Nitrogen waste is a component of sewage that comes primarily from human excreta and detergents but also from fertilizers and such industrial processes as steel-making. Nitrogen waste consists primarily of nitrates and nitrites as well as compounds of ammonia. Because they tend to clog waterways and encourage algae growth, nitrogen wastes are undesirable. They present a problem for wastewater treatment since they are not removed by either primary or secondary treatment steps. Their removal at the tertiary stage can be achieved only by specialized procedures. Another approach is to use wastewater on farmlands. This use removes about 50 percent of nitrogen wastes from water by turning it into nutrients for the soil .
See also Sewage treatment