Biotreatment of anaerobically digested swine manure with microalgae: Fid-Bau Portal

Biotreatment of anaerobically digested swine manure with microalgae

de la Noüe, J. / Bassères, A.

AbstractAnaerobic treatment of swine manure generates effluents that must be further treated before their final discharge. The required tertiary treatment can be effected by growing microalgae on the anaerobic effluent. We tested the ability of three species (two Chlorophyceae, Chlorella sp. and Scenedesmus obliquus, and a cyanobacterium, Phormidium bohneri) to exhaust inorganic nitrogen and orthophosphate and to produce biomasses from anaerobically digested swine manure obtained from a 5-m³ farm digester. The effluent to be treated (COD: 7·7 g/liter; NNH4⁺: 3·3 g/liter; PPO4³⁻: 0·3 g/liter; pH: 8·0) was diluted with tap-water to final manure concentrations of 0·6-3·0%. Batch culture was carried out in 1-liter flasks for 12 days at 228 μE/m² s (L:D, 12:12), at 10 and 20°C, starting with inocula of 80 mg dry wt algae per liter. Semicontinuous cultures were also performed with P. bohneri (1·0% manure, dilution rate of 50% per 4 days, 20°C, 14 days). The results show that biomass production was good (up to 500–750 mg dry wt per liter after 12 days) for all three species at 20°C with productivities (mg dry wt per liter per day) averaging 31 for P. bohneri, 37 for Chlorella sp. and 53 for S. obliquus. Total NNH4⁺ exhaustion was obtained at 20°C with all three species (2·0% manure) within 12 days; corresponding reduction of PPO4³⁻ was over 90%, and COD abatement was 60–90%, depending on the species. Under natural conditions, the best candidate for batch treatment would appear to be Chlorella sp. Under semicontinuous conditions, P. bohneri, which can be easily harvested, is indeed interesting, with removal rates (10·4 mg NNH4⁺/g dry wt per day and 0·6 mg PPO4³⁻/g dry wt per day) similar to those obtained with Chlorella sp. grown in batch at similar manure concentrations.