Does a collection tank require a hydraulic retention time? Isn’t its purpose simply to collect water? Beginners don’t understand this; please provide an explanation

The function of a collection tank is to gather, store, and balance the quality and quantity of wastewater. The amount and quality of wastewater generated by various production workshops are generally uneven; wastewater is produced during manufacturing processes but not when there is no production, and significant variations can occur even within a single day or between shifts. This is especially true for wastewater from the fine chemical industry. If dirty wastewater and clean wastewater are not separated, the quality and quantity of highly concentrated wastewater and less polluted wastewater can vary greatly. Such variations are detrimental to the proper operation of wastewater treatment facilities and equipment, as well as to the effectiveness of the treatment process. Therefore, before wastewater enters the main sewage treatment system, a wastewater collection tank with a certain capacity must be installed to store the wastewater and ensure its homogeneity, so as to guarantee the proper operation of the wastewater treatment equipment and facilities. The capacity of this collection tank should be determined based on factors such as the variations in the flow rate of wastewater entering the system, the model and number of sewage pumps selected, their operating mode, as well as the operational characteristics and startup times of the pump station. An excessively large capacity of the collection tank leads to significant silt accumulation within it and increases construction costs; on the other hand, an insufficient capacity fails to meet the requirements for water level regulation. Therefore, the volume of the collection tank should be determined reasonably based on the above circumstances.

Reservoirs are still necessary, and for operational management, the larger they are, the better – as a larger size provides greater buffering capacity.