Recovery of high-quality calcium phosphate fertilizer products from anaerobic membrane bioreactor treated swine wastewater

Abstract

The aim of this study is the sustainable recovery of phosphorus as high-quality calcium phosphate from anaerobic membrane bioreactor treated swine permeate for targeted use as fertilizer or raw material for the fertilizer industry. Phosphorus removal efficiencies from treated swine permeate were evaluated by adding various calcium/phosphorus molar ratios ranging from 1/1 to 12/1. Results showed that removal efficiencies were inconsistent in duplicate trials at the same calcium doses (maximum P removal 93 % in Trial 1 and <20 % removal in Trial 2). The variability in P removal was due to the high bicarbonate alkalinity of the swine permeate, which buffered the system and thereby prevented it from reaching alkaline pH conditions ideal for P removal. Total alkalinity and initial solution pH had the greatest impact on P removal and caused unintended precipitation of non-specific calcium minerals (Calcite). The carbonate alkalinity from the permeate was removed using process modifications that included acid addition and aeration for removal as CO2. Carbonate removal resulted in 97 % P removal with increased total P content (11.8 % P) in the final product and better solubility. Additional COD removal was also observed during the flocculation process.