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

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.