CHARACTERIZATION OF INDUSTRIAL VOLATILE ......FACULTY OF BIOSCIENCE ENGINEERING CENTRE FOR...

FACULTY OF BIOSCIENCE ENGINEERING

CENTRE FOR ENVIRONMENTAL SCIENCE AND TECHNOLOGY

Academic year 2015-2016

CHARACTERIZATION OF INDUSTRIAL VOLATILE ORGANIC

COMPOUNDS EMISSION IN RWANDA AND BIOFILTRATION

OF ACETONE, DIMETHYL SULFIDE AND HEXANE

Juvenal MUKURARINDA

Promoter: Prof. dr. ir. Herman VAN LANGENHOVE

Tutors: Dr. ir. Christophe WALGRAEVE

Ir. Joren BRUNEEL

Master’s dissertation submitted in partial fulfillment of the requirements for the degree of

Master of Science in ENVIRONMENTAL SANITATION

i

COPYRIGHT

The author and promoter give permission to use this thesis for consultation and to copy parts of it

for personal use. Every other use is subject to the laws of copyright; more specifically the source

must be extensively specified when using results from this dissertation.

Gent, June 2016.

Juvenal MUKURARINDA (author)

Ir. Joren BRUNEEL (tutor)

Dr. ir. Christophe WALGRAEVE (tutor)

Prof. dr. ir. Herman VAN LANGENHOVE (promoter)

ii

ACKNOWLEDGEMENTS

First of all, I want to say thank you to God Almighty for his faithfulness, mercy, provision,

protection and support during my entire study period.

I would never have been able to finish my thesis without guidance from my tutors and professor.

My deepest gratitude goes to my promoter Prof. dr. ir. Herman Van LANGENHOVE for allowing

me to do research at the EnVOC lab. I am also particularly grateful to him for his scholastic

guidance, innovative suggestions, and supervision throughout the period of research work.

I gratefully thank my tutors, Dr. ir. Christophe WALGRAEVE and Ir. Joren BRUNEEL for their helpful

attitude, constant encouragement, providing information constructive comments and great

endurance throughout the research and manuscript writing. They consistently allowed this paper

to be my own work, but steered me in the right direction whenever they thought I needed it.

I also gratefully acknowledge the valuable comments and suggestions from

Prof. dr. ir. Kristof Demeestere during the EnVOC presentation seminars.

I wish to extend my gratitude to all members of the EnVOC family especially Lore and Patrick for

their kind assistance during the research time.

My sincere gratitude and cordial respect to Prof. dr.ir. Peter Goethals to have allowed me to join

the challenging but wonderful program (Master of Science in Environmental Sanitation). My

sincere thanks to the coordinators of the program: Sylvie, Veerle for their kind cooperation,

valuable advice and continuous encouragement during the entire study period.

I would like to like to thank the Flemish Interuniversity Council i.e. Vlaams Interuniversitaire Raad

(VLIR-OUS) for offering me a scholarship to pursue higher education at Ghent University, Belgium

as well as for their blessed aim of transferring knowledge towards developing countries such as

Rwanda.

Finally, I must express my very profound gratitude to my parents, sisters and brother for providing

me with unfailing support and continuous encouragement throughout my years of study.

iii

ABSTRACT

Rwanda’s economic transformation is based on the service delivery, mining sector and industrial

activities. Technologies to handle the emissions in industries from production processes especially

VOC are yet to be established. In addition to that, no studies have been conducted before to

check the status of emissions made in different local manufacturing industries in Rwanda. VOC

are organic compounds which have adverse effects on human health as well as the

environment when exposed to high concentrations for long time.

This study was divided into two parts: In the first part, samples by means of Tenax TA sorbent

tubes were collected indoor and outdoor in three different industries, Sulfo Rwanda industry,

AMEKI color and Inyange industries. Samples were analyzed by TD-GC-MS and a total new data

of 45 VOCs concentrations levels were monitored to both indoor and outdoor environment of

the three local manufacturing industries. In Sulfo, soap production unit, the TVOCs indoor and

outdoor were 3.38 103 and 3.51 103 μg.m-3 respectively. Still at Sulfo, cosmetic production unit,

the TVOCs was 0.13 103 μg.m-3 for indoor and 0.06 103 μg.m-3 for outdoor. In AMEKI color, the

indoor and outdoor was 39.2 103 and 0.02 103 μg.m-3 respectively. At Inyange, the TVOCs

encountered were 0.45 103 μg.m-3 indoor and 0.02 103 μg.m-3 outdoor. The second part of the

study investigated the performance of a biofilter contaminated by three compounds with

different physical chemical properties, acetone, DMS and hexane. By means of SIFT-MS, VOC

concentrations were measured at different position along the BF and perform dynamic

partitioning coefficient of BF packing materials. The performance assessment of the biofilter was

done by comparing inlet concentrations (IL), elimination capacity (EC) and removal efficiency

(RE). The maximum RE of the mixed target total VOC was 74 % to IL of 22.4 ± 4.80 mg C.m-3.min-1

and EC of 16.6 ± 4.07 mg C.m-3.min-1 at an EBRT of 57 s. The highest maximum RE for individual

contaminants was 99.9 % for acetone at an IL of 20.9 mg.m-3.min-1 and 20.9 mg.m-3.min-1 EC. The

maximum RE of DMS was 74 % at IL of 34.9 mg.m-3.min-1 and 25.72 mg.m-3.min-1 EC. The maximum

RE for hexane was 47 % at IL of 67.33 mg.m-3.min-1 and 31.68 mg.m-3.min-1 EC.

Based on this performance, biofiltration can be seen as an urgent technology for the treatment

of the target VOC in manufacturing and production industries where technology for VOC

treatment is yet to be implemented.

Keywords: VOC, thermal desorption, gas chromatography, mass spectroscopy, biofiltration,

selected ion flow tubes mass spectroscopy (SIFT-MS), Ion Chromatography.

iv

TABLE OF CONTENTS

COPYRIGHT ................................................................................................................................................... i

ACKNOWLEDGEMENTS................................................................................................................................ ii

ABSTRACT .................................................................................................................................................... iii

GENERAL INTRODUCTION ........................................................................................................................... 1

PROBLEM STATEMENT ................................................................................................................................... 1

CHAPTER 1 LITERATURE REVIEW ................................................................................................................... 2

1.1 Volatile organic compounds ..................................................................................................................... 2

1.2 Sources of Volatile organic compounds ................................................................................................ 2

1.2.1 Natural sources ....................................................................................................................................... 3

1.2.2 Anthropogenic sources ........................................................................................................................ 3

1.3 Hazards of VOCs ............................................................................................................................................ 4

1.3.1 Human health effect ............................................................................................................................ 4

1.3.2 Tropospheric photochemical ozone formation ............................................................................ 5

1.3.3 Stratospheric ozone depletion ........................................................................................................... 6

1.3.4 Global Greenhouse effect .................................................................................................................. 6

1.4 Air pollution control technologies for VOCs ........................................................................................... 7

1.4.1 Non-biological technology for VOCs ............................................................................................... 9

1.4.2 Biological treatment of VOCS ............................................................................................................ 9

1.4.2.1 Biotrickling filters ............................................................................................................................ 10

1.4.2.2 Bioscrubber .................................................................................................................................... 11

1.4.2.3 Biofilter ............................................................................................................................................. 12

1.4.3 The biodegradation of hydrophobic compounds ..................................................................... 15

1.4.4 Parameters used to check the performance of the biological systems .............................. 16

1.5 Scope and objectives ................................................................................................................................ 16

CHAPTER 2 MATERIALS AND METHODS .................................................................................................... 18

PART I: ANALYSIS OF INDUSTRIAL VOC CONCENTRATIONS IN RWANDA ............................................ 18

2.1 Tenax TA tubes ............................................................................................................................................. 18

2.2 Conditioning ................................................................................................................................................. 18

2.2.1 Loading with internal standards ...................................................................................................... 19

2.2.1.1 Chemicals ...................................................................................................................................... 19

2.2.1.2 Preparation of the closed two-phase system ...................................................................... 19

2.2.1.3 Calculation of the headspace concentration .................................................................... 20

v

2.2.1.4 Loading ........................................................................................................................................... 20

2.2.2 Pump Calibration ................................................................................................................................. 20

2.3 Sampling Campaigns ................................................................................................................................. 20

2.3.1 Description of the sampling locations............................................................................................ 22

2.3.1.1 Sulfo Rwanda Industries .............................................................................................................. 22

2.3.1.2 AMEKI Color ................................................................................................................................... 23

2.3.1.3 Inyange Industries ........................................................................................................................ 23

2.4 Analysis of Tenax TA sampling tubes ...................................................................................................... 24

2.4.1 TD-GC-MS ............................................................................................................................................... 24

2.4.2 Calibration of the TD-GC-MS ............................................................................................................ 25

2.5 Quantification .............................................................................................................................................. 26

2.5.1 Calculation of the analyte concentration ................................................................................... 26

PART II: ABATEMENT TECHNOLOGY ......................................................................................................... 28

2.6 BIOFILTRATION ............................................................................................................................................... 28

2.6.1 Physical chemical properties of the representative VOC compounds ............................... 28

2.6.2 Biofiltration process .............................................................................................................................. 28

2.6.2.1 Biofiltration design ........................................................................................................................ 28

2.6.2.2 Biofiltration setup .......................................................................................................................... 28

2.6.3 Characterization of the packing materials .................................................................................. 30

2.6.3.1 Bulk Density .................................................................................................................................... 31

2.6.3.2 Moisture content .......................................................................................................................... 31

2.6.3.3 Water holding capacity ............................................................................................................. 31

2.6.3.4 Porosity ............................................................................................................................................ 31

2.6.4 Environmental conditions of the filter bed .................................................................................... 34

2.6.4.1 Temperature .................................................................................................................................. 34

2.6.4.2 pH ..................................................................................................................................................... 34

2.6.4.3 Nutrients .......................................................................................................................................... 34

2.6.4.3 Pressure drop ................................................................................................................................. 34

2.6.5. Analytical instrumentation ............................................................................................................... 35

2.6.5.1 Analysis with SIFT-MS .................................................................................................................... 35

2.6.5.2 Analysis with Ion chromatography .......................................................................................... 35

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CHAPTER 3 RESULTS AND DISCUSSION ..................................................................................................... 36

PART I: INDUSTRIAL VOC ANALYSIS IN RWANDA .................................................................................... 36

3.1 Results ............................................................................................................................................................. 36

3.2 Discussion ....................................................................................................................................................... 41

3.2.1 General discussion ............................................................................................................................... 41

3.2.1 Indoor to outdoor concentrations of the sampling sites .......................................................... 44

Part II: BIOFILTRATION OF VOC ................................................................................................................ 46

3.3 Results and discussion ................................................................................................................................ 46

3.3.1 Partition coefficient of the pollutants to the packing materials ............................................. 46

3.3.2 Biological oxidation of pollutants. ................................................................................................... 48

3.3.3 Bioreactor bed ..................................................................................................................................... 49

3.3.4 The Carbon dioxide (CO2) and Elimination capacity (EC) ...................................................... 51

3.3.5 The effect of pH on the removal of target VOC ......................................................................... 52

3.3.6 Sulfate measurement ......................................................................................................................... 53

3.3.7 Effect of Silicon on the removal of hexane .................................................................................. 54

3.3.8 Inhibitory effect for hexane degradation ..................................................................................... 54

CHAPTER 4 CONCLUSION AND RECOMMENDATION ............................................................................. 56

4.1 CONCLUSION ............................................................................................................................................... 56

4.2 RECOMMENDATION.................................................................................................................................... 57

REFERENCES ................................................................................................................................................ 58

APPENDIX I ................................................................................................................................................. 69

APPENDIX II ................................................................................................................................................ 72

A. Breakthrough curves for dry silicon foam ............................................................................................... 72

B. Breakthrough curves for dry wood chips ................................................................................................ 72

C. Breakthrough curves for dry compost .................................................................................................... 73

D. Breakthrough curve of compost at normal and dry condition. ...................................................... 73

vii

LIST OF FIGURES

Figure 1: Industrial sector VOC emissions in EU-27 ....................................................................................... 4

Figure 2: A tree diagram of the VOC emissions abatement technology (Khan & Ghoshal, 2000). . 8

Figure 3: Application limit of flow rate vs VOC concentrations of different air pollution

technologies control. ..................................................................................................................... 8

Figure 4 : Biotrickling filter setup . .................................................................................................................. 11

Figure 5: Bioscrubber setup. ......................................................................................................................... 12

Figure 6: A typical setup of biofilter. ............................................................................................................ 12

Figure 7: Conditioning oven ......................................................................................................................... 19

Figure 8: Tol-d8 structure. ................................................................................................................................ 19

Figure 9 : Sampling locations on the map of Kigali city........................................................................... 21

Figure 10: Soap production unit. Figure 11: Cosmetics production unit. .......................... 22

Figure 12: Paint production. .......................................................................................................................... 23

Figure 13: Juice and milk production unit. ................................................................................................. 24

Figure 14 : The TD-GC-MS with (1) the TD (2) the transfer line from GC to MS, (3) GC and (4) MS. 24

Figure 15: Schematic diagram of the biofiltration setup. it. .................................................................... 29

Figure 16: Actual setup of the biofilter ........................................................................................................ 30

Figure 17: Packing materials used in biofiltration process. ...................................................................... 30

Figure 18: The peak injection experiment of acetone, DMS and hexane. .......................................... 32

Figure 19: The peak injection experiment using methane gas. ............................................................. 32

Figure 20: Breakthrough curve of the pollutant to the packing material and blank. ....................... 33

Figure 21: Pressure drop in the filter bed. .................................................................................................... 34

Figure 22: The total indoor and outdoor concentrations of four sampling sites. ................................ 41

Figure 23: The indoor total VOC concentrations of chemical groups in four sampling sites. .......... 42

Figure 24: The outdoor total VOC concentrations of chemical groups in four sampling sites. ....... 42

Figure 25: Indoor target groups’ abundances in four sampled sites. ................................................... 43

Figure 26: Outdoor target groups’ abundance in four sampled sites. ................................................. 43

Figure 27: Partitioning coefficient of acetone, DMS and Hexane ......................................................... 47

Figure 28: The normalized start up concentrations of acetone, DMS and hexane at EBRT of 57 s.49

Figure 29: The Total inlet concentrations ( ) and total removal efficiency ( ) of the three

pollutants at EBRT of 57 s. ............................................................................................................ 50

Figure 30: EC in function of IL of acetone, DMS and hexane at an EBRT of 57 s. ............................... 51

Figure 31: Produced CO2 in function of total EC at an EBRT of 57 s. ..................................................... 52

Figure 32: RE in function of pH of acetone, DMS and hexane at an EBRT of 57 s. ............................. 53

Figure 34: The EC in function of IL for hexane in mixture and hexane only at EBRT of 57 s. .............. 55

viii

LIST OF TABLES

Table 1: Related health effects to exposure of high VOC concentrations. .......................................... 4

Table 2: Classification of vapor phase biotechnology systems. ............................................................ 10

Table 3: Performance parameters used in biological treatment systems. .......................................... 16

Table 4: The overview information of the VOC sampling campaign collected at three local

industries in Rwanda. ....................................................................................................................... 22

Table 5: Physical chemical properties of acetone, dimethyl sulfide and hexane. ............................ 28

Table 6: Calculated physical chemical properties of the packing materials. .................................... 32

Table 7: The precursor and products ion used to measure concentrations in SIFT-MS. .................... 35

Table 8: Indoor VOC concentrations (μg.m-3) measured at four sampling sites, Kigali, Rwanda. . 37

Table 9: Outdoor VOC concentrations (μg.m-3) measured at four sampling sites, Kigali, Rwanda.

.................................................................................................................................................................... 39

Table 10: Indoor to Outdoor ratio concentrations of the four sampling sites. .................................... 44

Table 11: Calculated partitioning coefficients of the dry packing material ....................................... 47

Table 12: Performance parameters of the biofilter. ................................................................................ 49

ix

LIST OF ABBREVIATION

AMEKI

Atelier des Meubles de Kigali

BF

Biofilter

Cin Inlet Concentration

Cout

Outlet concentration

CTS Closed two phase system

DMS

Dimethyl Sulfide

EBRT Empty Bed Residence Time

EC Elimination Capacity

EPA Environment Program Agency

GC Gas Chromatography

GWP Global Warming Potential

I/O Inlet to Outlet ratio

IL Inlet Load

IS Internal Standards

MINICOFIN

Ministry of Finance and Economic Planning, Rwanda

NIST National Institute of Standard and Technology

NOx Nitrogen Oxides

Q Flow

RF Response Factor

RSRF Relative Sample Response Factor

SIFT-MS Selected Ion Flow Tubes Mass Spectroscopy

TD Thermal Desorption

TVOCs Total Volatile Organic Compounds

V Volume

VOC Volatile Organic Compounds

1

GENERAL INTRODUCTION

PROBLEM STATEMENT

Air is an important free available commodity which defines life on earth but due to mostly

human activities the quality of air is changing and this reflect negative effects to human health

as well on environment.

The atmospheric emissions trends in developing countries are increasing mainly because of their

rapid economic transformation especially in urban places. In the last decade, emissions in

developed countries are reported to have decreased but some are still in higher concentrations

than the air quality standards for the protection of human health (Guerreiro et al., 2014). The

World Health Organizations (WHO) report that about seven million death globally attributed by

both indoor and outdoor air quality (WHO, 2014).

Atmospheric emissions are composed of (in) organic compounds and particulate matter.

Volatile organic compounds (VOCs) are part of organic compounds. They are harmful

pollutants with the ability to form the undesired photochemical tropospheric ozone smog and

potentially carcinogenic and mutagenic (Mohammed et al., 2013). Also VOCS participate in

destruction of stratospheric ozone which protects us from UV radiation (Mohammed et al., 2013).

Rwanda is an African developing country striving to transform its economy on average to 11.5 %

of Gross Domestic Products (GDP) growth by 2018 (MINECOFIN 2013). To attain that goal,

industries are increasing day to day in the country but know-how of handling emissions from

industrial activities is still lacking and there are no available air pollution control technologies. To

the best of our knowledge, so far in Rwanda no studies have been conducted to check the air

quality status in local manufacturing industries.

Therefore, to start bridging the gap, it is fortunate to characterize VOCs emitted from local

manufacturing industries in Rwanda and evaluate the performance of the cost effective

abatement technology which can be used to handle emission emitted during production

processes.

2

CHAPTER 1 LITERATURE REVIEW

1.1 Volatile organic compounds

Air is an essential component of life on earth. Therefore, air pollution is seen as a serious threat to

human being and the environment. Volatile organic compounds also commonly shorten as

VOCs, are organic compounds usually distinguished based on two groups definition; effect

definition and definition based on physical chemical properties (Demeestere et al., 2007).

Firstly, effect definition, US EPA define VOC as any compound containing at least one atom of

carbon, excluding carbon monoxide, carbon dioxide, carbonic acid, metallic carbides or

carbonates, and ammonium carbonates which participate in atmospheric photochemical

reactions (EPA, 2016). Secondly, based on physical and chemical properties, Solvent Emission

Directive (SED) defines VOC as any organic compound having at 20 °C a vapor pressure of

0.01 kPa (Directive 1999/13/EC).

Methane is often viewed separately due to non-absolute reactivity in the troposphere and

different concentrations range observed in different part of the atmosphere

(Demeestere et al. 2007). Therefore, it is imperative to take care of VOCs due to damage they

cause to both human health and as well as environment. They contribute to major

environmental problems to mention, global warming, stratospheric ozone depletion and

photochemical smog (Do et al., 2015). In presence of light, VOC react with nitrogen oxides to

form tropospheric ozone which in high concentrations cause human health problem

(Do et al., 2015). Many other VOCs like styrene and benzene are said to be responsible for

numerous adverse health effects, mainly respiratory, heart disorders and carcinogenic

(Stoji et al., 2015).

1.2 Sources of Volatile organic compounds

Sources of VOCs are divided into anthropogenic and natural sources. Anthropogenic sources

are the man-made VOCs while natural are emitted naturally mostly from vegetation. Often a

term biogenic is used to describe natural emissions of non-methane hydrocarbons (Evuti, 2013).

Emissions distribution depends on the industrial activities, climate and vegetation and varies

region to region (Evuti, 2013).

Globally, the biogenic VOCs, 1150 106 ton.yr-1 (Goldstein & Galbally, 2007), emissions in remote

areas are almost 10 times higher than the anthropogenic VOCs, 142.106 ton.yr-1 (Müller, 1992),

per carbon per year in the forms of VOCs. The inverse happen in urban places where

anthropogenic surpasses biogenic emissions concentrations (Burrows et al., 2007).

3

1.2.1 Natural sources

VOCs are naturally emitted from vegetation (Guenther et al., 2006). They account isoprenoids

(terpenes and monoterpenes) as well as alkanes, alkenes, carbonyls, alcohols, esters, ethers and

acids (Guenther et al., 2006) .

The concentrations of the emitted compounds reveal isoprenoids to be most prominent

compounds followed by alcohol and carbonyl compounds (Kesselmeier and Staudt, 1999).

The oxidation of the biogenic VOCs produce products with low volatility which participate in the

formation of Secondary Organic Aerosols (SOAs) (Kavouras et al., 1998; O’Dowd et al., 2002;

Kanakidou et al., 2005; Jimenez et al., 2009).

SOAs have an important impact on air quality and climate (Fiore et al., 2012; Scott et al., 2014).

To climate, SOA absorb and scatter solar radiation and they indirectly affect the cloud

condensation (Gouw, 2009).

Methane is not accounted in the oxidation process although it is produced naturally from

wetlands, rice field, livestock, landfills, biomass burning, forests, termites and oceans; it’s total

emissions is in between 145 to 260 106 ton.yr-1 (EPA, 2016).

1.2.2 Anthropogenic sources

Human made emissions encounter indoor and outdoor environment and they vary from various

sources (Bari et al., 2015). Indoor VOC concentrations are generally found in higher levels than

the ambient outdoor levels (Fellin et al., 1994; Spengler, 1995; Zhu et al., 2005; Heroux et al., 2008;

Stocco et al., 2008 ). Indoor VOCs are most emitted from building materials (e.g, floor and wall

coverings, carpet, insulation, paint), combustion processes (e.g, smoking, cooking, home

heating), consumer products (e.g, cleaners, solvents, air fresheners, and mothballs), attached

garages, dry-cleaned clothing, municipal tap water, or personal care products

(Wallace et al., 1987; Batterman et al., 2007; Stocco et al., 2008; wheeler et al.,2013;

Ye et al., 2014).

According to European Environment Agency, the main sectors involved in high VOC emissions

for the EU-27 are solvent and product use (41 %), the road and no road transportation

(18%), and commercial, institutional and household associated emissions (14 %)

(European environment Agency, 2010). Still in the EU-27 at the industry level, the most occurred

VOC sources are in; (1) energy (41 %), (2) chemical industry (22 %) and (3) coating and surface

treatment activities (18 %) (European Pollutant Release and Transfer Register, 2016) (Figure 1).

Ambient outdoor sources combine natural (e.g, vegetation and fires) and anthropogenic

sources (e.g, evaporation processes associated with industry and transportation, or paints and

solvents use) (Watson et al.,2001; Liu et al., 2008). In urban atmosphere, motor vehicles exhaust

4

and evaporative emissions are reported to have higher VOCs emissions concentrations than

other sources (Cetin et al.,2003; Lin et al., 2004).

Figure 1: Industrial sector VOC emissions in EU-27 (Adapted from European Pollutant

Release and Transfer Register, 2016).

1.3 Hazards of VOCs

1.3.1 Human health effect

The exposure to higher permissible limit of VOCs concentrations lead to acute or chronic health

effects (e.g, exposure to ceiling concentration for an 8 hours shift than 500 ppm of toluene

causes headache and dizziness (Jiang et al., 2005) (Table 1). But biochemical pathways and

physiological functions of most VOCs to human health are still uncertain (Rudnicka et al., 2014).

Table 1: Related health effects to exposure of high VOC concentrations.

Chemical compound Health effect

Benzene Carcinogenic

Ethers Producing peroxides, affecting the reproductive

system

Xylene Eye and respiratory tract irritation, narcotic effect,

nervous system depression and death

Chloroform Affect central nervous system causing depression,

dizziness, liver and kidney damages, skin infection

Acetone and Acetaldehyde Respiratory and eye irritation

Phenol Offensive odor and toxicity

Epoxides Toxic, carcinogenic, explosive

N-containing compounds

(Amines)

Bad Odor, carcinogenic (affecting urinary bladder)

Source: Viswanathan et al (2007).

41%

18%

8% 1%

22%

6% 1% 3%

Energy Sector

Coating & Surface treatment

activitiesProduction and processing of metals

Mineral Industry

Chemical Industry

Paper and wood production

Waste and Wastewater

management

5

1.3.2 Tropospheric photochemical ozone formation

Troposphere is the region of the Earth’s atmosphere where people reside and in which most

chemical compounds are emitted as a result of human activities (Atkinson 2000). Nitrogen

oxides (NOx= NO + NO2), VOCs and sulfur compounds lead the chemical and physical

transformation which results in the formation of tropospheric ozone globally (Logan, 1994), acid

deposition (Schwartz, 1989). The production of ozone in troposphere relies on the photolysis of

NO2 (Equation 1) and the subsequent association of the photoproducts O(3P) with O2 via

(Equation 2) through the molecular reaction with the third body (M being used to present any

third body co reactants, i.e N2) (Monks et al. 2015).

The mechanism reaction of tropospheric ozone formation is a complex branched chain reaction

between the VOCs and NOx in the presence of light (Evuti 2013). Equation 3 to 9 depicts the

mechanism reaction of tropospheric reaction. Ozone is first used as source of hydroxyl radicals

(OH) (Monks et al., 2015) through

O3 + ℎ𝑣 → O2 + O(1D) (Eq.3)

O(1D) + H2O → 2OH∙ (Eq.4)

Where O(1D) is the electronic excited state atomic oxygen formed through photolysis at

wavelengths

6

The tropospheric O3 produced from hydrocarbon reactions as well as other sources is reportedly

to harm plants by reducing their growth due to limitation of carbon dioxide in stomata of

vegetation (Felzer et al., 2007).

1.3.3 Stratospheric ozone depletion

Stratospheric ozone layer is known to protect lower part of the earth’s atmosphere from high

frequency Ultraviolet (UV) light (Albritton, 1998). The ozone layer is reduced as a result of

imbalance between the formation and loss of ozone, where destruction is higher than

production (T et al., 2011).

Chlorine and Bromine released from man-made compounds such as chlorofluorocarbons

(CFCs) (example of CFC is dichlorodifluorocarbon [CCl2F2]) prone highly to the destruction of

stratospheric ozone (Angell et al., 2005). CFCs have long life time in the atmosphere (10 to 120

years) (Angell et al., 2005). As a matter of fact, CFCs are transported to the stratosphere where

they are eventually broken down by UV rays forming free chlorine (Equation 10) which reduce

ozone to oxygen molecule (equation 11 to 13).

CCl2F2 + ℎ𝑣 → Cl∙ + CF2Cl

. (Eq. 10)

Cl. + O3 → ClO. + O2 (Eq. 11)

ClO. + O → Cl. + O2 (Eq. 12)

O3 + 0 → 2O2 (Eq. 13)

1.3.4 Global Greenhouse effect

Earth has the capacity to balance the absorption and emission of solar radiations (Evuti, 2013). It

absorbs the energy in the form of ultraviolet, visible light and infrared and emits the infrared to

outer space(Mohammed et al., 2012). Any process which interfere with this balance result in the

phenomenon of global warming also termed as climate change or greenhouse effect

(AEA group, 2007).

The Infrared (IR) absorption of atmospheric trace gases, water vapor and carbon dioxide

(Derwent, 1995; Mohammed et al., 2012) disturbs the radiative balance. Therefore, earth’s

surface and the atmosphere react to the disturbance by warming to restore the radiative

balance. This process is termed as radiative forcing and the warming is the greenhouse effect.

Halogenated compounds are also claimed to be powerful greenhouse gases and deplete

stratospheric ozone, they are ozone depleting substances (ODSs) especially compounds which

have chlorine and bromine attached on, hence, causing global warming (Myhre et al. 2013)

7

The effect of the compounds to cause global warming compared to carbon dioxide is

expressed in term of Global Warming Potentials (GWPs)(Evuti, 2013) (Table 2). The GWP is defined

as a ratio of the radiative forcing from a given mass emission of the trace gas compared to that

from the same mass emission of carbon dioxide, integrated over a given time horizon

(Mohammed et al., 2012).

Table 2: Global warming potential (GWP) of some VOCs in a 100-year time horizon.

Source: AEA group (2007).

1.4 Air pollution control technologies for VOCs

Many technologies have been introduced for VOC emission control. The available techniques

are basically classified into two different categories: (i) process and equipment modification and

(ii) add on control technique (Khan & Ghoshal, 2000) (Figure 2). In the first category, control of

VOC emissions are made by modifying the process equipment, raw material, and / or change

the process (Khan & Ghoshal, 2000).

On the other hand the latter category, require an additional control method to regulate the

VOC emissions. It has two subgroups dubbed destruction and recovery of VOCs

(Khan & Ghoshal, 2000; Delhoménie & Heitz, 2005).

VOC GWP VOC GWP

Carbon dioxide 1 Dimethylether 1

Bromomethane 5 propylene 4.9

Propane 6.3 ethylene 6.8

Butane 7 1,1- Difluoroethane 122

Ethane 8.4 Difluoromethane 670

Dichloromethane 10 1,1,1,3,3,-Pentafluorobutane 782

Chloromethane 16 1,1,1,3,3-Pentafluoropropane 1020

Dichlorotrifluoroethane 76 1,1,1,2-Tetrafluoethane 1410

Dichloropentafluoropropane 120 1,1,1,2,3,4,4,5,5,5-Decafluoropentane 1610

1,1,1-Trichloroethane 144 1,1,1,2,3,3,3 Heptafluoropropane 3140

Dichlorotetrafluoroethane 599 Pentanfluoromethane 3450

Dichlorodifluoroethane 713 1,1,1-Trifluoroethane 4400

Chlorodifluoromethane 1780 1,1,1,3,3,3- Hexafluoropropane 9500

Chlorodifluoroethane 2270 Trifluoromethane 14310

8

*RFR: Reverse Flow Reactor

Figure 2: A tree diagram of the VOC emissions abatement technology (Khan & Ghoshal, 2000).

The adaptation or choice of technology lies on the operating conditions (flow rate,

temperature, humidity and VOC concentrations) and the pollutants physico-chemical

characteristics (solubility, vapor pressure, biodegradability level and inflammability)

(Crocker & Schnelle, 1998). An illustration is given in Figure 3, of the application limit for flow rate

in function of VOC concentrations of destruction and recovery technologies.

Figure 3: Application limit of flow rate vs VOC concentrations of different air pollution

technologies control (Delhoménie and Heitz 2005).

VOC removal technique

Process and equipment

modification

Condensation Oxidation

Add on control techniques

Destruction Recovery

Absorption Adsorption Biofiltration Membrane

separation

Thermal

oxidatio

n

RFR*

8

Catalytic

oxidation

Activated carbon based adsorption Zeolite based adsorption

9

Biofiltration is the only biological VOC treatment technology found in recovery technologies. The

remaining ones found in recovery and all destruction control techniques are non-biological

treatment technologies.

1.4.1 Non-biological technology for VOCs

As indicated in Figure 3, the non- biological technologies are physical chemical technologies

generally applied to reduce off-gas with high VOC emission concentrations. The lower VOC

concentrations in the flue gases the higher energy input will be required to get rid of the VOC

especially in the oxidation processes (incinerations)(Khan and Ghoshal, 2000). In terms of cost,

physical chemical treatment technologies for VOCs emission involve higher cost than biological

treatments (Font and Artola 2011).

1.4.2 Biological treatment of VOCS

The biological treatment technology (biotechnology) for VOCs emissions was introduced first by

the European countries (Germany followed by The Netherlands), in 1960 (Leson & Winer, 1991;

Cloirec et al, 2005). The fundamental purpose of that biological treatment technology was to

handle odor and VOC emission at the industrial scale (Álvarez-hornos et al., 2011).

In 2003, the European IPPC reported that vapor-phase biotechnologies, including biofilters,

biotrickling filters and bioscrubbers, have proven to be more environmental friendly and chosen

as best available technologies for the reduction of the VOC emissions in chemical sector

(European commission, 2003).

Hence, biological gas treatment (biotechnologies) are seen as potential alternative to the

conventional physico-chemical processes for removal of VOCs with high flow rate emission

streams with relative low VOC concentrations; conditions observed more particular in painting,

coating and printing processes (Álvarez-hornos et al., 2011).

Biotechnologies or biological VOC treatment technologies rely on the capacity of

microorganisms of using their metabolisms to translate the organic pollutants to less harmful

compounds. Since the pollutants are in gas phase, they have to be transferred in aqueous

phase to be ready and used by microorganism (Álvarez-hornos et al. 2004).

The overall degradation process of the biofiltration is presented in Equation 14

( Álvarez-hornos et al., 2011; Font & Artola, 2011).

Organic pollutant + O2 CO2 + H2O + heat + biomass + other byproduct (Eq. 14)

microbes

10

The main types of biological treatment of VOC emissions include biofilters, biotrickling filters and

bioscrubbers (Delhoménie and Heitz 2005). The basic idea for the removal of VOCs mechanism

for these three biological technologies is similar but there notable differences with regards to the

aqueous phase and microorganism growth (Álvarez-hornos et al., 2011) (table 2).

Table 2: Classification of vapor phase biotechnology systems.

Biotechnology system Microorganism growth Aqueous phase

Biofiltration Attached growth Stationary

Biotrickling filter Attached growth Flowing

Bioscrubber Suspended growth Flowing

Source: Álvarez-hornos et al (2011).

1.4.2.1 Biotrickling filters

In biotrickling filters, biodegrdation happen when the gas is first transferred to the biofilm which

grow to the packing materials. The packing materials are made from chemical inert materials

such as plastic rings (Waweru et al,. 2000), resins, ceramics, celite, polyurethane foam

(Yamashima and Kitagawa, 1998), and no nutrients are available in such materials for

microorganism to grow. Nutrients are continuously supplied from the top to bottom in

countercurrent with the flue gas, the leachate is collected at the bottom and recycled back up

(Berenjian et al., 2012)( Figure 4). This feeding process facilitates control of biological operating

parameters like nutrients and pH (Muñoz et al., 2015). Soluble VOC are reported to be highly

removed by biotrickling flters (Berenjian et al., 2012).

The major bottleneck of this system is the clogging of excess biomass in the filter bed and

research has developed three major solutions, mechanical, chemical and biological

(Delhoménie and Heitz 2005). Mechanical by bed stirring (Wübker et al., 1997;

Laurenzis et al., 1998) or bed backwashing with water which allows drainage of the excess

accumulated biomass (Smith et al., 1996).

Chemical treatment to breakdown the chemical bindings between biomass and bed particle

by using disinfecting reagents (Diks et al.,1994; Schönduve et al., 1996; Cox and Deshusses, 1999;

Armon et al., 2000; Chen and Stewart, 2000). Biological use biomass predators such as protozoa

(Cox and Deshusses, 1997). Amongst all these solutions mechanical treatment using water for

backwashing is claimed to be most efficient and at least friendly to the ecosystem

(Cai et al., 2004).

11

Figure 4 : Biotrickling filter setup (Delhoménie and Heitz, 2005).

1.4.2.2 Bioscrubber

The bioscrubber contains two reactors, the absorption tower and bioreactor. In the absorption

tower, the gas is absorbed or diffused into aqueous solution via the countercurrent gas-liquid

flow through the inert packing materials. Packing material within the absorption tower provides

a better surface transfer between VOC and aqueous phase (Kellner and Flauger, 1998)

(Figure 5). The washed off or clean gas flow to the top and the contaminated liquid is pumped

in the bioreactor (Berenjian, Chan, and Malmiri 2012). The bioreactor is inoculated with

degrading constrains in aqueous phase and contains nutrients essential for their growth and

maintenance

(Delhoménie and Heitz 2005). The major limitation of bioscrubbing system is that they are applied

to only soluble contaminants with low Henry’s constant (

12

Figure 5: Bioscrubber setup (Delhoménie and Heitz, 2005).

1.4.2.3 Biofilter

This is the most basic biological treatment process that uses organic packing materials in which

culture of microorganisms are developed to degrade pollutants into less harmful compounds.

The contaminated air pass through a biofilter packed with organic carrier materials where

biofilm are fixed (Figure 6). Before the inlet gas stream enters the filter bed, it is pre-humidified to

avoid clogging in filter bed (Waweru et al., 2000). Biodegradation happen when the pollutant is

first transferred from gas to liquid phase. In the liquid phase, the pollutant is either absorbed in

water or adsorbed on the packing material. The unavailable pollutants for biofilm diffuse through

the filter bed.

Figure 6: A typical setup of biofilter (Delhoménie and Heitz 2005).

Aqueous solution Clean air

Bioreactor

Waste solutions containing pollutants

Polluted air

Activated sludge, suspended in

nutrient solution

Absorption

column

Treated air

Nutrient solution

Occasional irrigation

Waste solutions possible recycling Polluted air

Bed packed

with organic

materials

13

The successfulness of microorganisms to degrade pollutants depends on a good follow up of

physical, chemical and biological parameters of the biological system:

(I) Filter bed, is an important part of the biological treatment process because they support the

growth of microorganism communities responsible for pollutants degradation and increase the

contact between the gas and biofilm (Iranpour et al., 2005; Kennes et al., 2009).

A good packing material should have a high specific area favorable for microbial activity, good

water retention to avoid dehydration, high porosity to provide a homogeneous gas distribution

entirely into bed, availability of intrinsic for nutrients and diverse microflora

(Delhoménie & Heitz, 2005; Berenjian et al., 2012).

The most used organic packing media are compost, peat, soil, and at smaller scale woodchips

and bark(Easter et al., 2005; Delhoménie & Heitz, 2005; Gabriel et al., 2007). Studies made on

woodchips or bark found that these packing materials are less satisfactory as compared to peat

and compost because of their low pH buffering capacity, low specific area and nutrient

availability (Smet et al., 1996a; Smet et al., 1999; Hong & Park, 2004).

(II) Moisture content is a crucial parameter for effective filter bed as microorganisms need water

to carry their metabolic activity (Shareefdeen et al., 2005). Less bed moisture content lead to

dehydration and gas channeling which affect particularly the microflora

(Delhoménie and Heitz 2005). On the contrary too much water in the filter bed cause flooding

which leads to compaction and anaerobic conditions (Delhoménie and Heitz 2005). The

moisture content of the overall carrier materials must have a value between 40 and 60 (w/w)

(Ottengraf 1986; Waweru et al., 2000).

(III) Temperature, microbial activity also depends on the biofilter operating temperature. The

microbial growth in biological systems works at a temperature between 10 and 40oC

(Cloirec et al., 2005). Most of microorganisms grow in the biofilter are mesophilic

(Kennes & Thalasso, 1998) at a temperature ranging between 20 and 40 oC. And this

temperature ranges define the optimum temperature in biofilters (Delhoménie and Heitz 2005).

(IV) pH, to support the microbial growth a pH range from 5 to 9 is normally used and the stability

of this parameter in the biofilter increase the microbial activity (Cloirec et al. 2005). The optimum

pH is around neutrality, pH≈7 (Delhoménie and Heitz 2005). Compounds containing heteroatoms

(sulfur, chlorine and nitrogen) are oxidized to acid by-products which in turn lower the pH of the

biofilter (Devinny and Hodge, 1995; Christen et al., 2002). The effect of pH on biofiltration

efficiency depends on types of microorganisms (Clark et al., 2004). Fungi has the ability to grow

14

at both neutral as well as acidic medium conditions and they are metabolically active at pH

approximately between 2 and 7 (Delhoménie and Heitz 2005). On the other hand, bacteria are

very sensitive to pH, they are less tolerant to pH below 7 (Kumar et al., 2011). Two methods used

by authors to maintain pH to neutrality are either to irrigate the biofilter by nutrients solution

which have buffer capacity or insert the buffer materials in biofilters

(Delhoménie and Heitz 2005). Nevertheless, the ideal pH of the biofilter medium depends on the

pollutant being treated and the characteristics of the microbial ecosystem (Kumar et al., 2011) .

(V)Nutrient requirement, aerobic microorganisms’ performance in biofilter depends on the

availability of nutrients. The most elements needed for the growth of the biomass are nitrogen,

phosphorous, potassium, sulfur and trace elements in additional to oxygen and carbon

(Álvarez-hornos et al., 2011). For the long term performance of the biofilter an additional of

nutrients is required (Yang et al., 2002). Due to the importance of nitrogen towards biomass

growth, an additional of nitrogen to the biofitler media is reported to enhance the performance

of the biofilter (Morales et al., 1998).

(VI) Bed porosity, this is an essential parameter which maintains even air flow rate and decrease

the pressure drop across biofilter (Álvarez-hornos et al., 2011). The filter bed which used only

compost as packing material report to be 44.4 % for dry compost and 39.6 % for wet compost

(Douglas & Devinny, 1997). To increase the porosity and decrease degree of compaction in the

bed filter, a mixture of packing materials are used (Bohn, 1992).

(VII) Inlet pollutant concentration, obviously biofilter perform best for treating pollutant which are

in concentration less than 1000 ppm. High inlet VOC concentration in the biofilter lead to

inhibition of microbial activity (Álvarez-hornos et al., 2011). Also, high inlet concentrations lead to

insufficient oxygen availability in biofilter (Ottengraf, 1987). Studies have found that 30 ppm of

toluene had 99% removal efficiency but when doubled its concentration, the removal get down

to 82% removal efficiency (Álvarez-hornos et al., 2011).

(VIII) Microorganisms and acclimation time, the natural organic packing material used in bed

media parent microorganism in biofiltration. Microorganism such bacteria and fungi are used for

the degradation of VOCs (Kumar et al., 2011). The degradation of the pollutant depend on the

nature of the filtering materials and the biodegradability level of VOC to be treated

(Kumar et al., 2011). A single type of microorganism is enough to degrade certain pollutants and

for certain group of pollutants or even a culture of microorganism is used (Nanda et al., 2012).

15

Compost has been reported to use bacteria belonging to a group of Proteobacteria,

Actinobacteria, Bacteroidetes and Firmicutes (Chung, 2007).

An acclimation, time required obtaining stable high removal efficiency over a long time, for

microorganism to handle new substrate environment may take 10 days to 10 weeks

(Ralebitso et al., 2012). Introduction of inoculum to the bed media can shorten the lag phase

(Álvarez-hornos et al., 2011). A typical biofilter usually contains 106-1010 cfu of bacteria and

actinomycetes per gram of bed and fungi in the range of 103-106 cfu per gram of bed

(Ottengraf, 1987). Degrading species in a biofilter are normally between 1 and 15 % of the total

microbial population (Pedersen et al., 1997; Delhomenie et al., 2001).

(IX) Empty bed residence time (EBRT), both air flow rate and EBRT are important parameters with

reasonable impact on the biodegradation performance of the biofilter (Elmrini et al., 2004).

Increasing EBRT will produce high removal efficiency. EBRT can be relied on to increase the

biofiltration performance and should be greater the time needed for diffusion processes for low

operating flow rate (Álvarez-hornos et al., 2011).

1.4.3 The biodegradation of hydrophobic compounds

Hydrophobic compounds have high Henry’s constant as compared to hydrophilic compounds.

That said, they are less soluble in water than hydrophilic compounds a factor which make them

often hard to reach the biofilm layer in biofilter thus providing low removal efficiency.

The composition of the filter materials is a critical parameter for effective biofilter toward the

removal efficiency of the hydrophobic and less soluble compounds. Studies conducted on

biofiltration of hydrophobic compounds proposed that improved adsorbing materials such as

granular activated carbon (GAC) may have characteristics that may promote higher

elimination capacity particularly for compounds with low solubility that emitted in variable loads

(Tonekaboni, 1998). Also, a way suggested by researchers to reduce solubility and transport of

hydrophobic compounds into filter bed was the use of Fungi (Woertz et al., 2001;

García-Peña et al., 2001). García-Peña et al (2001) described elimination capacity for toluene

up to six times higher than usually reported for bacteria using Paecilomyces variotii. Again for

hexane, which is around 100 times less soluble than toluene, EC between 100 and 150g.m-3.h-1

were obtained by Aspergillus níger (Spigno et al., 2003), while only between 10 and 60g.m-3.h-1

have been reported with bacterial consortia (Budwill and Coleman, 1999; Paca et al., 2001;

Kibazohi et al., 2004).

16

1.4.4 Parameters used to check the performance of the biological systems

The most common parameters used to check and compare the performance of biological

systems are summarized below (table 3)

Table 3: Performance parameters used in biological treatment systems.

Parameter Formula [unit] Description

EBRT EBRT =

V

Q[𝑠]

EBRT is the time taken by a gas in the biofilter.

Where V= Volume of the reactor (m3)and Q =

the flow of the gas (m3.h-1)

Inlet Load (IL) IL =

Q

Vx Cin[g. m

−3. h−1]

This is the amount of the pollutant introduced in

biofilter per unit volume per time. Where Cin is

concentration of pollutants in the inlet gas

stream (g.m-3)

Elimination

capacity

(EC)

EC

=Q

V (Cin − Cout)[g. m

−3 . h−1]

This is the amount of the pollutant removed per

volume of a filter bed per unit time

Removal

efficiency

(RE)

RE =(Cin−cout)

Cin x 100 [ %] This is the amount of the pollutant removed in

fraction converted in percentage.

Source: Waweru et al (2000).

1.5 Scope and objectives

Rwanda is a landlocked country whose economy has shown to be increasing since the tragedy

of the 1994 Tutsi’s Genocide (MINECOFIN 2013). Despite the tragedy of Tutsi’s Genocide,

population density (people per km2) is increasing year to year (449 in 2010 and 460 in 2015)

(World Bank, 2016). The basic country’s economic transformation is helped by the industrial,

service delivery and mining sector (Rwanda national institute of statistics, 2011). Industrial

activities and traffic are believed to be the main contributors of high atmospheric emissions in

the country especially in the capital city, Kigali.

Prior to industrial emissions, there are no available abatement technologies for the already

implemented industries. In addition to that, no studies have been conducted before to check

the status of emissions made in different local manufacturing industries. This is a common

problem shared by almost all African countries where data on the concern of air quality status

are hardly or not even found (Do et al. 2013).

17

To start bridging the gaps, a VOC study was conducted to make a new qualitative and

quantitative data in three different local industries namely Sulfo Rwanda industries producing

soap and cosmetic, Atelier Des Meubles de Kigali (AMEKI) making paints and Inyange industries

producing milk and juices by means of active sampling using Tenax TA tubes and TD-GC-MS

analysis.

This study is divided into two main objectives:

1. To characterize the VOC emitted in three local manufacturing industries, Sulfo Rwanda

Industries, AMEKI color and Inyange industries. Specific objectives on this first part are:

To characterize VOCs emitted in three industries

To identify and comparing the most occurring compounds from Indoor to outdoor in all

industries.

2. To evaluate biofiltration for the cost effective treatment of the waste gases containing

important pollutants, focus given to acetone, dimethyl sulfide and hexane.

Specific objectives on are:

To compare removal efficiencies of the three compounds (acetone, dimethyl sulfide and

hexane) in a biofilter packed with compost, silicon foam and wood chips.

To check the effect of using adsorbing materials, silicon foam, for the removal of

hydrophobic organic, hexane and assess inhibitory effects.

To check the partition coefficient of target VOC to the packing materials.

18

CHAPTER 2 MATERIALS AND METHODS

This chapter is split into two parts; Part (I) is the analysis of the industrial VOC concentrations

sampled in Rwanda. Samples were taken at three different local manufacturing industries by

means of active sampling using Tenax TA sorbent tubes. After sampling, they were transported

to the environment organic chemistry and technology lab for analysis. Part (II) is the Technology

based part, where biofiltration a cost effective abatement technology was used to evaluate the

removal efficiency of VOC where focus was given to acetone, dimethyl sulfide (DMS) and

hexane as representative VOC.

PART I: ANALYSIS OF INDUSTRIAL VOC CONCENTRATIONS IN RWANDA

2.1 Tenax TA tubes

Tenax TA tubes are tubes filled with sorbent resin (2, 6 diphenylene oxide) to capture VOCs and

semi-VOCs. They have standard dimensions of 1/4 inch (6.4 mm outer diameter x 5 mm internal

diameter), the length of 3.5 inch( 89 mm) and are filled with 200 mg of Tenax TA) (Anon, 2011).

Tenax TA tube can be heated up to 350 °c, has low affinity for water and has a specific surface

area of 35 m2.g-1 and average pore size of 200 nm based on Scientific Instrument Services

(SIS, 2016). The tubes are closed with 1/4 inch brass closure caps (Anon, 2011). The cap has a

white Teflon ferrule (Alltech SF-400T) that creates a better airtight seal. Each tube has an external

groove which indicates the sampling side (Do et al, 2009). The tube can be used more than 100

and after that period the resin should be replaced out of precaution (SIS, 2016).

2.2 Conditioning

Prior to sampling, the Tenax TA tubes should be conditioned to make sure that no residual

components remain on sorbents. Stainless steels, Tenax TA tubes, were put in an oven at 300 oc

for an hour under the flow of 10-50 ml.min-1 helium, to remove all residual components. During

heating oxygen should be avoided to enter since it is detrimental to the adsorbent resin. The

Tenax TA tubes in the oven are positioned with the sampling side mounted out. The oven

(Carlo Erba Instruments, MFC 500) is capable of heating nine tubes all at once.

19

Figure 7: Conditioning oven

2.2.1 Loading with internal standards

2.2.1.1 Chemicals

Deuterated Toluene (Tol-d8; 99.5%; Acros organics, Geel, Belgium) was used as an internal

standard (IS) (Figure 8).

Figure 8: Tol-d8 structure.

The solvent used for IS is methanol (LC-MS grade, 99.5%, Biosolve, Valkenswaard, Netherlands).

Tenax TA sorbet tubes have low affinity for methanol that’s why methanol was used as a solvent.

The stock solution of 223.7 µg.ml-1 was prepared by putting 24 µL of Tol-d8 in 100 mL of methanol

then kept in total darkness at -18 oC.

2.2.1.2 Preparation of the closed two-phase system

To prepare a gaseous Tol-d8, 20 μL of stock solution was added to 20 ml of deionized water

present in 119.8 mL of a glass bottle. Then, the bottle containing a mixture of stock solution and

deionized water was gas tightly sealed with a mininert valve (Alltech, Lokeren, Belgium) and

incubated in a thermostatic water bath at 25 ± 0.2 oC for 12 hours to assure the equilibrium

between gas and the liquid phase is reached.

D

CD3

D

D

D

D

20

2.2.1.3 Calculation of the headspace concentration

A given gas and water volumes at a specific temperature with known total mass and Henry’s

law constant of Tol-d8 (Dewulf et al., 1996), the headspace concentration of IS can be

calculated from the mass balance equilibrium. First, the total mass of Tol-d8 (m total) added to

the CTS was equal to 4474 ng. Based on the mass balance and Henry constant of Tol-d 8 at

25 oc (H= 0.183), we can derive,

Equation 15 can be rewritten into Equation. 17

4474 ng =Cair

0.183∗ Vwater + Cair ∗ Vair

(Eq. 17)

Then with Vwater= 20 mL; Vair =99.8 mL, the concentration of Tol-d8 in the headspace can be

calculated as 21.4 (ng.mL-1). This means that 0.5 mL air in the CTS contains 10.7 ng of Tol-d8.

2.2.1.4 Loading

In CTS, 0.5 mL of headspace was taken by 0.5 ml gastight pressure lock VICI precision analytical

syringe (Series A, Alltech). The desired volume was loaded onto the sorbent tubes through an

injection system flushed with helium (He) (flow rate of 100 mL.min-1). And finally, the He stream

was held on for 3 min before the tubes were sealed with ¼ inch brass long term storage

endcaps, equipped with ¼ inch one-piece PTFE ferrules.

2.2.2 Pump Calibration

A Gil Air sampling pump was calibrated before use by Gilibrator to make sure the targeted flow

rate is at least repeatedly obtained, and it was regulated on an average flow rate of 100 ± 0.5 %

mL.min-1 (n = 8).

2.3 Sampling Campaigns

The sampling campaign of VOCs in Rwanda was held at three different local industries namely

Sulfo Rwanda industries, AMEKI color and Inyange industries producing cosmetics, paints and

beverages respectively (Figure 9).

mtotal = mair + mwater=cair × Vair+cwater × Vwater ( Eq. 15)

H =Cair

CWater=0.183 mol.L−1 mol.L−1⁄ ( Eq. 16)

21

The sampling campaign was performed by means of active sampling using Tenax TA sorbent

tubes (n = 1) at indoor and outdoor of the three local manufacturing industries on 16th July and

30th July 2015 (Table 4). Two samples (one for three minutes and another for 30 minutes) were

sampled indoor and outdoor at each sampling site and two blanks were among sampling Tenax

tubes which remained closed entirely the whole campaign. The three minutes samples are the

one which were analyzed as they were found to be loaded with enough VOC concentrations

for measurements.

(1) Sulfo soap production unit (2) Sulfo cosmetics production unit, (3) AMEKI color for paints (4) Inyange for

juice and milk processing (beverages)

Figure 9 : Sampling locations on the map of Kigali city.

2

1

3

4

1

2

3

4

40 km

22

Table 4: The overview information of the VOC sampling campaign collected at three local

industries in Rwanda.

Indoor Outdoor Date Time Sample

size

Sampling times

1. Sulfo Rwanda Industries

16-07-2015

11:00-13:50

8 I. Soap production 30 30

3 3

II. Cosmetics 30 30

3 3

2. AMEKI color 30 30 16-07-2015 14:30-16:00 4

3 3

3. Inyange Industries 30 30 30-07-2015 16:00-17:45 4

3 3

2.3.1 Description of the sampling locations

2.3.1.1 Sulfo Rwanda Industries

Sulfo Rwanda Industries is a local manufacturing industry producing drinking water, hard and soft

soap, and cosmetics (body lotion, glycerin and toilet soap). The industry has four production

units. Samples were taken in late morning between 11:00 and 13:50 on 16th July, 2015 at two

manufacturing units, hard soap production and cosmetics unit.

The two production units are built in the middle of a busy place downtown in the capital city; on

the street of soap production unit there is a lot of traffic, big public parking lot at the back and

like in 300 m there is also a big city market hall and other many retailing business around it. The

cosmetic production unit is close to a national museum and prison (Figure 10) and (Figure 11).

Figure 10: Soap production unit. Figure 11: Cosmetics production unit.

23

2.3.1.2 AMEKI Color

AMEKI color is a paint production company located at the industrial park; it neighbors different

industries and is no far away from a polyclinic and petro station. Samples were taken in

afternoon between 14:30 and 16:00 on 16th July, 2015.

AMEKI color is the leading paint local manufacturing industry in Rwanda. Paints produced are;

(1) latex matt, based on styrene acrylic emulsion, suitable for ceilings and walls internally or

externally whether new or previously painted and (2) Silk Vinyl emulsion, water-based emulsion,

noted to be environmental friendly (Figure 12).

The company is mostly manual based paints production and permanent employees are in

direct contact with the raw products for paint making. Diesel is entirely used for cleaning all used

materials in the process.

Figure 12: Paint production.

2.3.1.3 Inyange Industries

The Inyange industry is located outside the capital, there is no high traffic as compared to the

city center and it is built in the lowland close to marchland. There is little habitation across the

industry. Inyange is the first ranked industry for the production of beverages in the country. Their

daily production is drinking water, juices, milk packaging and milk processing. All production

units are combined in the same site. After the production and packaging, caustic soda is

passed in the tanks for cleaning purposes. Samples were collected in the afternoon from 16:00 to

17:45 on 30th July, 2015 in the milk and juice production units (Figure 13).

24

Figure 13: Juice and milk production unit.

2.4 Analysis of Tenax TA sampling tubes

2.4.1 TD-GC-MS

Tenax TA tubes used in three sampling campaign location in Rwanda were transported to

laboratory and analyzed by TD-GC-MS in a method described by Do et al (2009) (Figure 14).

Figure 14 : The TD-GC-MS with (1) the TD (2) the transfer line from GC to MS,

(3) GC and (4) MS.

The desorption of analytes pre-concentrated on the Tenax TA sorbent tubes was performed by

a unity 2 thermal Desorption system (Markes, Llantrisant, UK) at 260 oC with 20 mL.min-1 helium

flow for 10 minutes. Each Tenax TA tube was put in the TD system equipped with two special

diffusion caps.

Desorption process was first pre-purged at 34 oC for two minutes to make sure that water vapor is

eliminated inside Tenax TA tubes and then a temperature of 260 oC for 10 min was set to tube

desorption. Next, analytes were refocused on a microtrap 100 % Tenax TA (noC-TNXTA)

(Markes, Llantrisant, UK) cooled at -10 oC. The Tenax TA tubes were heated up sharply from

-10 oC to 280 oC within three minutes.

2

4

3

1

25

Analytes were carried by a helium flow and injected onto a 30 m factor four VF-1 ms low bleed

bounded phase capillary GC column (Varian, Sint-Katelijne-Waver, Belgium;

100 % polydimethylsiloxane, internal diameter 0.25 mm, film thickness 1µm), after splitting helium

flow at 5 ml.min-1. The column head pressure was set at 50 kPa, resulting into a flow of

1.0 mL.min-1 (at 130 oC) through the GC column.

The GC (Focus GC, Thermo Scientific, Italy) oven temperature was initially set at 35 oC for

10 minutes. Next, the temperature in the GC was increased gradually up to 240 oC into four

stages (1) from 35 to 60 oC (2 oC.min-1), (2) from 60 to 170 oC (8 oC.min-1), (3) from 170 to 240 oC

(15 oC. min-1) and (4) (240 oC) was held for 10 minutes before cooling down to 35 oC. Even

though GC was cooled down, the transfer line from GC to MS was kept at 240 oC.

Mass from m/z 29 to 300 were recorded in full scan mode (200 ms per scan) on a DSQ II.

Quadrupole MS (Thermo Scientific, Austin, TX, USA), hyphenated to the GC, and operating at an

electron impact energy of 70 eV. Chromatograms and mass spectra were processed using

Xcalibur software (Thermo Finnigan, version 2.2)

Compound identifications were predicted based on (i) their fragmentation patterns and by

comparison of their mass spectra with the US National Institute of Science and Technology (NIST,

Gaithersburg, MD, USA) 2.0 database [NIST/US Environmental Protection Agency (EPA)/US

National Institute of Health (NIH) Mass Spectra Library], and (ii) comparison of retention time with

the standards.

2.4.2 Calibration of the TD-GC-MS

To have the correct concentration values, calibration was performed. A total set of 78 LC-MS

grade standard VOCs were used for the calibration.

These VOCs were purchased at the Acros Organics (Geel, Belgium) and/or at Sigma-Aldrich

(Bornen, Belgium) and all had a purity of at least 99.8 %. Methanol (LC-MC grade, 99.95 %,

Biosolve, Valkenswaard, Netherlands) served as a solvent for all standard compounds.

The 78 standards compounds were prepared and divided into three stock solutions (A, B and C)

(in methanol) together with a known mass of Tol-d8. A known volume 1µL of the stock solution

was loaded on two Tenax TA sampling tubes corresponding with a loaded mass between 31.3

and 81.2 ng. For each calibration of the TD-GC-MS, there were six calibration files corresponding

with 2x3 sampling tubes. The six tubes were then analyzed in the TD-GC-MS in full scan mode.

The quantification, data were processed by an extracted ion chromatogram.

26

The sample response factor (SRFi) in the chromatography is defined as the signal output per unit

mass of the substance injected. Therefore, SRFi can be calculated based on the Equation 18.

Where, Ai is the peak area and mi the mass (ng) of the substance i on the sorbent tube. Based on

the concept of SRF, the RSRF (Relative Sample Response Factor) is defined as the ratio of sample

response factor of the analyte (SRFa) and Tol-d8 (SRFst).

It is worth noting that RSRF is dimensionless. During the calibration of the TD-GC-MS, both

analyses and Tol-d8 were loaded from the liquid phase.

Demeestere et al. (2008) have found RSRF L,L (both loaded from liquid phase) and RSRF G,G (both

loaded from air phase) are the same.

2.5 Quantification

2.5.1 Calculation of the analyte concentration

Since we know (i) the mass of the IS (mst = 10.7 ng as calculated in section 2.2.1.3 from CTS (ii) the

peak areas of the analyte and the IS and (iii) RSRFL,L from the calibration of TD-GC-MS we can

depict the mass of the target compound (ma) on the sorbent in active sampling.

The Volume of the sampled air can be obtained from Eq.23.

SRFi =Aimi

(Eq.18)

RSRF =SRFaSRFst

(Eq.19)

RSRFL,L =SRFaSRFst

(Eq.20)

RSRFL,L ≈ RSRFG,G =SRFaSRFst

(Eq.21)

ma =mast × Aa

Ast × SRFL,L

(Eq.22)

27

And Qsample is the flow rate of the sampling pump and tsample is the sampling residence time. And

the concentration can be calculated as:

All components’ peaks were determined from respective extracted ion chromatographs and

the RSRFL, L was determined from the calibration of the TD-GC-MS. A blank correction was also

performed during the concentration calculations.

V = QSample × tsample (Eq.23)

Ca =maV

(Eq.24)

28

PART II: ABATEMENT TECHNOLOGY

2.6 BIOFILTRATION

Given state of the art cost effective abatement technology, biofiltration was used to evaluate

the removal efficiency of VOCs where focus was given to three compounds, acetone, dimethyl

sulfide and hexane.

2.6.1 Physical chemical properties of the representative VOC compounds

The most important physical chemical properties describing acetone, dimethyl sulfide and

hexane are summarized in Table 5.

Table 5: Physical chemical properties of acetone, dimethyl sulfide and hexane.

Parameters Acetone DMS Hexane

Functional group Ketone Sulfur compound Alkane

Molecular weight (g.mol-1) 58.08 62.13 84.17

Odor threshold(ppmv)2 42 0.003 1.5

Boiling point (0C)2 46.5 29.5 68.5

Vapor pressure at 25 0C (mmHg)3 231 502 153

Solubility in H2O at 25 oC( g.L-1)2 94 45 0.016

Henry’s law constant (-) (Cg/CL)1 0.012 0.048 44

1Calculated using the solubility and vapor pressure

2 (Nagata, 2003); 3 (SciFinder, 2016); (Daubert, 1989)

2.6.2 Biofiltration process

2.6.2.1 Biofiltration design

The biofiltrer was built using six identical cylindrical modules of Plexiglas and the total height of

the setup was 1.2 m with internal diameter of 10 cm. The packing materials in the biofilter

occupied only 1 m height and the remained 0.2 m at the bottom was occupied by glassbits

purposed to homogenize gas flow streams before enter the filter bed.

2.6.2.2 Biofiltration setup

The biofiltration setup used in the experiment was divided into three major parts: (A) generation

of the flow air controlled by mass flow controllers (B) the filter bed equally packed by compost,

woodchips and silicon foam and (C) analysis of VOC concentrations and CO2 produced by

29

SIFT-MS (Syft technology, the Voice 200®, Christchurch, New Zealand) and Vaisala CARBOCAP®

hand held carbon dioxide analyzer (GM70 model, vaisala, Finland) respectively (Figure 15).

Figure 15: Schematic diagram of the biofiltration setup. (1) pressure regulator (PR), (2) mass flow

controllers (MFC1; Q1 = 5 L.mim-1, MFC2 ; Q2 = 2.5 L.min-1, MCF3; Q5 = 0.2 L.min-1 and

Q3= Q1+Q2) (3) acetone bottle, (4) DMS bottle, (5) hexane bottle, (6) pressure control valve, (7)

humidifier column, (8) filter bed, (L1) leachate collection port, (P1) inlet port, (P2), (P3), (P4) and

(P5) are intermediate ports, (P6) outlet port, (9) flow monitoring valve, (10) rotameter, (11) clean

gas exit.

The aim of the setup was to measure the overall performance of the filter bed polluted with

acetone, DMS and hexane. The polluted air flow streams were generated by passing streams of

air into capillaries attached to liquid bottles filled with acetone, DMS and Hexane

(Acros Organics) controlled by mass flow controllers (Brooks Instruments, Mass flow controllers®,

Hartfield, USA). The capillary used for acetone and hexane was 5 cm long and 1/8 inch

diameter, and DMS was 10 cm long and 1/8 inch diameter. They were connected to ¼ inch

white Teflon PFTE tubing which connected the streams in the entire system. The main

Q4

Q3

Q5

Q3

Q1

Q2

2

11

9

1

1

2

2

6

3 4 5

7

L1

1

P1

10

P6

P2

P3

P4

P5

MFC 1

SIFT-MS

CO2

8

A B

b

C

MFC 2

MFC 3

30

contaminated stream flow (Q3) was pre-humidified in humidifier filled with water before getting

in the filter bed packed equally in volume by compost, woodchips and silicon foam.

The stream (Q3) flows upward in the filter bed which had six measuring ports (i.e. inlet, outlet and

four intermediate measuring ports). The leachate collection port was at the bottom of the filter

bed. Valve on measuring port was manually switched to start a small flow (Q4) that was

analyzed from the big stream (Q3) in the BF. This stream flow (Q4) controlled by valves and

measured with rotameter was diluted with a stream flow (Q5) of nitrogen before reaching

measuring instruments to avoid high concentration in the SIFT-MS. Figure 16 represent the actual

experimental set up for the study

Figure 16: Actual setup of the biofilter (1) PR, (2) polluted bottles, (3) humidifier column,

(4) biofilter, (5) SIFT-MS.

2.6.3 Characterization of the packing materials

The packing materials used for the experiments were compost (port grand, Belgium), woodchips

and silicon foam (sponge cord®, Netherlands). They were mixed and put in a filter bed at equal

volume fractions (1/3 v/v) (Figure 17). The physical chemical properties conducted for the

packing materials were density, moisture content, water holding capacity and porosity.

Figure 17: Packing materials used in biofiltration process. (1) Compost, (2) woodchips and

(3) Silicon foam.

5

2 3

4

1

1

2

3

31

2.6.3.1 Bulk Density

The apparent density of the three packing materials was measured by weighting packing

materials at ambient conditions into a known volume dimension. The Equation (25) was used to

calculate the bulk density, where mP and VB are weight of the packing material and volume of

used column respectively.

Bulk density =mPVB

(Eq.25)

2.6.3.2 Moisture content

The moisture content of the packing materials was calculated based on Equation (26) with mP

and mDP the mass of the packing material at ambient conditions and the mass of the dry

packing material after 72 h at 358 K in oven.

Moisture content =mP − mDP

mpx100 (Eq.26)

2.6.3.3 Water holding capacity

The water holding capacity of the packing materials was calculated by applying Equation (27)

with mw and mWP the amount water poured on the dried packing material and the mass of the

packing material 15 min after pouring water.

2.6.3.4 Porosity

The porosity of the mixed packing materials (1/1/1 volume ratio) was calculated based on an

online method using SIFT-MS. It was calculated as the ratio of net residence time (NRT) over

empty bed residence time (EBRT) (Equation 28). Compounds with high Henry’s law constants

behave as inert compound into biofilter and no degradation and absorption might happen to

such compounds (Volckaert, 2014). Dynamic experiment to calculate the porosity in a first

attempt was done by injecting 10 μL of hexane liquid into the biofilter. No peaks were found at

the outlet port for acetone, DMS and hexane. This can be cause by the interaction of the

packing materials with the contaminants (Figure 18). The second experiment, a 15 ml of

methane (± 35000 ppm) gas was injected and the peaks were recorded by the SIFT-MS to both

Water holding capacity =mWP −

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