Self-Cleaning Filter Helps Reduce Solids in Non-Potable Water

The wastewater treatment plant in the city of Steamboat Springs, Colo., needed a solution to reduce solids in its non-potable water (NPW).

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Case Study #1: Steamboat Springs, Colo.

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City of Steamboat Springs, Colo. After extensive processing, the city's treated effluent is discharged into the Yampa River. Digested sludge from the aerobic process (biosolids) is applied to the land as soil conditioner for grass hay crops.

The wastewater treatment plant in the city of Steamboat Springs, Colo., needed a solution to reduce solids in its non-potable water (NPW). Gilbert Anderson, the plant's superintendent for over 20 years, explained that in Steamboat Springs, treated effluent from a secondary wastewater treatment plant (WWTP) is stored in an open pond and is then used for NPW.

"Previously, solenoids that control water flow for wash water on the bar screen would become inoperable due to solids in the NPW," Anderson said. The filters they had added to keep solids out of the solenoids required frequent filter replacement and were costing the facility money and excessive labor.

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Forsta A2-90 model filter at the city of Steamboat Springs WWTP. The treatment plant handles approximately 3 MGD with a design flow capacity of 5MGD, enough to serve a population of about 50,000.

The facility sought a way to improve NPW quality that was cost-effective, reliable and that required a minimum amount of labor. After some research, they chose a Forsta self-cleaning filter. Anderson said, "We now utilize a Forsta A2-90 model filter to enhance the quality of the NPW for use as wash water on a bar screen. The system has been in service for several years with no solenoid failures and almost no maintenance." The A2-90 model filter offers 1 sq. ft. of screen area, uses a 1-in. flush valve, has a cleaning duration of approximately six seconds, and requires roughly four gallons of water per cleaning cycle.

The quality of the NPW entering the self-cleaning filter is variable due to solids such as duck weed, algae and other various fauna and flora blooms that originate in the open pond. In light of this, the filter came equipped with a stainless-steel 100- micron screen. The filtration degree was selected to be tight enough to prevent the passage of particles clogging the solenoids and coarse enough to easily withstand the fluctuations in solids concentration in the NPW at the inlet.

Case Study #2: Throop, Pa.

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Susquehanna River Bank. The Lackawanna River is a 40.8 mile tributary of the Susquehanna in northeastern Pennsylvania.

The Throop Wastewater Treatment Plant at the Lackawanna River Basin Sewer Authority in Throop, Pa., underwent a series of upgrades in 2012 that called for an amplified usage of its NPW. It became increasingly important to ensure that the NPW did not contain particles that would clog equipment. After a thorough analysis of various filter manufacturers, design engineers selected Forsta's filter for the job.

The Forsta self-cleaning filter at Throop was sized to treat effluent for use throughout the plant. The sanitation of equipment at the facility includes the spray water in treatment tanks to clean foam, a spray nozzle system to clean the belt press and the cleaning of the gravity belt thickener and a mechanical bar screen. All of these cleaning locations utilize the NPW that enters the filter, a total flow of approximately 200 gpm (with capacity for a maximum flow up to approximately 800 gpm).

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Forsta A6-LP180I-CS model filter at the Throop WWTP. The plant has a capacity of 7.0 MGD and is one of the Lackawanna River Basin Sewer Authority's three sewage treatment plants.

The A6-LP180I model filter that was selected offers 3 sq. ft. of screen area, uses a 1-in. flush valve, has a cleaning duration of 15 to 20 seconds, and requires roughly 13 gallons of water per cleaning cycle. The filter came equipped with a stainless-steel, 250-micron wedge-wire screen that's well-suited to handle the fibrous particles originating intermittently from the source water.

Water entering the filter flows from a chlorine contact tank. Total suspended solids concentration at the inlet of the filter averages <10 ppm, with the large majority of particles too small to see. Occasional strands of algae and other larger particles are the primary concern with regard to clogged equipmet. Pressure pumps are upstream of the filter, which sends water into a pneumatic tank, and from which water is distributed to the various cleaning requirements.

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Forsta's filter is set to clean on a timer at 30-minute intervals or when differential pressure is reached (though according to plant operators, the filter rarely, if ever, reaches differential prior to the pre-set cleaning cycle). This is a good indication that the filter was sized properly for the maximum flow and outfitted with an appropriate screen to trap hazardous particles. Treated water from the Throop plant is ultimately discharged into a receiving stream.

Conclusions

In both of these cases, care was taken to understand the nature of incoming particulate to the extent that each filter could be sized to impede unwanted particles. It was important not to compromise operations with an unnecessarily fine degree of filtration in order to require excessive amounts of screen area to accommodate the flow of its NPW. Accordingly, the 100-micron and 250-micron screens each offered the operators insurance against clogged equipment without making the equipment prohibitive in size or cost.

The city of Steamboat Springs and the Lackawanna River Basin Sewer Authority WWTPs offer excellent examples of the ability of Forsta self-cleaning filters to ensure the quality of NPW in treatment applications. The automatic nature of the cleaning cycle (which does not interrupt a main system's flow) makes the self- cleaning filter an excellent choice for facilities seeking to eliminate downtime and excessive labor. The reliability of the filtration mechanism to capture unwanted particles during normal operation coupled with the highly-efficient and automated cleaning cycle further corroborate the case for Forsta's filters in WWTPs.

Forsta Filters is an exhibitor at the WEFTEC.13 event and can be found at Booth No. 872.

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