Reclaimed Water - Tertiary Filters

Secondary effluent is pumped into the bottom of the tertiary filters, the water then flows upward through a series of riser tubes and is evenly distributed into the sand bed through an open bottom of an inlet distribution hood. This water flows upward, through a downward moving sand bed which entraps the solids. The clean filtrate exits from the sand bed, overflows a weir where it is discharged from the filter.

The filter media is continuously cleaned by recycling the sand internally through an airlift pipe and sand washer. At the same time the filtrate is flowing out the top, sand and accumulated solids are drawn downward into the suction of an airlift pipe. A small volume of compressed air is introduced into the bottom of the airlift. The air lifts the dirty sand up the airlift pipe. The impurities are scoured loose from the sand during this violently turbulent upward flow. Upon reaching the top of the airlift, the dirty slurry spills over into the central reject compartment, and the sand is returned to the sand bed through a gravity washer/separator which allows the fast settling sand to penetrate, but not the dirty liquid. Since the sand has a higher settling velocity than the dirt particles, it is not carried out of the filter. The regenerated sand is redistributed on top of the sand bed, allowing for a continuous uninterrupted flow of filtrate and reject (backwash) water. A continuous reject flow exits near the top of the filter, carrying away the dirt and impurities removed in the filter.

So what do we do with the water now? Storage and Pumping.