Study of reaction kinetics of a submerged membrane activated sludge process

The recent advancement in the membrane technology especially in microfiltration, has given an impetus to the development of membrane bioreactors for the treatment of various wastewaters especially for the treatment of municipal wastewater. A submerged membrane activated sludge process (SM-AS) is one of the modifications to the conventional activated sludge process. It is the combination of a membrane module and a bioreactor. This SM-AS process can retain a high concentration of mixed liquor suspended solids (MLSS) in the aeration tank, giving numerous benefits over conventional wastewater treatment processes. Behavior of microorganisms in the SM-AS processes was needed to be understood so that these types of treatment plants could be designed to meet required effluent standards.; In this research a lab scale submerged membrane activated sludge process was operated for over one year period to study the kinetic coefficients of the SM-AS system under different MLSS (3000 mg/l, 5000 mg/l, 10 000 mg/l and 15 000 mg/l) concentrations. The Monod kinetic coefficients, Yield (Y) varied from 0.487 to 0.583 mg/mg; Endogenous decay coefficient (kd) varied from 0.151 to 0.0261 day-1; Maximum specific growth rate (μm) varied from 1.28 to 6.46 day-1 and Saturation constant (Ks) varied from 289 to 2933 mg COD/l. The study also identified the microorganisms present in the aeration tank. Fouling of the membrane was controlled by intermittent pumping schedule, back flushing with air and/or mechanical cleaning with a brush. The system could withstand easily shock loading of 16 000 mg/l COD at an MLSS concentration of 15 000 mg/l giving over 98% COD removal efficiency. The system was also tested for the ability to withstand toxic loadings. The SM-AS system could withstand 400 mg/l phenolic toxic loading giving an effluent COD removal of 77%. With acclimatization with phenol, the effluent COD removal efficiency increased to 81%. The system could withstand chromium dosage of 50 mg/l and the system regaining its capacity within couple of days of removal of toxic loading.