Improving the performance of anaerobic digesters at wastewater treatment works: the coupled cross-flow microfiltration/digester process

Abstract

Trials at a wastewater treatment works indicate that cross-flow microfiltration, using flexible woven fibre tubes, could significantly enhance the performance of anaerobic digesters. The cross-flow microfiltration unit decouples the solids residence time from the liquid residence time and thus enables the volumetric throughput of the digester to be significantly increased while maintaining a constant solids residence time and volatile solids destruction. In trials on a pilot-plant digester, the volumetric throughput was almost doubled, from 70 to 130 1 d−1, while the solids residence time was maintained at 26 days. The economic feasibility of the coupled system was evaluated, using permeate flux data obtained from a cross-flow microfiltration unit coupled to a full-scale digester. The evaluation indicates that the coupled process is economically favourable when compared to conventional digester systems. The coupled system is currently being developed into a full-scale process. A full-scale CFMF unit is being constructed and will be coupled to a full-scale digester. Over a three year project the long-term reliability and operability of the process will be investigated, together with its effect on digester fluid dynamics and biomass viability.

Characterization of biofoulants illustrates different membrane fouling mechanisms for aerobic and anaerobic membrane bioreactors

“…Electrostatic repulsion may be a factor in causing the rejection of biopolymers of sizes smaller than the physical pore size of membranes [41]. Another contributing factor could be related to the deposited biofoulants on the membrane surface, as seen in studies where the biofilm layer acted as a secondary self-forming dynamic membrane that modified the membrane's rejection properties [42][43][44][45].…”

A hybrid anaerobic membrane bioreactor coupled with online ultrasonic equipment for digestion of waste activated sludge

“…In a conventional anaerobic sludge digester, the solids retention time (SRT) is identical to the hydraulic retention time (HRT) which results in a large reactor volume, since a long SRT (20-30d) is required for effective volatile solids destruction (Pillay et al, 1994). Anaerobic membrane bioreactor (AnMBR) employs membrane as an efficient separation method to separate solid from sludge suspension.…”

Anaerobic membrane bioreactors: Are membranes really necessary?

“…Formation of a gel or cake layer over the membrane surface can determine rejection properties of the system, since the deposited layer can act as a secondary membrane. Modification of the membrane rejection properties by the formation of a fouling layer has been observed for both aerobic and anaerobic MBRs (Harada et al 1994;Pillay et al 1994;Choi et al 2005). Consequently, under such conditions, the membrane itself may be no longer necessary, since solids rejection will be provided by the cake layer, which will apparently act as a self-forming dynamic membrane.…”

“…Both woven and non-woven materials have been tested as support for the dynamic membrane formation. The use of a fouling layer as a dynamic membrane determining the rejection properties was applied by Pillay et al (1994), for an AnMBR treating sludge. No other reports are available regarding the application of self forming dynamic membranes in AnMBRs.…”