Implementation of an Innovative, Severe Duty, Grit Removal System at the Blue Plains Advanced Wastewater Treatment Plant in Washington, D.C.

The District of Columbia Water and Sewer Authority's Blue Plains Advanced Wastewater Treatment Plant has headworks facilities capable of treating an average daily design flow of 370 million gallons per day (mgd) and a design peak flow of over 1.0 billion gallons per day (1,000 mgd). The facilities are prone to very heavy grit loads during wet weather events, and the facilities are forced to schedule and rely on outside vactor contractors to remove grit from their process. Excess grit frequently washes into the primary clarifiers and sludge processes, causing further damage and failures downstream.The key item in the design of the upgrade to the plant's grit removal facilities included a completely automated, heavy-duty, custom-made traveling bridge grit removal system. The bridges are cog-wheel driven, constructed of Type 304 stainless steel, and are powered via festooned power cable system. Bridges are operated by VFDs, and in conjunction with track limit switches, are able to travel at various distances, directions, and speeds according to the current plant operating conditions. The control system employs a variety of additional instrumentation and features that provide for a safe, reliable, and efficient grit removal process, even during wet weather events. Each bridge supports two, dual heavy-duty submersible pump/suction plate systems, that continuously remove settled grit from the tanks and transfer to the grit dewatering processes. Conceptual studies were performed to quantify and characterize the grit encountered at the plant. Pilot testing results provided critical design information for the grit pumps, and allowed the innovative design of the grit pump suction plate and plow concept. Observations from numerous plant visits were also addressed in the specialty design of the system. This paper presents the innovative design features of the traveling bridge grit removal system, pilot and factory testing information and results, and field testing results obtained thus far in construction.