Impact of natural and climatic factors on the efficiency
of open wastewater treatment facilities operation

Summary

The problem associated with the impact of natural and climatic factors on the efficiency of wastewater treatment in open treatment facilities is considered. The analysis of methods for calculating the basic units for mechanical treatment (primary settling tanks) and biological treatment (aeration tanks and secondary settling tanks) of municipal wastewater is presented. It is indicated that at the design stage of the complexes it is important to calculate correctly the temperature of the incoming wastewater. The long-term practice of operating municipal wastewater treatment facilities has shown that with a long retention time in open facilities waste liquid can be cooled during the cold period of the year and heat up to about 1.5–6 °C during the warm one. In the first case this negatively affects the processes of sedimentation of suspended solids in settling tanks and oxidation of organic substances in aeration tanks; whereas in the second case this negatively affects the saturation of mixed liquor in aeration tanks with oxygen resulting in a reduced treatment level. The purpose of the work was to develop recommendations that allow at the design stage of wastewater treatment facilities to correctly calculate the temperature of waste liquid in open structures for a certain project that has specific climatic conditions. To achieve this goal the data of laboratory and in-process control of the operating wastewater treatment complexes were analyzed. A theoretical analysis of the currently used methods for designing wastewater treatment facilities has been made; research has been carried out at the operating facilities. Mathematical models widely used in heat engineering have been studied to determine heat losses from the open surface and through enclosing structures as well as the heat input from solar energy and exothermic reactions.

Key words

aeration tank , sewerage treatment facilities , evaporation , primary and secondary settling tanks , wastewater temperature , cooling , evaporation , convection heat exchange