ABSTRACT
Surface overflow rate is used to determine loading on clarifiers. It is similar to hydraulic loading rate-flow per unit area. However, hydraulic loading rate measures the total water entering the pmwss (plant flow plus recirculation) W hereas surface overflow rate measures only the water overflowing the pmess (plant flow only). As indicated in the diagram to the right, surface overflow rate calculations do not include recirculated flows. This is because recirculated flows are taken from the bottom of the clarifier and hence do not flow up and out of the clarifier (overflow). Since surface overflow rate is a measure of flow (Q) divided by area (A), surface overflow is an i n h c t measure of the upward velocity of water as it overflows the clflier:*
This calculation is important in maintaining proper clarifier operation since settling solids will be drawn upward and out of the clarifier if surface overflow rates are too high.
