This study investigated the response of an AnMBR to various organic load rates by evaluating COD removal efficiency, biogas production and membrane fouling behaviour. The reactor was equipped with a submerged hollow fibre UF membrane and operated in continuous mode. Performances at three HRTs (5, 2 and 1 day) were investigated. Wide fluctuation of feed characteristics was observed, though it did not cause significant variation in performance. Average MLSS was 2.0-2.6 mg/L, SRT was constant at 50 days and average OLRs were 0.44, 1.43 and 3.14 Kg m-3 d -1 in Phase I, II and III. The reactor was able to achieve total COD removal efficiencies of 88 -95% with effluent COD concentrations of 96, 170 and 373 mg/L in the three Phases. Daily biogas production went up from 0.36 L/day in Phase I to 2.7±0.6 L/day in Phase III showing a positive correlation with the increase of OLR. The membrane had a maximum flux rate of 6.4 LM -2 H -1 and showed no significant sign of fouling until towards the end of Phase III. High level of EPS (97-105 mg/gVSS) supposedly aggravated membrane fouling due to development of cake sludge. The study clearly supports the applicability of submerged AnMBR in treating meat processing wastewater.

Membrane bioreactor fouling is a complex process, which is typically driven by extracellular polymeric substances (EPS), a complex mixture of polysaccharides, proteins, lipids, humic substances, and other intercellular polymers. While much is known about fouling in aerobic membrane reactors, far less is known about fouling in anaerobic membrane bioreactors (AnMBR). Much of this knowledge, including EPS extraction methods, has been extrapolated from aerobic processes and is commonly assumed to be comparable. Therefore, several extraction methods commonly used for aerobic EPS quantification, including ultrasonication, ethylenediaminetetraacetic acid (EDTA), and formaldehyde plus sodium hydroxide (CH2O+NaOH), were evaluated to determine the most suitable extraction method for EPS of anaerobic microorganisms in an AnMBR. To maximize EPS yields, each extraction was performed four times. Experimental results showed that the EDTA method was best for EPS quantification, based on chemical oxygen demand (COD), dissolved organic carbon (DOC), and protein yields: 1.43 mg COD/mg volatile suspended solids (VSS), 0.14 mg DOC/mg VSS, and 0.11 mg proteins/mg VSS. In comparison, the CH2O+NaOH method maximized the extraction of carbohydrates (0.12 mg carbohydrates/mg VSS). However, multiple extraction cycles with EDTA and ultrasonication exhibited lower extracellular adenosine triphosphate (ATP) concentrations compared to CH2O+NaOH extractions, indicating lower levels of released intracellular substances. Successive EPS extractions over four cycles are better able to quantify EPS from anaerobic microorganisms, since a single extraction may not accurately reflect the true levels of EPS contents in AnMBRs, and possibly in other anaerobic processes.