EFFECT OF THE REDOX POTENTIAL ON SLUDGE LIQUOR PHOSPHATATION IN BIOLOGICAL PHOSPHORUS REMOVAL TECHNOLOGIES

Introduction. The metabolic activity of phosphate accumulating organisms (PAOs) under anaerobic conditions plays a decisive role in optimizing the process of removing phosphorus compounds in the Enhanced Biological Phosphorus Removal (EBPR) technology when alternating anaerobic and aerobic modes. A number of chemical, physical, physical-and-chemical, hydraulic, and biological factors affect the efficiency of biological wastewater treatment aimed at the removal of phosphates. Since the removal of phosphates using PAOs is associated with the transfer of ions through the cell membrane, the impact of the redox potential of the aquatic environment on phosphatation and dephosphatation in systems with activated sludge is of scientific and practical interest. Methods. Phosphatation of wastewater under anaerobic and anoxic conditions was studied during laboratory experiments and inspection of existing wastewater treatment plants with aeration tanks with and without zoning. In laboratory experiments, quantitative dependences of the wastewater phosphatation rate on the ORP values in the environment and the difference between the ORP values in different areas of aeration tanks were established. Results. The maximum achieved phosphate accumulation capacity of the unadapted sludge in the flow-through mode of cultivation under laboratory conditions was 61.1 mg of PO4/g of sludge. At the existing wastewater treatment plants, the ORP indicator of aquatic environments is more sensitive and describes the oxidationreduction situation in more detail than the oxygen concentration. As for wastewater treatment in aeration tanks with zoning, the ORP value and the phosphorus concentration in phosphates in the sludge liquor had the opposite dynamics. Conclusion. The analysis of the phosphate concentration and ORP values in aeration tanks with zoning suggests that for wastewater phosphatation/ dephosphatation, not the absolute ORP value, but the difference between the ORP values of aquatic environments created in different zones of an aeration tank is more significant. In general, oxidation-reduction characteristics of interacting aquatic environments play an important role in the migration of phosphates in the system of activated sludge–wastewater in the EBPR technology and can be used as control actions.