Removal of Phosphorus from livestock effluents
Received for publication December 12, 2007. For removal of phosphorus (P) from swine liquid manure before land application, we developed a treatment process that produces low P effluents and a valuable P by-product with minimal chemical addition and ammonia losses. The new wastewater process included two sequential steps: (i) biological nitrification and (ii) increasing the pH of the nitrified wastewater to precipitate P. We hypothesized that by reduction of inorganic buffers (NH4+ and carbonate alkalinity) via nitrification, P could be selectively removed by subsequent hydrated lime [Ca(OH)2] addition. The objective of the study was to assess if this new treatment could consistently reduce inorganic buffer capacity with varied initial concentrations of N (100–723 mg NH4+ L–1), P (26–85 mg TP L–1), and alkalinity (953–3063 mg CaCO3 L–1), and then efficiently remove P from swine lagoon liquid. The process was tested with surface lagoon liquids from 10 typical swine farms in North Carolina. Each lagoon liquid received treatment in a nitrification bioreactor, followed by chemical treatment with Ca(OH)2 at Ca rates of 0, 2, 4, 6, 8, 10, and 12 mmol L–1 to precipitate P. This configuration was compared with a control that received the same Ca rates but without the nitrification pretreatment. The new process significantly reduced >90% the inorganic buffers concentrations compared with the control and prevented ammonia losses. Subsequent lime addition resulted in efficient pH increase to ≥9.5 for optimum P precipitation in the nitrified liquid and significant reduction of effluent total P concentration versus the control. With this new process, the total P concentration in treated liquid effluent can be adjusted for on-farm use with up to >90% of P removal. The recovered solid Ca phosphate material can be easily exported from the farm and reused as P fertilizer. Therefore, the new process can be used to reduce the P content in livestock effluents to levels that would diminish problems of excess P accumulation in waste-amended soils.