Operation of Submerged Anaerobic Membrane Bioreactors at 20 °C: Effect of Solids Retention Time on Flux, Mixed Liquor Characteristics and Performance

Abstract

Four flat-sheet submerged anaerobic membrane bioreactors ran for 242 days on a simulated domestic wastewater with low Chemical Oxygen Demand (COD) and high suspended solids. Organic loading was maintained around 1.0 g COD L−1 day−1, while solids retention time (SRT) was varied from 20–90 days. This was achieved at a constant membrane flux, maintained by adjusting transmembrane pressure (TMP) in the range 1.8-9.8 kPa. Membrane fouling was assessed based on the required TMP, with mixed liquors characterised using capillary suction time, frozen image centrifugation and quantification of extracellular polymeric substances (EPS). SRT had a significant effect on these parameters: fouling was least at an SRT of 30 days and highest at 60 days, with some reduction as this extended to 90 days. Operation at SRT <30 days showed no further benefits. Although operation at a short SRT was optimal for membrane performance it led to lower specific methane productivity, higher biomass yields and higher effluent COD. Short SRT may also have accelerated the loss of essential trace elements, leading to reduced performance under these conditions. A COD-based mass balance was conducted, including both biomass and methane dissolved in the effluent.

Unlocking the Full Potential: New Frontiers in Anaerobic Digestion (AD) Processes

“…Biogas production from residues of industrial insect protein production from black soldier fly larvae Hermetia illucens (L.): An evaluation of different insect frass samples [5] X X Batch and semi-continuous anaerobic digestion of industrial solid citrus waste for the production of bioenergy [6] X X X Hydrothermal pretreatment of wheat straw-Evaluating the effect of substrate disintegration on the digestibility in anaerobic digestion [7] X X Anaerobic co-digestion of sewage sludge and trade wastes: Beneficial and inhibitory effects of individual constituents [8] X X X Operation of submerged anaerobic membrane bioreactors at 20 • C: Effect of solids retention time on flux, mixed liquor characteristics and performance [9] X X X Exploring farm anaerobic digester economic viability in a time of policy change in the UK [10] X X…”

“…Another approach to improve the performance of AD in the wastewater sector is the implementation of highly efficient bioreactors. Pacheco-Ruiz et al [9] reported findings from long-term experiments conducted over 242 days with submerged anaerobic membrane bioreactors. A key result indicated that operation without chemical or external cleaning was feasible if the process conditions were adequately set by controlling solids retention and, thus, mean cell residence time.…”