Recycling and treatment of anaerobic effluents from pig waste using Lemna sp. under temperate climatic conditions

Abstract

The use of Lemna sp. for the recycling and treatment of anaerobic effluents from digested pig waste, was evaluated under the temperate climatic conditions of Xalapa City (19°32′31′N and 95°54′35″W at an altitude of 1580 m above sea level). Preliminary evaluation under temperature and light controlled conditions, established that Lemna sp. grew well in anaerobic effluents and that its productivity was 47% higher when cultivated on the complete anaerobic effluents containing an average of 4.15% total solids, than when cultivated with the sedimented fraction containing only an average of 1% of total solids. Furthermore, it tolerated a total nitrogen concentration as high as 450 mg I−1 when it was adapted to this nutrient source for one batch cycle of 15 days. Protein content varied as a function of nitrogen concentration in the medium and it reached a maximum of 42% dry wt. after 3 days of batch culture at a concentration of 350 mg I−1 of total nitrogen. Under outdoor conditions, maximum productivity was 6.75 g m−2 d−1 at an initial total nitrogen concentration of 200 mg I−1 and at an inoculum density of 27 g m−2 during a period in which average light intensity and temperature were 404 μmol photon m−2 seg−1 and 27°C respectively. Protein content was 45% dry wt. at the same conditions mentioned above. Removal efficiencies for total nitrogen, ammonia nitrogen, phosphates and COD (77%, 80%, 92% and 90%, respectively), were similar or higher than those reported for Eichhornia crassipes by other researchers. It was concluded, that Lemna sp. has a great potential and represents a very good alternative among other aquatic plants, for the recycling and treatment of anaerobic effluents from digested pig waste.