Effects of alkali-treated sludge supplementation for enhanced biological phosphorus removal in a membrane bioreactor

Waste activated sludge treated with an alkaline solution was used as external carbon substrates to improve the performance of enhanced biological phosphorus removal (EBPR) in a pilot plant. Supplementation of the alkali-treated sludge significantly enhanced the phosphorus removal of the pilot plant from 81.6 to 98.7%. Microscopic observations revealed that alkali treatment was effective in killing bacterial cells in the sludge, and deconstructed its morphology into a reticular form. The change in cell viability and morphology facilitated organic matter release, mostly in the form of proteins. Furthermore, supplementation of the alkali-treated sludge changed the major phosphorus accumulating organisms (PAOs) from Accumulibacter to Tetrasphaera. Enrichment of PAOs within the Tetrasphaera was due to specific carbon substrates (i.e. proteins) released by the alkali-treated sludge. Taken together, this study strongly suggests that supplementation of alkali-treated sludge was an efficient method for improving EBPR performance by enrichment of Tetrasphaera PAOs.