Ultrafiltration of biologically treated wastewater by using backflushing

Membrane technologies offer a possibility to further improve the quality of the wastewater. In this study a biologically treated wastewater from a municipal wastewater treatment plant was ultrafiltered with monotubular ceramic membranes of nominal pore size 20 and 50 nm. Backflushing was introduced with different levels of frequency and duration to reduce the formation of fouling during filtration. The results showed good retentions of main wastewaters components as BOD5, COD, TKN, TP, total coliform and TDS. Moreover with membrane of nominal pore size 20 nm the results showed that the higher permeate flux was obtained when backflushing was carried out for 0.5 s every 1 min without an excessive worsening of permeate quality (improvement of flux about 9%). With membrane of nominal pore size 50 nm, backflushing caused a higher improvement of flux (17%) but also a decrease in permeate quality. The increase in permeate flux decreased slightly the retention of main quality parameters with a small contamination of the permeate with total coliform.