Lipolysis of domestic wastewater in anaerobic reactors operating at low temperatures

Abstract

Poor breakdown of lipids is a major barrier to the anaerobic treatment of domestic wastewater at low temperatures. Lipids are degraded by extracellular lipases that are produced by, as yet, unknown bacteria. We wished to know if the poor degradation of lipids at low temperatures is due to a lack of lipase or to a lack of lipase activity. We therefore conducted an assay of the lipase activity in biomass adapted to the treatment of settled domestic wastewater at 4, 8 and 15 °C and compared this with the activity of the same biomass at 37 °C. Lipase activity decreased with temperature and was un-measurable at 4 °C. When the lipase activity in the biomass was evaluated at 37 °C, the lipase activity was 21.7 ± 14.0% greater in the biomass adapted to 4 °C than in the biomass adapted to 15 °C. We conclude that enzymes are produced at low temperatures but that the activity at these temperatures is low. Settled and unsettled wastewaters were used as controls and we were surprised to see lipolytic activity in the unsettled wastewaters at low temperatures. The activity was too high to be accounted for by the presence of biological detergents and we infer that is caused by bacteria naturally present in domestic wastewater. The presence of lipolytic activity at low temperatures was associated with the presence of members of the genera Trichococcus and Devosia, and the families Caldilineaceae and Bacteroidaceae.