Low in maintenance, the only submerged moving part is the effluent weir
used for desludging.
A diffuser for sulfur dioxide solution was added to the end of each chlorine contact tank ahead of the effluent weir
. With the cascading steps for postaeration following the weirs, adequate turbulence for mixing was readily achieved.
The clarified water flows over the effluent weirs
and discharges to the excess flow chlorine contact basin, where the flow is disinfected by sodium hypochlorite and dechlorinated with sodium bisulfite.
As plant flow increased, however, the ferric chloride floc tended to rise over the effluent weirs
. Evidently, a coagulant-aid polymer was required to settle the floc at these higher flows.
To meet Phase III plant capacity requirements, the original basin effluent weirs
were raised 1.5 ft to increase the operational level of the basins.
After passing over the effluent weirs
, the chlorinated wastewater flows over cascade aerators before discharge into the Salisbury Plain River.