Characterization and biodegradability of sludge from a high rate A-stage contact tank and B-stage membrane bioreactor of pilot-scale AB system treating municipal wastewaters

In light of global warming mitigation efforts, increasing sludge disposal costs, and need for reduction in the carbon footprint of wastewater treatment plants, innovation in treatment technology has been tailored towards energy self-sufficiency. The AB process is a promising technology for achieving maximal energy recovery from wastewaters with minimum energy expenditure and therefore inherently reducing excess sludge production. Characterization of this novel sludge and its comparison with the more conventional B-stage sludge are necessary for a deeper understanding of AB treatment process design. This paper presents a case study of a pilot-scale AB system treating municipal wastewaters as well as a bio- (biochemical methane potential and adenosine tri-phosphate analysis) and physico-chemical properties (chemical oxygen demand, sludge volume index, dewaterability, calorific value, zeta potential and particle size distribution) comparison of the organic-rich A-stage against the B-stage activated sludge. Compared to the B-sludge, the A-sludge yielded 1.4 to 4.9 times more methane throughout the 62-week operation

Identification of recalcitrant compounds in a pilot-scale AB system: an adsorption (A) stage followed by a biological (B) stage to treat municipal wastewater

This manuscript presents a comparison of the A-stage and B-stage sludges in terms of anaerobic biodegradability and low molecular weight compounds present in the supernatant using Gas Chromatography–Mass Spectrometry (GC–MS). The GC–MS analysis of A-stage and B-stage supernatants identified respectively 43 and 19 organic compounds consisting mainly of aromatics (27.9% and 21%), alcohols (25.6% and 15%) and acids (30.2% and 15%). The methane potential was found to be 349 ± 1 mL CH4/g VS and 238 ± 12 mL CH4/g VS, respectively. After anaerobic digestion of these sludges, a greater proportion of aromatics (42% and 58%) and a lower proportion of acids (10% and 10%) and alcohols (16% and 10%) was observed

Organics transformation and energy production potential in a high rate A-stage system: a demo-scale study

Current high-rate activated sludge (HRAS) process is an aerobic A-stage process that would cause significant organic loss resulted from the mineralization. In this study, the feasibility of operating a high rate A-stage without aeration (HRNS) was carried out in a demo-scale plant (275 m3/h). The organics transformation and energy production potential in A-stage were explored. The developed A-stage process was demonstrated to be more effective for organics recovery compared to that operated with aeration (53.82% versus 40.94%), despite its relatively low total COD removal efficiency (54.3% versus 63.5% with aeration). Minor organics (accounted for 1.75% of incoming COD) was found to be lost in HRNS process. Moreover, sludge generated from HRNS had higher degradability and higher methane compared to that from HRAS. Overall, this study documented the feasibility of high rate A-stage without aeration, and acted as a guide in achieving energy neutrality or even energy-positive wastewater treatment.Public Utilities Board (PUB)The authors would like to thank the Public Utilities Board (PUB) of Singapore for financial support of the project “Investigation of energy production potential and sludge rheology of an A/B process in UPWRP Integrated Validation & Demonstration Plant”

Optimization of operating conditions in forward osmosis for osmotic membrane bioreactor

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Pilot-scale test of industrial wastewater treatment by UASB and MBR using a ceramic flat sheet membrane for water reuse

A pilot plant was studied to investigate a new method for reclaiming wastewater from the industrial area of Jurong, producing high quality water from it for industrial reuse. The new process used an up-flow anaerobic sludge blanket (UASB) and a membrane bioreactor (MBR) with a submerged ceramic flat sheet membrane. The feedwater from the chamber with the industrial wastewater was high in chemical oxygen demand (COD), which varied between 644 and 2,380 mg L–1 and had a pH range of 6.7–7.1. The MBR process was operated in series at a flux of 18–25 Lm–2 h–1 for 100 days. The average COD and the biological oxygen demand of products of the above system were 155 and 9 mg L–1, respectively. The results of this study indicated that a UASB-ceramic MBR process was capable of stably producing high quality water for industrial reuse from industrial wastewater

Preliminary study of osmotic membrane bioreactor : effects of draw solution on water flux and air scouring on fouling

Preliminary study on a novel osmotic membrane bioreactor (OMBR) was explored. Objective of this study was to investigate the effects of draw solution on membrane flux and air scouring at the feed side on fouling tendency in a pilot OMBR system composing the anoxic/aerobic and forward osmosis (FO) processes. Domestic sewage was the raw feed, FO membrane from HTI and NaCl/MgSO(4) draw solutions were used in the experiments. Fluxes of 3l/m(2)/h (LMH) and 7.2 LMH were achieved at osmotic pressure of 5 and 22.4 atm, respectively. No significant flux decline was observed at 3 LMH over 190 h and at 7.2 LMH over 150 h when air scouring was provided at the feed side of the membrane. However, without air scouring, the flux at 22.4 atm osmotic pressure declined by 30% after 195 h and then levelled off. The potential advantages of the fouling reversibility with air scouring under the operating conditions of the pilot OMBR and better water quality in OMBR over the conventional MBR were preliminarily demonstrated