Wet Weather Protection

Like many communities in the U.S., water companies in the U.K. are initiating wet weather watershed control projects to protect the beneficial uses of their waterways. Welsh Water is a not-for-profit water company with a 2050 vision to become a world-class, resilient, and sustainable service to benefit future generations. The vision, called Welsh Water 2050, sets out a plan to extend, improve, and...

PFET is what Welsh Water calls the process of treating more flow arriving at the water resource recovery facility (WRRF) to the required regulatory standards, without compromising the existing biological treatment processes. The principle of PFET is that a proportion of flow in excess of the current biological treatment of the WRRF will be treated via a side-stream treatment process. This is...

The two Welsh Water facilities in Gowerton and Llanelli are being implemented through a design–build partnership, including the contractor lead of Morgan Sindall, designer Sweco (Stockholm, Sweden), concrete structure design engineer FLI Carlow (Bristol, U.K.), and manufacturer WesTech Engineering (Salt Lake City, Utah). Both projects are in the final stages, with startup and commissioning...

End-of-pipe source controls are typically the least expensive solution to the CSO problem. Transport of wet weather flow generally adds to the total cost as treatment is still required at some point in the system. Storage can help reduce the treatment rate; however, the treatment structure volume itself will attenuate some of the short-term peaking. Consolidation of multiple outfalls also will add...

Wet weather discharges from the sewer infrastructure require a high-level solids removal for effective disinfection. Suspended solids greater than 10 microns tend to occlude bacteria from UV light. The same solids include oxidant-demanding substances that, if not removed to a significant level, will reduce the effectiveness and consistency of chemical disinfection. This is the case for all types...

Narrative water quality standards require any settleable solids and floatables are removed for discharge to U.S. waters, and thus are basic requirements for any treatment scheme. Numeric water quality criteria typically require minimum oxygen levels and magnitude, duration, and frequency criteria for bacteria indicators. Toxic criteria are expressed both as narrative and numeric. When designing...

Wet weather pollution is expensive to control because bacteria are ubiquitous in the environment and runoff volumes and flow rates can be very large. The largest precipitation events can result in wet weather flow as much as two orders of magnitude greater than the dry weather wastewater flow generated in the same catchment. The largest flows may be used for the design of transport. However, when...