The United States Environmental Protection Agency estimates that nutrients impair 15-41% of assessed surface water area (including lakes, rivers, estuaries, etc.) in the United States. Phosphorus, specifically, is the limiting nutrient for harmful algal growth and eutrophication in many freshwater ecosystems. To protect or restore US waters, states are adopting numeric water quality criteria for nitrogen and phosphorus by identifying impaired water bodies and adjusting effluent permits for water resource recovery facility (WRRF) to meet waterbody-specific loadings. As of 2021, eight states had gained state-wide phosphorus criteria for at least one waterbody type, while another sixteen states had added numeric criteria for select waterbodies (headwaters, wadeable streams, reservoirs requiring algicide, etc.). To meet increasingly prevalent and increasingly stringent effluent phosphorus limits to protect natural waterbodies, wastewater treatment plants are in need of effective and cost-efficient technologies that reliably achieve phosphorus removal or recovery.