Influent Fluctuation Analysis and Operation Strategy of Wastewater Treatment Plants during Shanghai's City-wide Lockdown Period

ABSTRACT

The city-wide lockdown management was implemented in Shanghai from the end of March to the beginning of June in response to the prevention and control of COVID-19 epidemic. The sudden change of the way of work, lifestyle and industrial structure in the megacity would inevitably influence the characteristics of wastewater production, the composition of wastewater, the influent conditions, and operations of wastewater treatment plants（WWTPs）. The main countermeasures of operation in typical WWTPs were analyzed, which could provide a reference for early-warning and precaution when similar situations occur in WWTPs in the future. In order to eliminate the interference caused by the hysteresis effect after the rain stops in the combined drainage system, the corresponding relationship between the rainfall conditions and the influent quantity and quality of WWTPs was studied.The new statistical standard was established for distinguishing"rainy days"or"count dry days". The contemporaneous data of WWTPs in Shanghai central area during dry season in the past three years was analyzed. It was found that the quantity and quality of the influent showed a reverse trend during Shanghai's city-wide lockdown period. The quantity of wastewater decreased by 6% in the corresponding period, and the concentration of COD and NH3-N decreased by 33% and 17%, respectively. The addition of a large amount of chlorine-containing disinfectants led to an increase in the concentration of residual chlorine in the influent of some WWTPs. Based on the analysis of treatment process and design parameters of the existing WWTPs, the operation mode of exploiting potentialities was finally adopted.WWTPs operated stably and the effluent quality could meet the discharge standards through measures such as strengthening pretreatment, prolonging sludge retention time, controlling the concentration of dissolved oxygen in the biological reaction section, and increasing the dosage of phosphorus removal agents.