New Screenings Processing System Eliminates Remote Disposal Costs

Installation of a new system that grinds, washes, compacts, and dewaters bar screenings at the Meriden (CT) Water Pollution Control Facility has reduced organic content and overall volume, eliminating remote landfill disposal costs, while also significantly reducing handling needs and odor, according to the plant's manager.

The Screenings Washer Monster™device, installed in May 2001 as an alternative to a costly, complex and burdensome procedure forced by closure of a nearby landfill, is manufactured by JWC Environmentaltrademark of Costa Mesa, CA.

After grinding, washing, compression, and dewatering, the final product has the appearance of shredded newspaper.

"Before the landfill adjacent to our site was closed, all we had to do was haul the screenings over there in our own eight cubic yard truck," said Robert T. Mercaldi, Assistant Director, Water Pollution Control Division, Department of Public Works, and manager of the 11.6 mgd plant. The Meridan plant is a two-time winner of EPA Region 1's Operation and Mainten-ance Excellence Award.

"After the closure, we had to find a company licensed to haul over the road, certify testing for a list they gave us of screenings parameters to be analyzed, rent a 15 cubic yard, specially lined dumpster for $1200 a month, and pay landfill drop-off charges ranging from $40-50 a ton at sites in Ohio, Pennsylvania, and New Jersey," he said. "Meanwhile, we had a complex new task to take care of in the plant, moving around solids heavily loaded with organics, with heavy odor, and requiring double and triple handling."

Meriden staff were able to install the new screenings washer without the need for any outside contractors, including all wiring and controls and haven't had any operational problems with it since, Mercaldi said.

"We just had to re-torque the drum head for the augur conveyor one time when the LED light told us to. It's basically totally unattended. The control panel is routinely checked daily by regular plant operators, who have a manual to follow if they need it, and we'll be using our regular maintenance mechanics for biannual checks of gear oils and transmission fluids," he said.

A controller accepts the input signal as synchronized with a screen or conveyor, and the augur operates automatically in an on/off cycle. During normal operation, the grinder operates continuously, or is sequenced to run only when the controller senses a signal from the screen or conveyor.

"I was a little concerned when nothing had come out the end for the first five days after startup, but I also noticed there wasn't any odor," he said. "Finally, a very dry solid, resembling shredded newspaper, extended six or eight inches above the exit chute, like ashes at the end of a cigarette. That falls off into a bin, and we bag it up for disposal as Special Waste."

"We've been able to reduce the weight of our bar screenings from eight tons per month to 660 lbs. per month, and their volume was reduced from 15 cubic yards per month to one cubic yard per month," he said. "In addition to eliminating the cost for the out-of-state dumping, and all that extra work we were doing with a backhoe, front-end loader, wheelbarrows, and the dumpster, we no longer need the bar screen at our pump station. All the screenings formerly removed there can be pumped to the inlet building where the new unit is."

Mercaldi said his two remaining bar screens are fine types, with 11/2 inch spacing, and automatic raking systems. A single chute receives scrapings from each screen, with effluent water piped in to push them into the Screening Washer Monster's square-funnel hopper. They then move through a grinder, and into a wash box, where a high-pressure spray cleans the ground particles and washes out organics. Compression and dewatering follows, with more water squeezed out in the tapered exit chute.

The unit is driven off the bar screen, with a vertical float tripping the switch as the level rises. Fifteen to 20 minute cycles are repeated as needed. Plant backflow water is used to wash screenings down the chute, and potable water is used for the spray in the washbox.

The Screenings Washer Monster is a self-contained unit that can process screenings that have been captured by bar screens or other screenings removal devices. Discharge is said to be virtually free of organic (fecal) matter, with the exit plug typically 40-50 percent dewatered, and reduced in volume by about 75-80 percent.

Captured solids are diverted from a hopper through a grinder and then passed to an auger, which washes and separates soft organics from plastics, paper, and other undesirable elements. Grinding then exposes more surface area for spray water to further clean out unwanted solids.

Organics and wash water pass through the augur's perforated trough and are returned to the plant's waste stream. Remaining material is conveyed, compacted, dewatered, and discharged as cake.

A controller accepts the input signal as synchronized with a screen or conveyor, and the augur operates automatically in an on/off cycle. During normal operation, the grinder operates continuously, or is sequenced to run only when the controller senses a signal from the screen or conveyor.

Screenings capacities are 150 cu. ft./hr for a 10 hp unit, or 25 cu. ft./hr for a 5 hp alternative. The unit is available in a grinder-less version for use with the company's Auger Monster® system.