Phycoremediation to reduce the pollution load of piggery wastewater: results of semi-continuous lab tests using chlorella and scenedesmus spp

This work concerns the possibility of using phycoremediation of piggery wastewater (PW) in order to remove nitrogen and to send the produced algal biomass to anaerobic digestion. A semi-continuous culturing test was performed in 150 mL glass test tubes (4.5 cm diameter, 20 cm high), in four replicates, and run for 90 days. Light was provided artificially, with 12 h dark/light periods, mixing was allowed by air bubbling and temperature was 20±2°C. Algae developed quickly with values over 1 g TSS L-1 after one week and maximum concentrations between 2.4 and 2.7 g TSS L-1, and the community was made by Chlorella and Scenedesmus spp., in similar proportion all over the test. The average productivity was 0.26 to 0.40 g L-1 day-1. In the absence of pH control, the intense photosynthesis raised pH, whose value was proportional to the TSS concentration. The pH raise caused the production and stripping of NH3-N (26% of the inflow N), while the algal assimilation of N accounted for 45% and the oxidation for 25%. The overall % removal was about 96% for NH4-N, 85% for P and 74% for COD. The maximum methane production was 267 NmL CH4 g VS-1 (mean of the two replicates), higher than reported for pig and cow manure.