The performance of membrane bioreactor in treating high temperature municipal wastewater

Abstract

Membrane bioreactor (MBR) is a promising technology which has been applied to treat a wide range of municipal wastewater in different regions around the world. However, it has not yet been employed in arid and semi arid areas such as Arabic Gulf Cooperation Council States (AGCCS). The application of MBR process in treating high temperature municipal wastewater (HTMW) has not been documented and could pose as an obstacle. Therefore, the aim of this study was to investigate the effect of high temperature on MBR process in treating municipal wastewater. The objectives were to study the biomass properties, the membrane fouling tendency and the biological and final removal efficiencies (Bio and Fin R E) of COD, NH3-N and turbidity. In this study, a 3.6 L lab-scale aerobic MBR was seeded with 1.5 L activated sludge inoculum from Oman and was fed with a real municipal wastewater from Taman Pulai Utama sewage treatment plant in Johor. The system was then run under four main experimental stages. For the first three stages, it was run at three various temperatures (25, 35 and 45°C) and two different fluxes (10 and 15 LMH). In the fourth stage, it was run at drastic temperature changes with constant flux (10 LMH). The study demonstrated that the increase in temperature caused biomass shock. This resulted in the biomass reduction, lowered sludge settling properties and higher supernatant’s turbidity. Due to biomass reduction (low richness and diversity), DO and ML pH increased. The temperature increase led to increase in SMP carbohydrate and protein, and decrease in EPS protein. Biomass reduction, high pH, SMP concentration increase and EPS decrease were the factors that caused relatively high membrane fouling. TMP and BWP ascended critically with temperature and flux increase. The highest TMP values scored were 348 mbar at 10 LMH flux and 429 mbar at 15 LMH flux, and both of them were at 45°C. Membrane openings widen with temperature increase, thus membrane fouling tended to be internal rather than external at higher temperatures. As a result of biomass shock the removal efficiencies dropped temporarily and then improved gradually with the acclimatization despite the flux increase. COD Bio R E was 90%, 84% and 62%, while Fin R E was 95%, 91% and 79% at 25°C, 35°C and 45°C respectively. Both NH3-N removal efficiencies were very high up to 100% at 25 and 35°C, while at 45°C they were 52% Bio R E and 56% Fin R E as high nitrification has not yet been achieved at high temperatures. Despite the higher biomass shock at drastic temperature changes stage, COD and turbidity Fin R E were very high up to 90% and 100% respectively, while NH3-N Fin R E was nearly 50%. The viscosity decreased with the increased in temperature and SVI. In spite of the critical operating conditions, the use of hollow fiber membrane module was able to achieve comparatively good removal efficiencies, however at the highest temperature i,e (45°C) the membrane fouling was the highes