What is a disadvantage of using a constant percentage return activated sludge flow control?

Using a constant percentage return activated sludge flow control can indeed lead to the clarifier being subjected to maximum solids loading. This means that as the flow rate of the wastewater entering the system changes, the return flow of activated sludge is adjusted by a set percentage of the influent flow. Consequently, if the influent flow increases, the return sludge flow also increases by the same constant percentage. This can potentially overload the clarifier with excessive solids, particularly during peak influent flow times.

When the clarifier is subjected to maximum solids loading, it can struggle to effectively separate the solids from the liquid. This may lead to issues such as poor effluent quality, decreased treatment efficiency, and a higher risk of sludge carryover into the treated effluent. Therefore, the disadvantage of maximum solids loading highlights a significant operational concern associated with this flow control method.

While increased energy costs, decreased settling rates, and higher maintenance requirements can be concerns in various contexts, the most direct and significant impact of constant percentage return flow control is indeed seen in how it can overload the clarifier.