Conclusions

1. Permeate water quality is consistently high for all membranes tested. The membrane with the highest pore size (M3) proved the most economical to operate with no detectable deleterious effect on effluent quality.

2. The resistance of the fouling layer is minimised at a cross flow velocity of approximately 3ms"1 for the membrane modules tested.

3. The semi-stable permeate flux after 24 hours continuous operation shows a logarithmic decline with increasing suspended solids concentration. The relationship between semi-stable flux and suspended solids concentration of the feed solution has been compared for the membranes used in this trial and other published reports. The wide differences between findings indicate that membrane surface properties play a large part in the fouling characteristics.

4. The lowest energy consumption for the filtration was 1.75 kWhm"3 and was achieved at the lowest cross flow velocity using the membrane with the largest pore size.

5. The high energy consumption of a sidestream MBR must be justified by a need for the particular benefits offered by the process. This need could arise from strict effluent control, high land costs, prohibitive sludge handling and disposal costs or high strength wastewater requiring specific biological conditions.

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