On-Site Wastewater ReuseAug 2009, Dr. Marcus N. Allhands, PE, VP Business Development Orival, Inc.
Located along the banks of one of the largest tributaries to the Mississippi River, this 100 MGD (million gallons per day) wastewater treatment plant has a large demand for service water with low suspended solids. Nearly 3 MGD of water are needed for cleaning devices on the bar screens, spray water to keep the belt presses clean and porous, pump seal water, service water at hose bibs and equipment wash stations and water to cool several large engine/generator sets that run off of methane gas produced from sludge digestion.
Typically, wastewater treatment plants take this service water from potable water supplies. An automatic self-cleaning screen filtration system was installed recently using effluent from the plant for all of these non-potable needs saving enough potable water each day to supply over 7000 homes in the area.
Each filter takes less than 15 seconds to clean without interrupting the filtration process.
Figure 1 shows the operating installation. The controls initiate a cleaning cycle when a 7 psi loss across the filtration system is reached due to captured debris. A manually set timer in the control panel can also initiate the cleaning cycle. During the cleaning cycle a “dime-size” area of screen is forcefully cleaned by pulling water backward through the screen at a velocity of over 50 feet per second and then moving that “dime-size” area of cleaning action across every square inch of screen surface. Each filter takes less than 15 seconds to clean without interrupting the filtration process. Simplicity, dependability, performance and the manufacturer's commitment to customer service drove the selection process by the engineering firm commissioned to design the reuse system.