Biochemical models for biological excess phosphorus removal from wastewater

The objectives of this research were to propose some biochemical models that would explain the basic mechanisms of biological excess phosphorus removal from wastewater, and to provide selected experimental confirmations of the proposed models. The models postulated had to be based on the observations available from the literature as well as to be consistent with principles of bacterial biochemistry and microbiology. The phenomena of phosphate release and uptake were explained by the role of carbon substrates being stored anaerobically as poly-β-hydroxybutyrate (PHB), and by the aerobic utilization of PHB for energy production. It was postulated that under anaerobic conditions (in absence of both free oxygen and nitrate), substrates such as acetate would diffuse in cells and de-energize the membrane. Bacteria that had polyphosphate reserves could re-energize their membrane by neutral phosphate expulsion, thus causing a net ejection of protons. Speculations on the possible role of polyphosphate as an anaerobic energy source were provided. The experimentation involved preliminary technique development, and batch testing under aerobic and anaerobic conditions. The effect of the addition of acetate, nitrate, and 2,4-dinitrophenol (a toxicant) and of various pH's on phosphate release were also studied. The following observations were made from the experimentation. The expected role for PHB was confirmed. Nitrate addition anaerobically resulted in phosphate uptake. Potassium, magnesium, and calcium were found to be co-transported with phosphate. Under anaerobic conditions, with identical amounts of acetate addition, a higher pH resulted in an increased magnitude of rapid phosphate release. The addition of 2,4-dinitrophenol resulted in a higher degree of anaerobic phosphate release when acetate was added. The postulated models were found to be consistent with most observations from the literature and from this research. From the understanding provided by these models, recommendations were given for efficient approaches to the operation of treatment plants removing phosphorus biologically, and for optimum processes for biological excess phosphorus removal.Applied Science, Faculty ofCivil Engineering, Department ofGraduat