Thermophilic aerobic membrane bioreactor for industrial wastewater treatment | |
| Author | Abeynayaka, Amila |
| Call Number | AIT Thesis no.EV-09-01 |
| Subject(s) | Aerated package treatment systems Membrane reactors |
| Note | A thesis submitted in partial fulfillment of the requirements for the Degree of Master of Engineering in Environment Engineering and Management |
| Publisher | Asian Institute of Technology |
| Abstract | Thermophilic aerobic high strength wastewater treatment has been an interesting field of research for the past 50 years. Poor sludge settleability and biomass washout remain major concerns in thermophilic aerobic process. Application of membrane bioreactor (MBR) for thermophilic aerobic wastewater treatment process was researched to overcome these concerns. In this study the performance of sequencing batch reactors (SBRs) and MBRs were investigated. SBRs were operated under organic loading rates 8.25 and 24.75 kg COD / m³.d for 190 days. Under each loading rate three SBRs were operated simultaneously at 30, 47 and 60°C. Mixed liquor volatile suspender solid (MLVSS) was maintained in the range of 7000 to 9000 mg/L throughout the study period. MBRs with ceramic micro filter (MF) of 0.45 11m pore size were operated under similar temperatures, 30°C, 47 °c and 60°C at an organic loading rate of 24.75 kg COD / m³.d for 90 days. MF MBRs were operated under two filtration modes (mode 1 and mode 2). Mode 1 had continuous constant flux rate filtration while mode 2 was operated with daily air back-flush followed by high rate 5 minute filtration and long-term normal filtration. Mode 2 operation provided a thin cake layer pre-coat to protect the membrane from fouling. At the end of 60°C MF MBR operation the MF was replaced by ultra filter (UF) with molecular weight cut off 150 kD and operated for 35 days. Observations of SBRs indicate, thermophilic aerobic process has two times higher maximum specific growth rate (μm) than that of mesophilic process; thermophilic aerobic process has higher half velocity constant (Ks) values; thermophilic aerobic process has ten fold higher endogenous decay coefficient (kd) than aerobic mesophilic process. After endogenous decay become effective in thermophilic process in SBRs, an increment of soluble COD with time was found. It was explained with the knowledge of relative biodegradability's of the fresh substrate and soluble microbial products (SMP). This helps to understand the reasons for successful and unsuccessful performances of thermophilic aerobic systems. Under substrate limited conditions, observed biomass yield (Yobs) for thermophilic MBR was 0.08-0.10 mg VSS/ mg COD while that was 0.36 mg VSS/ mg COD for mesophilic MBR. Thermophilic MBRs achieved organic removal rate of 21 to 22 kg COD / m³.d while mesophilic MBR achieved 17 kg COD / m³.d. It was found that assimilation and stripping are the major TKN (total kjedahl nitrogen) removal mechanism in thermophilic process while in mesophilic process the mechanisms are assimilation and nitrification. However under substrate limited conditions same degree (but less than mesophilic) of nitrification was observed in thermophilic SBRs. It was found that provision of both forms of TKN, (organic and ammoniacal nitrogen), supply nitrogen continuously for biodegradation. Mode 2 filtration (air back-flush followed by high rate filtration and normal filtration) has increased the cycle time of sidestream air lift membrane by a factor of 1.4-1.7. It was found that in sidestream MBRs at all three temperatures, cake layer pre-coat has ability to remove more soluble proteins than soluble polysaccharides. Soluble polysaccharides found in the all three MBRs have relatively smaller molecular weight than proteins. Cake layer pre-coat is capable of removing higher molecular weight proteins. Ultra filtration has better fouling resistance and removal efficiencies than micro filtration for MBRs operated at 60 DC due to complete rejection of higher molecular weight soluble products. |
| Year | 2009 |
| Type | Thesis |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Energy and Climate Change (Former title: Department of Energy, Environment, and Climate Change (DEECC)) |
| Academic Program/FoS | Environmental Engineering (EV) |
| Chairperson(s) | Visvanathan, C.; |
| Examination Committee(s) | Annachhatre, Ajit P.;Shipin, Oleg V.; |
| Scholarship Donor(s) | Government of the Netherlands; |
| Degree | Thesis (M.Eng.) - Asian Institute of Technology, 2009 |