IMPLEMENTATION EXPERIENCE OF CSO POLLUTION CONTROL POLICIES AND PROCEDURES IN THE UK

摘要

Historically, combined sewer overflows (CSOs) in the UK have been designed to discharge at fixed multiples of the dry weather flow in the sewer, usually 6 x DWF. Flows in excess of 6 x DWF would be spilled and the remainder carried forward to a Wastewater Treatment Plant (WTP). Problems arising from this pragmatic approach were recognised as early as the 1960s when a new approach, 'Formula A' [1], was proposed to calculate an acceptable pass forward flow from a CSO. This is still in use as a minimum CSO spill setting criteria. In the 1960s, new designs of overflow were adopted to provide for retention of pollution in the sewer, such as the use of storage, and stilling pond or high side weir overflows. A method for estimating storage requirements was developed in the late 1970s [2]. Referred to as the SDD method, it is based on a Formula A spill threshold, plus storage within the CSO related to the available dilution in the river and the upstream sewer population equivalent. Neither the Formula A nor the SDD approach can be directly related to compliance with receiving water standards.