Phosphorus vs Nitrogen - what would the environment choose?

In recent times, upgrade strategies for existing municipal wastewater treatment plants and construction of new treatment plants in New Zealand that discharge to water, have focused on nutrient reduction in the discharge to protect the downstream receiving environment. Nutrient reduction strategies incur not only additional capital costs but also substantial operating costs.

A few years ago, the majority of regional councils required nitrogen removal rather than total phosphorus. However, in recent times there is a trend towards requiring both nitrogen and phosphorus removal. Do you really need both?

This paper will present the case of providing phosphorus removal, which is cheaper in capital, less complex to operate and easier to control compared to nitrogen removal involving anoxic reactors. The paper will examine the issue from a receiving environment perspective. Are we over doing it?