M Vogts, et al. “The Removal of N and P in Aerobic and Anoxic-Aerobic Digestion of Waste Activated Sludge from Biological Nutrient Removal Systems”. Water SA, vol. 41, no. 2 WISA 2014 Special Edition, Mar. 2015, https://doi.org/10.4314/wsa.v41i2.05.