Luận văn thạc sĩ khoa học OILY WASTEWATER TREATMENT BY MEMBRANE BIOREACTOR PROCESS COUPLED WITH BIOLOGICAL ACTIVATED CARBON PROCESS

OILY WASTEWATER TREATMENT BY MEMBRANE BIOREACTOR PROCESS COUPLED WITH BIOLOGICAL ACTIVATED CARBON PROCESS Title page by Phan Thanh Tri A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering Examination Committee: Prof C Visvanathan (Chairman) Dr Josef Trankler Dr Preeda Parkpian Nationality: Previous Degree: Vietnamese Bachelor of Chemical Engineering Ho Chi Minh City University of Technology Ho Chi Minh City, Vietnam Scholarship Donor: Japan - Asian Development Bank Asian Institute of Technology School of Environment, Resources and Development Thailand August 2002 i Acknowledgement The author wishes to express his deepest respect and profound gratitude to his advisor, Prof C Visvanathan, for the valuable guidance, advice and encouragement throughout this study Sincere thanks are extended to Dr J Trankler and Dr P Parkpian who served as members of the thesis examination committee Their suggestive and stimulating comments are highly treasured The author gratefully acknowledges the Asian Development Bank and the Government of Japan for the scholarship grant which allowed the author to pursue his study at AIT Grateful thanks are given to the staffs of the Environmental Engineering Laboratory, AIT for the precious assistances during this study The author would like to acknowledge the Research and Development Center for Petroleum Safety and Environment, PetroVietnam, for providing favorable condition for the author to pursue his study at AIT The author is very grateful to Dr N.P Dan and other friends at AIT for their helps and encouragement Special appreciations are given to Mrs T.T.H Nhien, who devotedly stimulated and helped the author to pursue graduate study The author is most grateful to his darling wife, who encouraged and shared with the author the difficulty times during the study Finally, the author wishes to dedicate this achievement to his respected and beloved mother, who has sacrificed her life for the growing-up of her children ii Abstract Preliminary study of biodegradation of the oily wastewater was evaluated by activated sludge (AS) process and biological activated carbon (BAC) process operated in sequencing batch reactor (SBR) mode In BAC process, powdered activated carbon (PAC) was added into the reactors at different doses of 100 – 500 mg/L The feed wastewater had COD of 550 mg/L and Oil & Grease (O&G) concentration of 150 mg/L The reactors were experimented at hydraulic retention time (HRT) of 3, 6, 10, 13 and 16 h The results showed that the removal efficiency of AS process reached 80% for COD and 90% for O&G at HRT=13h There was a tendency of effluent quality improvement of the BAC process at PAC dose = 500 mg/L and HRT = 3h in comparison with the AS process Lab scale submerged membrane bioreactor (MBR) system with microfiltration membrane module was used to investigate the treatment of oily wastewater The MBR system provided excellent effluent quality with COD in range of 11.2 to 85.9 mg/L and O&G in range of 0.2 – 7.3 mg/L when influent COD varied from 495 – 1835 mg/L and O&G varied from 150 – 600 mg/L The removal efficiency was 89.9 – 99.9 mg/L for COD and 97.6 – 99.9 mg/L for O&G The MBR system provided stable effluent quality against shock loading The system could stand for the COD loading of 10.5 g COD/L.day and oil loading of 3.5 g oil/L.day without deteriorating the effluent quality Combination of MBR process and BAC process to treat oily wastewater was investigated by adding PAC to the reactor at the dose of g/L The hybrid system showed little improvement in effluent quality Membrane clogging of the hybrid system occurred more quickly in comparison with the same system without PAC addition about days The reason would be due to the plugging of PAC particles in the pores of the membrane The membrane fouling in the MBR system was found reversible while that of the hybrid system with PAC addition was partially irreversible The resistance of the cake layer was found the highest component contributing to the total resistance of the clogged membrane It is suggested that during operation there was a critical point when the blockage of the membrane pores reached a level that made the air backwash ineffective, the formation of the cake layer became intensive leading to the membrane clogging iii Table of Contents Chapter Title Page Title page Acknowledgement Abstract Table of Contents List of Abbreviations List of Figures List of Tables i ii iii iv viii vi vii Introduction 1.1 General 1.2 Objectives of the study 1.3 Scopes of the study 1 2 Literature Review 2.1 Introduction 2.1.1 Sources of car wash wastewater 2.1.2 Characteristics of oil/water emulsion 2.1.3 Pollution of oil/water emulsion 2.1.4 Oily wastewater treatment system 2.2 Application of MBR process in wastewater treatment 2.2.1 MBR process 2.2.2 Advantages of MBR process 2.2.3 Membrane fouling 2.2.4 Application of MBR process in oily wastewater treatment 2.3 Biological activated carbon process 2.3.1 Activated carbon adsorption 2.3.2 Biological activated carbon process 2.3.3 MBR process coupled with BAC process 3 3 5 7 10 11 12 12 13 14 Methodology 3.1 Materials and microorganisms 3.1.1 Feed wastewater 3.1.2 Powdered activated carbon 3.1.3 Microorganisms 3.2 Overall experimental course 3.3 Adsorption isotherm experiments 3.4 Batch experiments 3.5 Membrane bioreactor experiments 3.5.1 Membrane bioreactor set-up 3.5.2 Experimental conditions 3.5.3 Measured parameters in the MBR experiments 3.5.4 Membrane cleaning 3.5.5 Membrane resistance measurement 3.6 Analytical methods 16 16 16 17 17 17 19 19 20 20 20 23 23 24 24 iv Results and Disscussions 4.1 Adsorption isotherm of the PAC 4.2 Batch experiments 4.3 MBR experiments 4.3.1 Membrane resistance measurement 4.3.2 Optimum HRT run 4.3.3 Shock loading run 4.3.4 Long run A and B 4.4 Conceptual idea for application of MBR system in wastewater treatment and reuse at gas station 26 26 27 31 31 32 35 37 Conclusions and Recommendations 5.1 Conclusions 5.2 Recommendations References Appendix A: Experimental results Appendix B: Membrane resistance measurement data Appendix C: Photographs of experimental works 43 43 44 46 49 56 68 v 41 List of Figures Figure Title 2.1 2.2 2.3 2.4 2.5 Process flow diagram of car wash process (Awas, 1997) Oil/water emulsion conventional treatment systems Different configurations of MBR process Membrane fouling Schematic diagram of dynamic porous PAC layer in cross flow membrane filtration (Pirbazari et al., 1996) Relative contributions of COD and BOD from the oil, glucose and emulsifier of a typical feed wastewater sample having oil concentration of 150 mg/L Overall experimental course Membrane bioreactor setup Laboratory scale MBR system to treat oily wastewater Variation of equilibrium COD vs different contact times (PAC dose = 100 mg/L; T = 25oC; agitation speed = 100 rpm) Experimental data plotted according to Freundlich isotherm Experimental data plotted according to Langmuir isotherm Variation of COD removal efficiency vs HRT Variation of O&G removal efficiency vs HRT Comparison of COD removal efficiency between AS process and BAC process (PAC = 500 mg/L) Comparison of COD removal efficiency between AS process and BAC process (PAC = 500 mg/L) Resistance of the membrane before used and after chemical cleaning Variation of COD of the influent and effluent during Optimum HRT run 33 Variation of O&G in the reactor and in the effluent during Optimum HRT run O&G mass balance of Optimum HRT run Variation of transmembrane pressure and MLSS during Optimum HRT run Variation of COD of the influent and effluent of Shock loading run Variation of O&G in the reactor and in the effluent during Shock loading run Variation of COD of the influent and effluent of Long run A and B Variation of O&G in the reactor and in the effluent during Long run A and B Biofilm development on carbon surface after 14 days of Long run B BAC sludge after 14 days of Long run B (x580) Variation of transmembrane pressure and MLSS during Long run A and B Conceptual diagram for a wastewater treatment and reuse system using MBR process at gas station 3.1 3.2 3.3 3.4 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10 4.11 4.12 4.13 4.14 4.15 4.16 4.17 4.18 4.19 4.20 Page vi 10 11 17 18 21 22 26 27 27 29 29 30 30 32 33 34 35 36 36 37 38 39 39 40 42 List of Tables Table Title 2.1 Characteristics of wastewater from various gas stations in Bangkok, Thailand (Limpananon and Yodsang, 1997) Composition of lubricant oil Comparison of operation parameters between industrial-scale applied ultrafiltration system treating oil-contaminated wastewater from machine factoring and the membrane bioreactor system (Scholz and Fuchs, 2000) Composition of the feed wastewater The major properties of the PAC Experimental conditions for equilibrium adsorption time test Characteristics of the membrane module Operational condition of the MBR experiments Analytical methods Average results of the batch experiments Membrane resistances of the new membrane and the membrane after chemical cleaning Membrane resistances after each step of chemical cleaning course after Long run B Oil loading of Optimum HRT run Oil loading of Shock loading run Comparison of EPS content in the sludge of Long Run A and Long Run B Various components of membrane resistance contributing to membrane clogging Results of equilibrium adsorption time test Results and calculation of adsorption isotherm test Results of the batch experiments Experimental results of Optimum HRT run Experimental results of Shock loading run Experimental results of Long run A Experimental results of Long run B 2.2 2.3 3.1 3.2 3.3 3.4 3.5 3.6 4.1 4.2 4.3 4.4 4.5 4.6 4.7 A.1 A.2 A.3 A.4 A.5 A.6 A.7 Page vii 12 16 17 19 20 23 24 28 31 32 34 37 40 41 50 50 51 52 53 54 55 List of Abbreviations AC API AS BAC BOD COD CPI DAF Eff EPS GAC HRT Inf MBR MLSS O&G PAC PAH PPI Rc Rf Rm Rt SBR SRT T TMP Activated Carbon American Petroleum Institute Activated Sludge Biological Activated Carbon Biochemical Oxygen Demand [mg/L] Chemical Oxygen Demand [mg/L] Corrugated Plate Interceptors Dissolved Air Floatation Effluent Extracellular Polymeric Substance Granular Activated Carbon Hydraulic Retention Time [h] Influent Membrane Bioreactor Mixed Liquor Suspended Solid [mg/L] Oil and Grease concentration [mg/L] Powdered Activated Carbon Polyaromatic Hydrocarbon Parallel Plate Interceptors Cake layer resistance [m-1] Fouling resistance [m-1] Intrinsic membrane resistance [m-1] Total membrane resistance [m-1] Sequencing Batch Reactor Solid Retention Time [day] Temperature [oC] Transmembrane Pressure [mmHg, kPa] viii Chapter Introduction 1.1 General Oil contaminated wastewater has been recognized as one of the most concerned pollution sources This kind of wastewater comes from variety of sources such as crude oil production, oil refinery, petrochemical industry, metal processing, compressor condensates, lubricant and cooling agents, car washing The oily wastewater is considered as hazardous industrial wastewater because it contains toxic substances such as phenols, petroleum hydrocarbons, polyaromatic hydrocarbons which are inhibitory to plant and animal growth and also are mutagenic and carcinogenic to human being Physical treatment of oily wastewater such as API gravity separator, dissolved air floatation (DAF), ultrafiltration etc does not remove the pollutants completely but just transfer them to a more concentrated waste (Schols and Fuchs, 2000) Moreover, the physical treatment cannot remove soluble fraction of the wastewater (Seo, 1997) Currently conventional biological treatment techniques are mostly incapable of complete elimination of hydrocarbon in stable emulsion Removal efficiency of the conventional biological processes is also low due to inhibitive effects of toxic substances and hydrophobic characteristics of oil components (Schols and Fuchs, 2000) Therefore, there is a need to develop a more efficient treatment technique based on biological process to treat oily contaminated wastewater Membrane bioreactor (MBR) process is a novel technology in wastewater treatment in recent years It is a modification of conventional activated sludge process in which solid/liquid separation is accomplished by membrane filtration instead of using a secondary sedimentation tank One of the advantages of MBR process is that it can be operated at very high sludge retention time (SRT) in comparison with conventional activated sludge process This will create favorable conditions for the growth of slowgrowing microorganisms which can degrade recalcitrant and toxic compounds such as petroleum hydrocarbons (Fuchs and Braun, 2001) Other advantages include stability against shock loading, low rate sludge production, compact size and high effluent quality which is attractive for water reuse However, membrane fouling which leads to high-energy consumption and high cleaning chemical requirement has limited the application of the MBR process due to high operation cost Researches have been conducted to find out various causes relating to the membrane fouling phenomenon The presence of extracellular polymeric substances (EPSs) and the characteristics of the polarization cake layer such as porosity and particle size are among the factors affecting the membrane clogging process Recent efforts have been made to modify the MBR process to make it widely applicable in wastewater treatment and reclamation in term of high removal efficiency and reduction of membrane fouling Among the modifications is the addition of filter aid into the mixed liquor to control the membrane fouling by increasing the porosity of the cake layer Some researchers have proposed the addition of iron oxide particles (Chang et al., 1998) and powdered activated carbon (PAC) (Pirbazari et al., 1996; Kim et al., 1998) Among the filter aids, PAC has gained special interests because it also develops biological activated carbon (BAC) process which is expected enhancing biodegradation and producing less EPSs (Kim et al., 1998) The concept of biological activated carbon (BAC) process has been applied in water treatment as well as wastewater treatment In the BAC process, activated carbon either in powdered form (PAC) or in granular form (GAC) is added into the mixed liquor The removal of contaminants is achieved by a combination of biodegradation and adsorption The use of PAC in MBR process has been shown to enhance the biodegradation and also maintain a high permeate flux for a long duration (Pirbazari et al., 1996) This study focuses on the development of a MBR system to treat the oily wastewater from gas station effectively to meet the effluent standards for car wash wastewater and to meet the requirements for water reuse Effect of PAC addition into the reactor to the performance of the system is also investigated 1.2 Objectives of the study to investigate the oil adsorption isotherm of powdered activated carbon to investigate the biodegradation of oily wastewater in the activated sludge process and biological activated carbon (BAC) process to evaluate the performance of a MBR system to treat oily wastewater in term of membrane fouling, removal efficiency and process stability to investigate the effect of PAC addition on the performance of the MBR system in term of membrane fouling and removal efficiency 1.3 Scopes of the study Synthetic wastewater containing lubricant oil, surfactant and nutrient salts, representing for oily carwash wastewater, was used in this study as feed wastewater Mixed bacterial culture acclimated to oily wastewater was used in the biological process Batch experiments were used to determine the adsorption isotherm and biodegradation of the feed wastewater in the AS and BAC processes Laboratory scale submerged MBR with hollow fiber membrane module was used to evaluate the performance of MBR system to treat oily wastewater Effluent quality and removal efficiency were mainly addressed in term of COD and O&G concentration Results and Discussions Adsorption Isotherm Experiment Freundlich Isotherm Langmuir Isotherm 0.35 1000 Ce/(x/m) = 0.0341 + 0.0012Ce Ce/(x/m) (g/L) x/m (mg/g) 0.30 1/n x/m = Kf Ce x/m = Kf = 225.84 1/n = 0.2244 0.2244 225.84C e R2 = 0.6892 R = 0.9520 0.25 0.20 Ce 0.15 - = + Ce (x/m) ab a a = 833; b = 0.352 0.10 0.05 0.00 100 10 100 COD equilibrium, Ce (mg/L) ƒ ƒ PTT 1000 50 100 150 200 COD equilibrium, C e (mg/L) 250 Based on R-squared values, Langmuir isotherm more appropriate Oil Æ long chain compounds Æ large molecule size Æ monolayer adsorption (Langmuir isotherm) 16/30 Results and Discussions Batch Experiments 100 100 Variation of COD removal vs HRT 90 90 85 85 80 75 70 65 R1 (without PAC addition) 60 PTT 80 75 70 65 60 55 55 50 50 10 HRT (h) 12 14 Variation of O&G removal vs HRT 95 O&G removal (%) COD removal (%) 95 16 R1 (without PAC addition) 10 HRT (h) 12 14 16 ƒ COD removal efficiency increased from 64% to 86% when HRT increased from 3h to 16h ƒ At HRT=13h, the removal efficiencies of COD and O&G reached 80% and 90% respectively ƒ ƒ Æ biodegradation of oily wastewater took place at significant level Æ MBR experiments should be conducted at HRT < 10 h 17/30 Results and Discussions Batch Experiments 100 100 Variation of COD removal vs HRT 95 90 85 80 75 70 R1 (without PAC addition) R2 (PAC = 100 mg/L) R3 (PAC = 300 mg/L) R4 (PAC = 500 mg/L) 65 60 55 O&G removal (%) COD removal (%) 90 85 80 75 70 R1 (without PAC addition) 65 60 R2 (PAC = 100 mg/L) R3 (PAC = 300 mg/L) 55 R4 (PAC = 500 mg/L) 50 50 PTT Variation of O&G removal vs HRT 95 10 HRT (h) 12 14 16 10 HRT (h) 12 14 16 ƒ There was no distinguished difference between the performance of BAC process (Reactors 2, and 4) and AS process at HRTs longer than 10h ƒ Æ biodegradation was predominant over the effect of adsorption at long contact times ƒ There was a tendency of effluent quality improvement of the BAC process with increasing PAC dose 18/30 Results and Discussions 161 60 50 R4 (PAC = 500 mg/L) 165 142 150 COD (mg/L) Comparison of effluent O&G of AS process and BAC process (PAC = 500 mg/L) Comparison of effluent COD of AS process and BAC process (PAC = 500 mg/L) 197 R1 (without PAC addition) 126 111 109 111 100 78.4 77.4 O&G (mg/L) 200 Batch Experiments 40 39 37 R4 (PAC = 500 mg/L) R1 (without PAC addition) 34 24 20 20 16 15 12 12 13 16 50 0 PTT 10 HRT (h) 13 16 10 HRT (h) ƒ The most pronounced enhancement was observed at PAC dose = 500 mg/L and HRT = 3h ƒ Æ the adsorption of PAC helped to remove the oil from the supernatant and therefore improve the performance of the BAC process at short HRTs ƒ Æ PAC dose in MBR experiments should be higher because MLSS in MBR is much higher 19/30 Results and Discussions MBR Experiments – Optimum HRT run ƒ COD (mg/L) 700 Excellent effluent quality: 600 ƒ COD: 26.3 – 59.8 mg/L 500 ƒ O&G: 0.2 – 3.2 mg/L ƒ Visually, clear and oil free 400 HRT=8h HRT=6h HRT=4h 300 HRT=2h Influent COD Effluent COD 200 100 ƒ MBR performance better batch experiment ƒ Æ due to higher MLSS (6040 – 8700 mg/L) and the enhanced removal by membrane separation 10 11 12 13 14 15 16 200 ƒ There was a pronounced increase in the reactor O&G concentration at HRT = 2h : Reactor O&G = 138 – 179mg/l > influent O&G of 150 mg/L ƒ Æ should check for oil accumulation in the reactor O&G (mg/L) Time (day) 150 HRT=8h HRT=6h HRT=4h HRT=2h 100 Influent O&G Reactor O&G Effluent O&G 50 10 11 12 13 14 15 16 Time (day) PTT 20/30 Results and Discussions MBR Experiments – Optimum HRT run 120 100 Oil remaining in the reactor 80 O&G (g) Operating Average Average O&G time HRT loading (day) (h) (g O&G/day) Total oil input from the influent 1–4 5–8 – 11 12 – 16 60 40 20 0 10 Time (day) 12 14 16 TMP (kPa) HRT=8h HRT=6h HRT=4h 0.50 0.48 0.57 0.97 Oil fed into reactor up to 95.3g ƒ Oil remaining in reactor: 0.4 – 1.1g ƒ At HRT = 2h, reactor O&G increased 0.4 g vs increase in oil loading of 5.45 g/day ƒ Æ most of the oil degraded within reactor HRT=2h 15 10 ƒ TMP: stable in range of 9.6 kPa – 10.7 kPa at HRT = 8, & 4h ƒ HRT = 2h, TMP increased rapidly from 12.1 to 22.7 kPa Æ membrane clogging ƒ Æ HRT = 4h was selected for next runs Time (day) PTT 2.72 3.58 5.35 10.8 ƒ 25 20 7.94 6.03 4.04 2.00 Average O&G remaining in reactor (g O&G) 10 11 12 13 14 15 16 21/30 Results and Discussions MBR Experiments – Shock loading run ƒ MBR system showed good stability against shock loading: ƒ Inf COD = 1021 - 1835 mg/L Æ Eff COD = 11.2 - 54.1 mg/L ƒ Inf O&G = 300 - 600 mg/L COD (mg/L) 2000 Influent COD Effluent COD 1500 1000 500 Æ Eff COD = 1.2 – 4.1 mg/L ƒ Reactor O&G increased quickly to 946 mg/L when inf O&G = 450 mg/L - 600 mg/L Æ possibility of oil accumulation in the reactor Æ capacity of the system at high loading should be investigated in long term basis O&G (mg/L) 1000 900 800 700 600 500 400 300 200 100 7 Influent O&G Reactor O&G Effluent O&G Time (day) PTT 22/30 Results and Discussions MBR Experiments – Long run PAC addtition PAC addtition 1200 800 Influent COD Effluent COD 600 400 Long Run A Long Run B 200 ƒ ƒ ƒ ƒ PTT O&G (mg/L) COD (mg/L) 1000 400 350 300 250 200 150 100 50 Long Run A Long Run B Influent O&G Reactor O&G Effluent O&G 11 13 15 17 19 21 31 33 23 25 27 29 11 13 35 15 11 13 15 17 19 21 31 33 23 25 27 29 11 13 35 15 Time (day) Time (day) Effluent was stable at low level over long run Eff quality of Run B was slightly better than Run A : ƒ Run A: COD = 29.3 – 85.9 mg/L; O&G = 2.9 – 7.3 mg/L ƒ Run B: COD = 22.8 – 48.8 mg/L; O&G = 0.4 – 5.2 mg/L ƒ The difference was not significant because the improvement was hidden behind the enhanced removal of MBR process Reactor O&G of the first days of Run A were significantly higher than the rest 16 days Æ degradation of oil accumulated in Shock loading run Reactor O&G of the first days of Run B were at low level of 50 – 108 mg/L then increased to 165 – 182 mg/l Æ adsorption effect decreased gradually as attached growth 23/30 developed Results and Discussions MBR Experiments – Long run Biofilm Activated sludge ƒ There was biofilm attached on carbon surface 10 µm ƒ But the attached growth would not predominant in this reactor because most of PAC particles were trapped in bigger flocs Carbon particles PTT 24/30 Results and Discussions MBR Experiments – Long run PAC addtition 25 TMP (kPa) 20 Long Run A Long Run B 15 10 23 25 27 29 11 15 11 13 15 17 19 21 31 13 33 35 Time (day) PTT ƒ Membrane clogging happened sooner in Run B (13 days vs 18 days of Run A) ƒ Initial TMP of Run B was higher than that of Run A (10.5 kPa vs 9.2 kPa) ƒ There was a stage that the TMP remained very stable for both Run A and B before the TMP increased sharply 25/30 Results and Discussions MBR Experiments – Long run 80 70 Membrane resistance (x 10 11 1/m) Cake layer resistance was the highest contribution to total membrane resistance of the clogged membrane The formation of the cake layer occured gradually from the beginning ? Pressure 60 Fouling resistance Rf Cake layer resistance Rc Intrinsic membrane resistance Rm 13.7 (20.0%) 50 40 46.0 (47.4%) 30 20 7.7 (28.1%) 10.7 (39.1%) 10 8.9 (32.8%) 8.6 (12.6%) Run A Run B RtRt Rc Time PTT 26/30 Results and Discussions MBR Experiments – Long run Cake layer TMP Effective air backwash Membrane Fouling and pore plugging Effective air backwash Ineffective air backwash Time PTT 27/30 Results and Discussions MBR Experiments – Long run Membrane resistance (x1011 1/m) ƒ 12 +17.9% 10 -2.5% +0.3% ƒ Resistance of the clogged membrane recovered back to initial value after chemical cleaning except Run B ƒ Fouling after Run B was partial irreversible Æ carbon plugging -3.9% New membrane PTT Membrane clogging of Run B Æ plugging of PAC particles into the membrane pores Æ air backwash becomes ineffective sooner After Optimum HRT run After Shock After Long loading run run A After Long run B 28/30 Conclusions PTT ƒ The adsorption isotherm of the PAC to the lubricant oil was determined following Langmuir isotherm model ƒ There was a tendency of effluent quality improvement of the BAC process run at SBR mode for oily wastewater treatment when increasing PAC dose ƒ Application of MBR process for oily wastewater treatment provided excellent effluent quality which is suitable for water reuse at gas station ƒ MBR system provided stable high quality effluent against high oil loading ƒ Combination of MBR process and BAC process for oily wastewater treatment showed little improvement in effluent quality because the improvement was hidden behind the enhanced removal of MBR process Attached growth was not predominant in the combined system ƒ The hybrid system caused membrane clogging more quickly due to the plugging of PAC particles into the pores of the membrane ƒ Cake layer resistance was found the highest contribution to total resistance of the clogged membrane It is suggested that during operation there was a critical point when the blockage of the membrane pores reached a level that made the air backwash ineffective, the formation of the cake layer became intensive and lead to membrane clogging 29/30 Recommendations ƒ Application of MBR process for other sources of oily wastewater such as oilfield wastewater should be investigated ƒ As the membrane clogging process and the possible accumulation of pollutants in the MBR are long time processes, it is recommended that future researches on MBR process should be designed on a long term run basis ƒ Future work should focused on the modeling of the membrane clogging course in the submerged MBR An interrelation between membrane plugging and fouling process and cake layer formation process would be a good approach ƒ Composition and quantity of common foulants such as EPS, protein, carbohydrate as well as other inorganic compounds in the used cleaning solution should be determined somehow for better understanding of the cause of membrane fouling PTT 30/30 [...]... of the activated sludge process 2.3.2 Biological activated carbon process Rice and Robinson (1982) used the term Biological Activated Carbon (BAC) for the water and wastewater treatment system in which aerobic microbial activity is deliberately promoted in an activated carbon adsorber system Both types of activated carbon, PAC and GAC, can be used in the BAC process In this study, the term BAC process. .. always problematic for physical-chemical treatment of oily wastewater because the oily waste is considered as hazardous waste Biological processes have also been applied in oily wastewater treatment These processes are mainly to remove soluble organic matters remaining after physico-chemical treatment Biological treatment is only effective for highly diluted oily wastewater since oil components are adsorbed... susceptible to biological degradation (Sawyer et al., 1994) 2.1.4 Oily wastewater treatment system Treatment methods for oily wastewater can be classified into three categories namely, primary or gravity treatment units, secondary processes and tertiary processes (Figure 2.2) The primary treatment of oily wastewater is usually conducted by the API separator which treats the free oil effectively by gravity... the treatment of oily wastewater from road and rail car cleaning using SBR process indicating that COD removal in range of 80 – 90 % and oil removal of less than 100 mg/L can be achieved 2.2 Application of MBR process in wastewater treatment 2.2.1 MBR process Membrane bioreactor (MBR) process is a novel technology in wastewater treatment in recent years Investigation and innovations to develop MBR process. .. components The oily wastewater is normally accompanied with emulsifier which is used in oil cleaning processes While the free oil can be removed mostly by gravity oil separator, the other components of the oily wastewater cannot be removed simply by gravity separation In this study, car wash wastewater from gas station will be studied as a representative for oily wastewater 2.1.1 Sources of car wash wastewater. .. completely, indicated by TOC values of the effluent ranging from 40 – 70 ppm The metabolites from the biodegradation of phenanthrene were not biodegraded further under biodegradability test No membrane fouling phenomenon was reported Sorption of phenanthrene onto biomass and membrane were not investigated 2.3 Biological activated carbon process 2.3.1 Activated carbon adsorption Activated carbon has been... configurations of MBR process 9 2.2.3 Membrane fouling Despite the advantages of the MBR process, the present cost of treatment by MBR is unfortunately higher than that of the conventional treatment One of the major reasons for this higher cost of treatment is attributable to membrane fouling Membrane fouling causes the increase in filtration resistance resulting in the decline in permeate flux Membrane fouling... surface (Figure 2.5) Kim et al (1998) conducted a study to compare ultrafiltration characteristics of activated sludge and biological activated carbon (BAC) sludge The activated sludge reactor was fed with synthetic wastewater using glucose as carbon source The BAC sludge was prepared by adding PAC to activated sludge reactor for one month The biomass suspended solids of the two systems were maintained... biodegradation of the oily wastewater through activated sludge process (AS) and biological activated carbon (BAC) process The batch reactors were operated at sequencing batch reactor (SBR) mode in which each cycle went through the four main steps: fill, react (aeration), settle and draw Twoliter-glass-bottles were used as model reactors There were four reactors: one was run as activated process (AS) and... lasted for four days The feed wastewater used in the batch experiments had the oil concentration of 150 mg/L The reactors were operated without sludge wastage except for sampling purpose 3.5 Membrane bioreactor experiments 3.5.1 Membrane bioreactor set-up Laboratory scale membrane bioreactor was used in this study Schematic diagram of the experimental set-up for the membrane bioreactor experiments is presented