Microbial release of soluble phosphate in an activated sludge environment

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Water Resources Research Center, Virginia Polytechnic Institute

The rapid increase in population and technology associated with modern civilization has resulted in increased water usage and, through the accumulation of waste products, increased deterioration of the quality of water that can be obtained from natural resources. One obvious manifestation of the change in water quality has been the overgrowth of algae and other aquatic plants. This effect has been attributed to the presence of increased concentrations of inorganic nutrients, particularly nitrogen and phosphorus, in the waterways.

A major source of fertilizer elements is treated sewage effluents, since nitrogen and phosphorus are incompletely or, in most cases, insignificantly removed in sewage treatment plants as conventionally operated. However, a profile of phosphorus concentrations through most plants will show that significant quantities of phosphorus are sorbed during biological treatment, but are then desorbed back to solution before the biological solids are removed. It has also been demonstrated that as much as 90% of the phosphorus can be removed by conventional treatment under certain, but as yet undefined, conditions.

The research reported herein was undertaken to increase the general understanding of the phosphorus removal mechanisms of activated sludge and to investigate ways that desorption of soluble phosphorus can be reduced or prevented in conventional treatment processes. It was the intention to provide designers and operators with knowledge that could be used to attain economical phosphorus removal.