Pump blockages and rags are significant barriers to energy and operational efficiencies at pump stations, causing unscheduled shutdowns, safety hazards for operators, costly equipment repairs and increased power usage due to a decrease in the pumps’ hydraulic performance. Scottish Water observed these negative effects—caused by an influx of wipes and rags—throughout a network of area pump stations. Engineers looked to a solution from two JWC Environmental Channel Monster grinders at one of its most problematic sites.
Mosside Sewage Pump Station has been in operation since 1961 and comprises three submersible pumps (duty/standby/assist) installed in the facility’s wet well to process a flow rate of 489 cu meters per hour. Over the past few years, Mosside has experienced a heavier-than-usual volume of rags and solids flowing into the station. This debris is especially problematic during heavy storms, as the material would create a “raft” of solids, which led to pump blockages during peak capacity periods and caused sewage to overflow in and around the pump station. This required Scottish Water operators to visit the site on a regular basis to uplift and unblock the submersible pumps and also clean up the spillages—a time-consuming and unpleasant task.
Rag Buildup & Pump Blockage Issues
The submersible pumps originally were protected by a coarse manually raked bar screen, yet the volume of rags was so heavy that operators were concerned about the large amount of debris being manually removed from Mosside. Scottish Water realized that the bar screen alone was not enough to deal with the volume of debris, so it sought a solution that would immediately resolve the issues.
Scottish Water was familiar with the screening and grinder product families from JWC Environmental—a Muffin Monster in-channel grinder has been successfully operating at another installation in the area since 2007. The company looked for a similar system to be installed at Mosside. Scottish Water contacted WGM Eng., distributor for JWC Environmental in Scotland, to find a solution that would resolve the rag buildup and pump blockage issues. WGM conducted a thorough assessment, and design engineers recommended that the manual bar screen be removed, the levels of the wet well walls and access flooring be raised to accommodate high-capacity periods, and two Channel Monsters be installed in the wet well, each on a guide rail system to facilitate easy installation.
The grinders feature a rotating screening drum with 6-mm perforations, which allow small particles to pass through, while capturing and feeding the larger debris into a dual-shafted grinder. This allows the grinder to shred solids effectively and completely while maintaining proper flow rates so capacities at pump stations are not compromised by clogs and equipment breakdowns. The system also is a durable, cost-effective and versatile way to protect valuable pumps, pipeline and other treatment equipment from the harmful effects of wipes and other debris. The design of the screening drums accommodates periods of high flow and is suited for pump stations, headworks, fine screen protection and treatment plants. The automated controller is adaptive to specific application requirements and plant SCADA systems, and stores operational information so operators can observe performance data over time.
Since installation in March 2014, Mosside has seen a drop in the number of pump blockages, freeing operators from having to visit the site to unblock the submersible pumps.
“The grinders have made a difference to both our operational and overtime costs, freeing up a lot of our operator time to concentrate on other sites,” said Graham Black, area manager for Scottish Water. “They have taken away the fear of being called to Mosside time and again.”
In addition to the reduction in unscheduled maintenance, the installation has allowed Scottish Water to cancel other planned capital investments downstream in its catchment area that no longer were required due to the conditioning of the rags being pumped from the facility. The capital and cost savings advantages, coupled with the elimination of the operators having to manually unblock the pumps and clean up raw sewage from overflows, made this project