V. 1. Process theory: kinetics and sludge quality control / P. Gradu, J. Wanner
Activated sludge treatment of municipal wastewater: U.S.A. practice / M. Hsu, T.E. Wilson
European practices / A.L. Downing
Activated sludge treatment of industrial waters / W.E. Eckenfelder, J.L. Musterman.