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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.
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.
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.
[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]
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.
Takács developed new concepts in process modeling including settling, chemical and biological phosphorus removal, side-stream treatment, carbon capture for energy recovery, biofilms, granules and granulation, equilibrium chemistry, natural and engineered precipitation, such as for nutrient recovery. [11]
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]
Aluminium sulfate is used in water purification and for chemical phosphorus removal from wastewater. It causes suspended impurities to coagulate into larger particles and then settle to the bottom of the container (or be filtered out) more easily. This process is called coagulation or flocculation.
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