Faculty of Bioscience Engineering

Academic year 2010 – 2011

CONTROL OF THAI VOC EMISSION BY USING

BIOFILTER PACKED WITH MACADAMIA NUTSHELL

CHIDNAPA KITTIKOON

Promoter: Prof. dr. ir. HERMAN VAN LANGENHOVE

Supervisor:ing. DIËGO VOLCKAERT & dr. ir. FRANCISCO JAVIER ÁLVAREZ-HORNOS

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

Master of ENVIRONMENTAL SANITATION

  i 

Acknowledgement This dissertation would not have been possible without the guidance and the

help of several individuals who contributed and extended their valuable assistance in

the preparation and completion of this study.

Firstly, I would like to express my sincerest gratitude to my supervisor, ing.

Diëgo Volckaert, who has supported me thorough my thesis with his great patience,

wise advices and invaluable assistance, yet providing me the space to work in my own

way. Simply, one could not wish for a better supervisor. Without him, this thesis and

my Master degree would not have been achieved.

Secondly, I would like to thank dr. ir. Francisco Javier Álvarez-Hornos, my

co-supervisor for teaching me how a professional conduct research and reading this

report simultaneously giving me many vital comments.

I owe my deepest gratitude to Prof. dr. ir. Herman Van Langenhove, for the

chance to be a member of ENVOC research group, being my trustworthy promoter

and prudent guidance.

Special thanks to all ENVOC members and the staffs of the Environmental

Sanitation programme for being there and making my heart warm. Without you guys,

it would have been a cheerless time.

And the last and foremost, my family that always unconditionally supports me

in every means with love.

Chidnapa Kittikoon, July 2011

  ii 

Abstract

A biofilter was used to treat air polluted with ethylbenzene. Macadamia

nutshells, which are a cheap waste product in Thailand, were chosen as the packing

material for the biofilter. The moisture content (6.6 w%), water holding capacity (16.8

w%), nutshell density (1.3 g ml-1) and organic content (78.0 w%) of the macadamia

nutshell were measured. The biofilter was operated during 5 months, in which several

inlet loads (IL) and empty bed residence times (EBRT) were applied. At the

mesophilic temperature, 30 ± 4 °C, removal efficiencies (RE) higher than 87 % were

obtained for IL lower than 95 g m-3 h-1 and 85 g m-3 h-1 at EBRTs of 150 and 90 s,

respectively. Determined from the carbon balance, 47.56 % of inlet carbon was

mineralized into CO2 and 41.65 % was gone into biomass. The results illustrate that a

biofilter with macadamia nutshells as carrier material is a good option for air

treatment in the mesophilic area.

  iii 

Contents Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii

List of abbreviations and acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v

List of figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi

List of tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii

Definition of operating parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . x

1. Literature Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1. Volatile Organic Compound (VOC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.2. VOC in Thailand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.2.1. Ethylbenzene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.2.2. N-hexane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.3. VOC abatement techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.4. Biofitration and others biological technologies . . . . . . . . . . . . . . . . . . . . . 7

1.5. Macadamia Nutshell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

2. Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3. Materials and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3.1. Biological procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3.1.1. Preculture and inoculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3.1.2. Nutrient solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3.1.3. Batch biodegradation test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.2. Analytical techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.2.1. Pollutant concentration in air stream . . . . . . . . . . . . . . . . . . . . . . . . 13

3.2.2. Carbon dioxide in air stream . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . 13

3.2.3. Leachate analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

3.2.3.1. pH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

3.2.3.2. Conductivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

3.2.3.3. Chemical oxygen demand (COD), and nitrate,

total nitrogen, phosphate content . . . . . . . . . . . . . . . . . . . . . 14

  iv 

3.2.3.4. Dissolved carbonate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

3.3. Macadamia nutshell properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

3.3.1. Moisture content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

3.3.2. Density of the macadamia nutshell . . . . . . . . . . . . . . . . . . . . . . . . . . 15

3.3.3. Water holding capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

3.3.4. Organic content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

3.3.5. Solvent absorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

3.4. The biofilter reactor setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

3.4.1. Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

3.4.2. Building up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

3.4.3. Starting up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

3.4.4. Ethylbenzene experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

3.4.5. Hexane experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

4. Results and discussions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

4.1. Batch biodegradation test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

4.2. Macadamia nutshell properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

4.2.1. Moisture content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

4.2.2. Density of the macadamia nutshell . . . . . . . . . . . . . . . . . . . . . . . . . . 21

4.2.3. Water holding capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

4.2.4. Organic content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

4.2.5. Solvent adsorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

4.3. The biofilter reactor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

4.3.1. Start-up period . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

4.3.2. Ethylbenzene experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

4.3.2.1. Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

4.3.2.2. EC VS IL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

4.3.2.3. Concentration profile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

4.3.2.4. Carbon dioxide production . . . . . . . . . . . . . . . . . . . . . . . . . . 29

4.3.2.5. Carbon mass balance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

4.3.3. Hexane experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

5. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

6. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

  v 

List of abbreviations and acronyms COD chemical oxygen demand

BTEX mixture of benzene, toluene, ethylbenzene and xylene

d day

DO oxygen demand

EB ethylbenzene

EBRT empty bed residence time

EC elimination capacity

GAC granulated activated carbon

GC gas chromatograph

h hour

H n-hexane

IL inlet load

MBR membrane bioreactor

RE removal efficiency

SS suspended solids

U.S. EPA Unites States Environmental Protection Agency

VOCs volatile organic compounds

VSS volatile suspended solids

  vi 

List of figures

Figure 1-1: Structure of ethylbenzene

Figure 1-2: Structure of n-hexane

Figure 1-3: Application limits (flow rate-VOC concentration) of different air pollution

control technologies (Delhomenie and Heitz, 2005)

Figure 1-4: Schematics of air pollution control biotechnologies

Figure 3-1: Scheme of the bioreactor

Figure 4-1: Solvent degradation activity of sludge over time

Figure 4-2: Chronologically overview of the study

Figure 4-3: Elimination capacity as a function of inlet load

Figure 4-4: Normalized concentration profile along the biofilter bed length

Figure 4-5: Correlation between EC and produced CO2 in mol m-3 h-1

  vii 

List of tables

Table 1-1: Principle, characteristics, and limitation of the main APTT applied to VOC elimination

Table 4-1: Moisture content of macadamia nutshell

Table 4-2: Density of the nutshells

Table 4-3: Water holding capacity results

Table 4-4: Organic content of the nutshells

Table 4-5: Solvent adsorption of the nutshells

Table 4-6: Summary and comparison of fibrous peat, compost, and macadamia

nutshells’ properties.

Table 4-7: The summarized results

  viii 

Definition of operating parameters Followings are some general definitions used in purification reactor and are

going to be mentioned frequently in this report.

Volumetric gas flow rate (Q)

The volumetric gas flow rate, Q, is the volumetric amount of waste air that

enters the reactor per unit of time (Nm3 h-1).

Total volume of the reactor (Vtotal)

The total volume of the reactor, Vtotal, is the volume of the empty reactor. In

many cases Vtotal is used instead of gas phase volume (Vgas), volumetric amount of the

gas phase in the reactor, because it is difficult to know the exact Vgas.

Empty bed residence time (EBRT)

The empty bed residence time, EBRT, is the total volume of the reactor, Vtotal,

over the volumetric gas flow rate, Q (s).

Inlet and outlet concentration (Cin and Cout)

The inlet concentration, Cin, is the pollutant concentration of the waste air

stream entering the reactor, while the outlet concentration, Cout, is the pollutant

concentration of the air stream leaving the reactor. The concentrations of a solvent in

the air stream are measured by a gas chromatograph and are indicated in g Nm-3.

Removal efficiency (RE)

The removal efficiency, RE, is a percentage of the removed pollutant over the

initial concentration. It can be calculated as following.

𝑅𝐸 =𝐶!" − 𝐶!"#

𝐶!"×100

  ix 

Inlet load (IL)

The inlet load is the amount (mass) of pollutant supplied to the reactor per unit

reactor volume and per unit of time. Here, it is expressed in g Nm-3 h-1. Generally, it is

obtained by this formula.

𝐼𝐿 =  𝐶!"×𝑄𝑉!"!#$

Elimination capacity (EC)

The elimination capacity, which is amount (mass) of pollutant eliminated from

the waste air stream, is shown in the same unit of the inlet load, g Nm-3 h-1. It can be

calculated from the following equation.

𝐸𝐶 =(𝐶!" − 𝐶!"#)×𝑄

𝑉!"!#$

  x 

Introduction The air pollution problems are usually ignored although they have many

effects to living organism and environment, especially to human health. It might be

because they take a long period to see the effects clearly and the cost of detection is

very due to the high resolution of the equipment. Fortunately, the attention has been

drawn into these issues significantly in this last decade because of global warming.

Volatile organic compounds (VOC), the major concern of this study, are

problematic in Thailand. Especially in a petrochemical industrial area, cancer

incidents are numerous. Having n-hexane and ethylbenzene as representatives,

degradation of pollutants in biofilter was investigated by imitating Thailand condition.

Furthermore, macadamia nutshells, the leftover from macadamia nut production, were

examined for their properties and potential to be an alternative packing material.

Chronologically, this report contains chapters of literature review, objectives,

materials and methods, results and discussions, conclusions and references.

Chapter 1: Literature Review 1

Chapter 1

Literature Review 6.1. Volatile Organic Compounds (VOC)

Generally, VOC refers to organic compounds, which have a high vapor pressure

and have a tendency to disperse easily into the environment; as a result, they can harm

humans and the environment. European Solvent Emission Directive 1999/13/CE

defines VOC as any organic compound having a vapour pressure of 0.01 kPa or more

at 293.15 K, or having a corresponding volatility under the particular condition of use.

According to Non-methane volatile organic compounds (NMVOC) emissions report

(APE 004) of the United Nations Economic Commission for Europe/Co-operative

programme for monitoring and evaluation of the long-range transmission of air

pollutants in Europe (UNECE/EMEP) Nomenclature for Reporting (NFR), these

sectors are identified as VOC sources; Energy production and distribution (emissions

from public heat and electricity generation, oil refining, production of solid fuels,

extraction and distribution of solid fossil fuels and geothermal energy), Energy use in

industry (emissions from combustion processes used in the manufacturing industry

including boilers, gas turbines and stationary engines), Industrial processes

(emissions derived from non-combustion related processes such as the production of

minerals, chemicals and metal production), Road transport (light and heavy duty

vehicles, passenger cars and motorcycles), Non-road transport (railways, domestic

shipping, certain aircraft movements, and non-road mobile machinery used in

agriculture and forestry), Commercial, institutional and households (emissions

principally occurring from fuel combustion in the services and household sectors),

Solvent and product use (non-combustion related emissions mainly in the services and

households sectors including activities such as paint application, dry-cleaning and

other use of solvents), Agriculture (manure management, fertilizer application, field-

burning of agricultural wastes), Waste (incineration, waste-water management), and

Other (emissions included in national total for entire territory not allocated to any

other sector).

Chapter 1: Literature Review 2

6.2. VOC in Thailand

The main VOC sources in Thailand are mobile sources in heavy traffic areas as

well as stationary sources at industrial sites. This study was inspired from VOC

problems of Map Ta Phut town in Rayong Province. The Eastern Seaboard Project is

located in this area, which gathers many refineries and petrochemical plants. Due to a

lack of sufficient cleaning technologies, the local people have been suffering from

respiratory problems and cancers. A report from Bureau of Policy and Strategy, the

Ministry of Public Health indicated that during 2001 to 2005 respiratory systems

diseases in that area were higher in number than the national average and tend to

increase every year. In 2005 annual death case report of the Ministry of Public Health

revealed that the number of deaths by cancer in Rayong Province was higher than the

average of 83.74 incidents per hundred thousand of inhabitants. In fact, many VOC

are problematic, so this study focuses on the removal of n-hexane and ethylbenzene,

which are representatives of an alkane and an aromatic hydrocarbon compound.

6.2.1. Ethylbenzene

Ethylbenzene (C6H5CH2CH3) is an aromatic hydrocarbon compound that smells

like gasoline and has a molecular weight of 106.16 g mol-1 and a vapour pressure of

9.53 mmHg at 25 °C (U.S. EPA, 2000a). It is used widely as a substrate for styrene

synthesis, as a solvent in some paints, glue and varnishing products and as a

constituent of asphalt and naphtha (U.S. EPA, 2000a). Ethylbenzene is one of the

VOCs largely emitted by the Thai industry (Sarawut, 2006).

Figure 1-1: Structure of ethylbenzene

Ethylbenzene can cause irritation to the eyes or to the respiratory tract after

inhalation and can cause some neurological effects such as dizziness at short-term

Chapter 1: Literature Review 3

exposure (Calabrese, 1991). The effect of chronic exposure is still unclear and it was

classified as not classifiable to human carcinogenetic (ATSDR, 1999).

Many microorganisms have the ability to degrade ethylbenzene. For instance, it

was reported that bacteria like Rhodococcus sp.(Lee et al., 2010) and Pseudomonas

spp. (Utkin et al., 1990; Littlejohns and Daugulis, 2008) could digest ethylbenzene.

The fungus, Trametes versicolor, can also degrade ethylbenzene by generating OH

radicals (Aranda et al., 2010).

6.2.2. N-hexane

Normal hexane or n-hexane (C6H14) is an aliphatic hydrocarbon with 6-carbon

atoms connected in a row with single bonds. According to the U.S. EPA database

(U.S. EPA, 2000b), hexane is a water insoluble, highly flammable and colorless liquid.

Its molecular weight is 86.18 g mol-1 and it has a vapour pressure of 150 mmHg at

25 °C (U.S. EPA, 1987). At 1 atm, hexane boils at 69 °C and melts at -95 °C. Mostly,

hexane is obtained from crude oil refining and is normally used for cooking oil

extraction, textile manufacturing, screen cleaning and in the glue industry.

Figure 1-2: Structure of n-hexane

Acute effects of hexane exposure are CNS depression (U.S. EPA, 1987)

(dizziness, giddiness, slight nausea and headache), dermatitis and irritation of the eyes

and to the digestive tract (Sittig, 1985). At long-term exposure, hexane may cause

sensorimotor polyneuropathy e.g. numbness, muscular weakness, blurred vision

(Sittig, 1985), but there was no information indicated that it is carcinogenic.

According to research, Rhodococcus sp. plays a major role in n-hexane

degradation. Rhodococcus sp. EC1 can mineralize hexane (Lee and Cho, 2008). In

addition it was reported that, Rhodococcus sp. EH 831 could break down n-hexane to

CO2 (Lee et al., 2010). Furthermore, Aspergillus niger was applied in bioreactors and

could degrade hexane (Spigno et al., 2003) by using a biofilter packed with sterilized

Chapter 1: Literature Review 4

granular expanded clay (Leca) at 4×10-3 m3 h-1 inlet air flow rate with hexane

concentration varied from 2 to 20 g m-3 h-1, as a result; over 70 % of the removal

efficiency was obtain for the lowest concentration.

6.3. VOC abatement techniques

Many air pollution treatment technologies (APTT) are applied in order to control

the emission of VOC. Delhomenie and Heitz (2005) described and indicated the

characteristics, limitations and costs of the different technologies, which can be seen

in Figure 1-3. Recently, membrane bioreactor (MBR) has been investigated

intensively too.

Commonly, VOC abatement technologies are divided into 2 groups, destructive

and non-destructive. The non-destructive technologies mainly focus on up

concentrating the VOC by adsorption, absorption, condensation and regeneration in

order to reuse because they are expensive. However, the non-destructive ways have a

limitation. The concentration of VOC in waste streams have to be high enough to

reach the desirable performance and in economic aspect a balance between new

solvent price and retained value should be taken into concern. For more details,

Figure 1-4 shows the application limits of each technology. The destructive

technologies are the answer for waste air streams with a low concentration of VOC.

VOC are usually burned together with natural gas or fuel. A catalyst can be added to

reduce the reaction temperature (lower cost) and to produce less toxic by-products.

Chapter 1: Literature Review 5

Table 1-1: Principle, characteristics, and limitation of the main APTT applied to VOC elimination (Delhomenie and Heitz, 2005)

Chapter 1: Literature Review 6

Figure 1-3: Application limits (flow rate-VOC concentration) of different air pollution

control technologies (Delhomenie and Heitz, 2005)

Recently, biological processes (destructive processes) have been considered as

interesting technologies for waste gas treatment because of the potential to degrade

VOC and the low installation and operational costs. In addition, the high temperature

(about 26 to 34 °C) in the tropical area induces a high biomass activity that leads to a

better performance of the biofiltration. Generally, the biomass activity doubles every

10 °C within the working range (10 to 40 °C). Besides, CO2 production from

biological processes is lower than from incineration, which consumes high amounts

of fuel mainly natural gas to have high removal efficiencies at the low concentrations

of VOCs. These reasons make biotechnologies outstanding and very attractive to

invest in tropical regions.

FIGURE 1 Application limits (flow rate—VOC concentration) of different APCT, based on references of Crocker and Schnelle, 1998;Juteau, 1997, and Devinny et al., 1998.

is released at the top of the column whereas the sepa-rated contaminated liquid phase is pumped towards anagitated, aerated bioreactor. This reactor contains thedegrading microbial strains suspended in the aqueousphase, and the nutrients essential for their growth andmaintenance. Most of the presently operating bioscrub-bers are inoculated with activated sludge, derived fromwastewater treatment plants, for example (Ottengraf,

TABLE 2 The technical characteristics of bioscrubbers, biotrickling filters and biofilters.

Bioprocess Microorganisms Liquid phase Depollution step

Bioscrubber Suspended in the bioreactor,in the aqueous growthmedium

• Mobile• Continuously

dispersed• Recycled

• VOC/air separation withinthe absorption column

• VOC oxidation in theaerated bioreactor

Biotrickling filter Immobilized on the filteringmaterial

• Mobile• Continuous trickling

over the filter bed• Possible recycling

• In the filter bed• In the biofilm

Biofilter Immobilized on the filteringmaterial

• Occasional bedirrigation withnutrient solutions

• In the filter bed• In the biofilm

1987). In some cases, bioreactors are directly inoc-ulated with specific degrading strains. The residencetimes for aqueous solutions in bioreactors range be-tween 20 and 40 days. After a treatment step (filtration,sedimentation of biomass), part of the waste solutionmay be recycled in the absorption unit while part ofthe sedimented biomass may be reintroduced into thebioreactor.

57 Biofiltration of Air

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Chapter 1: Literature Review 7

6.4. Biofitration and others biological technologies

Biofiltration is the oldest and simplest biotechnology for air treatment, which was

first invented in the beginning of the 20th century for an odour treatment (Pomeroy,

1957). Later on, it has been applied to treat other air pollutants. The other

biotechnologies like biotrickling filter, bioscrubber and membrane bioreactor (MBR)

were invented afterwards; especially MBR has only been in the spotlight the last

decade. Generally, these 4 technologies follow the same concept, namely using

microorganisms to degrade and mineralize pollutants into biomass, H2O and CO2.

However, there are some differences among them in the aspect of the place where

microorganisms grow and the flowing of the liquid phase. Microorganisms in a

biofilter and a biotrickling filter are immobilized on the packing material, while those

in a bioscrubber are suspended in the liquid medium and those in a MBR grow on the

membrane surface. The outstanding advantage of MBR is that some parts of

pollutants to go into the water and some go directly to microorganisms without

passing through water layer. This enables us to treat some water insoluble compounds

more efficiently. The differences between biofilter and biotrickling filtration are the

packing material and the irrigation. In a biofilter, organic materials are used as

packing material, whereas, in a biotrickling the synthetic materials are packed. In

addition, the liquid phase of a biotrickling filter flows continuously while in a biofilter

liquid is added discontinuously (only to add nutrients and to avoid dry out of the

packing material). The schematics of 4 mentioned biotechnologies are shown in

Figure 1-5.

a) bioscrubber b) biotrickling

FIGURE 2 Bioscrubber description.

The advantages of bioscrubbers are as follows:

! operational stability and good control of the biolog-ical parameters (pH, nutrients);! bioscrubbers do not generate high pressure drops(Rho, 2000);! their installation does not require large spaces.

However, the major limitations of bioscrubbers are:

! bioscrubbers are adapted to treat readily solubleVOC (alcohols, ketones), with low Henry coefficients(<0.01), and at concentrations in the gaseous phaseof less than 5 g · m!3 (Kellner and Flauger, 1998);! only quite low specific surface areas are available forgas/liquid transfer (generally <300 m!1);! production of a sedimented sludge at the bottom ofthe bioreactor;! production of waste water.

Some recent studies show that the addition of emulsi-fying agents (silicon oil, phthalate) in the aqueous so-lution can significantly improve the elimination of lesssoluble compounds, because they favor the VOC masstransfer from gas to liquid phases (Mortgat, 2001). De-spite this progress, the utilization of bioscrubbers stillremains rare.

THE BIOTRICKLING FILTERThe description of a typical biotrickling filter is pro-

vided in Figure 3. In such a filter, the gas flows through a

FIGURE 3 Biotrickling filter description.

fixed-bed, which is continuously irrigated with an aque-ous solution containing the nutrients required by thebiological system. Several studies have shown that thechoice of a co- or counter-current configuration for liq-uid and gaseous phases does not influence the biodegra-dation performance (Cox and Deshusses, 1998).Microorganisms are immobilized on the packing ma-terial. The pollutants are initially absorbed by the aque-ous film that surrounds the biological layers (biofilm),then the biodegradation reaction takes place within thebiofilm that gradually develops on the bed particles.

The filtering materials have to (1) facilitate the gasand liquid flows through the bed and the gas/biofilmtransfers, (2) favor the development of the microflora,and (3) resist crushing and compaction. Biotrickling fil-ter packings that best meet these specifications are madefrom inert materials such as: structured plastics, resins,ceramics, celite, polyurethane foam (Yamashita andKitagawa, 1998), lava rock (Sorial et al., 1995; Loy et al.,1997). However, most of these materials present limitedspecific surface areas (between 100 and 300 m!1) (Rho,2000), with some cases >1000 m!1 for polyurethanebased beds. As they are made from inert or synthetic ma-terials, biotrickling filters need to be inoculated, mostof the time with activated sludge (Oh and Bartha, 1997;Lu et al., 2000).

Due to the permanent trickling mechanism, biotrick-ling filters are “cousins” of bioscrubbers. In this way,they are more adapted for the elimination of quite sol-uble VOC. Nevertheless, as the contact between mi-croorganisms and pollutants occurs simultaneously to

M.-C. Delhomenie and M. Heitz 58

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Chapter 1: Literature Review 8

c) biofilter d) membrane bioreactor

Figure 1-4: Schematics of air pollution control biotechnologies (a-c Delhoménie,

2005; d Mudliar et al., 2010).

Nowadays, biofilters are practically used in the chemical process industry for

odour treatment, while using it for VOC elimination is still in a pilot study. A typical

biofilter can deal with large volumes of air streams having low concentrations of

contaminants (Delhoménie, 2005; Mudliar et al., 2010). Advantages of this

technology are the low operating and capital cost, the low pressure drop and the fact

that no secondary waste stream is produced (Mudliar et al., 2010). The drawbacks are

the deterioration and clogging of the packing material, the lower efficiency at high

pollutant concentrations and te maintainance of a constant pH and moisture level

(Mudliar et al., 2010).

Many parameters contribute to the performance of a biofilter. Micororganisms

need water for their metabolism, so the water level is an important factor to take into

concern. Too much water could create an anaerobic zone by inhibiting oxygen

transfer and could reduce gas capacity in the filter bed (Shareefdeen and Singh, 2005).

However, insufficient water could lead to poor performance. An optimal moisture

content should be 30-60 % by wet weight, which could be fulfilled by pre-

humidification of the inlet air stream and direct water supply to the filter bed (Mudliar

et al., 2010).

the absorption step (Cox and Deshusses, 1998), thesolubility specifications are less drastic than for bio-scrubbers (Henry coefficient <0.1) (van Groenestijnand Hesselink, 1993), and the VOC inlet concentra-tions are generally less than 0.5 g · m!3. Moreover, thecontinuous distribution of a nutrient solution facilitatesthe control of the biological operating parameters (nu-trients, pH). Further, as the contact between the mi-croorganisms and the pollutants occurs once the VOChave diffused in the liquid film, the flow rate and therecycling rate of the liquid phase, through the filter bed,are recognized to be critical parameters of biotricklingfilters. Indeed, some authors have suggested that an in-crease of the liquid flow rate should involve a propor-tional increase of the active exchange surface, and thenimprove the oxidation rate (Pedersen and Arvin, 1995;Zhu and Suidan, 1999). However, other researchers haveshown that maintaining a minimum water and nutri-ent supply is sufficient to reach better performance(Deheyder et al., 1994; Thalasso et al., 1996; Lu et al.,2002). In addition, as the distribution and the recyclingof nutrient solutions generate energy costs, other stud-ies suggest that the optimum recycling and distributionflow rates have to be found experimentally and on acase-by-case basis (Diks and Ottengraf, 1991; Dolfing etal., 1993; Kennes and Thalasso, 1998).

The major drawback of biotrickling filters is the ac-cumulation of excess biomass in the filter bed. Someauthors have demonstrated that, in the course of theprocess, the biofilm thickness can achieve several mil-limeters (Janni et al., 2001; Cohen, 2001), which cancause problems that lead to performance loss (Alonsoet al., 1997): pressure drop increases, bed channeling,and the creation of anaerobic zones. Several studieshave attempted to develop solutions to clogging prob-lems. The proposed methods are of three types: me-chanical, chemical or biological. Most of mechanicaltreatments consist of bed stirring (Wubker et al., 1997;Laurenzis et al., 1998) or bed backwashings with water(counter-current washings), which permits the drainingof excess accumulated biomass (Smith et al., 1996). Theobjectives of the chemical treatments are to dissociatethe chemical bindings between biomass and bed par-ticles surfaces, or to damage the biomass by creatingnutrients or water deficiencies, or by utilizing disinfect-ing reagents (Diks et al., 1994; Schonduve et al., 1996;Cox and Deshusses, 1999; Armon et al., 2000; Chenand Stewart, 2000). Biological methods utilize biomasspredators, such as protozoa (Cox and Deshusses, 1997).

Amongst all of these methods, the backwashings withwater are the most efficient and certainly the least dras-tic for the ecosystem (Cai et al., 2004). Nevertheless,the biotrickling filter technology is still employed toa lesser extent than biofiltration, which is certainly re-lated to its more consequential operating costs and tothe VOC solubility restrictions.

THE BIOFILTERA biofilter, as depicted in Figure 4, is a fixed-bed

bioreactor, in which degrading microorganisms are im-mobilized. The contaminated gases flow through theporous material and the VOC biological oxidation oc-curs after they have diffused into the biofilm, synthe-sized by the microflora. Two biofilter configurationsexist:

! the open designed biofilters, with ascending gas flows,installed outside because they require large spaces,and therefore exposed to climate changes.! the enclosed designed biofilters need more restrictedvolumes than the open configuration; they are ofteninstalled in closed rooms, and they can employ eitherascending or descending gas flows (Ottengraf, 1986).

The most important physical, chemical and biologicalparameters influencing the biofiltration process are de-scribed in the following sections.

FIGURE 4 Biofilter description.

59 Biofiltration of Air

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treatment of large volumes of waste gas and industrial emissionswith low concentration of odorants with poor solubility wasinvestigated by Cesario et al. (1992). The modified system consistsof two bioreactor units, which include (a) a spray column bioreactorwith liquid impelled loop reactor (LILR) and (b) a spray columnbioreactor connected to an airlift loop reactor (AIR). In both thesystems, gaseous odorants/liquid contactor is a spray column fortransfer of the odorants from gas to the water phase. This is inter-connected to either liquid impelled loop reactor or airlift loopreactor. Both the attached systems (LILR and ALR) contain culturemedium and the biomass. The spray column and LILR/ALR areinterconnected having a provision for recycling of the contents ofthe reactor (Cesario et al., 1992).

The spray column reactor with LILR contains nutrient medium.It is necessary that the nutrientmedium in the reactormust possesscharacteristics such as immiscibility with water, non-biodegrad-ability, should be non-toxic to the biocatalyst, should have lowvapor pressure, relatively low viscosity, and a density different fromthe density of water. The water immiscible liquid is recycledbetween the absorber and the bioreactor. However, the operation(recycling) depends upon (a) the volume of industrial emission tobe treated, (b) physicochemical characteristics and (c) theconcentration of the odorants in the gaseous emission and also (d)the targeted removal efficiency.

The novel reactor of a spray column systemwith LILR/ALR is stillon laboratory scale and requires extensive investigations to ascer-tain the odorant transfer from gas to the liquid absorber (ALR).

5.2. Future needs

Bioscrubber are generally considered to be useful for the treat-ment of waste gases containing water soluble pollutants (Henry’slaw coefficient, H< 0.01), but depending on the concentration andtype of pollutant, bioscrubbers may also efficiently be used forodorous gases with other characteristics. Bioscrubbers, providesubstantial advantages for waste gas treatment because of theirsmaller space requirements, high loading rates, reliable operation,process control, low risk of clogging, and low operating cost. Whenhigh concentrations of contaminants are to be treated, bioscrubbersoffer more advantages than conventional BFs, BTFs, and chemicalscrubbers. Combination of bioscrubbers and some polishing stepsmay improve the treatment efficiency for gases with mixture ofhydrophobic and hydrophilic compounds.

Bioscrubbers offer higher elimination efficiencies for gasesgenerated from liquid wastes, viz. H2S, NH3, and organic sulfurcompounds. However, due to the acidifying nature of thesesubstances, substantial oxidation and sulfuric acid production inthe scrubber may cause the pH to drop and decrease mass transferefficiency. The capacity of the adsorption section for handlinghigher H2S concentration needs to be further improved. This couldbe achieved by increasing the buffering capacity of the scrubbingmedium and also through pH control.

The bioscrubber application can be made more attractive thanthe use of other conventional BF or BTF at relatively high pollutantconcentration (>0.5 gm!3) with necessary modifications. There isalso a need to develop integrated/hybrid reactor configurations toachieve optimal and efficient bio-treatment of VOCs/odours, indi-vidually and in mixtures.

6. Membrane bioreactors

Membrane bioreactors were designed as an alternative toconventional bioreactors for waste gas treatment. The membranebioreactor allows the selective permeation of the pollutant, whichis not allowed in any of the reactors discussed previously.

Application of membrane bioreactors for waste gas treatment hasbeen reviewed before (Reij et al., 1998; Kumar et al., 2008a,b). Theconcentration difference between the gas phase and the biofilmphase provides the driving force for diffusion across the membrane.A pressure difference is not applied. The driving force dependsstrongly on the air–water partition coefficient of the diffusingvolatile component. For components with a high partition coeffi-cient the driving force for mass transfer is small. The concentrationin the liquid, which depends on the biodegrading activity of themicrobial population, also affects the driving force. The surface ofthe membrane forms the contact area (Reij et al., 1998).

In a BF bioreactor unit, waste gas is blown through a bed ofcompost or soil, where microorganisms consume or degrade thegaseous organic pollutants. No separate water phase is present. Anadvantage of the membrane bioreactor over the BF is the presenceof a discrete water phase allowing optimal humidification of thebiomass and removal of the degradation products, thus avoidinginactivation of the biomass. In a membrane bioreactor, themembrane serves as the interface between the gas phase and theliquid phase (Fig. 4, Reij et al., 1998). The gas–liquid interface thuscreated (e.g. in hollow fibre reactors) is larger than in other types ofgas–liquid contactors (Yang and Cussler, 1986). Moreover, in bio-trickling filter and the bioscrubber, a packed bed of inert material ispresent on which water is continuously sprayed. The pollutants inthese reactors have to diffuse through the water phase before it isconsumed by the microorganisms. For pollutants with poor water-solubility such a layer of water causes a substantial additionalresistance for mass transfer (De Heijder et al., 1994). In themembrane bioreactor, on the contrary, the liquid phase is situatedat the opposite side of the biofilm and hardly forms a barrier formass transfer of the poorly water soluble pollutants (Fig. 4). Asmentioned before, large gas–liquid interfaces of 1000–10,000 m2m!3 can be created in hollow fibre reactors (Rautenbachand Albrecht, 1989), allowing highmass transfer rates. The pressuredrop in the gas phase is much lower than observed in BFs, wherepressure drop may become significant.

Advantages of membrane bioreactors include.

(a) No moving parts(b) Process easy to scale up(c) Flow of gas and liquid can be varied independently, without the

problems of flooding, loading, or foaming

Disadvantages of the bioreactor are-

(a) High construction costs(b) Long-term operational stability (needs investigation)

Fig. 4. Schematics of a membrane bioreactor containing microporous hydrophobicmembrane, a biofilm and suspended cells.

S. Mudliar et al. / Journal of Environmental Management 91 (2010) 1039–10541046

Chapter 1: Literature Review 9

Microorganisms work in team (Delhomenie et al., 2001), even so, they are

naturally selected when acclimatizing. As a result, only the population that is resistant

to the applied conditions could survive. Sludge from a wastewater treatment plant is

frequently used as a contributor community, in some cases a pure culture of specialist

species is applied to the filter bed to enhance degradation of tough pollutants.

Biofilters generally contain 106 to 1010 cfu of microorganism per gram of packing

material (Krailas et al., 2000).

The packing material in the biofilter should have a high specific surface area for

biofilm attachment and for gas-biofilm mass transfer, a high porosity, a good water

retention capacity, an availability of intrinsic nutrients and a presence of a dense and

diverse local microflora (Mudliar et al., 2010). Peat, soil, compost and wood chips are

popular materials for biofilter beds. To prevent compaction but still having high

efficiency, rigid medium as bed structuring agent (e.g. wood chips or barks, glass

beads, lava rocks, perlite, vermiculite and polostyrene) is mixed with nutrient rich

medium (e.g. compost and soil). In brief, the characteristics of the packing material

contributes to properties of the biofilter bed that have an influence on the biofilter

performance.

Pollutant transfer from the air to the water could be described by Henry’s law

(Cg = HCw; with Cg the concentration in the gas phase, H the Henry coefficient at

acquiring temperature and Cw the concentration in the water) (Shareefdeen and Singh,

2005). The higher the value of the Henry coefficient, the less water soluble. The

elimination capacity decreases when the Henry law coefficient increases because

pollutants tend to stay in the gas phase, consequently, microorganism cannot take the

contaminant into the degradation process.

To ensure a good biological acitvity, the amount of macronutrients (C, H, O, N,

P, K, and S) is important. The inlet pollutant servs as the main carbon source for the

bacteria, while hydrogen and oxygen are available out of the water and the air. The

other macronutrients are provided by the packing medium and by nutrient addition

which can be supplied in a solid form or an aquous solution (Delhomenie et al.,

2001). A proper range for C:N:P ratio is 100:5:1 (Shareefdeen and Singh, 2005).

Most of the bacteria in a biofilter are neutrophilic that can work between a pH of

5 and 9 (Delhomenie et al., 2005). Some VOC are converted into acidic products

Chapter 1: Literature Review 10

which could acidify the filter bed what can lead to a poor performance of the biofilter.

Maintaining the neutral pH can be done by buffer material insertion (e.g. calcium

carbonate and dolomite) into the filter bed (Smet et al., 1996; Smet et al., 1999 cited

in Mudliar et al., 2010) or by pouring nutrient solution containing pH buffers (e.g.

Ca(OH)2, NaOH, NaHCO3 and urea) on the bed (Tang and Hwang, 1997; Zilli et al.,

2002; Delhomenie et al., 2002 cited in Mudliar et al., 2010).

Future research trends on biofiltration are improvements of the treatment on

mixed pollutants or on complex pollutated airstreams, quantification of biomass

turnover and understaning the ecological complexity of the microorganism

community (Cox and Deshusses, 1998).

6.5. Macadamia Nutshell

Macadamia is a name of a flowering plant genus in the family of Proteaceae that

originally grows in eastern Australia, New Caledonia and Indonesia. Two out of nine

species i.e. Macadamia integrifolia and Macadamia tetraphylla, are eatable and from

Australian in origin.

Nowadays, 3 strains that give good quality seed are planted widely over Thailand

and are for commercial use. The most of the crop areas are situated in the northern

region. These strains; Chiangmai 400 (HAES 660), Chiangmai 700 (HAES 741) and

Chiangmai 1000 (HAES 508), are different from each other due to their appropriate

altitude for planting, which are more than 400, 700 and 1000 m above sea level.

After the macadamia seed production, the nutshells were left over as a waste

material and were usually burned to ashes. In 2006, making use of waste from

macadamia nut production has been studied. It has been found that macadamia

charcoal has some anti-oxidant compound and can emit far-infrared ray (6-14

micrometre) (Wang et al., 2001), which helps accelerating cooking time and also can

be applied for many medical purposes.

Chapter 2: Objectives 11

Chapter 2

Objectives This study aims to investigate the following 3 topics.

Peat, soil, compost and wood chips are generally popular packing material.

There has been no reports about using macadamia nutshell for this purpose.

Therefore, this study aims to examine the potential of macadamia nutshell as packing

material because it’s a waste material and cheap.

To investigate the removal efficiency of ethylbenzene by using a biofilter and

inlet concentrations of 0.5, 1, 2 and 3 g/Nm3 of inlet concentration at an EBRT

between 90 and 150 seconds at a tropical temperature (30 ± 4 °C) setting up a

elimination capacity (EC) profile through the reactor by using different sampling

ports along the length of the filter bed.

To study the hexane removal efficiency with an inlet concentration of 0.5

g/Nm3 at an EBRT of 150 seconds and at a tropical temperature (30 ± 4 °C).

 

Chapter 3: Materials and Methods 12

Chapter 3

Materials and Methods 6.6. Biological procedures

6.6.1. Preculture of wastewater treatment sludge

A 2 L glass reactor was seeded with activated sludge from a wastewater

treatment plant (Aquafin, Gent, Belgium) and was continuously pre-adapted with a

vapour mixture of toluene, hexane and ethylbenzene. Two air pumps were used, one

for oxygen (air) supply and another one for air polluted with solvent. Air passed the

conical bottle, which contained the mixture of 3 solvents, and took vapour to the

sludge as carbon source. By this way, the bacterial community adapted itself to match

the pollutant; as a result, an adapted bacteria culture is obtained. Sludge respiration is

measured every week to ensure that bacteria were still alive. A dissolved oxygen

meter (WTW Oxi 3210) was put into the sludge culture bottle to quantify the

dissolved oxygen (DO) at the saturated level and the DO after switching off all air

supply at 30, 60, 120, 150, and 180 s. The amount of oxygen consumed indicated the

bioactivity of the sludge. Biomass was purged to maintain a constant suspended solid

concentration and nutrients were supplied periodically. This sludge bottle was

maintained separately from the reactor throughout the entire experiment period for

additional inoculation and starting up a new reactor.

6.6.2. Nutrient solution

The nutrient solution or mineral medium consisted out of 2.5 g L-1 MgSO4, 15 g

L-1 KH2PO4, 15 g L-1 K2HPO4, 53.6 g L-1 KNO3, 0.7 g L-1 multivitamins (B1, B2, B6,

B9, B12 , C, and D3) (Vitarmonyl) and 125 ml L-1 micronutrients. Micronutrient

solution contained 530 mg L-1 CaCl2, 200 mg L-1 Fe2(SO4)3, 10 mg L-1 ZnSO4·7H2O,

10 mg L-1 CoCl2·6H2O, 10 mg L-1 H3BO3, 4 mg L-1 MnCl2·4H2O, 4 mg L-1

Na2MoO4·2H2O, 3 mg L-1 Na2MoO4·2H2O, and 2 mg L-1 NiSO4·6H2O. This solution

was used to supply nutrients to both bioreactor and sludge culture.

Chapter 3: Materials and Methods 13

6.6.3. Batch biodegradation test

The batch biodegradation test was performed to examine the bacterial ability of

solvent mineralization. 5 mL of ethylbenzene was introduced into a 1 L bottle then it

was put in a thermostatic cabinet at 25 °C for 2 days. Subsequently, 500 µL of the

headspace from the prepared solvent bottle was fed into a penicillin bottle, which

contained 5 mL of nutrient solution (a reference bottle), and another 500 µL was put

into a penicillin bottle carrying 5 mL of pre-treated sludge. Ethylbenzene headspace

concentrations from these penicillin bottles were analysed in triplicate at 0, 30, 60,

120, 150, and 180 minutes. During the test, the bottles were shaken continuously at

150 rpm by a shaker (Edmund Bühler Swip). The same procedure was used for n-

hexane.

6.7. Analytical techniques

6.7.1. Pollutant concentration in air stream

Concentration of hexane and ethylbenzene in the air stream was determined by

a gas chromatograph (GC), Agilent 6890 GC System, equiped with a Flame

Ionisation Detector (FID). 0.5 mL of gas was taken with a 1 mL Hamilton® gas tight

syringe coupled with a Hamilton® side-pore needle and then was injected in the GC.

There were at least 3 replications for each sampling point (inlet air, outlet air, and

reactor parts 1, 2, 3, 4, and 5).

To calculate a calibration curve, bottles with a known volume of 0.3 L, 0.6 L,

1.1 L, and 5.6 L were sealed firmly with Teflon tape. Afterwards 1 µL of

ethylbenzene was injected into the 0.3 L, 0.6 L, and 1.1 L bottles, whereas, 0.5 µL of

ethylbenzene was fed to 1.1 L and 5.6 L bottles. In this way, 5 points for the

calibration curve were obtained to be around 2900, 1500, 800, 400, and 80 mgEB

Nm-3 (the exact values vary upon the volume of the bottles used). Hexane calibration

curve was calculated in the same way as the one of ethylbenzene, but the

concentrations were slightly lower because hexane has a smaller density.

6.7.2. Carbon dioxide (CO2) in air stream

The CO2 concentrations at the 7 sampling points mentioned above were

measured by using a CO2 meter (Vaisala CARBOCAP® MI70) in order to ensure that

Chapter 3: Materials and Methods 14

pollutants were degraded into CO2. Moreover, it can be used for carbon balance

calculation.

6.7.3. Pressure difference (ΔP)

The differences between the inlet pressure and the pressures at the outlet, 5th, 4th,

3rd, 2nd and 1st part of the reactor were measured by a pressure gradient meter (Testo

511) to detect any clogging problems.

6.7.4. Leachate analysis

Leachate properties reflect working condition of the reactor and imply health of

microorganisms in the reactor; consequently, many parameters are inspected every

week. In addition, before performing any analysis, the leachate is filtered by 0.45-

micron filter paper.

6.7.4.1. pH

The pH level of the leachate was checked regularly with a pH meter (Jenway

3310). Generally, a suitable pH range in a biofilter is between 5 and 9 (Delhomenie et

al. 2005).

6.7.4.2. Conductivity

A conductivity meter (Hanna EC/TDS HI98312) was used to determine the

conductivity level of the leachate.

6.7.4.3. Chemical oxygen demand (COD) nitrate, total nitrogen and phosphate

content

The chemical oxygen demand (COD), nitrate, total nitrogen and phosphate

content were investigated by use of standard kits from Macherey-Nagel Nanocolor®.

Nitrate amount was tested by using Nanocolor® Nitrate 50 standard kit, while

Nanocolor® gesamt-Stickstoff TNb 220 standard kit was used for total nitrogen.

Nanocolor® ortho-Phosphate 15 standard kit was applied for phosphate test and

Nanocolor® CSB 160 was for COD.

Chapter 3: Materials and Methods 15

6.7.4.4. Dissolved carbonate

The dissolved carbonate was measured by the method of Lahav et al. 2002.

The leachate was diluted until conductivity was lower than 1 mS cm-1. The pH was

measured from 50 ml of the diluted leachate was titrated with 0.0667 M HCl solution

to get a pH of 6.85, 5.85, 5.25, 4.25, 2.70, 2.50 and 2.40 respectively. The carbonate

concentrations were calculated by the homemade software obtained from the author.

6.8. Macadamia nutshell properties

The macadamia nutshells used for this experiment were waste materials of the

macadamia nut production of 2010 from the Royal Agricultural Station Doi Tung,

Chiangrai, Thailand. The nutshells were crushed by using a woodchopper and were

screened for sizes between 13 to 7 mm in order to increase the surface area and to

prevent an increase of pressure drop through the reactor caused by too small pieces.

6.8.1. Moisture content

The moisture content of the nutshells was explored by these following steps.

The exact weight of the nutshells in room conditions was measured. Afterwards the

nutshells were put in the oven at 110 °C for 24 hours and were weighed again.

6.8.2. Density of the macadamia nutshells

In order to obtain the density of the macadamia nutshells, a bottle with a known

volume and weight was completely filled with nutshells and was weighed for the

exact weight of the nutshells. Then distilled water was added to the bottle until it was

entirely full and was weighed again so the correct volume of the nutshells could be

calculated.

6.8.3. Water holding capacity

To measure the water holding capacity of the nutshells, the dried nutshells (in

the oven for at least 6 hours at 110 °C) were weighed, put in a funnel and poured over

with 100 g of distilled water. Ten minutes later, the nutshells were weighed again.

Chapter 3: Materials and Methods 16

6.8.4. Organic content

The organic content was determined by putting 5 g of nutshells in each of 3

preheated (6 hours at 120 °C) and dried crucibles with known weight. These cups

were placed in a furnace at 600 °C for 12 hours and were weighed afterward.

6.8.5. Solvent adsorption

The adsorption of hexane and ethylbenzene was determined by injecting 0.5, 1.0,

1.5, 2.0, and 2.5 µL of the solvent in each penicillin bottle, which were firmly sealed

and contained 500 mg of nutshells. Those bottles were left in a thermostatic cabinet

(Lovibond) for 4 at 25 °C. The solvent concentration in the headspace of the bottles

was measured in triplicate. After that, all bottles were kept in the cabinet for 2 more

days and then the headspace concentration was measured again to ensure that all

bottles were in equilibrium.

6.9. The biofilter reactor setup

6.9.1. Design

The biofilter reactor was made from poly methyl methacrylate (PMMA), a

transparant thermoplastic, which is generally known as plexiglass. The reactor has an

internal diameter of 10.4 cm, and a total height of 120 cm of which approximately

100 cm was filled with nutshells. The reactor could be separated into 6 parts, which

made it flexible in remodeling for each circumstance. Each part had a water channel

for temperature regulating, so experiments could be done at various temperatures. At

each part, there was also a sampling port and a humidification tube. In this way

measurements and water supply could be done at places in the reactor. For more

details see appendix part 1.

6.9.2. Building up

For this study, all 6 parts were assembled and bound together with 4 metal rods

as one tall reactor. The temperature was maintained around 30 ± 4 °C to imitate the

Thai climate. Connections between any tubes and the reactor were secured by natural

rubber pieces. Nutshell placement was divided into 3 sections by plexiglass sieve

pairing up the 1st with the 2nd, the 3th with the 4th, and the 5th with the 6th part of the

reactor. Each section had a volume of 2832 cm3, which corresponds with a height of

Chapter 3: Materials and Methods 17

33 cm of nutshells in each section. Thus, over the whole reactor the height of the

material measured around 1 metre.

Figure 3-1: Scheme of the bioreactor

Ambient air was pumped by an air pump (1) (Neuberger D-79112) connected

to a silica gel chamber (2), a mass flow controller (3) (Brooks MFC 5850s) with a

read-out unit (Brook MFCD ±24 Vdc), a flow meter (4), and a humidifier (5)

respectively. To pollute the air, a programmed syringe pump (7) (NE1000-Single

Syringe Pump) withdrew some solvent from the solvent bottle (8) and fed the exact

amount of the solvent to the air stream. The direction of solvent flow was controlled

by 2 one-way valves (9). The tubing for solvent supply was a transparent

perfluoroalkoxy (PFA) tube of 1/8 inch in diameter, whereas the other tubes and

connectors were made of polytetrafluoroethylene (PTFE). A mixing bottle (10)

containing glass marbles was placed before the reactor to assure that the inlet air was

mixed homogeneously and had a stable concentration. In order to control the

temperature, water in a water bath (13) was heated up and circulated by a membrane

pump (12) (Milton Roy CEP163-361NM) to the water channel (11) that surrounds the

biofilter.

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Chapter 3: Materials and Methods 18

Picture 3-1: Overall picture of the reactor

6.9.3. Starting up

When the reactor was packed with nutshells, 500 ml of pre-treated sludge was

poured at the top of the reactor. For acclimatization, 0.5 g Nm-3 of ethylbenzene and

0.5 g Nm-3 of hexane were introduced in the system to enhance a bacteria community

that could degrade both pollutants. During this period, inlet and outlet concentrations

were followed up to see the development of the reactor. Nutrient solution was mixed

to the leachate and poured at the top of the reactor every morning and in the late

afternoon after finishing all measurement to obtain a C/N ratio of 100/5. This step was

done at 150 s of empty bed resident time (EBRT). In this study, the starting up period

took 3-4 weeks.

6.9.4. Ethylbenzene experiment

Ethylbenzene inlet concentrations of 0.5, 1.0, 2.0 and 3.0 g Nm-3 were obtained

while varying the EBRT between 150 and 90 seconds. All of the ethylbenzene used in

this study was analytical grade solvent of 99.8 % purity from Acros®. Nutrient

supplement had the same composition as in the starting up period. The leachate was

mixed with the mineral solution and was reused to humidify the reactor. Once a week,

Chapter 3: Materials and Methods 19

the leachate was purged. Pollutant concentrations, CO2 concentrations and pressure

differences were measured daily at every sampling point.

6.9.5. Hexane experiment

An n-hexane inlet concentration of 0.5 g Nm-3 was fed to the reactor at 150 s of

EBRT. The n-hexane used in the experiment was analytical grade solvent of 99+ %

pure from Acros®. The nutrient supplement had the same composition as in the

starting up period and the ethylbenzene experiment. The leachate was mixed with the

mineral solution and was reused to humidify the reactor. Once in a week, the leachate

was purged. Pollutant concentrations, CO2 concentrations and pressure differences

were measured daily at every sampling point.

Chapter 4: Results and Discussions 20

Chapter 4

Results and Discussions 6.10. Batch biodegradation test

The batch biodegradation test was explained in 3.1.3 in the material and method

chapter and sludge activity can be obtained by the following equation.

Sludge activity (mg solvent ml-1sludge h-1) = ∆Csludge-∆CrefVsludge× t

×Vbottle×m3

106 ml

(ΔC = concentration difference between the start and the end (mg Nm-3),

V = volume (ml), t = time (h))

Figure 4-1: Solvent degradation activity of sludge over time

The sludge could eliminate solvent in the rate of 9.0215×10-3 mg ml-1 sludge h-1

for hexane and 2.6067×10-2 mg ml-1 sludge h-1 for ethylbenzene. The degradation of

ethylbenzene is around 29 times higher than that of hexane. The obtained result

Chapter 4: Results and Discussions 21

agreed with the view of the fact that hexane is a barely biodegradable compound

(single bonds and no reactive functional groups) and it should be more difficult to

break down than ethylbenzene. According to this result, the experiment would be

designed for the longer EBRT and the lower hexane concentration in the hexane

experiment.

6.11. Macadamia nutshell properties

6.11.1. Moisture content

The moisture content of the nutshells, which was measured as described in

3.3.1 of the material and method chapter, was calculated by the following equation.

(W = weight of macadamia nutshell (g))

Table 4-1: Moisture content of macadamia nutshell

Wroom condition (g) Wdry (g) Moisture content (w%) 353.33 328.10 7.14 346.78 324.99 6.28 325.49 304.50 6.45

Average 6.62

The average of triplicate of macadamia nutshells’ moisture content is 6.62 %

by weight, which is very low. The optimal moisture content should be within 30-60 %

by weight (Mudliar et al., 2010) because it supports biofilm to grow and to degrade

the pollutants, however; the very high moisture content might cause anaerobic zone

because oxygen cannot penetrate through the water layer to the biofilm that leads to

the dying of biofilm and the poor bioreactor performance. Comparing the obtained

result to the optimum value, the moisture content of macadamia nutshell is low,

therefore; to compensate this downside, direct water and/or medium solution supply is

indispensible.

6.11.2. Density of the macadamia nutshell

The density of the nutshell, measured as described in 3.3.2 of the previous

chapter, was figured by the following equation.

Moisture content = Wroom condition !Wdry

Wroom condition

"100

Chapter 4: Results and Discussions 22

(W = weight (g), V = volume (ml))

Table 4-2: Density of the nutshells

Wnutshell (g) Vnutshell (ml) Density (g ml-1) 31.71 25.37 1.25 32.30 25.87 1.25 31.32 24.37 1.28

Average 1.26

The average density of the macadamia nutshell was 1.26 g ml-1 or 1260 kg m-3.

It is close to density of compost, which is 1.26 g ml-1, but comparing to peat (0.133 g

ml-1), it is considerably heavier. This property has a significant effect to the design of

the bioreactor because the high-density packing material requires some frequent and

strong supporting layers. In addition, the high weight materials tend to have a collapse

or clogging at the bottom of each partition, so more frequent supporting plates are

needed. And these reasons directly raise the installation cost. For this study, 3

supporting plats were placed in thereactor.

6.11.3. Water holding capacity

The water holding capacity, measured as mentioned in 3.3.3 of the material

and method chapter, was obtained by following this equation.

(W = weight (g))

Table 4-3: Water holding capacity results

Water input (g) Water retained (g) Water holding capacity (w%) 100.18 17.23 17.20 99.70 16.00 16.05

100.24 17.28 17.24 Average 16.83

Density of nutshells = Wnutshell

Vbottle ! [(Wbottle filled with nutshell and water !Wbottle filled with nutshell )"1gH2O ml-1]

Water holding capacity = Wwet nutshell after 10 min !Wdry nutshell

Wpoured water

"100

Chapter 4: Results and Discussions 23

The average value is 16.83 w%, which is quite low when compare with that of

popular packing materials like fibrous peat (88 w%) (Álvarez-Hornos et al., 2008).

Similar to the moisture content, the water holding capacity is a crucial factor for the

biofilter performance. Poor water retention means more frequent direct water supply

and needs more attention on the irrigation.

6.11.4. Organic content

The organic content, which has been measured as explained in 3.3.4 of the

material and method, was calculated by the following equation.

(W = weight (g))

Table 4-4: Organic content of the nutshells

Nutshell weight before burning (g)

Nutshell weight after burning (g) Organic content (w%)

5.01 1.10 77.95 5.05 1.09 78.42 5.02 1.13 77.56

Average 77.98

Macadamia nutshell averagely contains 77.98 w% of organic content. It is

similar to a popular packing material like compost, which has 77.8 w% of organic

content (Abumaizar et al., 1998). Whilst, fibrous peat has a very high organic portion

that accounts for 95 w% of the total (Álvarez-Hornos et al., 2008).

6.11.5. Solvent adsorption

After following the instruction mentioned in 3.3.5, the solvent adsorption was

obtained by the average of the following equation.

(C = concentration (mg Nm-3), W = weight (g), V = volume (ml))

Organic content = Wnutshell before burning !Wnutshell after burning

Wnutshell before burning

"100

Solvent adsorption =Cheadspace at start - Cheadspace after

Wnutshell

!V bottle

Chapter 4: Results and Discussions 24

Table 4-5: Solvent adsorption of the nutshells

Concentrations of adsorbed solvent (g Nm-³) Mass nutshell (g)

EB Adsorption (mg solvent g-1

nutshell)

4th day 6th day

Hexane

0.31 0.49 504.90

0.52 1.47 1.69 504.60 2.88 3.27 504.20 2.58 2.75 504.90 3.04 3.65 505.10

Ethylbenzene

2.19 2.29 503.90

0.80 2.97 3.16 505.50 3.48 3.53 505.30 4.61 5.01 503.80

The nutshells can adsorb 0.52 and 0.80 mg solvent g-1 nutshell, for hexane and

ethylbenzene respectively. The obtained results are very low (Mudliar et al., 2010).

This means small amount of hexane and ethylbenzene might stay in the nutshells, so

the toxicity from accumulating solvent will not take place. However, the buffering

ability is also low, therefore; the microorganisms might encounter the fluctuation of

solvent concentration.

The general properties of macadamia nutshell are shown in comparison with 2

popular packing materials, compost and peat, as in the 4-6.

Table 4-6: Summary and comparison of fibrous peat, compost, and macadamia

nutshells’ properties.

Fibrous peat Compost

Macadamia nutshell

Moisture content, % 68* 65*** 6.62 Density, g ml-1 0.133** 1.1*** 1.26 Water holding capacity, % 88** high**** 16.83 Organic content, % 95** 77.8**** 77.98

(*Langenhove et al., 1986, ** Álvarez-Hornos et al., 2008, ***Morgan-Sagastume

and Noyola, 2006, **** Abumaizar et al., 1998)

As can be seen, the nutshells are similar to compost in density and organic

content aspects, but are obviously poor at moisture content and water holding capacity.

As a result, the macadamia nutshell reactor needs an intensive attention in

humidification for the good performance.

Chapter 4: Results and Discussions 25

6.12. The biofilter reactor

In general, the study was divided into 3 phases: ethylbenzene at 150 s of EBRT,

hexane at 150 s of EBRT and ethylbenzene at 90 s of EBRT, chronologically. The

overall results of ethylbenzene experiment showed good removal efficiency, whereas

hexane experiment gave out no pollutant elimination. The obtained results were

summarized into the table 4-7.

Figure 4-2: Chronologically overview of the study

Table 4-7: The summarized results

-100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100

0

20

40

60

80

100

120

140

160

180

200

0 10 20 30 40 50 60 70 80 90 100 110 120

Rem

oval

effi

cien

cy (%

)

Inle

t loa

d (g

m-3

h-1

reac

tor v

olum

e)

Time (d) Inlet load of Ethylbenzene Inlet load of Hexane RE ethylbenzene total reactor RE hexane total reactor

I II III IV V VI VII VIII IX

Phase EBRT (s)

Inlet concentration (g Nm-3)

Theoretical IL (g Nm-3 h-1) Max. RE (%) Max. EC

(g Nm-3 h-1)

I 150 0.5 each 6.01 EB, 6.01 H

89.55 EB, 5.35H

4.70 EB, 0.28 H

II 150 0.5 of EB 12.04 100.00 11.12 III 150 1.0 of EB 23.97 100.00 24.73 IV 150 2.0 of EB 48.04 98.57 48.07 V 150 3.0 of EB 72.01 95.57 81.56 VI 150 0.5 of H 12.00 6.14 0.86 VII 90 0.5 of EB 19.88 100.00 18.98 VIII 90 1.0 of EB 39.99 99.20 44.16 IX 90 1.5 of EB 59.98 98.59 66.39

Chapter 4: Results and Discussions 26

6.12.1. Start-up period

During the start-up period, the mixed pollutants (0.5 g Nm-3 of ethylbenzene

and 0.5 g Nm-3 of hexane) were introduced into the system; however, only

ethylbenzene was degraded (maximum RE was 89.55 %). Even though, the longer

residence times (120 and 150 s) were applied, there was no removal of hexane

throughout this period.

6.12.2. Ethylbenzene experiment

6.12.2.1. Performance

Within EB experiment, it could be divided into two-experiment phases 150 s

(phase II-V) and 90 s of EBRT (phase VII-IX). 150 s of EBRT was originally

continued from the starting-up period, while 90 s of EBRT came from general setting

of previous reports of BTEX degradation. It was like this because most of research

preferred focusing the study on the mixture; only few studies worked on solely EB.

At 90 s of EBRT the inlet concentration was fed at 0.5, 1.0 and 1.5 g Nm-3

and at 150 s of EBRT the inlet concentration were at 0.5, 1.0, 2.0, and 3.0 g Nm-3.

Normally, the reactor took 1 or 2 days after changing the conditions to meet the high

zone RE (more than 85 %) which could be seen in Figure 4-3.

Figure 4-3: Elimination capacity as a function of inlet load (at 90 and 150 s of EBRT)

0

20

40

60

80

100

0 10 20 30 40 50 60 70 80 90 100

EC (g

Nm

-3h-1

)

IL (g Nm-3h-1)

90 s of EBRT 150 s of EBRT

100% RE

90% RE

75% RE

50% RE

Chapter 4: Results and Discussions 27

6.12.2.2. EC VS IL

Figure 4-3 demonstrates the elimination capacity (EC) of the reactor according

to the inlet load (IL). The removal efficiency was higher than 85 % for both EBRT.

At 150 s EBRT, the maximum removal efficiency was 100.00 % at the inlet

concentration of 0.5 (IL = 11.12 g Nm-3h-1) and 1.0 (IL = 24.73 g Nm-3h-1) g Nm-3 and

was 98.57 % and 95.57 % for the inlet concentration of 2.0 (IL = 48.77 g Nm-3h-1)

and 3.0 g Nm-3 (IL = 85.47 g Nm-3h-1) chronologically. The experiment of 90 s EBRT

gave the similar result; the maximum remove efficiency was 100.00 % (IL = 18.98 g

Nm-3h-1), 99.20 % (IL = 44.52 g Nm-3h-1) and 98.59% (IL = 67.34 g Nm-3h-1) for 0.5,

1.0 and 1.5 g Nm-3 respectively. The maximum elimination capacity of 81.56 g Nm-3

h-1 was obtained at 150 s of EBRT. However, the higher inlet load at 90 s EBRT

should been explored further, because the elimination capacity results imply its bright

possibility.

Álvarez-Hornos et al. 2006 reported that the maximum EC of fibrous peat

biofilter at 127 s of EBRT was approximately 120 g m-3 h-1 for an IL of 135 g Nm-3 h-1

and the maximum EC of soil amendment reactor was 45 g m-3h-1 for an IL of 55 g m-3

h-1. Comparing with the obtained results, it could be seen that the macadamia nutshell

reactor showed better performances than the soil amendment reactor in the aspects of

the higher maximum EC and the shorter EBRT. However, it could reach only 81.56 g

Nm-3h-1 of the maximum EC, which was less than that obtained in the fibrous peat

biofilter despite of the longer EBRT.

Albumiazar et al., 1997 revealed that more than 90% RE of 200 ppm of each

BTEX (EB concentration is about 0.868 g m-3) at 156 s and 312 s of EBRT by using

compost-GAC biofilter. Mathur et al., investigating the BTEX degradation at the inlet

concentration of 0.4194 g m-3 by the biofilter packed with a mixture of compost sugar

cane bagasse and GAC in 2007, found that their biofilter reached more than 99% of

the maximum RE at 138 s of EBRT and got the maximum EC of 83.65 g Nm-3h-1 of

the IL of 126.5 g m-3h-1. Comparing the results with those of Albumiazar and Mathur,

the EBRT of the macadamia nutshell biofilter is significantly lower to get 99% of RE.

However, the pollutant IL is smaller than that of Mathur et al.

Chapter 4: Results and Discussions 28

6.12.2.3. Concentration profile

Considering the reactor as 6 subunits, the normalized concentration profile

(Figure 4-4) revealed that more than a half of the inlet pollutant was degraded in first

3 parts in almost all experiment conditions, except at the high inlet load 2.0 and 3.0 g

Nm-3 but they were just a little bit higher. There was removal observed in every part

of the reactor, which could see only in the high inlet load because at the concentration

of 0.5 and 1.0 g Nm-3 microorganisms were active enough to consume all of

ethylbenzene before it reached the last 2 parts. The bioactivity along the filter bed

indicates that the moisture content at the bottom of the bed was in the optimal

condition. If the bed is too wet, the oxygen transfer will be difficult and will lead to

anaerobic environment and no removal of pollutant. The concentration of 3.0 mg

Nm-3 was the highest limit of the biofilter in 150 s EBRT. Even though the removal

efficiency was still high but the outlet concentration (0.28 g Nm-3) was not preferable.

Figure 4-4: Normalized concentration profile along the biofilter bed length

0

0.2

0.4

0.6

0.8

1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

C/C

0

Reactor length (m)

90 s of EBRT

0.5 g Nm-3 1 g Nm-3 1.5 g Nm-3

0

0.2

0.4

0.6

0.8

1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

C/C

0

Reactor length (m)

150 s of EBRT

0.5 g Nm-3 1 g Nm-3 2 g Nm-3 3 g Nm-3

Chapter 4: Results and Discussions 29

6.12.2.4. Carbon dioxide production

Carbon dioxide production (mol m-3 h-1) corresponded to the elimination

capacity of ethylbenzene (mol m-3 h-1) very well in both EBRT as shown in Figure 4-5.

The relationship between these 2 factors was described by the following linear

regression equations.

90 s produced CO2 =4.5521EC + 0.4111 (R2 = 0.92069)

150 s produced CO2 = 4.7498EC + 0.2495 (R2= 0.91745)

As can be seen, the slopes of both equations are close to each other; therefore, the

average of 2 slopes (4.65) was used for further calculation. 1 molar of ethylbenzene

(C8 compound) was converted into 4.65 molar of carbon dioxide (C1 compound) that

meant 0.58 mol of CO2 would be produced per mol C of ethylbenzene consumed. To

simplify, 58% of inlet carbon was mineralized into CO2 then left the system via the

outlet stream and the rest (42 %) that might be converted into biomass or dissolved in

the leachate. Where the rest of carbon goes was discuss in the part of carbon mass

balance. This 58 % carbon mineralization is similar to the previous studies; 46 % of

ethanol (Cox et al., 2001) and 18-40 % of mixture of oxygenated VOCs (Sempere et

al., 2008).

Figure 4-5: Correlation between EC (mol m-3 h-1) and produced CO2 (mol m-3 h-1)

0

1

2

3

4

0 0.5 1

CO

2 pr

oduc

tion

(mol

m- ³

h-1)

EC Ethylbenzene (mol m-³ h-1)

90 s 150 s

Chapter 4: Results and Discussions 30

6.12.2.5. Carbon mass balance

To ensure that the biofilter does degrade ethylbenzene into CO2 without

creating a secondary waste stream, the carbon mass balance was calculated by using

the worst-case scenario as an example, which was the highest EB inlet concentration

(3.0 g Nm-3). All of carbon sources and outputs were converted to the unit of g C h-1.

The information used was from March 23rd, 2011. The data used are following; 3.06 g

Nm-3 of the inlet concentration, 0.27 g Nm-3 of the outlet concentration, 66.50 g Nm-3

h-1 of the IL, 150 s of EBRT, 0.1845 Nm3 h-1 of the volumetric gas flow rate (Q),

8.94×10-3 m3 of the total reactor volume (Vtotal), 60.56 g Nm-3h-1 of the EC, 104.92 g

Nm-3h-1 of CO2 produced, 4.96 g L-1 of suspended solid (SS), 5.21 g L-1 of dissolved

carbonate. And every week 0.70 L of leachate was purged. The chemical formula for

organic compound is C5H7O2N (molecular weight = 113.11 g mol-1) and EB is C8H10

with molecular weight of 106.12 g mol-1. Then the carbon mass balance was

calculated as following.

Carbonin= Carbonout+ Carbonbiomass

From the above equation, more details are described by these 3 equations.

Carbonin = Carboninlet

Carbonout= CarbonCO2+ CarbonVSS+ Carbondissolved CO32-+ Carbonoutlet stream

Carbonbiomass= Carbon in biomass accumulated in the reactor

With the mentioned data, these calculations were performed.

Carboninlet= IL × Vtotal ×weight of carbon in pollutantmolecular weight of pollutant

= 5.38×10-1 gC h-1

CarbonCO2= CO2produced× Vtotal ×weight of carbon in CO2molecular weight of CO2

= 2.56×10-1 gC h-1

CarbonVSS= 0.7SS × Vpurged leachate per h×weight of carbon in C5H7O2Nmolecular weight of C5H7O2N

= 7.67×10-3 gC h-1

Carbondissolved CO32-  = dissolved CO3

2- × Vpurged leachate per h×weight of carbon in CO32-

molecular weight of CO32-

Chapter 4: Results and Discussions 31

= 2.41×10-3 gC h-1

Carbonoutlet stream=  IL-EC  × Vtotal ×weight of carbon in pollutantmolecular weight of pollutant

=  4.80×10-2 gC h-1

In summary, all carbon amount could be directly measure via the exist

methods, except the amount of accumulated carbon in the system, which could be

calculated from the below equation.

Carboninlet= CarbonCO2+CarbonVSS+Carbondissolved CO32-+Carbonoutlet stream+Carbonbiomass

Carbonbiomass= 2.24×10-1 gC h-1

As can be observed from the carbon mass balance, most of the inlet carbon was

converted into carbon dioxide (47.56 %) and biomass (41.65 %). Only 10.79% of the

total carbon were transformed into VSS and carbonate compounds. Thus, there was

no secondary waste stream created and the biofilter could degrade ethylbenzene and

give carbon dioxide and biomass as products.

6.12.3. Hexane experiment

Hexane was not broken down until the end of the experiment. Many attempts

were done but no improvement was noticed. According to hexane characteristics,

hexane’s Henry coefficient at 35 °C (2.26×10-3) is roughly 3.5 times higher than at

20 °C (6.51×10-4), thus, the water bath was shut down in order to increase amount of

hexane in liquid phase. Even though, applying the nutrient solution only in the 2nd and

the 3rd section and letting the 1st part dried out in order to increase the opportunity of

hexane to reach microorganisms performed the selective humidification, no changes

was observed. This result is similar to the previous study (Kim et al., 2005), which

showed that degradation of hydrophobic compounds was tedious. The main reason is

hexane is hydrophobic compound that mainly stay in the gas phase, as a result, it is

not readily available for the microorganism. Some works (Hassan, 2010; Spigno,

2003) demonstrated the degradation of hexane by using fungus and working at dry

and acidic pH (around pH 4). To develop hexane elimination, the further works may

introduce some specialist species like Rhodococcus spp. or Aspagillus niger and work

at low pH with dry condition.

Chapter 5: Conclusions 32

Chapter 5 Conclusions

By using the nutshell biofilter working at 30 ± 4 °C, the maximum RE of

ethylbenzene reached at least 87.43 % of the inlet concentrations that ranged from 0.5

to 3.0 g Nm-3. The maximum EC at 150 s of EBRT was 81.56 g Nm-3 h-1 of IL 85.47

g Nm-3 h-1. The maximum EC at 90 s of EBRT was 66.39 g Nm-3 h-1 of IL 67.34 g

Nm-3 h-1, yet not final; the higher maximum EC could be examined further. There was

no secondary waste stream and the pollutant was mainly converted into carbon

dioxide and biomass. There is no hexane removal in any studied conditions.

The macadamia nutshell reactor showed the good performance; thus, they can

be used as a packing material yet the humidification of the nutshell bioreactor needs

to be watchful to prevent system drying out due to its low water holding capacity.

Furthermore, being waste material and cheap, they are an interesting choice for

packing material.

Chapter 6: References 33

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for Ethylbenzene (Update). Public Health Service, U.S. Department of Health

and Human Services, Atlanta, GA. 1999.

Abumaizar, RJ, Kocher, W, Smith, EH. 1997. Biofiltration of BTEX contaminated air

streams using compost-activated carbon filter media. J Hazard Mater

60(1998):111-126.

Álvarez-Hornos, FJ, Gabaldon, C, Martinez-Soria, V, Martin, M, Marzal, P, Penya-

Roja, JM. 2006. Biofiltration of ethylbenzene vapours: influence of the packing

material. Bioresour Technol 99:269–276.

Aranda, E, Marco-Urrea, E, Caminal, G, Arias, ME, Garcia-Romera, I, Guillen, F.

2010. Advanced oxidation of benzene, toluene, ethylbenzene and xylene isomers

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Gabriel, D, Maestre, JP, Martín, L, Gamisans, X, Lafuente, J. 2007. Characterisation

and performance of coconut fibre as packing material in the removal of

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Langenhove, HV, Wuyts, E, and Schamp, N. 1986. Elimination of hydrogen sulfide

form odorous air by a wood bark biofilter. Wat. Res. 20:1471–1476.

Chapter 6: References 34

Lee, EH, Cho, KS. 2008. Characterization of cyclohexane and hexane degradation by

Rhodococcus sp. EC1. Chemosphere 71:1738–1744.

Lee, EH, Kim, J, Cho, KS, Ahn, YG, Hwang, GS. 2010. Degradation of hexane and

other recalcitrant hydrocarbons by a novel isolate, Rhodococcus sp. EH831.

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Littlejohns, JV, Daugulis, AJ. 2008. Kinetics and interactions of BTEX compounds

during degradation by a bacterial consortium. Chemosphere 73:1453–1460.

Mathur, A. K., Majumder, C. B., and Chatterjee, S. (2007). Combined removal of

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ethylben.html. (Retrieved on 17/05/2011)

Chapter 6: References 35

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hexane.html. (Retrieved on 17/05/2011)

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Bezborodov, AM. 1990. Degradation of styene and ehtylbenzene by

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