In a pilot plant study at the Durban Corporation’s Northern’s Waste Water Treatment Works (NWWTW), a woven fibre cross-flow microfiltration (CFMF) unit was coupled to a pilot plant digester. The implication of these pilot plant trials is that existing digesters could be operated at volumetric flowrates which would exceed their current maximum values, while still obtaining the same extent of volatile solids destruction. This would enable Waste Water Treatment Works to cope with increases with inflows and delay the necessity to construct new digesters. Further development of the coupled membrane process will entail establishing and demonstrating its performance on a larger scale, as well as assessing its long term reliability and operability.

The overall aim of the project was to develop and demonstrate a cross-flow micro-filtration unit for the improvement of anaerobic digesters at Waste Water Treatment Works. The project was initiated in January 1993 and ended in December 1996, following an extension of one year due a variety of mechanical problems experienced.

The project team was forced to conclude that coupling an anaerobic digestor to an external microfilter is not likely to be viable in instances where there is a significant amount of hair/fibres in the digestor sludge. This would preclude operation at most waste water treatment works. The coupled process could however be viable when the sludge does not contain fibrous material. The process could thus be applicable in digestors treating industrial effluents.