Waste Technology

Waste TechnologyChan, Bea Jasmine V.Pacson, Ann Claudette A.Integration of microbial fuel cell techniques into activated sludge wastewater treatment processes to improve nitrogen removal and reduce sludge productionBy: Gajaraj, S. and Hu, Z.Article History:Received 23 October 2013Received in revised form 23 May 2014Accepted 5 June 2014

University of Missouri, Columbia, United StatesDefinition of TermsMicrobial Fuel Cell device that converts chemical energy to electrical energy by the catalytic reaction of micoorganismsAerobic - organisms that require the presence of oxygen to liveAnoxic greatly deficient in oxygenMixed liquor - a combination of raw or unsettled wastewater and activated sludge within an aeration tank; mostly of microorganisms and non-biodegradable suspended matter.AbstractBioelectrical systems are emerging for wastewater treatment.Microbial Fuel Cell technique was incorporated into the Modified Ludzack-Ettinger (MLE) process (phase I) and later with the membrane bioreactor (MBR) process (phase II) to evaluate the performance of MFC assisted wastewater treatment systems.IntroductionMFCs have been demonstrated to be successful in wastewater treatment although the power output is not high enough for the electricity production process.One more important benefit in the MFC systems is the enhanced nitrogen removal from wastewater.

Significance of the StudyObjective of the StudyTo evaluate the performance of MFC assisted wastewater treatment systems, to improve wastewater treatment and sludge management practices.

Materials

Constructing MFC Modulegraphite clothand titanium mesh soaked in 50% ethanol for 1 hrrinsed with tap water to wash away any impuritiesanode and cathode connected together with 1000 resistorinoculated with return activated sludge( Columbia Wastewater Treatment Plant) reactors were fed with synthetic wastewaterratio of 1:1 mixed liquor was maintained in all the systemsPhase I During phase I (from day 30 following acclimatization to day 100) the bioreactor was run in the MLE mode.

The influent was fed into the anoxic zone and the mixed liquor was returned from the settling zone to the anoxic zone.

The influent was fed into the anoxic zone and the mixed liquor was returned from the settling zone to the anoxic zonePhase IIDuring phase II (from day 100 to day 210) a membrane module was added to the aerobic zone so that the bioreactor was run as a MBR.An air pump supplied at a constant air flow rate of 6 L min^-1 to support aeration and control membrane fouling. Throughout the study period, magnetic stirrers were used to provide additional mixing of the mixed liquor in the anoxic and oxic chambers.Sludge activity measurementsActivated sludge activities were assessed with the specific oxygen uptake rate (SOUR) measurements.

Analytical methods and statistical analysisInfluent and effluent water quality was monitored twice a week during the study period.

The wastewater effluent (phase I) and the permeate water (phase II) parameters such as NH4 + N, NO3 ^N, NO2^N, and COD were analyzed according to the standard methods (APHA, 1998).Voltage generated by the MFC assisted system was monitored in real-time at 1 Hz using LabView data acquisition system (National Instruments, TX, USA) and the voltage was averaged every 24 h.

Coulombic efficiency (gc) defined as the ratio of electrons used as current to the maximum electron production was calculated as follows:

The analysis of variance (ANOVA) was applied to compare the means of different groups of the study.

Nitrifying bacterial community analysisTerminal restriction fragment length polymorphism (T-RFLP) was used to analyze and compare the effect of MFC assisted wastewater treatment systems on the nitrifying community structure (nitrification potential) between the MLEMFC in phase I and MBRMFC in phase IIResults and DiscussionA. Voltage Output

Results and DiscussionB. Nitrate Removal

Results and DiscussionC. Biomass Production

Results and DiscussionD. Membrane Fouling Trend

Results and DiscussionE. Organic and Ammonia Nitrogen Removal Efficiencies

23Membrane fouling trend in the MFC assisted systemsThe cylindrical cathode structure designed to snuggly fit onto a membrane module showed a significant reduction in membrane fouling in the MBRMFC system.

The cylindrical cathode structure had reduced biofouling because it was designed to act as a physical barrier with the unique filtering feature by reducing direct contact between sludge and the membrane moduleOrganic and ammonia nitrogen removal efficienciesRegardless of the use of MFC technique, both bioreactors performed well with an overall COD removal efficiency above 97%. The overall effluent COD concentrations in the MLE MFC and MBRMFC were 14 6 mg L^-1 and 17 5 mg L^-1, respectively.There was no nitrite detected in the effluent, suggesting complete nitrification.Based on the concentrations of influent and effluent nitrogen species, the total nitrogen efficiencies in the MLEMFC (phase I) and MBRMFC system (phase II) were 89% (2%) and 86% (2%), respectively. The removal efficiencies in the open circuit controls were 85% (3%) and 83% (2%), respectively, suggesting that the MFC integrated systems fared better in removing nitrogen from wastewater.There was no significant difference in the heterotrophic and autotrophic SOUR of the planktonic cells between the control and the MFC assisted systems.

This result suggests that organic matter degradation for electricity generation and the presence of electrode assembly do not interfere with the sludge activities in the MLEMFC and MBRMFC.T-RFLP analysis of the nitrifying community complements the nitrifying activity data. Nitrosomonas was identified as the dominant ammonia-oxidizing bacteria Nitrospira species were the dominant nitrite-oxidizing bacteriaCoulombic efficiencies of the MLEMFC and MBRMFC systems were lower than 0.05%.

The mixed liquor recirculation brings in significant quantities of nitrate from the aerobic zone. This can result in a significant reduction in the coulombic efficiency because of the competition between the anode and other common terminal electron acceptors such as oxygen and nitrateEven with such low coulombic efficiencies in the MLEMFC and MBRMFC, the results of this study suggest that MFC may be viable to activated sludge wastewater treatment due to its potential to reduce sludge production or the use of external carbon sources for denitrification and to produce effluent with higher water quality.ConclusionThis study demonstrated that with a simple change in process configuration and the use of low-cost electrode materials, the MLEMFC and MBRMFC systems increased the NO3^N removal efficiencies by 31% (12%) and 20% (12%), respectively, and decreased sludge production by 11% and 6%, respectively.

Opportunities exist to scale up the MFC assisted wastewater treatment facilities to reduce sludge production and improve effluent water quality.Critic for MethodologyThe researchers presented the materials used in this study precisely. They described each material and discussed their purpose. The specific measurements and the step by step procedure of making the module were also stated. It was not difficult for the readers to understand the bioreactor design. Different tests that would be used in the study were also discussed. The researchers used a standard for examination of their data. Critic for Results and DiscussionThe results on the different tests were presented. The researchers even explained their theory of the data they obtained. Different related studies were also stated and was very helpful to support the results of the tests. The researchers also suggested recommendations to help enhance their study.