Screens meet discharge permit

Problem
During rains, the combined sewer system of the Detroit Water and Sewer Department discharged 20 billion gallons annually to the Detroit and Rouge Rivers. The state mandated the flows at the outfall be filtered through 1/4-inch openings and disinfected. The screens had to sustain a 10-foot differential head in 10- by 21 1/2-foot-deep channels.

Solution
After a finite element analysis, the consulting engineer selected Aquascreen fine screens from Andritz Separation. Company personnel demonstrated that the design could handle extreme loads. The department installed six in-channel perforated panel traveling belt screens with 6 mm openings in the Oakwood CSO Retention Treatment Basin. Each unit handled 179 mgd.

Result
Since November 2011, the facility has had 10 CSOs and has met its permit requirements. 817/465-5611; www.andritz.com.

  Belt presses avert solids overload

Problem
Processing 38 to 40 gpm, the two 2-meter 16 s-wrap belt presses at the 30 mgd (design) Gloversville-Johnstown (N.Y.) Joint Wastewater Treatment Facility could not keep up with increased production caused by industrial high-strength influent.

Solution
The plant replaced the original equipment with two 2.5 meter 3DP belt presses from BDP Industries. Each handles 55 to 60 gpm and processes up to a dry ton per hour. Independent gravity belts and a vertical pressure zone optimize dewatering, while open construction simplifies maintenance and operation.

Result
The plant dewaters 150,000 and 230,000 gpd of material at 3 percent solids, resulting in 100 wet tons of biosolids. Reducing the amount of solids recycled back through the process has improved the plant’s performance. 518/527-5417; www.bdpindustries.com.

  Side-mount open-throat design prevents bridging

Problem
Biosolids at the Hay Road Wastewater Treatment Plant in Wilmington, Del., fell from a gravity belt thickener into a hopper. A floor below, biosolids bridged the inlet of the progressive cavity pump at the end of the hopper, causing the pump to run dry. Frequent repairs to the damaged stator strained the maintenance budget.

Solution
Officials purchased a custom CL390 rotary lobe pump from Boerger. The side-mount open-throat design prevented bridging, and the pump can temporarily run dry. Operators replace worn parts through the front cover without removing pipes or the drive systems.

Result
Management has inquired about two more pump-and-grinder applications. 612/435-73 00; www.boerger.com.

  Thickening centrifuge has multiple advantages

Problem
Odorous dissolved-air flotation thickener tanks at the Kenosha (Wis.) Water Utility Wastewater Treatment Facility occupied two floors of a 10,000-square-foot building and produced material at about 4 percent solids. The tanks required repairing, multiple pumps, and monitoring four hours per day.

Solution
Operators replaced the tanks with an enclosed THK18-3 thickening centrifuge from Centrisys. It has a 10 hp feed pump, a 50 hp main drive, and a 20 hp scroll drive, all controlled by variable-frequency drives. The unit, installed easily in a 1,000-square-foot building, produces material at 5 percent solids with thickening capabilities up to 7 percent. It requires minimal operator oversight and maintenance.

Result
The thicker biosolids improve digester operation and produce more biogas. The installation saved the utility $80,000 to $100,000 in pump and equipment upgrades. 262/654-6006; www.centrisys.us.

  Bar screen reduces maintenance

Problem
Maintaining the chain bar screen at the 3.2 mgd Brush Creek conventional activated sludge treatment plant in Cranberry Township, Pa., was stressing the operators. Debris jammed rotating parts or passed through the screen, which required a major repair about twice a year.

Solution
Operations manager Mike Sedon discovered the FlexRake bar screen from Duperon Corp. at WEFTEC 2005. “It’s a simple, effective piece of machinery that makes screening simpler and more reliable,” he says. The unit eliminates confined-space entries and has an energy-efficient 3/4 hp drive system.

Result
“We’re catching more rags and experiencing less pass-through,” says Sedon. “Maintenance is nothing more than greasing the unit every other month. Other than that, it just runs.” 800/383-8479; www.duperon.com.

  Cake bin system manages biosolids

Problem
The Blue Plains Advanced Wastewater Treatment Plant in Washington, D.C., needed cake bins with live bottoms to adjust the thermal hydrolysis process independently, and enough capacity to store biosolids at the 12-hour throughput rate.

Solution
The plant bought four 9,500-cubic-foot T-316 stainless steel cake bin systems from Jim Myers & Sons. The bins are 28 feet long, 35 feet tall and 18 feet wide. They taper to 9 feet wide and have four 20-inch-diameter shafted stainless steel screws in the live bottom pan. Options include local control stations, electric-actuated slide gates, load cells, level sensors, and 10 stainless steel chutes with sampling ports and spray water nozzles.

Result
Each bin receives biosolids from three centrifuges through chutes with electric actuated diverter gates. The covered tops support foot traffic. 704/554-8397; www.myersequipment.com.

  Sludge no match for dewatering system

Problem
The belt press at the 6 mgd (design) Leipsic (Ohio) Wastewater Treatment Plant was outdated.

Solution
When OR-TEC offered to demonstrate its screw press on waste activated sludge and septage, superintendent Tony Schroeder agreed to a five-day test. Cake and inlet solids numbers were run on a moisture balance supplied by the company. Capture rates, based on composite samples, were taken and tested by an independent laboratory.

Result
Cake was 15.8 to 29.29 percent solids for both materials using 10 to 18 pounds of polymer per dry ton. The lowest solids capture rate was 97 percent. The village bought the unit. “The press produces quality cake and filtrate, is economical, and requires minimal operator attention,” says Schroeder. 216/475-5225; www.or-tec.com.

  Screw press solves odor problems

Problem
Running the aging belt filter press at the Cardston (Alberta) Wastewater Treatment Plant required constant attention. Cake dryness, wash water consumption, odors, and maintenance were other issues.

Solution
The town purchased a RoS3Q screw press from Huber Technology. It occupies half the space of the original press, runs unattended, and produces dryer biosolids, eliminating odors. Water from the press is cleaner than influent at the headworks and produces no odor as it is fed back into the channel.

Result
“The screw press has become the premiere piece of equipment in the plant,” says foreman Barton Atwood. 704/949-1010; www.huber-technology.com.

  Rebuilding screens is economical solution

Problem
The five 60- by 7-foot self-cleaning influent screens at the Southside Wastewater Treatment Plant in Dallas were worn out. Replacing them would require removing the building’s roof. Officials decided to rebuild instead and put the project out to bid.

Solution
FilterONE USA was the low bidder. Workers installed two screens from 2010-2011, and three screens from 2012-2013. They replaced the filter elements, shafts, and chains without removing the screens from the channels. During the project, plant labor to remove screenings was minimized, as was downtime.

Result
Rebuilding the screens greatly reduced the project’s overall cost. 954/757-9741; www.filteroneusa.com.