Integrating ponds and activated sludge process in the PETRO concept

The activated sludge process (ASP) can be successfully integrated into the ponding system in the framework of the PETRO concept (ASP-variant). The role of microalgae in the ASP was elucidated and biological mechanisms of algae removal are suggested. Microalgae contribute to flocculation by the production of exopolysaccharides (EPS) under stress conditions. Superior flocculation appears to result in a greater nitrification rate contributing to N-removal in the ASP reactor. Consequences and advantages of the secondary position of the polishing ASP (downstream of the ponds) are discussed.