Structure and indicators of electric energy consumption in dairy wastewater treatment plant

The aim of the research was to determine the indicators of electricity consumption in every stage of the dairy sewage treatment process in relation to the sewage flow and the load of removed organics (BOD₅, COD) and nutrients (TN, TP). The research was conducted in a dairy wastewater treatment plant (WWTP) consisting of mechanical treatment, averaging tank, dissolved air flotation (DAF) and biological treatment with sequence batch reactors (SBRs). Energy consumption was measured with the help of transducers. Indicators of unit electricity consumption were determined on the basis of 95 measurement series of energy consumption, sewage flow and removed load. The mean value of total unit energy consumption relating to the flow for the entire WWTP was 2.29 kWh·m^-3, while for biological treatment 1.17 kWh·m^-3 and 0.05 kWh·m^-3 for DAF. The mean values of indicators relating to removed pollutants load for the entire WWTP were: 1.89 kWh·kg_rem BOD₅^-1, 1.30 kWh·kg_rem COD^-1, 48.61 kWh·kg_rem TN^-1 and 160.01 kWh·kg_rem TP^-1. During biological treatment, energy consumption indicators were on average: 1.65 kWh·kg_rem BOD₅^-1 and 1.19 kWh·kg_rem COD^-1, 52.90 kWh·kg_rem TN^-1 and 141.26 kWh·kg_rem TP^-1, while for DAF: 0.12 kWh·kg_rem BOD₅^-1, 0.09 kWh·kg_rem COD ^-1, 3.85 kWh·kg_rem TN^-1 and 16.17 kWh·kg_rem TP^-1. It was found that the biological treatment in SBRs was responsible for 54.1% of the total energy consumption of dairy WWTP. Aerobic sewage sludge treatment accounted for 17.0% of total consumption, mechanical treatment 17.1%, deodorization 2.6%, and other (social, lighting etc.) 6.9%, while DAF only 2.3%. The real-time electricity metering system enabled the optimisation of the electricity consumption in the WWTP, taking into account its consumption in unit processes and the removed pollutants load. The application of this system enabled to make corrections that reduced energy consumption while maintaining the required treatment efficiency.