ENHANCEMENT OF BIOGAS PRODUCTION FROM DOMESTIC FOOD WASTE BY BIOFILM

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ENHANCEMENT OF BIOGAS PRODUCTION FROM DOMESTIC FOOD WASTE BY BIOFILM

PRETREATMENT METHOD

BY

AMINA MOHAMED ALI

A dissertation submitted in fulfilment of the requirement for the degree of Master of Science (Biotechnology

Engineering)

Kulliyyah of Engineering

International Islamic University Malaysia

MAY 2019

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ABSTRACT

Food waste (FW) represents a significant portion of municipal solid waste (MSW).

Appropriate managements of FW are required to minimize its environmental problems. Hence, food waste is known as a great resource for renewable energy especially for biogas which is a clean and renewable energy. Utilization of food as feedstock for biogas production currently represents a challenge due to an efficient hydrolysis, a pretreatment process and the first step of biogas conversion process (anaerobic digestion, AD). This limitation is due to solubilisation and degradation of the polymers contained in food waste. As a result, the production of biogas volume in methanogenesis step is affected. There is a necessity of enhancing biogas yield by increasing the biodegradation of organic compounds (OC) in hydrolysis step.

Therefore, the present study focuses on the current knowledge available in the use of biofilm technologies for waste water treatment process and shows the opportunity of using biofilm in hydrolysis step of food waste to increase biogas. Thus, this study adopted the screened biofilm producer microorganisms to facilitate the biodegradation of OC and increase the volume of biogas production. As such, biofilm producing microorganism was first immobilized on granular activated carbon (GAC) surface and the optimum value of immobilization time, mass of GAC and size of microbial inoculum were found by using one-factor-at-a-time (OFAT) and response surface methodology (RSM) using face centered central composite design (FCCCD). Based on this result, 48 h of incubation, 8 g of GAC and 1 mL of inoculum were the optimum conditions when shaked at 37°C and 150 rpm. Different biofilm amounts (328 mg, 492 mg, 656 mg, 820 mg and 984 mg) were used in hydrolysis flask operated in a batch mode to increase the degradation of the OC. The optimal level of the hydrolysis degradation was at day 3 and 328 mg of biofilm where total solid (TS) decreased from 115 g/L to 79 g/L (31%) and TCOD decreased from 85330 mg/L to 54500 mg/L (36%). Development of anaerobic digestion of the hydrolyzed food waste operated in a semi-continuous mode has shown an increase of biogas volume to around 2000 ml/500 ml of feed for 50% of inoculum to feed ratio while 1523 mL, 753 mL, 502 mL of biogas for 30 %, 10 % of inoculum to feed ratio and the control, respectively which shows about 4-fold increased the biogas with biofilm pretreatment method. Thus, the analysis for TVS (volatile solid) reduction in the digester with 10%, 30%, 50% of inoculum and the control has increased to 30 %, 43.4 %, 45 % and 55 % respectively. TCOD removal has increased to 29 %, 33 %, 43 % and 56 % for the control, 10 %, 30 % and 50 % respectively for the inoculum to feed ratio. From these results, 50 % of inoculum to feed ratio has shown the highest biogas production and highest degradation of OC based on TVS reduction and TCOD reduction. Based on this study, biofilm pretreatment method can be considered promising method for the enhancement of biogas volume and the biodegradation of organic matter (OM).

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ثحبلا ةصلاخ

ABSTRACT IN ARABIC

( تبيظىا ثبفيخَىا ٍِ ا ًشٞبم اًءضج ًبعطىا ثبٝبفّ وّثَح ةاسدإ لىر بيطخحٗ ؛ٌىبعىا ٜف ) MSW

تقبطيى شٞبم دسَ٘م ًبعطىا ثبٝبفّ فشعُح ،ٌث ٍِٗ ؛تٞئٞبىا ومبشَىا وٞيقخى تبسبَْىا ًبعطىا ثبٝبفّ

داَ٘م ءازغىا ًاذخخسا ُإٗ ؛ةدذجخٍٗ تفٞظّ تقبط شبخعٝ ٛزىا ٛ٘ٞذىا صبغيى بَٞسلا ةدذجخَىا خّ بًٞىبد بًٝذذح وّثَٝ ٛ٘ٞذىا صبغىا جبخّلإ تطٞسٗ

تقبسٍ تجىبعٍ تٞيَع بّٖ٘نى ٜئبَىا ويذخىا تجٞ

ٜئإ٘لاىا ٌضٖىا( ٛ٘ٞذىا صبغىا وٝ٘ذح تٞيَع ٜف ٚىٗلأا ة٘طخىاٗ

ٚىإ ذٞقىا ازٕ عجشٝٗ ؛) AD

صبغىا ٌجد جبخّإ ٜف شّثؤٝ رإ ًبعطىا ثبٝبفّ ٜف ةد٘جَ٘ىا ثاشَٞى٘بىا سٕ٘ذحٗ ُببٗر تجٞخّ

صبغىا جبخّإ ٌجد ضٝضعخى ةسٗشض كبْٕٗ ؛ٛ٘ٞذىا ٛ٘ٞذىا ويذخىا ةدبٝص هلاخ ٍِ ٛ٘ٞذىا

( تٝ٘ضعىا ثببمشَيى ٚيع تساسذىا ضّمشح ،ازٕ ٍِ ًبقلاطّاٗ ؛ٜئبَىا ويذخىا ة٘طخ ٜف ) OC

ٜذظىا فشظىا ٓبٍٞ تجىبعٍ تٞيَعى ٌيٞف٘ٞب ثبْٞقح ًاذخخسا ٜف ًبٞىبد تدبخَىا ثبعلاطلاا تفشعٍ

ىا ويذخىا ة٘طخ ٜف تٝ٘ٞذىا تٞشغلأا ًاذخخسا تطشف شٖظحٗ

صبغىا ٌجد ةدبٝضى ًبعطىا ثبٝبفْى ٜئبَ

ويذخىا وٖٞسح ٚيع ٌيٞف٘ٞبيى تجخَْىا تقٞقذىا تٞذىا ثبْئبنىا ةسذق تساسذىا ضذفح ٌث ٍِٗ ؛ٛ٘ٞذىا جٞبثح هلاخ ٍِ ًلاٗأ لىر ٌخٝٗ ؛ٛ٘ٞذىا صبغىا جبخّإ ٌجد ةدبٝصٗ ٛ٘ضعىا بمشَيى ٜج٘ى٘ٞبىا س ٚيع تقٞقذىا تٞذىا ثبْئبنيى تجخَْىا ٌيٞف٘ٞب ( ٜبٞبذىا ظشَْىا ُ٘بشنىا خط

) GAC ٚيثَىا تَٞقىاٗ

تقٞقذىا ثبْئبنىا حبقى ٌجدٗ ٜبٞبذىا ظشَْىا ُ٘بشنىا تيخم ٚيع س٘ثعىا ٌخٝٗ ،ذَٞجخىا جقٗ ٍِ

( ةشٍ وم ٜف ذداٗ وٍبع ٜيٞيذخىا وٍبعىا ًاذخخسبب ( تببجخسلاا خطس تٞجٍْٖٗ ) OFAT

) RSM

( ٛضمشٍ بّمشٍ ٌَٞظح شبع ا ٚيع ًءبْبٗ ؛) FCCD

جّبم ،تجٞخْى 48

ٗ تّبضذىا ٍِ تعبس 8

ٗ ٜبٞبذىا ظشَْىا ُ٘بشنىا ٍِ ًاشج 1

ذْع بٖطبض ٌح بٍذْع ٚيثَىا تىبذىا ٜٕ حبقيىا ٌجد ٍِ وٍ

37 ٗ تٝ٘ئٍ تجسد 151

( ٌيٞف٘ٞبىا ٍِ تفيخخٍ ثبَٞم ًاذخخسا ٌحٗ ؛تقٞقذىا ٜف ةسٗد 328

،ٌجٍ

492 ،ٌجٍ

656 ،ٌجٍ

821 ٗ ٌجٍ

984 ذخىا قسٗد ٜف )ٌجٍ

ثبعفذىا تقٝشط ٜف ٜئبَىا وي

ثىبثىا ً٘ٞىا ٜف ٜئبَىا ويذخىا سٕ٘ذخى وثٍلأا ٙ٘خسَىا ُبمٗ ؛ٛ٘ضعىا بمشَىا سٕ٘ذح ةدبٝضى

ٗ 328 ،ٌغيٍ

492 ٍِ تٞينىا تبيظىا داَ٘ىا جضفخّا ثٞد ٌيٞف٘ٞبىا ٍِ غيٍ

115 ٚىإ شخى / ٌج

79 ( ٜينىا ٜئبَٞٞنىا ِٞجسملأا بيط جضفخّاٗ شخى / ٌج ٍِ ) TCOD

85331 ٚىإ شخى / ٌغيٍ

54511 تقٝشطب تى٘ذَىا ًبعطىا ثبٝبفْى ٜئإ٘لاىا ٌضٖىا شٝ٘طح تٞيَع ثشٖظأٗ ؛شخى / ٌغيٍ

ٜىا٘د ٚىإ ٛ٘ٞذىا صبغىا ٌجد ٜف ةدبٝص ةشَخسٍ ٔبش 2111

ٍِ وٍ

51 تبسّ ٚىإ حبقيىا ٍِ ٪

،تٝزغخىا 1523

،وٍ

753 ،وٍ

512 ،وٍ

31 ،٪

11 ٚىإ ٌٞقيخىا ٍِ تٝ٘ئَىا تبسْىا تٝزغخىا تبسّ

تٞينىا ةشٝبطخَىا تبيظىا داَ٘ىا وٞيقخب صبخىا وٞيذخىا عفحسا ذقى ،ازنٕٗ ؛ٜىا٘خىا ٚيع ٌنذخىاٗ

( ) TVS تبسْب ٌضٖىا ٜف 11

ٗ ٪ 31 ٗ ٪ 51 ٚىإ ةشطٞسىاٗ ٪ 31

ٗ ٪ 4334 ٗ ٪ 45 ٗ ٪ 55 ٪

ٚىإ ٜئبَٞٞنىا ِٞجسملأا بيط تىاصإ ثداص ذقٗ ؛ٜىا٘خىا ٚيع 29

، ٪ 33 ، ٪ 43 ٗ ٪ 56 ٪

، ٌنذخيى 11

، ٪ 31 ٗ ٪ 51 ُأ ٚيع تجٞخْىا ثشٖظأ 3تٝزغخى ٌٞقيخىا تبسْى ٜىا٘خىا ٚيع ٪ 51

٪

( ٛ٘ضعىا بمشَىا سٕ٘ذح ٚيعأٗ ٛ٘ٞذىا صبغيى جبخّإ ٚيعأ تٝزغخى حبقيىا تبسّ ٍِ

ٚيع ) OC

( تٞينىا ةشٝبطخَىا تبيظىا داَ٘ىا ضفخ طبسأ ٜينىا ٜئبَٞٞنىا ِٞجسملأا بيط ٍِ ذذىاٗ ) TVS

TCOD ( ًةذعاٗ ًتيٞسٗ تَٞيٞف٘ٞبىا تجىبعَىا تقٝشط سببخعا ِنَٝ ،تساسذىا ٓزٕ ٚيع ًءبْبٗ 3)

( تٝ٘ضعىا داَ٘يى ٛ٘ٞذىا ويذخىاٗ ٛ٘ٞذىا صبغىا ٌجد ِٞسذخى

) OM

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APPROVAL PAGE

I certify that I have supervised and read this study and that in my opinion; it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Master of Science (Biotechnology Engineering).

………..

Md. Zahangir Alam Supervisor

………..

Mohamed Saedi Jami Co-Supervisor

I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Master of Science (Biotechnology Engineering).

………..

Nassereldeen AhmedKabbashi Internal Examiner

………..

Azlin Suhaida Azmi Internal Examiner

This dissertation was submitted to the Department of Biotechnology Engineering and is accepted as a fulfilment of the requirement for the degree of Master of Science (Biotechnology Engineering).

………..

Nor Fadhillah Mohamed Azmin Head, Department of

Biotechnology Engineering This dissertation was submitted to the Kulliyyah of Engineering and is accepted as a fulfilment of the requirement for the degree Master of Science (Biotechnology Engineering).

………..

Ahmad Faris Bin Ismail

Dean, Kulliyyah of Engineering

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DECLARATION

I hereby declare that this dissertation is the result of my own investigations, except where otherwise stated. I also declare that it has not been previously or concurrently submitted as a whole for any other degrees at IIUM or other institutions.

Amina Mohamed ali

Signature ... Date ...

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COPYRIGHT PAGE

INTERNATIONAL ISLAMIC UNIVERSITY MALAYSIA

DECLARATION OF COPYRIGHT AND AFFIRMATION OF FAIR USE OF UNPUBLISHED RESEARCH

ENHANCEMENT OF BIOGAS PRODUCTION FROM DOMESTIC FOOD WASTE BY BIOFILM PRETREATMENT

METHOD

I declare that the copyright holders of this dissertation are jointly owned by the student and IIUM.

No part of this unpublished research may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise without prior written permission of the copyright holder except as provided below

1. Any material contained in or derived from this unpublished research may be used by others in their writing with due acknowledgement.

2. IIUM or its library will have the right to make and transmit copies (print or electronic) for institutional and academic purposes.

3. The IIUM library will have the right to make, store in a retrieved system and supply copies of this unpublished research if requested by other universities and research libraries.

By signing this form, I acknowledged that I have read and understand the IIUM Intellectual Property Right and Commercialization policy.

Affirmed by Amina Mohamed ali

……..……….. ………..

Signature Date

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This thesis is dedicated to:

The sake of Allah, my Creator and my Master, our messenger, Mohammed SAW (May Allah bless and grant him), my late father (Mohamed) whom I still miss every day and my mum (Fatima) my heroine, the most beautiful and strongest women who supports and encourages me, and brought me up without my father. She gave me constant love throughout my life and did her best to give me a meaningful life. I owe to her all success I achieve in life due to her strength and dedications.

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ACKNOWLEDGEMENTS

In the name of Allah, the Most Gracious and the Most Merciful, all praises to ALLAH, the Lord of the worlds for the strengths and His blessing in completing this thesis. May prayers and peace be upon His servant and messenger Mohamed (saw).

I would first like to express my deepest gratitude to my supervisor Prof. Dr Md.Zahangir Alam. His door was always open whenever I ran into a trouble spot or had a question about my research or writing. My appreciation also goes to my co- supervisor Associate Prof Dr.Mohamed Saedi for his kindness support and insightful comments on my writing.

My gratefully acknowledge go to all BTE lecturers who helped me during my academic journey, Prof. Dr. Nassereldeen Ahmed, Assoc. Prof. Dr. Ma’an, prof. Dr Azoura, Assoc. Prof. Dr Amani and all BTE lectures, for enlightening me the first glance of research.

Sincere thanks go to all Djibouti brothers from BTE department, especially Ibrahim for his guidance during my laboratory works, Moussa and Ayoub for their moral support during my study. Thus, my warm thanks go to my sisters from Djibouti doing master here with me especially Bilan, Nasteho, Moumina, Aicha, Ismahan, Nasra and others for their kindness and support during my study. Thanks for the friendship and memories my sisters.

I am using this opportunity to express my gratitude to my dear cousin Ahmed Ismael living in Brussels , Ibrahim Bello from Nigeria , Chehem Mohamed living in Rems and my close friends Rashidah from Malaysia and Wahyou from Indonesia who supported me throughout the course of this master. I am thankful for their aspiring guidance and truthful views on my study. I really want to thanks from the bottom of my heart my best friends, Masso Aboubacker, Momina taha, Fatouma ali, Sabrina Abdoulkader and dear Hamida Abass for always cheering me on and I will be forever grateful.

I owe a deep gratitude to Djibouti government for giving us an opportunity to study overseas and pursue a master degree. I would also like to give special thanks to my entire lecturer who taught me in my bachelor degree in Djibouti starting from Dr.Mahamoud Ahmed, Dr Abdoulkader Ali, Dr Idil Mouhoumed, Dr Sadat, Dr ali Houmed Adabo and all physical chemistry comities IN Djibouti.

Last but not the least, I would like to thank from my heart my family, my mum for her DUA, my eldest brother Aden Mohamed who always kept reminding me of my goals, remaining sisters and brothers for supporting me spiritually throughout my life and I take this opportunity to convey them my deepest love.

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LIST OF TABLES

Table 2.1: Generated municipal solid waste sources 11

Table 2.2: Characteristics of food waste 13

Table 2.3: Environmental impact of municipal solid waste management 16

Table 2.4: Average compositions of biogas 17

Table 2.5: Studies done on pre-treatment methods used to enhance biogas

production from FW 22

Table 2.6: Advantages and disadvantages of different biogas pretreatment

methods 24

Table 2.7: Groups of Anaerobic Bacteria 26

Table 2.8: Types of Anaerobic digesters 35

Table 4.1: Characteristic of collected food waste 64

Table 4.2: Experimental Data of the selected parameters by FCCCD 72 Table 4.3: ANOVA for immobilization optimization by FCCCD 73

Table 4.4: Characterization of inoculum 86

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LIST OF FIGURES

Figure 1.1: Flowchart of the methodology 8

Figure 2.1: Solid waste management steps 12

Figure 2.2: Amount of food waste generated sources 13

Figure 2.3: Incineration treatment technique 14

Figure 2.4: Sanitary Landfill of organic waste 15

Figure 2.5: Major component in aerobic composting of food waste 16

Figure 2.6: Overall anaerobic digestion plants 25

Figure 2.7: Two degrading enzyme of soluble waste 27

Figure 2.8: Sulfate-reducing and methane-forming bacteria Relationship 28 Figure 2.9: Methane-forming bacterial cells common shapes. Rod (a), curved

rod (b), spiral(c), spherical(c) 29

Figure 2.10: Anaerobic digestion process 29

Figure 2.11: Diagrammatic representation of various components of bacterial

biofilms 38

Figure 2.12: Various stages of biofilm formation and development 38 Figure 2.13: Granular activated carbon with 2-3 mm as a particle size 42

Figure 3.1: Flow chart for the research of this study 44

Figure 3.2: Immobilized biofilm at different incubation time (a) 24h (b) 48h

and (3) 72h. 52

Figure 3.3: Immobilization runs (a) shaked at 150 rpm and T=37 for two days

(b) after formation of biofilm onto GAC. 55

Figure 3.4: Pretreatment of food waste with immobilized biofilm at T=35±2°C

and rpm=150. 56

Figure 3.5: Schematic diagrams of gas measurement direct from a reactor using

cylinder meter digester. 58

Figure 4.1: Effect of time on the immobilization of biofilm producer bacteria at

temperature 37°C, 150 rpm and pH of 7. 67

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Figure 4.2: SEM images of a developing biofilm on GAC , A biofilm 24 h and B no biofilm 24h ; C biofilm 48 h and D no biofilm 48h; E biofilm

72h and F no biofilm at 72h. 70

Figure 4.3: 3D response surface curve (a) and contour plot of the interaction

effect between inoculum volumes and GAC masses 75 Figure 4.4: Changes in TS and VS of food waste hydrolysis with different

amount of biofilm and time of digestion. 79

Figure 4.5: Changes in total COD of food waste hydrolysis with different

amount of biofilm and time of digestion. 81

Figure 4.6: Soluble chemical oxygen demand (sCOD) content during of food

waste hydrolysis by one-factor-at-a-time 83

Figure 4.7: Changes in total dissolved solid (TDS) of food waste hydrolysis by

one-factor-at-a-time 84

Figure 4.8: Biogas volume produced daily in each digesters. 87 Figure 4.9: Cumulative of biogas produced in each digesters 88

Figure 4.10: Total biogas found from each digester. 90

Figure 4.11: Daily PH value in each digester. 92

Figure 4.12: TVS content in the digesters. 92

Figure 4.13: Percentage of TVS reduction in each digester. 93 Figure 4.14: Total COD concentration in the digesters on the first day and the

last day. 95

Figure 4.15: Percentage of TCOD removal of the considered digester. 95 Figure 4.16: Daily biogas production for digester with HRT=20. 98 Figure 4.17: Cumulative biogas produced for digester at HRT= 20. 99 Figure 4.18: Daily biogas production for digester with HRT=15. 97 Figure 4.19: Cumulative biogas produced for digester at HRT= 15. 98

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LIST OF ABBREVIATIONS

AD: Anaerobic Digestion (Process)

ANOVA: Analysis of variance

C/N: Carbon to nitrogen ratio

DOE: Design of experiment

DNA Deoxyribonucleic acid

TCOD: Total Chemical Oxygen demand

EPS: Extracellular Polymeric Substance

FCCCD: Face centered central composite design

FW: Food waste

GAC: Granular Activated Carbon

HRT: Hydraulic retention time

IIUM: International Islamic university of Malaysia

IWK: Indah Water Konsortium

MSW: Municipal solid waste

OFAT: One-factor at-a-time

OC: Organic compound

OD: Optical densities

OLR: Organic Loading Rate

OM: Organic Matters

POME: Palme Oil Mill Effluent

SCOD: Soluble chemical oxygen demand

SEM: Scanning electronic microscopic

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TCOD:

Solid Retention Time

Total Chemical Oxygen Demand (g/l)

TS: Total Solids (g/l)

TSS: Total Suspended Solid (g/l)

TVS: Total volatile solid (g/l)

TDS: Total dissolved solid (mg/l)

VFAs: Volatile fatty acids

rpm: Rotation per minute

RNA: Ribonucleic acid

RSM: Response surface method

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LIST OF SYMBOLS

- Minus Sign

% Percentage

+ Plus Sign

± Plus or Minus Sign

µ Micro

°C Degree Celsius

π Pi

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CHAPTER ONE INTRODUCTION

1.1 BACKGROUND OF THE STUDY

Municipal waste is massively generated in the world and the increase of its amount needs to be taken into consideration to continue to improve the management of Municipal Solid Waste (MSW) in the world. However, food waste (FW) deals with large amount of this municipal waste after paper (Nopharatana et al., 2007). The management of food waste continues to be a major challenge due to the uncontrolled discharge of considerable amount produced mostly by hotels, restaurants, families, canteens, companies, kitchens and so on (Zhang et al., 2014). Currently, municipal food waste is sent to incineration and landfills plants for final disposal but these processes have serious problems which include the increase of waste disposal cost, leachate problem causing groundwater pollution, the rise of toxic and greenhouse gases emission (Kiran et al. 2015).

On the other hand, renewable energy demand has increased due to the growing concerns of climate change, reliance on energy imports, insufficiency of fossil fuel (Rasi et al., 2011). Hence, biogas technology offers a very attractive way to use some categories of biomass to meet partial energy needs and appropriate functioning of biogas plant. Biogas can offer several benefits to the users and the municipal resulting in the conservation of the resources and the protection of the environment (Angelidaki et al., 2018). By definition, biogas is a bioenergy produced from anaerobic digestion of organic material (e.g. food, manure, wastewater sludge, crop residue and so on) by the action of bacteria.

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Nontheless, anaerobic digestion (AD) represents a more sustainable energy that can solve the issues observed in management of municipal solid waste and promotes minimization of large amount of domestic food waste by turning it into biogas energy.

Several approaches have been used to enhance biogas production from food waste such as pretreatment methods, co-digestion process, and variation in some operational parameters (Jain et al., 2015; Liu et al., 2016). Therefore, hydrolysis step known as pretreatment step that is generally considered as a rate limiting step for the overall AD as reported by most researchers. According to Carrere et al. (2016), hydrolysis is a slow step due to disintegration, solubilisation and enzymatic degradation of organic matter (OM) contained in FW, mostly when using solid waste as the substrate. Thus, Chen et al. (2016) added that low biodegradability may have negative effects such as long retention time, low methane yield and process instability. In this research, a detailed summary of the previous researches done on the enhancement of the anaerobic digestion process from food waste was discussed. A set of microorganisms and their immobilization methods could considerably improve the efficiency of food waste anaerobic digestion. Moreover, the controlling of AD parameters hydraulic retention time (HRT), organic loading rate (OLR) and inoculum to feed ratio as valuable parameters were also reviewed in detail.

In Malaysia, authorities are facing strenuous challenges in food waste management and treatment because the most common methods used for food waste disposal are landfill and incineration which are unsustainable for managing food waste. The management of food waste via landfills has reached their capacity in Malaysia and incineration methods are costly and cause air pollution. Therefore, the use of food waste as biogas feedstock could increase opportunity for effective food waste management in Malaysia (Fazeli et al., 2016).

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Therefore, the addition of biofilm carriers to the biogas reactors can be a possible approach to enhance biogas production from food waste by enhancing the digestion of food waste in hydrolysis step. This can be explained by the fact that the bacteria involved in biogas reactors could attach to the biofilm carrier and enhance digestion of organic waste (Langer et al., 2014b). Moreover, biofilms are set of many organisms forming communities by attaching to a surface and form an extracellular polymeric substance which can offer protection and provide mechanical stability, it can also be used as a diffusion barrier. Biofilm mediated anaerobic digestion is mostly used in waste water treatment as found indairy industry wastewater (Karadag et al., 2015), in industrial waste water treatment (Van Lier et al., 2015).Additionally, Liu et al (2017) have used biofilm for biogas production during anaerobic digestion of corn straw but it has not been yet explored deeply in domestic food waste. Therefore, in the production of biogas from manure wastewater, biofilm has been proven to improve biogas production (Szentgyörgyi et al., 2010) in which types and size of biofilm carriers play important role in both degradation of organic wastewater and production of biogas (Dutta et al., 2014; Jamali et al., 2016).

In addition, biofilm technology for biogas production from palm oil mill effluent (POME) was done by Fazil et al (2018). In the study, indigenous microorganisms were isolated from POME for biofilm formation and based on cellulolytic, lipolytic, amylolytic, proteolytic enzyme detection, potential biofilm for hydrolysis of POME was screened, and three properties of biofilm were characterized to understand deeply about biofilm, EPS composition, surface adhesion and bacteria interaction.

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Hence, in this study, the biofilm technology was used to enhance biogas production from domestic food waste. Prepared biofilm-producer-microbial strains were collected, inoculated and immobilized on the carriers. The mass of granular activating carbon (GAC) giving the best result for immobilization of biofilm based on biomass weight was chosen to evaluate hydrolysis process of food waste. In addition, two stages AD operated at semi-continuous mode was designed for biogas production and certain parameters of AD of food waste such as HRT, and inoculum to feed ratio were optimized using one-factor at-a-time (OFAT). Consequently, some of these parameters such as HRT and inoculum to feed ratio were optimized and the effect of these parameters were examined.

1.2 STATEMENT OF THE PROBLEM

Treatment of domestic food waste has become a major problem that needs to be solved as its generation keeps increasing due to the growth of population. At present, there are several treatment methods used commonly for food waste such as landfill, incineration, composting, and anaerobic digestion. The disposal of food waste on landfill has caused a lot of issues such as leached, air pollution, greenhouse gas due to high content of moisture contained in food waste. Therefore, researchers have found that the most attractive approach for domestic food waste treatment is anaerobic digestion which is considered to be a source of energy and this energy comes from biogas produced by anaerobic digestion technology.

On the other hand, several studies are currently conducted on biogas production by anaerobic digestion but the main problem is that the amount of biogas produced is low because of the rate-limitation of hydrolysis and acidogenesis steps in this process. This limitation is occurred particularly for high organic waste as food

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waste. Consequently, some researchers used pretreatment methods, mechanical, thermal, chemical and biological, to increase biogas production (Taherdanak &

Zilouei, 2014; Tedesco et al., 2013). Pretreatment was implemented to enhance hydrolysis step of anaerobic digestion but the limitations is about high energy demand and maintenance cost, corrosion problem and use of large amount of chemicals.

Identification of the above problems related with biogas production led to the search for alternatives to introduce a pretreatment method which is capable to increase biodegradability, facilitated hydrolysis of food waste and improve the performance of AD.

Biofilm technology is a well-developed technology in which assemblages of microbial cells are enclosed in a matrix of bacterial self-generated extracellular polymeric substances (EPS) formed when attached to the surface. Consequently, this matrix can offer protection, provide mechanical stability. Biofilm mediated anaerobic digestion of organic waste was used in wastewater treatment and shown several advantages including the removal of the pollutants, operational flexibility, low space requirements, reduced hydraulic retention time, increased biomass residence time.

Additionally, biofilm system was used in the production of biogas from manure and it has been proven to improve biogas production. The use of biofilm is becoming increasingly important because of its benefits but rarely studied in biogas production (Chai et al., 2014; Dutta et al., 2014) especially in the case of biogas production from food waste.

Fazil et al., (2018) have used biofilm to enhance biogas production from palm oil mill effluent (POME). In addition, Ibrahim et al (2018) have also used biofilm to enhance biogas production from sewage sludge. They have noticed an increase of biogas production of 15 % compared to the control digester operated without biofilm.

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Therefore, the purpose of this study is to enhance biogas production from domestic food waste collected from IIUM Gombak Campus in Kuala Lumpur, Malaysia by introducing biofilm bacteria in the hydrolysis step in order to overcome the rate limitation observed in anaerobic digestion steps and increase the volume of biogas.

1.3 RESEARCH OBJECTIVES

The main objective of this research is to enhance biogas production from food waste by pretreating food waste with biofilm immobilized onto granular activated carbon (GAC). Therefore, the specific objectives of this research are:

I. To develop the immobilization technique for potential biofilm producing microbes on a carrier granular activated carbon (GAC) for enhancing biogas production from domestic food waste.

II. To evaluate the hydrolysis process of food waste with immobilized biofilm for pretreatment of food waste.

III. To optimize single stage anaerobic digestion (AD) parameters with hydrolyzed food waste for the evaluation and enhancement of biogas production in AD digester based on HRT and OLR.

1.4 RESEARCH METHODOLOGY

This study is comprised of laboratory-based experimental work in a shake flask, and the procedures adopted were designed to enhance biogas production from food waste by using biofilm system. Therefore, the research started with the review of literature on current methods used in managing food waste that readily affect the environment.

This was followed by reviewing biogas produced from food waste with different

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pretreatment methods used to increase the production of biogas. Thus, biofilm technology and the purpose of using it as pretreatment of food waste were also reviewed in the literature review.

The experiment started by collecting and culturing four biofilm producer strains from previous study and the mixture of this strain was immobilized on the granular activated carbon to form biofilm. Therefore, the active biofilm was used in the hydrolysis of food waste. Some measurement parameters of hydrolysis were measured to see the efficiency of food waste hydrolyzed with immobilized biofilm, chemical oxygen demand (COD) and soluble chemical oxygen demand (SCOD), total volatile solid (TVS) and total solid (TS).

Finally, anaerobic digestion of hydrolyzed food waste was performed and the optimization of AD parameters such as HRT and OLR and inoculum to feed ratio was done to see the effect of these parameters on the AD of food waste and find the best condition that can form high volume of biogas. The summary of the main steps of research methodology is illustrated in Figure 1.1.