Automatic Filters Tackle Wastewater Reuse Challenge
In February of 2000, working through Cleland Environmental Engineering, the City of Carmel, IN, WWTP approached Amiad Filtration Systems and R.A. Ross and Associates with a filtering challenge. A project involving the installation of new centrifuges had already been approved; this provided an opportunity for Ed Wolfe, Plant Superintendent and staff to re-engineer the water supply system within the plant.
Wolfe wanted a new system for treating wastewater effluent for use around the facility. Heavy solids loading affected auxiliary equipment such as yard hydrants, heat exchangers, spray bar nozzles, and pump seals. Persistent basket strainer and belt press spray-bar cleaning (labor cost) and seal replacement (material and labor costs) were the main targets when looking at a new “strainer” system.
Carmel’s onsite water use was 300 gpm under peak demand with a minimum system pressure of 50-60 psi. Their water sources were potable municipal water, a non-potable well located onsite and secondary effluent. Very high iron concentrations in the nonpotable well had caused problems in the past.
The reuse of secondary effluent was the best use of resources and proved to be the most cost effective. The secondary effluent typically contained 10-15 ppm of total suspended solids with values above 30 ppm during clarifier upsets. After lab analysis of the solids in the secondary effluent, Amiad engineers recommended a filtration degree of 80 micron. The decision was made to install an Amiad 4" SAF-4500 Automatic Self Cleaning Filter with an 80-micron screen and PLC controller. An Amiad 4" Super Manual Filter with an 80-micron screen was placed in a by-pass line as a backup system.
Focused Back-Flushing
The Amiad filters use focused back flushing with a series of small nozzles cleaning less than two square inches of the screen element at a time. These nozzles are attached to a central hollow tube called a suction scanner that hydraulically connects to atmospheric pressure (zero gauge pressure). Taking only 12-30 seconds per cleaning cycle, the suction scanner and its series of nozzles slowly rotates in a spiral pattern inside the 316-L stainless steel filter screen element moving the small cleaning area across the entire screen surface.
The motorized scanner is rotated at a constant 24 rpm, thus ensuring that every square inch of the screen surface is cleaned of debris.
The company’s four-layer 316-L stainless steel screens protect the actual filtering layer from damage by rocks, pieces of metal or other hard foreign objects yet are designed so that each small opening in the filtering layer are available for the filtration process.
Plant personnel installed the entire system at the WWTP in the city of Carmel in May of 2002. In his letter to Amiad, Joe Faucett, Maintenance Manager, writes: “This filter is easy to operate and maintain.”
Faucett said before the installation, his crew had to clean the filter press spray bar nozzles every three weeks. Now this task is performed only twice a year. The city is now successfully reusing effluent throughout the plant. This equates to savings for the treatment plant, the city, and the taxpayer.WW