SouthWestWater Ltd (STW) is responsible for providing reliable, efficient and high quality drinking water and wastewater services to a population of 1.5m in South West England.
In order to improve the performance of the existing works at Plymouth Central STQ and to cater for future increases in loads, Veolia Water Technologies designed a solution that involved treatment of sludge liquors with VWT AnoxKaldnes™ MBBR technology.
At the Plymouth Wastewater Treatment Works the primary and return biological solids are co-settled in a chemically assisted lamella settler. This settled sludge is dewatered by centrifuges and the centrate liquors are combined with the incoming sewage for settlement in the lamella. There is a significant concentration of dissolved organic matter in the return liquors which is not removed in the primary process and leads to an increased load to the down stream Biological Aerated Flooded Filter (BAFF).
In order to reduce the dissolved organic content of the liquors, a side-stream liquor treatment plant “MBBR” was installed.
Primary and return biological solids are co-settled in a chemically assisted lamella settler. The settled sludge is dewatered by centrifuges. An existing sump has been converted to a balancing tank, providing an operating volume of 176m3. A balanced flow is pumped to the MBBR which consists of a single rectangular tank divided into two cells arranged in series. The 2 cell reactor configuration offers additional removal efficiency and provides significant process security. The MBBR process is a fixed film system and consequently provides a level of resilience to shock and toxic loads potentially present in this type of effluent stream. The MBBR effluent is returned to the inlet works.