Optimization of wastewater treatment plant based on polymer and electricity consumption - A case study of Finland

Wastewater treatment plants play a crucial role in water management by facilitating water reuse, recycling and maintaining a safe level of pollutants released into the environment. The operation of these plants varies according to a several factors, including the season, type of wastewater, and volumes to be treated. These factors commonly influence the consumption of electricity and other input materials, such as coagulants and flocculants. Despite the process being well-established and in use for decades, the use of chemical agents often remains at constant ratios, which may depend on inflow volumes. Consequently, the use of those chemical agents often surpasses the actual process needs, leading to unnecessary costs and environmental impacts. In this context, modelling was employed to analyze the typical operation of a wastewater treatment plant, with the polymer concentration and the electricity demand as the variables to be optimized. The reduction of the amount of polymer was determined by tracking the sedimentation kinetics at different polymer concentrations, combining zeta potential measurement and particle size distribution. Sedimentation data were obtained by interpreting the transmission and backscattering profile using a TurbiScan Lab®. The impact of the sample collection and analysis time on sedimentation kinetics was also investigated. It was found that the optimal concentration of cationic polyacrylamide to treat wastewater containing approximately 5 mg/L of suspended particles and initial concentration of phosphorous of 5.525 mg/mL can vary from 0.1 mg/mL to 1.3 mg/mL depending on the analysis time. Therefore, by implementing in-line sensing, the concentration of suspended particles can be used to optimize polymer consumption. Additionally, a new electricity operation mode is proposed for the wastewater treatment plant in Finland, a concept that could yield benefits beyond economic profit. These findings could be utilized to enhance the operation of wastewater treatment plants worldwide.