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Maintaining optimal pH is important for the removal of phosphorus from water. Phosphorus is most effectively removed at the neutral pH range, when the insoluble aluminum hydroxide is present. This hydroxide functions as a Lewis acid , [ 5 ] creating a flocculation environment similar to conventional wastewater treatment.
Thus, the phosphorus fraction of phosphorus accumulating biomass is 5-7%. In mixed bacterial cultures the phosphorus content will be maximal 3 - 4 % on total organic mass. If additional chemical precipitation takes place, for example to reach discharge limits, the P-content could be higher, but that is not affected by EBPR.
The most studied example of this phenomenon is in polyphosphate-accumulating bacteria (PAB) found in a type of wastewater processing known as enhanced biological phosphorus removal (EBPR), however phosphate hyperaccumulation has been found to occur in other conditions such as soil and marine environments, as well as in non-bacterial organisms ...
Phosphorus removal can also be achieved by chemical precipitation, usually with salts of iron (e.g. ferric chloride) or aluminum (e.g. alum), or lime. [ 25 ] : 18 This may lead to a higher sludge production as hydroxides precipitate and the added chemicals can be expensive.
Locally available laterite—a low-grade bauxite rich in iron and aluminum—is used in acid solution, followed by precipitation to remove phosphorus and heavy metals at several sewage treatment facilities. [30] Calcium-, iron- and aluminum-rich solid media are recommended for phosphorus removal. [30]
[24] [25] Phosphorus recovery methods from wastewater or sludge can be categorized by the origin of the used matter (wastewater, sludge liquor, digested or non-digested sludge, ash) or by the type of recovery processes (precipitation, wet-chemical extraction and precipitation, thermal treatment). [26]
Besides phosphorus precipitation, enhanced biological phosphorus removal can be implemented which requires an additional anaerobic process step. Some characteristics for membrane bioreactor technology render enhanced biological phosphorus removal in combination with post-denitrification an attractive alternative that achieves very low nutrient ...
The yield of PAOs (Polyphosphate Accumulating Organisms) is reduced between 70 and 80% under aerobic conditions. Even though the phosphorus can be removed upstream of the aeration tank by chemical precipitation (adding metal ions such as: calcium, aluminum or iron), the biological phosphorus removal is more economic due to the saving of chemicals.