A dissertation submitted in partial fulfillment of the requirements for the degree of doctor of technical science, School of Environment, Resources and Development

Thesis (Ph.D.) - Asian Institute of Technology, 1990

The hollow fiber membrane bioreactor combined with photosynthetic bacteria ,Rhodobacter sphaeroides was proved to b e suitable for only wastewater treatment The hollow fiber membrane enhanced the removal of grease and oil efficiency t o over 90% while the degradation by photosynthetic bacterial one could achieve 65-75%. The hollow fiber membrane was also necessary for solid/liquid separation since the settle able sludge of t his bacteria was only 10 ml/l in 30 min. which is difficult to settle b y gravity. Sludge treatment and disposal were not needed for this system since bacterial cells in the sludge can be directly used as sing l e cell protein for animal feed and fertilizer . The protein content o f the wasted sludge was 40% which was high enough to be used as single cell protein. Under long solid retention time ( SRT) of 3 0 d a nd s h or t hydraulic retention time (HRT) of 1. 5 d, maximum ML SS concentration of 3 , 910 mg/l could be obtain e d, and under short SRT ( 5 d ) and short HRT (1 .5 d), the maximum biomass harvested per d ay (660 mg/ d) was achieved. Too s h ort HRT caused clogging of the membrane a nd too short SRT caused cell washout of the system . When high organic loading (8 kgCOD/(m3 .d)) or high hydraulic loading (1.3 m3 /( m3 .d )) was applied to the system, the high concentration of grease and oil occurred a nd inhibited t h e bacterial growtl1 in the reactor. Never the less, the system was proved to b e stable to high organic loading and high hydraulic loading (8 kgCOD/(m3 .d) and 1. 3 m3 /(m3 . d ) respectively ). The COD removal efficiency of the system was 70 - 85%, and further treatment by other bio- oxidation processes is necessary. Batch study in small bottles was a l so conducted to study t h e performance o f Rhodobacter sphaeroides. The inoculum size of 596 was suitable for the system. The growth rate a nd the removal efficiency of this bacteria were more active under continuous illumination than under intermittent illumination either by artificial or s un light. The kinetic coefficients of Rhodobacter sphaeroides (æm, Y, Ks and kd ) were d e t ermine d. The value of kd for the bioreactor with membrane was bigger than the bioreactor with out membrane. This was possibly caused by some attached growth a t the membrane fibers which reduced the MLSS concentration in the reactor .