Headworks and Biosolids Management

Headworks and Biosolids Management
Scrapers clean solids from intake system

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Scrapers clean solids from intake system

Problem
Backwash strainers at a wastewater treatment plant in Toronto, were consistently clogging with oversized solids that made it past the intake bar screens. Downstream pumping equipment experienced high failure rates, and subsequent treatment stages were overwhelmed by the solids.

Solution
The plant installed two 16-inch Automatic Scraper Strainers from Acme Engineering Products rated for 6,000 gpm each. The scraper keeps the screen clean using aggressive brushes that clean out the slots of the wedgewire screen. It operates automatically, using line pressure to intermittently purge accumulated solids. Maintenance is infrequent and requires simple replacement of the scraper blade and brush.

Result
The plant has more uptime as the strainer effectively removes large solids, and downstream treatment equipment operates within normal parameters. Maintenance is reduced on related equipment in the pumping system. 518/236-5659; www.acmeprod.com.

Shaftless screw conveyors transport wet sand vertically 65 feet

Problem
The City of Alma, Quebec, spent $40 million over 16 years attempting to transport 360 cubic feet of wet sand per hour, vertically 65 feet, to discharge into trucks or onto the floor. Despite trying several methods, the city never achieved the desired results.

Solution
The city replaced its existing installation with a complete system from Atara Equipment comprised of six shaftless screw conveyors — four horizontals and two verticals. A grit chamber conveyor discharges into a settling hopper, where a spiral feeds the first vertical conveyor. That then feeds a crossing conveyor to a second vertical conveyor, which in turn feeds the out-loading conveyor. In summer, that conveyor level-loads a truck waiting below. In winter, when the truck is used for sanding the roads, the conveyor discharges onto the floor.

Result
The city tested the system for six months using a same-capacity vertical demonstration unit before purchasing. The unit easily brings the sand up and discharges it into a designated area. The final installation has operated since 2001 without repairs or major overhaul. The vertical screw conveyors also proved effective in dewatering the sand. By the time it is discharged, the sand is dry enough to leave no standing water in the truck or on the floor bin, and needs no further treatment. 866/931-5445; www.ataraequipment.com.

Presses provide temporary dewatering after hurricane damage

Problem
Hurricane Sandy wreaked havoc on the Bay Park Long Island wastewater treatment plant in New York. More than 4 feet of water in the solids-handling building wiped out the feed pumps, polymer systems and electrical equipment. Mobile Dredging of Chester, Pa., won a contract for temporary dewatering until the solids building could be rebuilt.

Solution
Mobile Dredging installed four Charter Machine Co. Sentry Tower Presses within eight weeks. The presses are skid-mounted and complete with feed pumps, polymer makeup systems, wash water booster pumps, conveyors and controls. The flexibility of the presses’ three-belt design allows operators to vary the gravity belt speed to optimize solids thickening and maximize solids loading to the pressure section. The units can be equipped with 15 pressure rollers to gain extra time under pressure, leading to drier cake solids and lower hauling costs.

Result
The presses have performed dewatering as required since installation. 732/494-5350; www.chartermachine.com.

Mixer helps plant produce marketable compost

Problem
In the mid-1990s, the Lynden (Wash.) Wastewater Treatment Plant was land-applying biosolids at 1 to 3 percent solids, and costs were adding up. Lynden chose composting as a less expensive alternative. However, initial operations lacked a suitable mixer. The old mixer could not handle the large, heavy loads of biosolids and wood waste. The unit broke down frequently.

Solution
The city replaced the original mixer with an ECS Luck/Now Compost Mixer from Engineered Compost Systems (ECS), designed for mixing biosolids. The heavy-duty 805-cubic-foot-capacity electric mixer is stainless steel lined and has four hardened horizontal augers. It includes readable scales that allow operators to follow weight-based recipes (biosolids and bulking agents) to create a proper compost mix.

Result
The mixer has given operators better control of the compost process, enabling them to produce a better-quality product more efficiently. The city is making and selling 3,000 cubic yards per year of U.S. EPA Grade A compost. 206/634-2625; www.compostsystems.com.

Heat exchangers eliminate fouling, snagging issues

Problem
United Kingdom waste management company Cory Environmental uses a thermal transfer solution to assist in waste treatment and energy production at its anaerobic digestion plant in Weston-super-Mare, England. Waste feedstock is anaerobically digested to produce methane gas. Once captured, the gas is used to generate green electricity for the national grid. Fouling or snagging of waste particles while heating materials for the digesters created problems, including system downtime and potential loss of valuable digestate.

Solution
Cory Environmental selected four DTI corrugated tube heat exchangers from HRS Heat Exchangers, used for digester and process tank heating and digestate heating to achieve pasteurization. The corrugated tube profile provides an internal tube that inhibits fouling and increases the heat transfer rate.

Result
Fouling and snagging were eliminated, as there was no change in the cross-sectional area along the length of the heat exchanger. The increased turbulence from the corrugation improved heat transfer efficiency. The remaining digestate can now also be used as a fertilizer, reducing material sent to landfill. 623/915-4328; www.hrs-heatexchangers.com.

Wastewater basin cover and liner protect groundwater and environment

Problem
To manage high growth in Riverside County, the Lee Lake Water District in Corona, Calif., was required by the California Regional Water Quality Control Board to add to its storage and treatment capacity by building a containment structure equipped with a geomembrane base liner to protect the groundwater. Also required was a floating cover to control odor, eliminate evaporation, exclude waterfowl and animals, and provide vector control.

Solution
Layfield Group installed the Enviro Liner 6060HD, a fortified polyolefin geomembrane manufactured from prime-grade resins, and an advanced UV antioxidant package. Three layers of geosynthetics were installed. A 10-ounce nonwoven geotextile fabric was installed directly above the subgrade surface as a cushion fabric. Next, a 6040HD 40 mil fabric was prefabricated (factory seamed into large panels) and installed for the base-liner geomembrane, followed by a 6060HD 60 mil floating cover geomembrane.

Result
The client is satisfied with the basin cover system and reported no groundwater contamination issues. 800/796-6868; www.layfieldenvironmental.com.

Headworks package protects MBR system

Problem
Shepherdstown, W.Va., needed a major upgrade to replace its conventional activated sludge treatment plant with a membrane bioreactor (MBR) to comply with the Chesapeake Watershed Nutrient Removal Permit. Space was at a premium, as the headworks building measured just 23 by 35 feet. The challenge was to deliver a traditional screen, a complete grit system including pump and classifier, two center-flow fine band screens and conveyance to a screening, washing and compaction system.

Solution
Hydro-Dyne Engineering custom designed and manufactured a complete integrated headworks package to protect the MBR. The system includes a Triden screen with a 3 mm laced link bar grid designed to remove bulk rags and plastics, a 7-foot vortex grit trap sized to catch 95 percent of grit particles greater than 200 microns at peak flow, and two 42-inch fine screen channels, each containing a Hydro-Flo screen with 2 mm UHMWPE perforated panels.

Result
The upstream security allowed Shepherdstown to capture the fibrous, stringy material and remove it from the flow stream. To date, all is working well. 813/818-0777; www.hydro-dyne.com.

Rotary fine screen used to protect large MBR

Problem
Operators of the City of North Las Vegas field facility membrane bioreactor plant worried that hair strings reaching the bioreactor membranes could wrap around and cause buildup on membrane strands, obstructing flow around the membrane or breaking the strands. Continuous buildup would damage many strands, jeopardizing water quality and requiring expensive repairs.

Solution
Rotamat RPPS center-feed drum screens from Huber Technology were installed as part of a new water treatment and reclamation process. It enables 24/7 processing, unmanned for 14 hours per day.

Result
Operators report trouble-free operation and no buildup on the bioreactor membrane. 704/949-1010; http://huberforum.net.

Pumps with urethane stators improve downtime at plant

Problem
The wastewater treatment plants in Hamilton, Ontario, collect sewage and stormwater. The city continuously battled with the abrasive quality of processed water. The abrasive material shortened life for the nitrile stators and imposed high costs for stator maintenance and replacement.

Solution
Moyno provided Moyno 2000 pumps equipped with new urethane stators and tested them. The pump has a crowned gear universal joint drive train configuration to provide torque and thrust control. Joint seals protect the gear joints from pumpage contamination. The pump line offers flow rates to 2,500 gpm and pressure capabilities to 1,000 psi.

Result
The pumps exceeded expectations. The city ordered five more urethane replacement stators for the pumps after the first urethane stator outlasted the nitrile stator by more than 10 times and continued to run without failure. As the city expands, the stator will lower maintenance costs and significantly reduce downtime. 877/486-6966; www.moyno.com.

City upgrades headworks to protect equipment and end odor problems

Problem
The 25-year-old original headworks at the Missoula (Mont.) Wastewater Treatment Plant required high maintenance and did not efficiently remove grit. “It was really tired,” says Gene Connell, treatment supervisor for the Wastewater Division. “It just wasn’t built to today’s standards, and there wasn’t any practical opportunity for expansion or upgrade.” The poor performance was exposing downstream equipment to damage and contributing to odors that lingered well beyond the treatment plant.

Solution
After consultation with a representative from Smith & Loveless, the city launched a new headworks facility in 2012 that included two PISTA Grit removal systems and two PISTA TURBO grit washers. The system was designed for an average daily flow of 7 mgd and a peak flow of 13 mgd.

Result
The facility achieves 95 percent grit removal down to 140 mesh, better protecting downstream equipment. “As operators, you can look and see the performance,” Connell says. “It’s clearly better. We’re getting much better grit removal.” Odors have been eliminated, thanks in part to the grit washers, which Connell says are highly durable and require very little maintenance. 800/898-9122; www.smithandloveless.com.

Screw press saves on landfill disposal costs

Problem
The Immokalee Water and Sewer District (IWSD) in southern Florida pays $470,000 annually for biosolids dewatering and hauling to a landfill. However, landfilling is not a long-term solution.

Solution
As part of a biosolids management strategy, IWSD directed the engineering firm Greeley and Hansen to issue a request for proposals in summer 2012, asking teams to provide a plan to design, build and finance a Class AA biosolids production facility. Schwing Bioset was selected to provide its high-performance screw press, offering an efficient dewatering solution. The dewatered solids will be fed through the Class AA Bioset process, producing a fertilizer-grade product.

Result
IWSD will use the Class AA biosolids on its 300-acre sprayfield site leased to a cattle farmer. Since IWSD is required to fertilize the property annually, the biosolids will eliminate commercial fertilizer and the costs of landfilling. Annual savings are expected to approach $400,000. 715/247-3433; www.schwingbioset.com.



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