written as: Malovanyy, A., 2014 Ammonium removal from municipal wastewater with application of ion exchange and partial nitrita-tion/Anammox process. Licentiate Thesis, TRITA-LWR LIC-2014:01, 30 p.

Ammonium removal with application of ion exchange and partial nitritation/Anammox process

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ACKNOWLEDGEMENTS

This study was carried out in a joint co-operation between Royal Institute of Technology (KTH), Department of Sustainable Development, Environmental Science and Engineering, and Lviv Polytechnic National University (LPNU), Department of Industrial Ecology and Sustainable Environmental Manage-ment within Visby Program. First of all I would like to acknowledge Ministry of Education and Science of Ukraine for individual scholarship for my PhD studies. Financial support from Swedish Institute that granted individual scholarship and financed the project “Future urban sanitation to meet new requirements for water quality in the Baltic Sea region”, from which part of my stay in Sweden was financed, is highly appreciated. Experimental part of work, performed at Hammarby Sjöstadsverk (Center for innovative municipal wastewater treatment, Stockholm, Sweden), would not be possible without financing from Swedish Water Development (SVU) and Swedish Environmental Research Institute (IVL), which is gratefully acknowledged. Prize for the best Master Thesis in 2009, received from ITT (now Xylem Water Solutions), helped balance my family budget for all these years of commuting between Ukraine and Sweden. I would like to express my gratitude to my supervisors prof. Elzbieta Plaza and prof. Yosyp Yatchyshyn who guided me through this long process of experi-ments, data analyses and preparing manuscripts. I would also like to thank my co-supervisor Jozef Trela for practical help with operation of reactors. Assis-tance of Hammarby Sjöstadsverket staff, especially Lars Bengtsson, Christian Baresel and Mila Harding is highly appreciated. Special thanks go to Jingjing Yang whose help, discussions and support helped me during the years of PhD studies. Thanks to Razia Sultana for the many discussions we had. Help of Master students Xin Zhang, Arslan Ahamd and Isaac Owusu-Agyeman with performing experimental work is highly appreci-ated. Last but not least, thanks to all staff of Land and Water Resources Engi-neering Division of Sustainable Development, Environmental Science and Engineering Department (KTH) and Industrial Ecology and Sustainable Envi-ronmental Management Department (LPNU) for your help. Finally I would like to thank my family, and especially my wife, for love and support.


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TABLE OF CONTENTS

Acknowledgements ........................................................................................................ iii List of papers ................................................................................................................. vii Acronyms and Symbols .................................................................................................. ix Abstract ............................................................................................................................ 1 1. Introduction............................................................................................................ 1

1.1. Biological nitrogen transformation processes ................................................ 2

1.2. Application of Anammox to mainstream – advantages and challenges ....... 3

1.3. Previous studies on direct application of Anammox process for mainstream wastewater treatment.................................................................................................. 4

2. Combining physical /chemical and biological methods of nitrogen removal .. 5

2.1. Possibilities for ammonium concentration ..................................................... 5

2.2. Proposed nitrogen removal system ................................................................. 6

2.3. Ammonium removal with ion exchange ......................................................... 6

2.4. Adaptation of partial nitritation/Anammox biomass to elevated salinity .... 7 3. Thesis objectives .................................................................................................... 8 4. Materials and methods .......................................................................................... 9

4.1. Ion exchange materials .................................................................................... 9

4.2. Ion exchange experiments (Paper I and II) ................................................... 9

4.3. Batch tests on spent regenerant treatment (Paper II) ................................. 10

4.4. Partial nitritation/Anammox MBBRs (Paper III) ....................................... 10

4.5. Activity tests (Paper II and III) ..................................................................... 11

4.6. Analytical methods ......................................................................................... 11 5. Results .................................................................................................................. 11

5.1. Concentration of ammonium by ion exchange (Paper I) ............................ 11 5.1.1. Comparison of ammonium exchange capacity .................................................................. 11 5.1.2. Regeneration with NaCl ................................................................................................... 11 5.1.3. Selectivity of ammonium exchange ................................................................................... 13 5.1.4. Predicting ammonium breakthrough ................................................................................ 13 5.1.5. Wastewater content, hydraulic loading influence ............................................................... 14

5.2. Partial nitritation/Anammox biomass adaptation to elevated salinity (Paper III) ................................................................................................................. 14

5.3. Influence of NaCl concentration on non-adapted and adapted biomass (Paper II and III) ...................................................................................................... 15

5.4. System testing in batch mode (Paper II) ...................................................... 17 5.4.1. Ammonium concentration from municipal wastewater ..................................................... 17 5.4.2. Biological nitrogen removal from spent regenerant ........................................................... 18

6. Discussion ............................................................................................................ 19

6.1. Ion exchange; which material and which conditions? ................................. 19

6.2. Adaptation to salinity ...................................................................................... 22

6.3. Possibilities of integration in wastewater treatment process ...................... 22

6.4. Challenges and perspectives .......................................................................... 22 7. Conclusions .......................................................................................................... 24 8. Further research ................................................................................................... 25


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References ...................................................................................................................... 26


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LIST OF PAPERS

This thesis is based on results presented in the following papers, which are appended in the end of the thesis:

I. Malovanyy, A., Sakalova, H., Yatchyshyn, Y., Plaza, E., Malovanyy, M., 2013. Concentration of ammonium from municipal wastewater using ion exchange process. Desalination. 329, 93-102.

II. Malovanyy, A., Plaza., E, Trela, J., Malovanyy, M., 2014. Combination of ion exchange and partial nitritation/Anammox process for ammonium removal from mainstream municipal wastewater. Submitted to Water Science and Technology.

III. Malovanyy, A., Plaza, E., Trela, J., Malovanyy, M., 2014. Ammonium removal by partial nitritation and Anammox processes from wastewater with increased salinity. Submitted to Environmental Technology.

Other papers, which are not appended in the thesis: Malovanyy, A., Plaza, E., Trela, J., 2009. Evaluation of factors influ-encing specific Anammox activity (SAA) using surface modelling. Proceedings of Polish-Ukrainian-Swedish seminar “Research and application of new technologies in wastewater treatment and municipal solid waste disposal in Ukraine, Sweden and Poland”, Stockholm, Sweden. E. Plaza, E. Levlin (editors). TRITA-LWR.REPORT 3026. Malovanyy, A., Plaza, E., Yatchyshyn, Y., 2011. Concentration of ammonium from wastewater using ion exchange materials as a preceding step to partial nitritation / Anammox process. Proceedings of International Conference “Environmental (Bio)Technologies”, Gdansk, Poland. Malovanyy, A., Plaza, E., Yatchyshyn, Y., Trela, J., Malovanyy, M., 2012. Removal of nitrogen from the main stream of municipal wastewater treatment plant with combination of Ion Exchange and CANON process (IE-CANON) - effect of NaCl concentration. Proceedings of Polish-Ukrainian-Swedish seminar “Future urban sanitation to meet new requirements for water quality in the Baltic Sea region”, Krakow, Poland. E. Plaza, E. Levlin (editors). TRITA-LWR.REPORT 3031.


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ACRONYMS AND SYMBOLS

AOB Ammonium Oxidizing Bacteria BOD Biochemical Oxygen Demand BV Bed Volume Ceff Effluent Concentration COD Chemical Oxygen Demand DO Dissolved Oxygen FA Free Ammonia FNA Free Nitrous Acid GC Grit Chamber HRAS High Rate Activated Sludge HRT Hydraulic Retention Time IE Ion Exchange MAP Magnesium Ammonium Phosphate MBBR Moving Bed Biofilm Reactor MW Municipal Wastewater NOB Nitrite Oxidizing Bacteria NLR Nitrogen Loading Rate NRR Nitrogen Removal Rate NZ Natural Zeolite OUR Oxygen Uptake Rate PN/A Partial Nitritation/Anammox PS Primary Settler SAA Specific Anammox Activity SAC Strong Acid Cation SCR Screens SF Sand Filter SRT Solids Retention Time SW Synthetic Wastewater SZ Synthetic Zeolite TH Total Hardness TOC Total Organic Carbon TN Total Nitrogen UASB Upflow Anaerobic Sludge Blanket Veff Volume of solution applied WAC Weak Acid Cation WWTP WasteWater Treatment Plant


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ABSTRACT

Nitrogen removal from municipal wastewater with application of Anammox process offers cost reduction, especially if it is combined with maximal use of organic content of wastewater for biogas production. In this study a new tech-nology is proposed, which is based on ammonium concentration from municipal wastewater by ion exchange followed by biological removal of ammonium from the concentrated stream by partial nitritation/Anammox process. In experiments on ammonium concentration four the most common ion exchange materials were tested in packed bed columns, namely strong and weak acid cation exchange resins, natural and synthetic zeolites. Experiments with synthetic wastewaters with different content and municipal wastewater showed that strong acid cation resin is the most suitable for ammonium concentration from municipal wastewater due to its high exchange capacity and fast regeneration. Since NaCl was used for regeneration of ion exchange materials, spent regenerant had elevated salinity. Experiments with activity determination showed that both nitritation and Anammox bacteria are inhib-ited by NaCl, where effect on Anammox bacteria is more severe. Adaptation of partial nitritation/Anammox biomass was studied using two strategies of salinity increase and it was possible to adapt the biomass to NaCl content of 10-15 g/L. The technology was tested in batch mode using strong acid cation resin for ammonium concentration from pretreated municipal wastewater, and partial nitritation/Anammox biomass for nitrogen removal from concentrated stream. It was shown that it is possible to remove 99.9% of ammonium from wastewater with ion exchange while increasing concentration of ammonium in spent regenerant by 18 times. Up to 95% of nitrogen from spent regenerant was removed by partial nitritation/Anammox biomass in batch tests. Moreover, possibilities of integration of the technology into municipal wastewater treatment technology, challenges and advantages were discussed.

Key words: wastewater; nitrogen removal; ion exchange; nitritation; Anammox

1. INTRODUCTION

Nitrogen, phosphorus and potassium are the chemical elements that are required in the biggest amounts (except of carbon, hydro-gen and oxygen) for growth of a living mat-ter. However, if concentrations of these elements become too high, it causes envi-ronmental problems. The process of exceeding the safe concentrations of nutri-ents in water bodies is called eutrophication. It can be caused by natural processes, such as inflow of high amounts of organic matter and nutrients with storm waters, but more often is a result of anthropogenic activity. The main outcome of higher nutrients avail-ability is the growth of phytoplankton. This leads to deterioration of water quality and increases the health risk if such water is used

for recreation purposes or as a drinking water source. Moreover, when phytoplank-ton quantity becomes high, competition for oxygen increases. During the night time it consumes dissolved oxygen (DO) from waters, which create the effect of “bottom death”, when fish and other oxygen-dependent organisms survive only in the top part of a water column. Among the point sources of nutrients dis-charge, the biggest contributors are wastewater treatment plants (WWTP) which treat municipal and industrial wastewaters. Therefore, the quality of wastewater treat-ment is strictly regulated in all the developed countries. In European Union the main law which regulates the quality of municipal wastewater treatment is the Directive


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91/271/EEC (EU Commission, 1991). According to the Directive, big municipal wastewater treatment plants (load of more than 100 000 person equivalents) should remove 70-80% of inflowing nitrogen and decrease concentration of total nitrogen (TN) to less than 10 mg/L if treated wastewater is discharged to a sensitive area. Therefore, it is important to develop wastewater treatment technologies which allow WWTP to reach the required efficien-cies and at the same time do not bring high treatment cost.

1.1. Biological nitrogen transfor-mation processes Nitrogen is removed from municipal wastewater by biological processes, per-formed by microorganisms. The main bio-logical nitrogen transformation processes involved are assimilation, nitrification, deni-trification and Anammox (Fig. 1). Nitrogen assimilation is the process of trans-formation of inorganic nitrogen into organic nitrogen-containing compounds during cell growth. The optimal ratio of BOD:N:P, which allows removal of nutrients by only assimilation, is 100:5:1 (Tandoi et al., 2006). Usually municipal wastewater contains more nitrogen and other biological processes need to be involved to reach high efficiency of nitrogen removal. Nitrification is a two-step autotrophic process of ammonium oxidation to nitrite by

ammonium oxidizing bacteria (AOB) with following oxidation further to nitrate by nitrite oxidizing bacteria (NOB). The complete reactions of these processes, which include biomass production, are as follows (Wiesmann, 1994):

1.382 1.982 →

0.018 0.982 (1)

1.04 1.891

0.0025 0.01

0.0025 0.488 → (2)

0.0025 0.0075 Denitrification is a process of nitrite and nitrate reduction to dinitrogen gas, which is performed by heterotrophic bacteria at the absence of oxygen (anoxic conditions). Organic carbon is required as an energy source and if the acetic acid is used, the metabolism of reaction can be written as:

3 8 →

4 10 6 8 (3) Until recently it was believed that oxidation of ammonium can proceed only in the pres-ence of oxygen. In 1977 it was shown by thermodynamic calculations that it is possible that there could exist lithotrophic bacteria, which can oxidize ammonium using nitrate or carbon dioxide as an electron acceptor (Broda, 1977). In 1992 the first experimental proof of ANaerobic

Fig. 1. Nitrogen cycle (modified after Naqvi (2012)).


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AMmonium OXidation (Anammox) bacteria existence was published (Mulder, 1992). It was believed that nitrate is an electron acceptor in the reaction. However, later it was proven that nitrite is a real acceptor (van de Graaf et al., 1995). The complete reac-tion, which includes biomass generation, was experimentally obtained in Strous et al. (1998):

1.32 0.066

0.13 → 1.02 0.26 (4)

0.066 . . 2.03 Anammox bacteria are autotrophs, which means that they do not require organic car-bon for biomass production, but instead utilize inorganic carbon. According to eq. 4, biomass production of Anammox reaction is 0.049 g/g N. This value is lower than for AOB and NOB (0.14 g/g N and 0.072 g/g N respectively in Blackburne and Vidivelu (2007)) and much lower than for heterotrophic denitrifiers (2.04 g/g N in Koike and Hattori (1975) and 1.1 g/g N in Strohm et al. (2007)). In Strous et al. (1998) maximum specific growth rate was determined to be 0.0027 h-1. Low specific growth rate and low biomass yield of Anammox bacteria result in long start-up period for Anammox reactors and poses a challenge for application of the process for treatment of low-concentrated wastewater. Based on nitritation and Anammox pro-cesses, fully autotrophic nitrogen systems were developed, where roughly half of ammonium is converted to nitrite by AOB and the produced nitrite is used as an elec-tron acceptor to remove the remaining ammonium by Anammox process. This combination is often referred to as partial nitritation/Anammox process or deammoni-fication process, and can be performed in separate reactors (2-stage process) or in one reactor (1-stage process). Biological reaction in 1-stage process, obtained after combining eq. 1 and eq. 4 can be written as:

0.793 1.165 →0.435 0.111 0.012 (5) The partial nitritation/Anammox process was mostly studied for wastewater with high nitrogen concentration (Cema et al., 2006;

Szatkowska et al., 2007; Yang et al., 2013) and applied already in a number of full-scale plants treating anaerobic digestion reject water (Wett, 2006; van der Star et al., 2007; Plaza et al., 2011). In this way nitrogen load to mainstream wastewater treatment plant could be lowered and nitrogen could be removed from side-stream with much higher rates. Application of nitrification-denitrification process would require exter-nal carbon addition, since reject water has a low COD:N ratio.

1.2. Application of Anammox to mainstream – advantages and challenges In many publications it is discussed that treatment of supernatant from digested sludge dewatering process by autotrophic nitrogen removal is more sustainable than nitrification/denitrification and allows saving of 50-60% of oxygen, does not need chemicals addition, produces little sludge and less greenhouse gases (Fux and Siegrist, 2004; Chen et al., 2009; Park et al., 2010). Treatment of such a wastewater stream, which is characterized by high ammonium concentration and low content of easy degradable organic matter, with traditional nitrification/denitrification process always requires addition of external carbon source, which compromises economy of the treatment. A new challenge is to apply Anammox process for nitrogen removal in a main stream of WWTP at low temperatures and low ammonium concentrations. The trend for developing future wastewater treatment is to treat wastewater as a resource trying to recover as much of energy as pos-sible in the form of biogas while satisfying requirements for removal of nutrients. In such systems the first treatment step can be based on organic matter removal by preci-pitation and coagulation/flocculation (Watanabe and Kanemoto, 1993; Guida et al., 2007), use of high-rate activated sludge (HRAS) process for maximum removal of organics in the form of sludge (Versprille et al., 1985) or a combination of these methods. Moreover wastewater can be


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treated anaerobically in, for example, upflow anaerobic sludge blanket (UASB) reactor (Mahmoud et al., 2004). However, effluent from organics removal step has low COD/N ratio, which makes impossible to remove nitrogen through nitrification-denitrification without external carbon addition. Utilization of Anammox process for treatment of such wastewater gives most savings. In Anammox-based systems for nitrogen removal in mainstream more biogas could be produced without compromising nitrogen removal efficiency. However, there are several challenges of partial nitritation/Anammox process appli-cation for treatment of mainstream wastewater:

Effective retention of Anammox biomass in a reactor is needed. This is because inflowing nitrogen concentration in main-stream wastewater is low (25-50 mg NH4

+-N/L) and together with low yield and growth rate of Anammox bacteria it leads to low Anammox biomass production per 1 m3 of treated wastewater.

Low nitrogen transformation rates. Change of reaction rate with changing temperature is usually described by activa-tion energy, where lower activation energy means that temperature dependence of reaction is lower. Activation energies for nitritation and Anammox processes are similar and are in the ranges of 60-72 kJ/mol (van Hulle et al., 2010) for nitritation and 63-85 kJ/mol (Strous et al., 1999; Dosta et al., 2008; Fernández et al., 2010) for Anammox process. Based on activation energies, process rates of the two steps change similarly with temperature change and decrease of temperature from 30 °C (temperature in reactor treating reject water) to 15 °C (temperature of municipal wastewater during winter period) should lead to decrease of rate by 71-83 %. Moreover, because of lower ammonium and nitrite concentrations in reactor even lower rate can be expected.

Suppression of NOB growth. At lower temperatures NOB have higher growth rate than AOB which makes selection of AOB

over NOB not always successful. Moreover, NOB suppression by free ammonia inhibi-tion is not possible because of low ammo-nium concentration. If NOB overcompete AOB, it leads to nitrate accumulation, which decreases significantly nitrogen removal efficiency.

1.3. Previous studies on direct application of Anammox process for mainstream wastewater treatment There were several studies conducted on investigating possibility of Anammox process application for nitrogen removal from mainstream wastewater after a step of organic matter removal. Different strategies of NOB suppression were discussed and tested in Regmi et al. (2013) using two-stage partial nitrita-tion/Anammox process. Anammox reactor showed good performance. However, nitro-gen removal efficiency of the whole system depended on partial nitritation step, where nitrate concentration was in average higher than nitrite concentration. Moreover, large part of nitrogen (often more than 50%) was removed in partial nitritation reactor, which indicates high heterotrophic denitrification activity. In Wett et al. (2013) results of Anammox process application in full scale plant are presented and it was shown that it is possible to maintain AOB activity in the reactor higher than activity of NOB. However, nitrogen removal efficiency and rate were not reported in the paper. Perfor-mance of one stage partial nitrita-tion/Anammox reactor with granular biomass is reported in Lotti et al. (2013). During the periods of stable reactor opera-tion average nitrogen removal efficiency of 29 % was observed, reaching to 48.8 % during the periods of best performance. It was shown that AOB/NOB competition can be successful at relatively high wastewater temperatures of 28-32 °C (Cao et al., 2013). Moreover, in the study it was esti-mated that approximately 75% of all the nitrogen removal was due to Anammox bacteria activity. However, with the step-feed wastewater treatment scheme that was used in the study organic content of


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wastewater could not be utilized efficiently for energy production and, therefore, advantages of Anammox process could not be fully used. Moreover, such results would be hard to reach in temperate and cold climate areas, where wastewater temperature is much lower. Therefore, until now there are no studies that show application of Anammox process for direct treatment of mainstream wastewater that has low temperature, where high efficiency was maintained during long period.

2. COMBINING PHYSICAL/

CHEMICAL AND BIOLOGICAL

METHODS OF NITROGEN

REMOVAL

Until now researchers were concentrated on finding possibility of direct treatment of mainstream wastewater with low ammonium content and low temperature by Anammox process, and several challenges were identi-fied. The other option is to first concentrate ammonium from wastewater and then remove it from concentrated secondary stream. In this case the knowledge about controlling the process when treating ammonium-rich wastewaters can be applied with slight modifications.

2.1. Possibilities for ammonium concentration The possible options that allow concentrating ammonium from mainstream wastewater include:

Assimilation of nitrogen by bacteria, followed by biomass digestion. As discussed earlier in chapter 1.1, when heterotrophic biomass grows, the ratio of COD:N:P consumption is 100:5:1 in systems with short sludge age. If sludge age is longer, then some part of biomass dies-off and the nutri-ents consumption is lower. When biomass is separated from wastewater and digested, nitrogen and phosphorus are released and their concentrations in reject water are about 50 times higher than in municipal wastewater. However, only part of nitrogen

can be concentrated in this way because of COD limitation.

Assimilation of nitrogen by algae. Algae are regarded to be the future source of renewable fuel production, since they have the highest yield per area unit and their production does not compete with culturing food crops. Since algae are phototrophic organisms, organic carbon is not required and it can remove all the remaining nitrogen from wastewater. After energy is extracted from algae (e.g. in the form of biogas), nitrogen-rich secondary stream is formed, the same as in the case of sludge digestion (Razzak et al., 2013).

Precipitation as magnesium ammonium phosphate (MAP). It is possible to precipi-tate both phosphorus and nitrogen in the form of MgNH4PO4. Since molar ratio of N:P in wastewater is always higher than 1, there is not enough phosphorus to bind all the ammonium. It is possible with the help of bacteria to dissolute MAP, remove ammonium and use Mg and P repeatedly until all the nitrogen is removed (Kulander and Mönegård-Jakobsson, 2010). The disad-vantage of such a concentration process is that MAP precipitation required pH around 9.5-10, which brings high cost for pH change.

Reverse osmosis, concentration by freezing. It is theoretically possible to concentrate nitrogen by applying advanced technologies, like reverse osmosis and concentration by freezing. However, these technologies bring very high cost of treat-ment and, therefore, are not feasible for municipal wastewater treatment (Owusu-agyeman, 2012; Sarker, 2012).

Ion exchange. Concentration of ammo-nium with ion exchange is a relatively cheap technology. It gives possibility to selectively concentrate ammonium ions without concentrating unionized inorganic and organic substances and suspended material. Therefore, in this study concentration of ammonium only by ion exchange technology is studied.


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2.2. Proposed nitrogen removal system In this study two-step process with concen-tration of ammonium from municipal wastewater followed by removal of ammo-nium from concentrated solution by partial nitritation/Anammox process was studied (Fig. 2). In such system wastewater passes through column filled with ion exchange material, where ammonium ion is exchanged for a sodium ion. When the capacity of material becomes exhausted, ammonium is detected in the effluent. Then, the ion exchange material can be regenerated by application of concentrated NaCl solution. Concentration of ammonium in spent regenerant is much higher than in influent mainstream wastewater and, therefore, some limitations of Anammox process can be overcome. Spent regenerant can be treated with partial nitritation/Anammox process in, for example, moving bed biofilm reactor (MBBR). System effectiveness depends on two tasks: how to make the ammonium concentration with ion exchange as efficient

as possible; and how to reach high rates treating spent regenerant, which has an ele-vated salt content.

2.3. Ammonium removal with ion exchange Comparing to other alternatives of ammo-nium concentration ion exchange has the advantage that it not energy intensive, process needs short contact time and is simple to operate. Natural zeolites are often used as ion exchange material for ammo-nium removal. Depending on origin of zeo-lite, particle size and wastewater type exchange capacity of 0.2-0.68 meq/g or 0.19-0.65 eq/L can be expected when treating municipal wastewater or greywater (Cooney et al., 1999; Widiastuti et al., 2011). This corresponds to nitrogen content of less than 1% and therefore one-time use of zeo-lite for large-scale nitrogen removal systems cannot be a sustainable option. Zeolites with different properties can also be synthesized (Breck, 1974; Zhang et al., 2011). Strong acid cation (SAC) resin offers high (approximately 2 eq/L) exchange capacity

Fig. 2. Proposed system, based on combination of ion exchange and partial nitritation/Anammox process.


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and is often used for water softening. Even higher capacity can be reached using weak acid cation (WAC) resin (approximately 4 eq/L), especially in the systems designed for divalent metal ions removal. Combined nitrogen and phosphorus removal from industrial effluents that have ion content similar to that of municipal wastewater by application of SAC resin with strong base anion resin was studied in Chen et al. (2002). It was shown in that study that capacity of SAC resin for ammonium was similar to capacity of natural zeolite. This suggests that it might be possible to use SAC resin in systems treating municipal wastewater. However, there were no studies in which SAC and WAC resins where tested for ammonium removal from municipal wastewater. Its high capacity makes them perspective for such wastewater treatment, even though it is not selective for ammo-nium ions. One-time use of ion exchange material is not feasible and materials are usually regenerated by application of regenerant with high concentration of salt or acid. Moreover, if spent regenerant is treated by one of the possible methods and nitrogen is removed from it, it can be used repeatedly bringing lower costs for regenerant recharging. The best performance of ammonium concentra-tion with ion exchange can be reached if material with high ammonium exchange capacity which offers high rate of ammo-nium removal and material regeneration is used. Moreover, it is better if ammonium is removed selectively from wastewater leaving other ion concentrations on the same level. Spent regenerant has high residual concen-tration of acid or salt which should be taken into account if nitrogen is to be removed biologically.

2.4. Adaptation of partial nitrita-tion/Anammox biomass to elevated salinity Anammox bacteria are present in virtually all the water systems and different genera of bacteria are found in systems that have dif-ferent water properties. Anammox bacteria of Candidatus Scalindua genus are found in

marine sediments (Dalsgaard and Thamdrup, 2002; Kuypers et al., 2003; van de Vossenberg et al., 2008). Since sea water has average salt concentration of 30 g/L anaerobic ammonium oxidation can be performed in high salt content environ-ments. In freshwater systems Anammox bacteria of freshwater genus Candidatus Brocadia, Candidatus Kuenenia, Candidatus Anammoxoglobus and others are found. Adaptation of Anammox of freshwater genera was studied in a number of works. Liu et al. (2008) showed that without salinity adaptation ammonium oxidation to nitrite is not inhibited to the level of 10 g NaCl/L and decreases with further increase of salinity to 15 g NaCl/L. Also it was proven in the work that salinity increase is more tolerated by ammonium oxidisers than nitrite oxidizers and can be used as a method of nitratation inhibition. At 10 g NaCl/L salinity no Anammox inhibition was observed. Based on PCR-DGGE analysis Anammox bacteria belonged to group KSU-1. Liu et al. (2009) succeeded to adapt Anammox bacteria of groups KSU-1, AnDHS-2 and KU2 in an anaerobic reactor to work at salinities of up to 30 g NaCl/L. Salinity was increased stepwise during 93 days. Further increase of salinity to 33 g/L led to Anammox inhibition. Dapena-Mora et al. (2010) also studied a possibility to run the Anammox process in saline environments and the results clearly show that small increase of salinity to 3 g NaCl/L increases specific Anammox activity (SAA) of Candidatus Kuenenia stuttgartiensis specie where further increase leads to decrease of SAA. After a 53-days adaptation, SAA was the highest at 15 g NaCl/L salinity. Application of 20 g/L salinity led to decrease of activity. Windey et al. (2005) also managed to adapt culture of nitritation and Anammox bacteria to efficiently remove ammonium from synthetic wastewater with salinity of 30 g NaCl/L. The period of adaptation was about 160 days during which salinity was stepwise increased with some loading rate correction. It was shown that shock load of 30 g/L of salinity leads to loss of 43% of


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specific nitritation activity and almost complete inhibition of Anammox process. After the adaptation of culture to 30 g/L salinity nitrogen removal capacity decreased by 31 % comparing to reference period with no salt addition. In research by Kartal et al. (2006) Anammox biomass comprised of equal shares of fresh-water bacteria Candidatus Kuenenia stuttgartiensis and marine bacteria Candidatus Scalindua wagneri was used. Salinity of feed solution was gradually increased during 90 days to concentration of 30 g/L and maintained at this level during 310 days. At the end of this period the share of freshwater Anammox specie was 70%. Increase of salinity to 45 g/L led to complete loss of Anammox activity after 5 days. Short-term salinity increase did not have such a drastic influence. Adapted biomass had activity maximum at 30 g NaCl/L and Anammox activity was observed even at 75 g/L (Fig. 3). In Jin et al. (2011) influence of salinity on activity of Anammox biomass working in UASB reactor was studied. Results show that shock increase of salinity to 30 g/L cause 67.5% activity drop while step-wise adaptation to the same salinity level during 77 days cause decrease of activity only by 45%. In Yang et al. (2011) Anammox reac-tor was operated with a step-wise increase of wastewater salinity to 30 g/L during 60 days. After adaptation period, efficiency of nitro-

gen removal was around 85% at nitrogen removal rate (NRR) of 4.5 kg N/(m3day), which is the highest result among the described studies. Microbiological analysis showed that Anammox bacteria of groups AnDHS-2 and KU2 were dominating in the culture. In the described studies it was proven that Anammox bacteria of Candidatus Scalindua and Candidatus Kuenenia genera as well as Anammox bacteria of groups KSU-1, AnDHS-2 and KU2 can be used for treat-ment of wastewaters with salinity of 30 g/L. Bacteria of genus Candidatus Brocadia was found as a part of Anammox culture which worked at salinity of 10 g/L in Zhang et al. (2010). Anammox bacteria of genera Candi-datus Anammoxoglobus and Candidatus Jettenia were not found in biomass working at elevated salinity. In most of these studies influence of salinity only on Anammox bacteria was studied using synthetic wastewater. Anammox reactor was fed with real wastewater (partially nitrified reject water after anaerobic digestion of fish canning effluent with NaCl content 8-10 g/L) was shown only in Dapena-Mora (2006). Moreover, adaptation of both nitrifiers and Anammox bacteria in rotating biological contactor was presented in Windey et al. (2005).

3. THESIS OBJECTIVES

The overall objective of the Licentiate Thesis is to study the possibility of nitrogen removal from municipal wastewater by combining concentration of ammonium by ion exchange and removal of nitrogen by partial nitritation/Anammox process. The specific objectives are:

i. Compare the performance of the most common used cation exchange materials in the process of ammo-nium concentration from municipal wastewater (Paper I);

ii. Test the proposed technology of ammonium removal in batch mode and investigate the influence of NaCl on performance of partial nitrita-tion/Anammox process (Paper II);

Fig. 3. Short batch experiments with salt and freshwater adapted Anammox biomass under different salt concentrations (Kartal et al., 2006).


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iii. Develop a strategy of partial nitrita-tion and Anammox bacteria adapta-tion to salinity and to assess stability of biological culture working at elevated NaCl content (Paper III).

4. MATERIALS AND METHODS

4.1. Ion exchange materials In this study four types of ion exchange materials were used: natural and synthetic zeolites and strong and weak acid cation exchange resins.

Natural zeolite rock (NZ) originated from Sokyrnytsya deposit (Transcarpathian region, Ukraine), which is one of the biggest zeolite deposits in the world. Mineral content of zeolite rock is comprised of zeo-lite clinoptilolite (70-75%) with admixtures of quartz, calcite, biotite, muscovite, chlorite, and montmorillonite (Sprynskyy et al., 2005).

Synthetic zeolite of NaA type (SZ) has the diameter of pores of 4 Å, which explains its commercial name of “zeolite 4A”. The brutto formula of zeolite is Na12[Al12Si22O48]27 H2O. This zeolite is chemically stable; contact with water and weak alkaline solutions does not cause structural changes. However, contact with strong acids lead to change of zeolite struc-ture. Synthetic zeolites are produced as small crystals with particle size of 1-6 µm. In

wastewater treatment granulated zeolites with bigger particle sizes are used.

Strong acid cation (SAC) resin is composed of polystyrene matrix, cross-linked by divinilbenzene, which contains sulphonic groups. Hydrogen ion of sulphonic group dissociates easily and can change for other ions, depending on cation content of environment. In this work SAC resin KU-2-8 was used. It is a gel-type resin with divinilbenzene content of 8%, grain size of 0.6-1.2 mm and total static capacity of 1.8 eq/L.

Weak acid cation (WAC) resin has carboxylic functional groups, where hydroxen ions dissociate to a much lesser extent than in SAC resin. Such a resin has very high content of mobile ions, which results in high exchange capacity. In this work WAC resin Purolite C104 was used. It is a gel-type resin with grain size of 0.3-1.2 mm and a total static capacity of 4.5 eq/L.

4.2. Ion exchange experiments (Paper I and II) All the experiments were done using glass columns with inner diameter of 10 mm, filled with the ion exchange materials described above (Fig. 4). To ensure the same conditions for all the materials, natural and synthetic zeolites were ground and sieved

Fig. 4. Ion exchange experiments setup (Paper I).


10

and the fraction 0.71-1.00 mm was used for experiments, which is close to resin grain size. After filling the columns all the materials were transferred to Na-form by contacting with NaOH or NaCl during 16 h. In total, there were 23 runs performed, which included phases of saturation and regeneration. Three types of synthetic wastewater solutions and a real municipal wastewater (MW) pretreated in primary settler and UASB reactor and filtrated through 1.6µm pore size filter were used for studying ammonium removal by ion exchange. The first type of synthetic wastewater solution (SW1) was prepared by dissolving NH4Cl in deionized water. The second solution (SW2) had cation content typical to real municipal wastewater in concentrations as described in Semmens et al. (1981) and had and pH of 9.12. The third solution (SW3) had the same cation content as in SW2 but pH of 6.2. Dynamic capacity was determined by integration of area above breakthrough curve using breakthrough concentration of 2 mg NH4

+-N/L. Ion exchange materials were regenerated counter currently using 10-30 g/L (0.17-0.51 M) NaCl solutions or 0.17 M HCl solution.

4.3. Batch tests on spent regenerant treatment (Paper II) Removal of ammonium from spent regen-erant of ion exchange was studied using 1 L reactor equipped with magnetic stirrer and air supply. Reactor was filled with 700 mL of spent regenerant from preceding ion exchange experiment and 250 mL of biomass carriers with biofilm of partial nitritation and Anammox biomass. For satisfying alkalinity need of nitritation reaction, liquid was supplemented with 8.4 mg of NaHCO3 per every mg of NH4

+-N, which corresponds to 135% of theoretical alkalinity, needed for ammonium removal through partial nitrita-tion/Anammox. Addition of NaHCO3 was divided into two equal portions, which were added in the beginning of batch test, and after 26 h. DO concentration was main-tained on the level of 1.5 mg/L in the first

test and on 1.0 mg/L in the following two tests in order to avoid over-aeration.

4.4. Partial nitritation/Anammox MBBRs (Paper III) In Paper III two identical moving bed biofilm reactors (MBBR) (Fig. 5) were used for studying adaptation to elevated salinity. The reactors were operated according to different strategies of salinity increase. The salinity increase step was 5 g/L in reactor 1 and 2.5 g/L in reactor 2. In previous studies salinity was increased after passing 3 to 65 days. Therefore it was chosen to have an adaptation period of 14 days at every salinity step in this study, which was prolonged if required. Each reactor had a volume of 10 L with a 40 % filling with Kaldnes K1 biocarriers with biofilm of AOB and Anammox bacteria. According to microbiological characterization of biomass (Winkler et al., 2012) the Candidatus Brocadia fulgida was the dominating Anammox bacteria in the biomass. Air supply was regulated using valves together with rotameters aiming keeping DO concentration in the range 0.4-1 mg/L. Reactor was fed with wastewater, prepared by dilution of anaerobic digestion reject water with tap water to ammonium concentration of 300-900 mg N/L and

Fig. 5. Schematic of the MBBR reactor (Paper III).


11

addition of NaCl in quantities 0 to 15 g per liter of wastewater depending on the experimental stage. The reactors were operated in a way to sus-tain high nitrogen removal efficiency and avoid inhibition of Anammox bacteria with nitrite and free ammonia (FA). Therefore DO concentration and hydraulic retention time (HRT) were changed so that nitrogen loading rate (NLR) would not be signifi-cantly higher than nitrogen removal rate (NRR).

4.5. Activity tests (Paper II and III) Oxygen uptake rate (OUR) tests were done using methodology modified from the ones described by Surmacz-Gorska et al. (1996) and Gut et al. (2005). In tests liquid medium that had ammonium concentration of 100 mg N/L, COD of 75 mg/L was filled into a bottle. Bottle content was thermostated at 25 C and aerated to DO concentration above 6 mg/L. When the test was started, aeration was turned off, 0.1 L of carriers was added and DO concentration was continuously measured. In order to determine oxygen consumption of different groups of aerobic bacteria, specific inhibitors of NOB and AOB (sodium chlorate and allylthiourea, respectively) were added. In experiments, explained in paper III inhibitors were not added in order to avoid deterioration of biomass quality. Activity of Anammox bacteria was deter-mined using measurement of gas pressure described in Dapena-Mora et al. (2007). The tests were performed in glass bottles of total volume of 38 mL, of which 25 mL were occupied by 15 carriers and liquid medium. The liquid medium was prepared using phosphate buffer with addition of ammonium and nitrite containing salts with final concentrations of NH4

+-N and NO2--N

of 70 mg/L. The tests were done at 25 C and the measured pressure increase inside the bottles was transformed into nitrogen removal rates.

4.6. Analytical methods Ammonium was analyzed photometrically by the Nesslerization method (ASTM

International, 2008), by flow injection analyses using Tecator Aquatec-5400 ana-lyzer or by Hach-Lange cuvette test. Nitrite and nitrate was analyzed by Hach-Lange cuvette tests. Total hardness (TH) as a sum of calcium and magnesium ion concentra-tions was determined by complexonometric titration method (ASTM International, 2009).

5. RESULTS

5.1. Concentration of ammonium by ion exchange (Paper I)

5.1.1. Comparison of ammonium exchange capacity Ammonium exchange capacities of the four ion exchange materials were compared in packed bed mode by pumping SW3, which can simulate municipal wastewater, through ion exchange columns. For SAC resin sepa-rate runs for Na- or H-form of resin were made. Results indicated that the SAC resin has the highest capacity for ammonium ion among the studied materials. Breakthrough for this material was reached after pumping 145-183 bed volumes (BV) of wastewater through the column (Fig. 6). Higher capacity was reached for the resin in H-form, which agrees with the higher selectivity of the resin to Na+ ions, shown in Alchin (1998). Similar capacities were reached for natural and synthetic zeolites, which were about 40% lower than that of SAC resin in Na-form (Table 1). Ammonium breakthrough for WAC resin was reached after pumping only 25 BV of wastewater and, therefore, this resin was not extensively investigated in this study.

5.1.2. Regeneration with NaCl For ammonium concentration by ion exchange fast regeneration of materials is equally important to reaching high exchange capacity in the saturation phase. Consider-ably different volume of regenerant was required for regeneration of SAC resin, NZ and SZ (Fig. 7). SAC resin was regenerated completely after supplying only 12.2 BV of regenerant, and, therefore, 13-fold increase of ammonium concentration was reached with average concentration in regenerant of


12

Fig. 6. Breakthrough curves for 4 ion exchange materials. SW3 used as an inflow (Paper I).

Fig. 7. Regeneration of ion exchange materials with 30 g/L NaCl (Paper I).


+

+

+


13

554 mg NH4+-N /L. To the contrary, regen-

eration of natural zeolite proceeded very slowly and even after pumping 123 BV of regenerant through the column, only 90% of ammonium content was removed. The rate of synthetic zeolite regeneration was higher than for NZ but lower than for SAC resin and only 3-fold increase of ammonium concentration was achieved. Spent regenerant except having high ammo-nium concentration has relatively high residual NaCl content. When SAC resin is regenerated with 30 g/L NaCl solution, ammonium ions constitute to only 8% of the total cation content. Salinity negatively influences biological processes (Dapena-Mora et al., 2010; Moussa et al., 2006). Therefore, salinity of regenerant should be kept as low as possible while sustaining high regeneration rates. Since fast regeneration was observed for SAC resin in previous experiments, regeneration with lower salt concentrations was tested. As expected, decrease in regenerant strength increased volume of regenerant required for complete regeneration (Fig. 8). Ammonium concentration in spent regen-erant dropped to 382 and 289 mg/L when 20 and 10 g NaCl/L regenerant was used respectively. Even the value reached for 10 g NaCl/L is much higher than ammo-nium concentration in municipal wastewater and many studies showed successful opera-tion of partial nitritation/Anammox reactors at such ammonium concentrations.

5.1.3. Selectivity of ammonium exchange Ion exchange materials uptake different ions to different extent and it is important to understand how selective is the ammonium

removal. In regeneration process virtually all the uptaken ions are eluted and its presence in spent regenerant can have an impact on its treatment and consequent use in another regeneration cycle. Ca2+ and Mg2+ are the ions which are usually present in relatively high concentrations and its removal was monitored by analyzing the sum of its concentrations as total hardness (TH) in several ion exchange runs. For all the studied materials, except of natural zeolite, removal of TH was almost complete during the whole runs (Fig. 9). For natural zeolite TH concentration increased fast from the first portions of wastewater applied and only approximately ¼ of exchange sites were occupied by hardness ions. These results are in agreement with the selectivity rows of SAC resin (Alchin, 1998), WAC resin (Meyers, 1999) and natural zeolite (Ames, 1960).

5.1.4. Predicting ammonium breakthrough In order to effectively perform concentra-tion of ammonium with ion exchange, it is important to be able to predict the exchange capacity and detect the breakthrough of ammonium ions. In this study it was attempted to correlate the ammonium concentration in the effluent from the column with electric conductivity of the respective solution. Using data from both experiments with synthetic wastewater and real municipal wastewater, it was shown that irrespectively of inflowing concentration of ammonium, if conductivity of influent is known, effluent ammonium concentration can be calculated from conductivity value. This gives possibility of predicting break-through even when ammonium in the effluent is very close to zero by placing

Table 1. Performance of ion exchange materials in saturation phase (modified after Paper I). Ion exchange material Flow rate (BV/h) Breakthrough

volume (BV) Breakthrough

capacity (eq/L) Ammonium

removal efficiency (%)

SAC resin (Na-form) 43.1 145 0.41 96.0

SAC resin (H-form) 32.7 183 0.52 98.0

Natural zeolite 31.2 97 0.27 95.5

Synthetic zeolite 29.9 105 0.27 93.2

WAC resin (Na-form) 50.6 41 0.12 88.0


14

conductivity probe in the ion exchange column close to the exit. Experimental data of ammonium break-through could be predicted well by Adams-Bohart (Bohart and Adams, 1920) and Thomas (Thomas, 1944) models. This gave possibility not only to calculate break-through capacity using experimental data, but to evaluate equilibrium exchange capaci-ties – maximum exchange capacities which could be reached for ion exchange materials at specific wastewater content independently of the used wastewater flow rate. Kinetic coefficients and equilibrium concentrations can help designing ion exchange columns and to predict concentration-time profile for the effluent, if the influent content does not change significantly with time. However, municipal wastewater does not have a stable content and modeling breakthrough curve requires more complicated models, which use in calculation concentration of ammo-nium and other ions as well as selectivity for them.

5.1.5. Wastewater content, hydraulic loading influence Influence of wastewater content on NZ, SZ and SAC resin capacity was studied using three synthetic wastewater solutions, discussed in chapter 4.2. It was shown that

pH of wastewater plays an important role on ammonium removal. Since SW2 had high pH, at which around 34% of nitrogen was in non-ionized ammonia form, breakthrough was observed almost immediately after starting the saturation phase. The total cation content was shown to have also a high importance, since capacity of materials for ammonium removal decreased by 40-64 % when wastewater with only ammonium ions was changed to solution with cation content typical to municipal wastewater. Experiments with different volumetric loading showed that SAC resin can be loaded much more than NZ without nega-tive impact on exchange capacity. NZ was shown to be more dependent on contact time and exchange capacity for ammonium could be doubled when flow rate was decreased from 31.2 to 17.1 BV/h, while there was almost no increase of exchange capacity when SAC resin loading was decreased from 110 to 40 BV/h.

5.2. Partial nitritation/Anammox biomass adaptation to elevated salinity (Paper III) Since results of Paper II showed that NaCl content have strong negative impact on AOB and Anammox bacteria activity and



15

effectiveness of ammonium concentration with ion exchange depends on strength of regenerant (Paper I), experiments were done on adaptation of biomass to elevated salinity. Previous studies were mostly focused on Anammox bacteria adaptation and very different adaptation periods were reported. Therefore, in Paper III two different strate-gies of salinity increase were studied aiming to get more knowledge about the possibili-ties of adaptation of partial nitrita-tion/Anammox biomass in a MBBR. The first strategy, in which salinity was increased by 5 g/L every two weeks was not success-ful. Salt content led to inhibition of both AOB and Anammox bacteria, which led to ammonium and nitrite accumulation, and rise of FA and free nitirous acid (FNA) concentrations above the Anammox bacteria inhibition threshold. The reactor, which was working with twice lower step of salinity increase, showed better stability during the adaptation process. From influent and effluent chemical analyzes results during the first two phases of reactor operation (Fig. 10a) it is seen that good reactor performance was achieved. Excluding the periods of unadequate aera-tion on day 12 and day 26 nitrogen removal efficiency of 75-92% was reached. Nitrogen removal rate slightly increased in the phase of 0 g/L salinity and in the phase of 2.5 g/L salinity remained constant (Fig. 10b). In the first two phases OUR increased from 0.9 to 1.7 g O2/(m2day) and rather stable Anammox activity was observed in the range of 1-1.5 g N/(m2day) (Fig. 10c). When salinity of inflow was increased to 5 g/L, inhibition of Anammox bacteria was observed. FNA concentration increased to 87.8 μg HNO2-N/L and ammonium concentration of over 200 mg NH4

+-N/L further inhibited AOB and Anammox bacteria. In order to stabilize reactor, nitro-gen loading was decreased which caused increase of nitrogen removal efficiency. To the end of phase with salinity of 7.5 g/L NRR slightly increases from 0.65 to 0.9 g N/(m2day). SAA was lower in these phases comparing to the first two phases. OUR significantly dropped in the beginning

of phase with 5 g/L salt content but was steadily growing to the end of phase with salinity of 7.5 g/L. When salinity in inflow was further increased to 10 g/L, accumulation of all forms of nitrogen (and corresponding high concentrations of FNA) was observed which indicated bacteria inhibition. In order to stabilize the reactor NLR was gradually decreased by changing ammonium concen-tration in inflow and HRT. During the period when bacteria were inhibited slight decrease of Anammox and aerobic activity was observed. After day 92 bacteria were getting adapted to the new salinity level and NRR was steadily growing. Activity of both aerobic bacteria and Anammox bacteria were also growing in this period. On day 162 of reactor operation NRR reached a value of 0.76 g N/(m2day) which is comparable with removal rate of 1 g N/(m2day) observed in the beginning of operation period.

5.3. Influence of NaCl concentration on non-adapted and adapted biomass (Paper II and III) Influence of NaCl concentration on nitrogen removal through partial nitrita-tion/Anammox pathway was evaluated in Paper II and III. In Paper II more tests were done and separate influence of salinity on different groups of aerobic microorganisms was evaluated. However, influence only on unadapted biomass was studied. Since it was shown in Paper II that most of aerobic activity is due to AOB presence, in Paper III total aerobic activity of biomass at different NaCl levels was determined. Influence of NaCl was studied separately for the two biological steps – nitritation and Anammox. OUR and SAA batch tests were done at salinities of medium in the range 0-30 g/L. Results of OUR tests showed that the main group of aerobic organisms in the biological culture was AOB. The second biggest group was heterotrophic bacteria and activity of NOB was always on the limit of detection. It is clearly seen that with increase of salinity activity of both AOB and hetero-trophs decreases. Since activity of NOB is on the very low level, it is hard to make


16

conclusions about impact of salinity on these microorganisms. However, it was shown in Liu et al. (2008) that NOB are more sensi-tive to increased salinity then AOB. Considering impact of salinity on AOB activity, it may be concluded that increase of NaCl concentration to 10 g/L leads to decrease of activity by 20-40 % and further increase to 30 g/L causes loss of 70-80 % of activity without NaCl stress. Results from

Paper III confirm the activity profile at dif-ferent NaCl levels for aerobic microor-ganisms, obtained in Paper II. Similarly, 30 % of aerobic activity was lost at NaCl concentration of 10 g/L and 85 % at salinity of 30 g/L (Fig. 11a). Results of SAA tests (Fig. 11b, Paper III) showed that Anammox bacteria are also inhibited by NaCl and the inhibition for

Fig. 10. Performance of MBBR during adaptation period: (a) influent and effluent nitrogen compounds concentrations; (b) NLR and NRR; (c) SAA and OUR of biomass (Paper III).


17

them is stronger than for AOB. At salinities higher than 10 g/L activity of Anammox bacteria is on the edge of detection limit of the method. Results of Paper II showed similar trend of SAA decrease and high vari-ation of SAA at salinity of 10 g/L was observed. At NaCl concentration of 10 g/L between 25 and 60 % of activity in unstressed conditions can be expected. Further increase of salinity concentration to 20 g/L and higher values leads to activity decrease to the detection limit of the method. Influence of salinity on activity of unadapted Anammox biomass was also investigated in Windey et al. (2005), Kartal et al. (2006), Dapena-Mora et al. (2010), Jin et al. (2011). In these studies decrease of Anammox activity between 50 % (Kartal et al., 2006) and 97% (Windey et al., 2005) at NaCL concentration of 30 g/L was observed, which is also confirmed by this work. How-ever, for lower salinity levels reported results are substantially different. Kartal and co-workers (2006) observed 100% increase of activity at salinity of 10 g/L. In Dapena-Mora et al. (2010) 10% lower activity was observed at NaCl concentration of 10 g/L. In this study no stimulatory effect of salinity was observed; on the contrary salinity of 10 g/L caused loss of 20-75% of Anammox activity. After the reactor operation during 159 days salinity has lower influence on biomass activity, which indicates adaptation of bacte-

ria to salinity stress. On the day 159 SAA was the highest at salinity of 15 g/L and OUR was the highest at salinities of 5-15 g/L.

5.4. System testing in batch mode (Paper II)

5.4.1. Ammonium concentration from municipal wastewater In order to confirm the results, obtained with synthetic wastewater, 5 runs of exhaus-tion/regeneration were performed, where pretreated municipal wastewater as a source of ammonium was used. In the first two runs regenerant with NaCl concentration of 30 g/L was used, whereas in the latter 3 runs less concentrated 10 g/L NaCl solution was used. Breakthrough of ammonium in 5 runs with municipal wastewater was detected after passing 4-6.5 L of wastewater (Fig 12a) and such a difference was caused by different initial ammonium concentration in separate runs. Supply of wastewater in batch 2 was stopped just after reaching breakthrough, whereas the other runs were allowed to continue until reaching ¼ of initial ammo-nium concentration. Ammonium breakthrough was observed after removal of 0.27-2.41 meq of ammo-nium per 1 mL of resin (Table 2). Since ammonium concentration in wastewater was different in different batches, breakthrough was reached after treatment of different wastewater volume. Regeneration of resin

Fig. 11. Activity of biomass at different salinity levels during the adaptation process: (a) aerobic bacteria (OUR tests); (b) Anammox bacteria (SAA tests) (Paper III).


18

required approximately the same volume of regenerant as in experiments with synthetic wastewater (Fig. 12b, Table 2). Complete regeneration was reached after supply of 0.33 and 0.7 L of regenerant with NaCl concentrations of 30 g/L and 10 g/L respectively. In batch 1 volume of ammonium-containing stream decreased 25 times from 8.35 L to 0.33 L. Results of batch 5 demonstrate that it is possible to reach efficiency of ammonium removal from municipal wastewater of 99.9 % and increase concentration of ammonium by 18 times.

5.4.2. Biological nitrogen removal from spent regenerant Spent regenerant from first two batches had NaCl concentration approximately 28 g/L.

As was shown above, such high NaCl content would totally inhibit ammonium removal with partial nitritation/Anammox process. However, regenerant with NaCl concentration of 30 g/L can be used if biomass is adapted to elevated salinities, since it will result in higher ammonium concentration in spent regenerant and higher nitrogen removal rates. Spent regenerant of the three following batches had estimated NaCl content of 8.5-9.2 g/L. At this salinity level partial nitrita-tion/Anammox biomass is inhibited partially, and, therefore, biological removal of nitrogen could be tested. Three separate batch tests were performed with nitrogen removal from spent regenerant and in all of

Fig. 12. Ammonium concentration from municipal wastewater: (a) – exhaustion; (b) – regeneration (Paper II).


19

them efficiencies higher than 86 % were reached (Table 3). Since Anammox bacteria are inhibited with NaCL more than AOB, accumulation of nitrite was observed in batch 3, in which DO concentration of 1.5 mg/L was main-tained. In the following batch tests DO concentration was lowered to 1.0 mg/L, decreasing the rate of aerobic ammonium oxidation, and there was no nitrite accumu-lation observed (Fig. 13). Thus, it was shown that spent regenerant of ion exchange can be treated with partial nitritation/Anammox process even when non-adapted biomass is

used. However, the batch tests were run only for 2 days and, as was shown in Paper III, inhibition with NaCl is more severe at longer exposure at saline environment. Therefore, biomass needs to be adapted before the spent regenerant of ion exchange can be treated.

6. DISCUSSION

6.1. Ion exchange; which material and which conditions? Among the tested ion exchange materials, SAC resin and natural zeolite showed the best performance. With SAC resin it was

Table 2. Ammonium concentration from municipal wastewater using SAC resin (Paper II).

Batch Concentration in wastewater (mg NH4

+-N/L)

Volume of wastewater applied (L)

Break-through capacity (eq/L)

Regene-rant

(g NaCl/L)

Volume of regenerant

required (L)

Average concentration in spent regenerant

(mg NH4+-N/L)

Concen-tration

increase factor

1 26.6 8.4 0.38 30 0.33 581 21.8

2 24.8 6.5 0.36 30 0.34 445 17.9

3 40.4 5.1 0.41 10 0.70 367 9.1

4 21.8 6.0 0.27 10 0.70 187 8.6

5 37.9 5.4 0.40 10 0.70 330 8.7

Table 3. Nitrogen removal from spent regenerant by partial nitritation/Anammox (Paper II).

Batch Starting ammonium concentration (mg

NH4+-N /L)

Final nitrogen concentrations NRR

(g N/(m2d)) Treatment

efficiency (%) NH4+-N

(mg/L) NO2

--N (mg/L)

NO3--N (mg/L)

3 367 0 29.05 21.25 0.71 86

4 187 0.1 1.06 7.93 0.46 95

5 330 0 3.44 17.02 1.06 94

Fig. 13. Batch test on nitrogen removal from spent regenerant using partial nitritation/ Anammox process.


20

possible to reach the highest ammonium concentrations in spent regenerant due to high exchange capacity and high regenera-tion rate. However, as shown in the litera-ture and confirmed by experimental results, this material is not selective to ammonium ion and will concentrate also calcium and magnesium ions from wastewater. WAC resin and SZ are also more selective for calcium and magnesium but have lower exchange capacity than SAC resin and, therefore, not recommended for technolo-gies of ammonium concentration. To the contrast, zeolite of clinoptilolite type has a very high affinity for ammonium ions and allows concentrating ammonium from wastewater more selectively. Moreover, it offers quite high capacity for ammonium, which is only 40% lower than for SAC resin, if calculated per volume of material.

However, regeneration process proceeds very slowly and high volume of regenerant needs to be applied to remove all the containing ammonium. This results in low ammonium content in the concentrated stream (36-94 mg N/L). These values are lower than the ones obtained in other studies (summarized in Table 4), where ammonium concentrations in spent regenerant of 125-350 mg NH4

+-N/L were reported, even though similar breakthrough capacity was reached. However, in many of the studies regenerant of higher strength and with high pH was used. Higher concentra-tions of ammonium in spent regenerant can be reached if regenerant supply is stopped when the rate of regeneration becomes low. This, for example, was used in Cooney et al. (1999) and Semmens and Porter (1979). In Cooney et al. (1999) regeneration was

Table 4. Natural zeolite regeneration process in selected studies. Zeolite origin

Particle size (mm)

Ammonium feed solution. Concentra-tion in [mg NH4

+-N/L] in brackets

Feed flow rate (BV/h)

Break-through capacity (meq/g)

Concentra-tion of NaCl in regene-rant in [g/L]. pH in bra-ckets

Rege-nerant supply rate (BV/h)

Average concentra-tion in spent regenerant (mg NH4

+-N/L)

Reference

Bigadiç, Turkey

-1.00 +0.125

DI* (15.6) 25-50 0.57

20 (12.3) 16 350 *

(Demir et al., 2002) -2.00

+1.00 50 0.38 125 *

Jinyun, China

-0.90 +0.45

DI* (19.4) 6-24 0.42-0.55 29.3 (11-12) 5 270 * (Du et al., 2005)

Semnan, Iran

-0.84 +0.589

DI* (31.1) 12 0.53 58.5 (7) 10 240 * (Rahmani et al., 2009)

Mount Gipps, Australia

-1.6 +0.5

Sedimented municipal wastewater, (25-45)

8-9.3 0.16-0.2* 35 (10) 0.83-1.92

255 * (Cooney et al., 1999)

Buck-horn, USA

-0.84 +0.3

Synthetic wastewater (30)

7 0.28 17.5 7 200

(Sem-mens and Porter, 1979)

N/A N/A

Pretreated municipal wastewater (52)

24 0.3 eq/L 35 20 280 (Liberti et al., 1981)

Sokyrny-tsya, Ukraine

-1.0 +0.71

DI* (40) 31.2 0.64 30

7.6 87

Paper I SW3 (40)

29 0.29 7.6 36

17.1 0.57 30 7.8 94

* - synthetic wastewater prepared by dissolution ammonium salt in deionized water. No other ions present. ** - Calculated from the data present in the reference article


21

stopped when effluent concentration of 50 mg NH4

+-N/L was reached in the effluent. Analyzing the data of zeolite regeneration (Fig. 14) it may be concluded that if the same strategy was applied in this work, it would be possible to reach average concentration of ammonium 190 mg NH4

+-N/L in spent regenerant and reach regeneration efficiency of 86 %. To reach higher concentrations of ammonium in spent regenerant, comparable with the ones obtained for SAC resin it can be modified by one of the available methods (Jha and Hayashi, 2009). In this study zeolite with a particle size of 0.71-1.00 mm. Decrease of particle size will also benefit in higher exchange capacity and faster regeneration (Huang et al., 2010). However, even with the used particle size of 0.71-1.00 mm it was not possible to maintain higher flow rates than 32 BV/h for the column with the height of 0.38 m due to high hydraulic resistance. Therefore, use of finer zeolite is only possible if column is substituted by a series of complete mixed reactors or hydraulic loading is considerable decreased. Lower hydraulic loading during the service and regeneration phases mean that bigger reactor volume is required. Moreover, other ion exchange materials can be tested. In Breck (1974) it was shown that synthetic zeolite F has even higher exchange capacity and selectivity coefficient for ammonium. However, this zeolite is not

available at the market and therefore it was not tested in this work. Moreover, there are many studies on synthesizing zeolites from fly ashes and application of it to wastewater treatment (Querol et al., 2002). Use of such materials could benefit in recycling of waste and improving the wastewater treatment. Regenerant content is another important issue when designing the concentration with ion exchange. In Paper I regeneration with both NaCl and HCl solutions was studied. Acid solutions are mostly used in ion exchange technologies for water deminerali-zation. If SAC and anion exchange resins in H- and OH-form are combined, mineral content of water can be decreased. Moreover, since WAC resin is extremely selective for H+ ions, it can be regenerated very efficiently by acid solution. However, in this study lower ammonium concentration increase was obtained when HCl solution was used, comparing to NaCl solution of the same molar concentration. Moreover, when regenerating with acid solution, spent regen-erant needs to be neutralized before it can be treated with biological processes, which increases the costs significantly. Regeneration of zeolite was studied only for 30 g NaCl/L solution. Even for this solution quite low concentrations of ammonium in spent regenerant were reached. Therefore, lower salt concentration will further decrease the effectiveness of concentration process and are not recommended. For SAC resin

Fig. 14. Regeneration of zeolite column with 30 g/L NaCl solution.


22

even at regenerant strength of 10 g NaCl/L sufficient concentration of ammonium in spent regenerant was reached. Regenerating with more concentrated solution will lead to higher ammonium concentrations and higher nitrogen removal rates. However, biomass need to be first adapted to tolerate such NaCl concentration.

6.2. Adaptation to salinity Comparing to other studies on Anammox bacteria adaptation to elevated salinity, in this study slower adaptation is reported. The adaptation period took 160 days and the biomass was adapted only to salinity of 10-15 g NaCl/L. The same time period was enough for adaptation to salinity of 30 g/L in Windey et al. (2005) and in other studies adaptation to 30 g/L took even less time (60 days in Yang et al. (2011), 77 days in Jin et al. (2011), 90 days in Kartal et al. (2006) and 93 days in Liu et al. (2009)). The possible explanantion could be that Anammox bacteria of genus Candidatus Brocadia, which was identified as the main Anammox organism in the used biomass, adapt slower to saline environment than the bacteria of Candidatus Kuenenia genus as well as Anammox bacteria of groups KSU-1, AnDHS-2 and KU2 used in other studies. Moreover, since it generally took less time to adapt biomass of only Anammox bacteria comparing to adaptation of one-stage partial nitritation/Anammox biomass (Paper III and Windey et al. (2005)), it can be suggested that Anammox bacteria adapt slower in presence of oxygen (even very low concentrations).

6.3. Possibilities of integration in wastewater treatment process The technology of ammonium concentra-tion by ion exchange with further removal by partial nitritation/Anammox process was shown to be a possible option for removal of nitrogen with Anammox process. This technology can be integrated in municipal treatment scheme in several ways. In Paper II three different alternatives were presented. The first option is to remove ammonium by ion exchange after removal of particulate matter from wastewater. Since

ion exchange column can be clogged with particulate matter, it is preferable to have a step of extensive suspended solids removal, for example using sand filters, before the ion exchange step. After ammonium is removed, wastewater is supplied to a system of dis-solved organics removal, which can be either of aerobic type (e.g. activated sludge process) or of anaerobic type (e.g. UASB reactor). Disadvantage of this system is that careful control of nitrogen supply to the following step of organics removal is needed. Nitrogen is needed as a nutrient for biomass growth, therefore, part of incoming nitrogen needs to be left in wastewater which is supplied to organic matter removal step. The second option is to remove ammonium after the high loaded activated sludge step. In this case all ammonium can be removed with ion exchange. Solids retention time (SRT) for activated sludge process needs to be controlled on low level to maximize the sludge volume and limit nitrification process. Some nitrite and nitrate will be produced in this case and the system still requires aera-tion which is a disadvantage comparing to systems based on anaerobic organics removal. The third option is to use anaerobic diges-tion of dissolved organics applying for example UASB reactors before ammonium removal step (Fig 15). In this case all ammo-nium content from the wastewater can be removed and the highest wastewater treat-ment economy can be expected.

6.4. Challenges and perspectives Several challenges of the proposed technology can be summarized here:

Selectivity of ammonium removal. If SAC resin is used, other ions (mainly calcium and magnesium) are concentrated as well. Depending on source of tap water, concentration of hardness ions in wastewater can be comparable, or even higher than concentration of ammonium. Then, ammonium exchange capacity is decreased and regenerant needs to be changed more often. Precipitation of carbonate salts should not be a problem if


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pH is controlled in biological reactor at the value around 7.

Fouling of ion exchange materials with organics. This problem is more severe for anion exchange resins, since many organic substances can dissociate and create organic anions, which can occupy the exchange sites. For cation exchange materials the problem is limited to physical adsorption of organic molecules in material structure. Usually organic molecules have much larger size than the small NH4

+ and Na+ ions, so it can not completely block the pores of materials. However, the rate of ions transfer can be negatively affected. In Jorgensen and Weatherley (2003) the effect of organic substances presence on ammonium removal with clinoptilolite and cation exchange resins was studied and the presence of organic matter was shown to have a positive effect on ammonium uptake, which was explained by change of surface tension.

Long bacteria adaptation period. The main challenge of biological part of the technology is adaption of biomass to elevated salinities. As shown in this work, adaptation process can be much longer than it is reported in the literature. While in short term (1h in SAA test, Paper II and III) and medium term (2 days in batch test, Paper II) biomass could remove nitrogen without prior adaptation, in long term (Paper III) NaCl presence caused instability to the process performance. Therefore, gradual increase of salinity is needed before spent

regenerant with NaCl concentration of 10 g/L could be treated.

Regenerant exchange. In the proposed technology regenerant can be used several times for ion exchange material regenera-tion, after biological removal of ammonium with partial nitritation/Anammox process. However part of regenerant has to be exchanged with a fresh solution, since other ions accumulation in it (mainly Ca2+, Mg2+, Fe3+, NO3

-). It may be also possible, after pretreatment, to use sea water as a regen-erant, since average salinity of sea water is approximately 30 g/L.

Alkalinity consumption. Based on stoichi-ometry of nitritation and Anammox processes (eq. 5), 1.17 moles of alkalinity is needed per 1 mole of ammonium nitrogen removed. This corresponds to 7 kg of NaHCO3, 3.34 kg of NaOH or 4.43 kg of Na2CO3 per 1 kg of nitrogen removed. If regenerant is prepared by NaCl dissolution in water, it has a very low alkalinity. Cation exchange materials do not bind hydrocar-bonate ions, so no alkalinity is recovered from wastewater, and therefore it needs to be added from external sources. One possi-bility of avoiding external alkalinity addition is to use microbial fuel cell for alkalinity transfer from wastewater stream (Modin et al., 2011). Moreover, alkalinity consumption will be lower if pretreated sea water is used for regeneration, since it has alkalinity of about 2.5 mmol/L. Despite the limitations of the technology, it offers several advantages:

Fig. 15. Application of ion exchange after dissolved organics removal with activated sludge process: SCR – screens, GC – grit chamber, PS – primary settler, SF – sand filter, IE – ion exchange column, PN/A – partial nitritation/Anammox reactor, UASB – UASB reactor (modified after Paper II).


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High efficiency of nitrogen removal by ion exchange. In most of experiments with nitrogen removal by ion exchange efficiency of 95% was reached. Efficiency depended mainly on volume of wastewater, which was pumped through a column after the first traces of ammonium were detected. If supply of wastewater was stopped just after detection, efficiency of 99.9% could be reached. The total efficiency of the system will be different and mainly depend on nitrogen content in wasted part of treated regenerant, but it is easier to control, since volume of wastewater is much lower.

Higher rates of biological nitrogen removal. The higher the ammonium concentration in inflow, the higher rates it is possible to maintain. Higher rates mean lower volume of reactor, needed for nitro-gen removal.

NOB inhibition by ammonium. In treat-ment of mainstream wastewater, which has low ammonium content, it is impossible to use ammonium inhibition for NOB suppression. This mechanism is often used in reject water treatment and can be used when treating spent regenerant, since ammonium concentrations in these streams are similar.

NOB inhibition by salinity. In Liu et al. (2008) it was reported that NOB are more sensitive to salinity than AOB. This also can be used as a mechanism for NOB suppres-sion.

Possibility to heat biological part of the system. One of the challenges of Anammox process application for treatment of main-stream wastewater is low temperature. At temperatures lower than 18 ºC NOB have higher growth rate than AOB and harder to be suppressed. If regenerant is recycled after nitrogen has been removed, then loss of heat in the system will be attributed only to heating ion exchange material and flow of heat with part of regenerant that is being exchanged to fresh solution.

7. CONCLUSIONS

Performed research proved that it is possible to obtain efficient nitrogen removal

from mainstream of wastewater treatment plant by application of technology, which is based on concentration of ammonium by ion exchange followed by partial nitrita-tion/Anammox process.

Four ion exchange materials were studied and results of comparison showed that the application of SAC resin in Na-form gives the highest increase in ammonium concen-tration and is recommended to be used in the technology of nitrogen removal, which is based on the combination of ion exchange and biological nitrogen removal.

Testing different regenerants it was found that by application of 30 g/L and 10 g/L NaCl solutions ammonium concentration in spent regenerant can be expected in the ranges of 445-581 mg NH4

+-N/L and 187-367 mg NH4

+-N/L, respectively.

Selective ammonium removal is possible with use of natural zeolite. However, due to slow regeneration much lower increase of ammonium concentration can be expected. Incomplete regeneration should be used to increase the average ammonium concentra-tion in spent regenerant.

Content of NaCl has a big influence on biological processes of nitritation and Anammox performance. Testing NaCl toler-ance of AOB and Anammox bacteria it was recognized that the latter are more inhibited by NaCl. Shock exposure to NaCl concen-trations of 15 g/L and higher lead to almost complete loss of activity.

Adaptation strategy with salinity increase by 2.5 g/L every two weeks should be selected as a starting point for adaptation of attached biomass of nitritation and Anammox bacteria. In this study adaptation of bacteria to NaCl concentration of 15 g/L was reached in 159 days of MBBR opera-tion.

Batch tests with ammonium concentra-tion from municipal wastewater with further removal by partial nitritation/Anammox culture showed that with ion exchange on SAC resin up to 99% of ammonium from wastewater can be removed and transfered into secondary stream. Biological part could


25

remove 86-95% of nitrogen from the concentrated stream.

The main limitations of the technology, proposed in the thesis, are long bacteria adaptation towards NaCl concentration and external alkalinity need.

8. FURTHER RESEARCH

In order to make possible use of Anammox process for nitrogen removal from main-stream wastewater further research should directed on solving the limitation of tech-nology, described in detailed in chapter 6.4 and include:

Further testing of natural clinoptilolite and other ion exchange materials which allow selective ammonium removal;

Testing fouling of ion exchange materials and change of performance with increasing number of saturation/regeneration cycles and techniques of capacity recovery after fouling;

Investigation of alkalinity transfer from mainstream wastewater to step of biological

removal of nitrogen from spent regenerant using microbial fuel cells;

Testing of combined ion exchange-biological system in continuous operation mode. Moreover other process configurations that allow Anammox application in mainstream wastewater treatment can be investigated and research can be directed on:

Possibility of direct mainstream wastewater treatment with partial nitrita-tion/Anammox process after pretreatment in UASB reactor working at temperatures of 20-25 °C;

AOB/NOB selection mechanisms and possibilities to avoid NOB accumulation at moderate and low temperatures;

Application of partial nitrita-tion/Anammox process after high rate acti-vated sludge step for treatment of municipal wastewater at low and moderate tempera-ture.


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