What can be a consequence of not removing nitrogen and phosphorus during treatment?

The consequence of not removing nitrogen and phosphorus during sewage treatment primarily leads to eutrophication of receiving waters. Eutrophication occurs when excess nutrients, particularly nitrogen and phosphorus, are introduced into aquatic ecosystems. These nutrients stimulate the growth of algae and aquatic plants, resulting in algal blooms.

As the algae die and decompose, it severely depletes the oxygen in the water, leading to hypoxic conditions that can harm or kill fish and other aquatic organisms. This process disrupts the natural balance of the ecosystem and can result in the loss of biodiversity. Furthermore, some algal blooms can produce toxins that are harmful to both humans and wildlife, exacerbating the problem and posing additional health hazards.

While other consequences may arise from excessive nitrogen and phosphorus in treated sewage—such as increased mineralization rates, formation of harmful by-products, or increased operational costs—these issues are secondary to the immediate and direct impact of eutrophication on water bodies, which can lead to long-term environmental degradation.