Uptake of Organic Substrates and Accumulation of Polyhydroxyalkanoates Linked with Glycolysis of Intracellular Carbohydrates under Anaerobic Conditions in the Biological Excess Phosphate Removal Processes

Abstract

Anaerobic uptake mechanisms of acetate, propionate and lactate by the sludge developed in an anaerobic aerobic biological phosphate removal process was investigated. Anaerobic batch experiments were conducted with these substrates, and mass balances of materials involved in substrate uptake metabolism were calculated. These substrates were accumulated in the sludge as polyhydroxyalkanoates composed of 3-hydroxybutyrate, 3-hydroxyvalerate, 3-hydroxy-2-methylbutyrate and 3-hydroxy-2-methylvalerate. The reducing power necessary for the formation of polyhydroxyalkanoates from acetate and/or propionate was shown to be supplied from glycolysis of intracellular carbohydrates. Lactate was converted to 3-hydroxyvalerate rich polyhydroxyalkanoate via acetyl-CoA and propionyl-CoA by using propionate fermentation pathway. Redox balance was found to be a factor regulating the anaerobic uptake of substrates and their further metabolism. Glycogen seemed to serve not only as a source of reducing power necessary for the redox balance regulation but also as an important energy source, because glycolysis can provide both reducing power and energy. It was indicated that some bacteria might be able to get energy necessary for substrate uptake under strict anaerobic conditions not by the polyphosphate hydrolysis but by the consumption of intracellular carbohydrates.