Assessment of hybrid attached growth membrane bioreactor system for domestic wastewater treatment

Abstract

Domestic wastewaters contain various and high amounts of organic matter and ammonia or nitrogen compounds which are difficult to oxidize biologically or chemically. A promising technology in treating wastewater which is membrane bioreactor (MBR) has been considered to be an advancement over the conventional activated sludge process. However, this type of MBR has a limitation which is membrane fouling problem that can reduce the perfomance of the system. Thus, in this study, advanced treatment technology in treating synthetic domestic wastewater called Hybrid Attached Growth Membrane Bioreactor (HyAG MBR) is proposed to help minimize and overcome the problem. The aim of this study is to find the optimum concentration of attached growth media that will be used in HyAG MBR system and compare the treatment and fouling tendency performance of conventional MBR (CMBR) with HyAG MBR. Synthetic domestic wastewater was treated with a 20 L lab-scale HyAG MBR equipped with a single microfiltration flat sheet membrane module. Batch tests with attached growth media concentrations from 10 to 40% were used to determine the best attached growth media concentration. Besides that, the treatment performances of HyAG MBR system were also compared with the performances of conventional MBR (CMBR) system by assessing the removal of chemical oxygen demand (COD), biochemical oxygen demand (BOD), total phosphorus, nitrate, nitrite and ammonia concentrations. Furthermore, fouling tendency was also compared between HyAG MBR and CMBR systems at the same operating condition by evaluating critical flux (Jc) enhancement, trans membrane pressure (TMP) profiles, membrane resistance analysis, soluble microbial products (SMP) and extracellular polymeric substances (EPS). The finding shows 10% of attached growth media was an optimum concentration for good removal of COD, nitrate, nitrite and phosphorus up to 93.29 %, 94.53%, 90.04% and 61.86%, respectively. The average COD, nitrate, nitrite, nitrogen ammonia, phosphorus and BOD removal of HyAG MBR were 96.82%,96.54% , 92.91%, 93.30% , 75.55%, and 89.70% while for CMBR were 96.10%, 83.60%, 80.21% , 85.68%, 77.74% and 91.49%, respectively. Average COD, nitrate, nitrite, and nitrogen ammonia removal efficiency for HyAG MBR were found to be greater than the CMBR system but vice versa for phosphorus and BOD removal. HyAG MBR significantly increased Jc up to 48 L m-2 h-1 hence producing low final TMP after cleaning. Low TMP also decreased the total resistance at 5.69 x 1011 m-1 and have distinct changes in the concentrations of SMP and EPS. Thus, it shows the reduction of membrane fouling problem hence prolonging the filtration process. In conclusion, HyAG MBR gives a better treatment performance and could minimize the membrane fouling problem.