Biological removal of phosphorus from wastewater

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Abstract
This paper reviews the present process technology for biological phosphorus (P) removal, the fundamental biological and chemical P removal mechanisms, analytical characterization methods for biological and inorganic P fractions, and finally conventional and new techniques for process design. The understanding of enhanced biological P removal has improved significantly in the past few years. Polyphosphate (poly‐P) accumulating bacteria appear to be selected by introducing an anaerobic fermentation reactor in which the biomass has access to readily biodegradable organics, like volatile acids, etc. The poly‐P bacteria are able to use poly‐P as an energy reserve to absorb and store the readily biodegradable organics, e.g., as ß‐polyhy‐droxybutyrate. This gives them an advantage over nonpoly‐P bacteria in their competition for substrate. In some biological P‐removal plants, phosphate precipitation by cations in the sewage may play a significant role. A few milligrams per liter of iron and/or aluminum in the wastewater appear to be important to promote precipitation at pH values near neutrality. Conventional design based on simple criteria like solids retention time and hydraulic retention times will most likely in the future be replaced by procedures based on process models. Such ones are able to predict how the P removal is affected by the composition of the sewage. However, there is still much to learn, qualitatively and quantitatively, about the fundamental biological and inorganic P removal process before such models will gain acceptance in practice.