Biological processes are the gold standard for nitrogen removal in municipal wastewater treatment, because they are more energy-efficient and require fewer resources than physico-chemical processes. Several studies have shown that biological processes can also be used for nitrogen removal from urine and blackwater, the two source-separated waste streams with the highest nitrogen loads. However, biological processes are not only used for nitrogen removal but also for nitrogen recovery: with nitrification the volatile ammonia in urine can be stabilized as nitrate or ammonium nitrate. This is a suitable pretreatment step for the evaporative recovery of all nutrients in one solid product.
In this chapter, we present the basic processes for biological nitrogen conversion in wastewater treatment and we discuss laboratory and pilot-scale experiments of nitrogen conversion in urine and blackwater.