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Systematically testing alternative cleaning agents and cleaning procedures on a large scale municipal membrane bioreactor, the Erftverband optimized the cleaning strategies and refined the original cleaning procedures for the hollow fiber membranes in use. A time-consuming, intensive ex-situ membrane cleaning twice a year was initially the regular routine. By introducing the effective means of cleaning in place in use today, which employs several acidic and oxidative/alkaline cleaning steps, intensive membrane cleaning could be delayed for years. An overview and an assessment of various cleaning strategies for large scale plants are given.

The paper outlines a model of the filtration performance of submerged capillary microfiltration modules in membrane bioreactor applications for wastewater treatment. The model was implemented for process simulation and calibrated by using operating data of the full-scale municipal wastewater treatment plant Rödingen, Germany, operated by Erft River Association (Erftverband), which is equipped with activated sludge treatment and microfiltration units for biomass retention. Mathematically recordable foundations of filtration resistances, such as cake layer forming and fouling, are presented along with a mass transfer model, describing the concentration polarisation on the feed-side and its dependence on a multiphase flow regime. The model simulates the long-term decrease in permeability of the membranes and outlines the influence of main operating parameters on flux performance. After parameter fitting for one filtration unit, the permeability evolution for a second unit could be also calculated.

Operations of an existing municipal MBR serving 80,000 inhabitants were improved energetically by implementing new automation routines for biology and membrane filtration. Finally, the MBR was refurbished by adding primary clarification and anaerobic sludge digestion to the treatment process, while specific energy consumption was reduced by one third to 0.65 kWh/m3 permeate produced. A combined heat and power engine generates electrical power on site from digester gas. The projected carbon footprint of plant operations will thus be halved by reducing indirect emissions from electricity consumption.