By YSI, a Xylem brand
Nutrient removal from wastewater is an increasingly common requirement for water resource recovery facilities (WRRF). Nitrogen and phosphorus are the nutrients being targeted. Both are essential components of the machinery of living organisms. Nutrients dissolved in the water are assimilated by algae. In waters enriched with nutrients, algae growth and death is accelerated leading to hypoxia, a low oxygen condition unsuitable for fish and other higher life forms. In brackish waters, such as in Chesapeake Bay, Long Island Sound, and Puget Sound, nitrogen is the primary concern. The result is substantial investment in improving the nitrogen removal capability of WRRFs that discharge to these watersheds. Utilities are motivated to remove as much nitrogen as possible to comply with mass loading limits or even to earn credits that can be sold to other utilities. In ground water, the concern is toxicity of the drinking water. Total inorganic nitrogen (TIN) in treated water to be land applied is typically restricted to not more than 10 mg/L to protect against a serious condition called methemoglobinemia which limits the ability of blood to carry oxygen. Infants and children are particularly susceptible.