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Non-woven fabric filter and poly-tetrafluoroethylene (PTFE) composite membrane were investigated to determine their applicability to treat low strength wastewater in an anaerobic membrane bioreactor (AMBR). Sludge cake resistance of the membrane was quantified using pure water flux of anaerobic sludge cake accumulated on the glass fiber filter of similar pore size. It is hypothesized that the formation of thin cake layer on the porous medium, e.g. non-woven and PTFE acts as a dynamic membrane. Thus, the capture of thin sludge cake inside the non-woven fabric matrix and accumulation on the PTFE membrane surface forms a membrane system equivalent to a commercial membrane system. The permeate quality was found to improve as the cake became more dense with filtration time. The PTFE composite membrane coated with thin PTFE film on the non-woven fabric filter enhanced the filtration performance by improving flux and minimizing the propensity of bio-fouling. The membrane flux was restored by back-flushing with permeate. The AMBR coupled with PTFE laminated membrane was operated continuously during the experiment at a cross flow velocity (CFV) of 0.1–0.2 m/sec and a transmembrane pressure (TMP) of 0.5–3 psi. Although about a month of acclimation was required to reach steady state, the effluent chemical oxygen demand (COD), volatile fatty acids (VFAs) as acetic acid, and suspended solids (SS) concentrations were below 30, 20 and 10 mg/L, respectively, during 90 days of operation with intermittent back washing. The lower operation TMP and CFV were subjected to less shear stress on the microbial community during continuous AMBR operation. In addition, thin sludge film accumulated on the membrane surface also acted as a biofilm bioreactor to remove additional COD in this study

Waste activated sludge (WAS) is more difficult to digest than primary sludge due to rate limiting cell hydrolysis. High-power ultrasound can effectively disintegrate the bacterial cells and thus enhance the subsequent digestion. This research examines the effectiveness of ultrasound pretreatment on WAS disintegration at different specific energy inputs, ultrasonic densities and total solids (TS) contents. The results show that the cut diameter (d50) for WAS with 2% TS content declined nearly 6.5-fold at an ultrasonic density of 0.67 W/ml. For higher TS contents of 4 and 6%, higher densities of 1.03 and 0.86 W/ml, respectively, were needed to achieve the same degree of particle size reduction. The efficacy of ultrasonic disintegration measured as soluble chemical oxygen demand (SCOD) release was primarily governed by ultrasonic density (W/ml); whereas ultrasonic density did not show a significant effect on protein release at all TS levels. SCOD release of about 320 mg SCOD/g TS was obtained at a TS content of 2% and specific energy input of 5 kWs/gTS. The SCOD release, however, decreased to 160 and 90 mgSCOD/gTS at 4 and 6% TS contents, respectively. The highest protein release of 73 mg/gTS was obtained at a TS content of 2% and specific energy input of 10 kWs/gTS. The sludge disintegration efficiency declined significantly at higher TS content. Thus, there is a limiting TS concentration that could be effectively disintegrated by ultrasound, and this is governed by the capability of an ultrasonic unit in producing cavitation. The degree of disintegration also depends on types of ultrasonic unit used.

In this study, oxidation-reduction potential (ORP) was used as a controlling parameter to regulate oxygen dosing to the recycled biogas for online sulfide oxidation in an upflow anaerobic filter (UAF) system. The UAF was operated with a constant influent COD of 18,000 mg/L, but with different influent sulfates of 1000, 3000 and 6000 mg/L. The reactor was initially operated under a natural ORP of -290 mV (without oxygen injection), and was then followed by oxygenation to raise its ORP by 25 mV above the natural level for each influent sulfate condition. At 6,000 mg/L sulfate without oxygen injection, the dissolved sulfide reached 733.8 mg S/L with a corresponding free sulfide of 250.3 mg S/L, thus showing a considerable inhibition to methanogens. Upon oxygenation to raise its ORP to -265 mV (i.e., a 25 mV increase), the dissolved sulfide was reduced by more than 98.5% with a concomitant 45.9% increase of the methane yield. Under lower influent sulfate levels of 1,000 and 3,000 mg/L, the levels of sulfides produced, even under the natural ORP, did not impose any noticeable toxicity to methanogens. Upon oxygenation to raise the ORP by +25 mV, the corresponding methane yields were actually reduced by 15.5% and 6.2%, respectively. However, such reductions were not due to the adverse impact of the elevated ORP; instead, they were due to a diversion of some organic carbon to support the facultative activities inside the reactor as a result of excessive oxygenation. In other words, to achieve satisfactory sulfide oxidation for the lower influent sulfate conditions, it was not necessary to raise the ORP by as much as +25 mV. The ORP increase actually needed depended on both the influent sulfate and also actual wastewater characteristics. This study had proved that the ORP controlled oxygenation was reliable for achieving consistent online sulfide control.

Corn processing wastewater was treated in an attached growth system of Rhizopus oligosporus fungi. The effects of hydraulic retention time (HRT) and plant-based components in the support media were evaluated in 1 L reactors under non-aseptic conditions. Plastic composite support (PCS) tubes, composed of 50% (w/w) polypropylene (PP) and 50% (w/w) agricultural products were used as support media or, as a test, PP only. A maximum chemical oxygen demand (COD) removal of 78% was achieved at a 5 h HRT with a biomass yield of 0.44 gVSS/gCODremoved. The biomass yield increased to 0.48 gVSS/gCODremoved while COD removal reduced to 70% at a 2.5 h HRT. Competitive bacterial growth was reduced at the shorter HRT. A lower HRT of 1.25 h led to biomass wash out from the reactor. Significantly lower COD removal of 28% and biomass yield of 0.19 gVSS/gCODremoved were observed in a biofilm reactor with PP tubes alone, indicating that the agricultural components in PCS media were essential for better biofilm formation and organic removal.