TREATMENT BY MICROALGAE OF EMERGING POLLUTANTS IN WATER FROM ANAEROBIC DIGESTION OF PIG MANURE

Abstract

Anaerobically digested pig manure are effluents still rich in ammonium, with high chemical oxygen demand, which contribute to the phenomenon of water eutrophication. Moreover, due to excess use of antibiotics in animal husbandry, unmetabolized drugs can still be found in manure and then in anaerobic digestion effluents, thus requiring further treatment. Microalgae could potentially offer many advantages in this treatment, being able to use the organic carbon as well as inorganic nutrients such as nitrogen and phosphorus from wastewater for their heterotrophic growth. The aim of this research was to investigate the effect of emerging pollutants added to digested swine manure on the growth of the microalga Chlorella vulgaris. C. vulgaris cultures were performed with different amounts of digested pig manure to achieve ammonium concentrations of 60, 120 and 170 mgN/L in the medium. Additional runs were performed in water enriched with pure ammonium at the same concentrations as above. These runs were compared with those carried out in classic Bold Basal Medium taken as a control. Moreover, after reaching the stationary phase of cultures with 60 mgN/L ammonium from manure we added 14.0 mg/L of Micospectone, an antibiotic mixture containing 33.3% Lincomycin and 66.6% Spectinomycin. Preliminary studies evidenced that higher antibiotic concentrations (56-112 mg/L) in medium lead to microalga growth inhibition. Biomass concentration was daily quantified spectrophotometrically by optical density measurements at 625 nm wavelength, while total ammonium and phosphate concentrations were monitored periodically. Optical and Scansion Electronic Microscopies were used to observe fresh and dried biomass, respectively. In the presence of digested manure and the antibiotic, C. vulgaris biomass reached concentrations around 1.3 gDB/L. Ammonium was removed efficiently, at rates of 5.6 and 3.4 mg/Ld when present in initial concentrations of 60 and 120 mgN/L, respectively, whereas higher ammonium level (170 mgN/L) strongly inhibited microalgal growth and almost suppressed its own removal.