Biological Wastewater Treatment Systems

Wastewater treatment (WWT) today probably is more focused on removing phosphorus and nitrogen than pathogens, since these elements contribute to eutrophication and deterioration of our natural water ecosystems. A large number of biological WWT techniques exist, from natural and constructed wetlands at one end to high-technology solutions based on the activated sludge process at the other end. The core of all WWT processes involves active microbial cells concentrated at biofilms or flocs. Knowledge of the cell and the structure and function of the microbial community is necessary in the design of effective conventional and new treatment systems. In this article, the importance of respiration, nitrogen mineralization, nitrification, denitrification, and biological phosphorus-removal processes is emphasized. Equally important is knowledge and theoretical modeling of water movement through the wastewater ecosystems. The understanding of the contact between the microbe and wastewater is a prerequisite for kinetic modeling of various enzyme reactions to describe the water purification process. Emphasis is given to the function of constructed wetlands and activated sludge processes. The future challenge of sustainable WWT is to design techniques that recycle the content of valuable plant nutrients. In addition, WWT by constructed wetlands will contribute in maintaining biological diversity in the ecosystem, as well as ideally in creating easy accessible recreational and educational meetings between urban citizens and the ecosystem.