Abstract
The paper summarizes the development in the understanding and practical application of the 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, 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 also required 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.
Highlights
Wastewater treatment since the 1970s when the IWA Specialist Group on the Design, Operation and Costs of Large Wastewater Treatment Plants was established
The reaction kinetics was applied to biological treatment to explain the difference in cultivation requirements of organotrophic and chemolithotrophic nitrification bacteria and to define the basic technological parameter controlling the conditions in their mixed culture (Jenkins & Garrison )
The SG on LWWTP has always collaborated with other specialist groups within the IWA because the design and operation of large wastewater treatment plants requires knowledge from other fields
Summary
Wastewater treatment since the 1970s when the IWA Specialist Group on the Design, Operation and Costs of Large Wastewater Treatment Plants was established. Application of microbial ecology in the further development of activated sludge process Growing practical experience from the operation of biological nutrient removal (BNR) activated sludge plants in the 1970s and 1980s indicated certain limits of the chemical engineering approach in explaining observed operational problems like instability of nitrogen and phosphorus removal efficiency and persistent difficulties in activated sludge separation in gravity clarifiers.
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