Originally, organized WWT was introduced for sanitation reasons. Today, in the industrialized world, WWTPs and arable land contribute with a substantial proportion to the anthropogenic nitrogen load to the marine recipients, which severely enhances eutrophication of aquatic environments. Most natural ecosystems are controlled by a deficiency in macronutrients like phosphorus and nitrogen, which means that eutrophic level often directly controls ecosystem responses. This interplay stresses the importance that WWT systems are adapted to natural biogeochemical cycles and are aligned with a vision of a durable society.
An important question is to what extent wastewater, for example, municipal wastewaters and sewage sludge, should be considered a waste or valuable resource and recycled as plant nutrients in crop and in energy production. Key constraints for the growing global population are due to food and energy. Today, both extraction ofphosphorus and production of mineral nitrogen fertilizers consume extensive resources of fossil fuels. Hence, one important future aim must be to create a sustainable loop ofplant nutrients through food production and refinement, urban consumption, waste handling, and back to arable land. To achieve this, the effluent wastewater stream must contain as much phosphorus and nitrogen as possible in addition to minimal amounts of organic and inorganic toxicants.
Such global aims have to be linked with the ability to treat a growing amount of wastewater. Not only is it important to select specific solutions for specific treatment situations, but it will also be essential to be able to optimize treatment with account to the broad scientific basis involving both water dynamics and biological processes. The coupled scientific basis is essential for an in-depth understanding of the key microbiological processes involved in nitrogen removal and for optimizing biological treatment systems.
Another future perspective is the contribution oftreat-ment wetlands to maintain biological diversity in the ecosystem as well as to create easy accessible recreational and educational meetings between urban citizens and the ecosystem. Most importantly, this would create awareness of the waste stream as a resource and probably encourage the citizen to contribute to this idea.
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