One of the major challenges faced by most wastewater treatment facilities today is the need to develop and operate a sound and responsive storm water management program in the absence of an assured and adequate source of funding. This paper will discuss various strategies, such as flow equalization and off-line storage of MLSS, which could be implemented to mitigate the negative impact of high flows from storms. It will also illustrate how storm water management guarantees adequate treatment throughout the storm event, using the Rogers WWTP, Arkansas, as an example.
Most wastewater treatment plants are designed to treat at least twice their average flows, but it is not uncommon for WWTPs to receive flows more than four times the average. Permit limits are becoming increasingly strict, and there is no room for any type of process upset. With the strict limits even diurnal flow fluctuations can stress the process, making it difficult for the facilities to maintain compliance with their permit. Though a relatively conservative design could be an option, it may not be the most cost-effective choice. The performance of a biological treatment system depends on the ability of the secondary clarifiers to handle peak flows. The increased flows through the aeration basins result in increased solids loading rates to the secondary clarifiers, potentially leading to solids washout, overflows, and permit violations. Shallow clarifiers often have difficulty containing the typically low-density activated sludge solids during high hydraulic loading events.