The development in biological wastewater treatment over the last 50 years

The paper summarizes the development in the understanding and practical application of activated sludge process over the last 50 years. Since its invention, the activated sludge process has been a big challenge to design engineers. Traditionally the technology was covered by sanitary engineers. However, with the development in the understanding of activated sludge process principles the further progress was not possible without knowledge of reaction kinetics and reactor theory. The shift from BOD removal only to combined removal of organic pollution, nitrogen and phosphorus required a chemical engineering approach with outputs of activated sludge microbiology and microbial ecology. Molecular biology enabled more accurate identification of important activated sludge microorganisms. The development in activated sludge process required also more efficient activated sludge separation and thickening. The paper describes the development from secondary clarifiers to membrane separation. Increasing water stress around the Globe has also changed the main wastewater paradigm from wastewater treatment and safe discharge to safe reuse.

Automated summary

The paper summarizes the development of activated sludge process over the past 50 years, highlighting the shift from BOD removal to combined removal of organic pollution, nitrogen, and phosphorus. The development required a combination of chemical engineering approaches, accurate microbial identification techniques, and a shift towards safe reuse of wastewater due to increasing water stress worldwide.