Effect of MLSS, Hydraulic Loading Rate and Dissolved Oxygen on Food to Microorganism Ratio in a Submerged Membrane Bioreactor

Membrane bioreactor (MBR) is a technique where membranes are applied to biological wastewater treatment for biomass separation. However, their widespread application is restricted due to membrane fouling. One of the important parameter that is crucial for membrane life is that of the food to microorganism ratio in the reactor. The current investigation attempted to find the effect of mixed liquor suspended solids (MLSS), hydraulic loading rate and dissolved oxygen levels on food to microorganism (F/M) ratio. The MBR system consisted of 68 modules of Zee weed 500 ultrafiltration membrane (UF) placed inside a reactor. The results showed that the hydraulic loading rate and MLSS showed direct proportionality to f/m ratio. On the other hand, the dissolved oxygen content was found to be independent of f/m ratio, however playing a crucial role in for microorganism growth. Overall it was optimized that the plant could be maintained at f/m ratio of 0.2 when operated at MLSS of 8 kg/m3 at hydraulic loading rate of 1500 m3/day with DO levels maintained at 1.5 mg/l. Maximum BOD and COD removal was achieved in the treated water with consistent settleable sludge