Specific features of chemical phosphorus removal in the process of biological wastewater treatment

Summary

Wastewater treatment in public sanitation systems in settlements and urban districts has been the field of application of the best available technologies. For small and medium-sized treatment facilities, the concentration of phosphate phosphorus in the effluent is not regulated; for the facilities with a capacity of more than 10 thousand m³/day – it should not exceed 0.7 mg/dm³, while biological treatment and chemical removal of phosphorus is recommended. The issues of the chemical removal of phosphates and determination of the effect of the dose of aluminum-containing chemicals and pH value on the bacterial community of activated sludge by the identification component – protozoa, are considered. During the studies it was found that both the type of chemical and the point of its introduction into the biological treatment facilities affect the value of the optimal chemical dose; the reasons for changing the dose of the chemical depending on the introduction point were identified. While chemical solution is introduced into primary settling tanks, the dose can exceed the theoretically determined one by 4–5 times. The pH values of the chemical treatment system were determined as a factor of dependence on the initial concentrations of phosphates in wastewater, at which poorly soluble aluminum phosphates are formed. It has been established that the relationship between pH of the system and the concentration of dissolved aluminum phosphates has a key effect on the state of protozoa. While the required pH value is maintained, the doses of the aluminum-containing chemical can be high (up to 116 mg/l), however not resulting in the biodegradation of the sludge system. The introduction of coagulant solution into the nitrification zone of an aeration tank can result both in the degradation of sludge, and violation of MPC for dissolved aluminum and phosphorus in the effluent. Therefore, in case of supplying the coagulant solution to the end of the nitrifying aeration tank, chemical phosphorus removal can be enhanced by the additional alkalization of the sludge liquor.

Key words

wastewater , biological treatment , phosphate ions , рН of sludge liquor , aluminium-containing coagulants , optimal dose , protozoa , microscopic examination of activated sludge