Influence of pH and biological metabolism on dissolved phosphorus during biological treatment of piggery wastewater

In areas with intensive animal farming, phosphorus from livestock waste contributes to the eutrophication of surface water. To increase the phosphorus recycling potential, mineral phosphorus products have to be obtained not only from the liquid but also from the solid phase of piggery wastewater needing new physicochemical processes to be investigated. Discarding phosphorus from organic matter by a previous solubilisation of phosphorus improves the potential recycling yield. In this aim, evolution of dissolved phosphorus was studied during a simplified sequencing batch reactor process. Two slurries were tested in a sequencing batch reactor pilot plant to see if the biological phosphorus metabolism could be used to obtain a phosphorusenriched effluent suitable for chemically recycling phosphorus. Dissolved phosphorus, calcium, magnesium and intracellular carbon storage as polyhydroxybutyrate were measured. When available carbon was sufficient both biological and chemical mechanisms were involved in phosphorus evolution. Dissolved P concentration was increased by up to seven fold by the biological treatment. However, the precipitation/dissolution of phosphate driven by the pH was dominant to explain the changes during one treatment cycle. Higher dissolved phosphorus concentration was obtained at the end of the acidification step due to nitrification. This result was discussed in the perspective to develop alternative strategies to obtain an enriched effluent suitable for a sidestream phosphorus recycling process.