The nutrients nitrogen and phosphorus have traditionally been viewed as problem substances that need to be removed, as far as water treatment plants are concerned. This has been needed to help prevent eutrophication of surface waters and deterioration in the quality of drinking water sources. This approach is a symptom of the linear economy, where resources are used once. Efforts are now underway to help create a circular economy. The water sector has a part to play in this in the recycling of nutrients. Phosphate is a finite resource, which provides a long term driver for recovering this from used water. Nitrogen needs to be removed, and there are opportunities for capturing the nitrogen-containing ammonia at different points in the water cycle.
Dutch researchers and companies are leaders in this area. A great deal of interest is currently focused on struvite recovery, but other options are being investigated. Ongoing work includes efforts to integrate nutrient recycling with the move towards energy positive wastewater treatment.