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, Ontario, Canada, 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.

Solution: The plant installed two 16-inch Automatic Scraper Strainers from Acme Engineering Products, rated for 6,000 gpm each. The scrapers use aggressive brushes that clean out the slots of the wedge-wire screen. They operate 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 strainers effectively remove 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.

Biosolids treatment system saves significant costs at naval station

Problem: The U.S. Naval Air Station (NAS) Jacksonville in Florida needed to meet the U.S. Navy’s aggressive energy reform targets.

Solution: NuTerra’s detailed financial analysis compared the base’s aerobic digestion operating data to BCR Environmental’s CleanB system. NuTerra installed a unit to treat waste activated sludge from the clarifier to Class B standards before dewatering; the final product is suitable for land application.

Result: The project delivered $75,000 in energy savings, a 95 percent reduction in energy for biosolids treatment, and a total operating cost savings of $105,000. Payback on equipment is projected at five years (six and a half years including installation). Projections indicate a reduction in greenhouse gas emissions of 480 tons annually. Improved dewatering reduced the total biosolids volume by 12 truckloads annually, saving more than $10,000 per year in hauling costs. Polymer consumption was reduced by 71 percent. 904/819-9170; www.bcrenv.com.

Thickening centrifuge operates more efficiently and in a smaller footprint

Problem: The Kenosha (Wisconsin) Water Utility Wastewater Treatment Facility faced a decision to repair an aging dissolved air flotation treatment (DAFT) system or move forward with emerging sludge thickening technology.

Solution: Kenosha installed the Centrisys THK 200 Thickening Centrifuge. The unit uses a smaller footprint and can be easily installed in a 1,000-square-foot building. Its enclosed process nearly eliminates odors. It produces material at 5 percent solids and has the capability to produce 7 percent solids. The thicker sludge improves digester operation and produces more biogas. It requires minimal operator oversight and less maintenance.

Result: The system, in place for three years, uses no polymer and saved $80,000 to $100,000 in pump and equipment upgrades. Electricity consumption is low, as it incorporates a 10 hp feed pump, a 50 hp main drive and a 20 hp scroll drive, all tied into variable-frequency drives. The city installed a second THK 200 for primary sludge thickening to improve digester performance. 262/654-6006; www.centrisys.com.

City contracts to replace rectangular clarifier parts

Problem: Five wastewater treatment facilities in New York City faced various rectangular clarifier components wearing out due to age and fatigue. The city issued a contract to address replacement of nonmetallic and metallic chain, segmented sprockets, laminated wood and FRP flights, screw conveyor assembly, metallic and nonmetallic wear strips and wear shoes, wall bearings, safety collars, shafting, torque limiters, gear reducer drives, and miscellaneous hardware.

Solution: Fairfield Service Company provided OEM replacement of all those components with a contract value of $5 million.

Result: Fairfield is in the final stages of completing the order, assuring the facilities of uninterrupted service. The city will issue the company another contract for replacement of additional clarifier components at other facilities. 219/872-3000; www.fairfieldservice.com.

Fine bar screen removes high amount of solids from headworks

Problem: The Andover (Kansas) Wastewater Treatment Plant serves a community of 12,000 next to Wichita. The original plant was built in 1977 and upgraded four times. In 1993, a coarse bar screen with 3/4-inch bar spacing was installed at the headworks. By 2012, the plant began investigating fine bar screens for greater solids removal.

Solution: “The best kind of process improvement is one that pays for itself,” says Brian Walls, wastewater superintendent. “In this case, the ongoing cost of cleaning the aeration basin, removing rags from diffuser tubes, unclogging return activated sludge pumps and improving the overall performance of the process had an obvious payback calculation.” The city selected the Enviro-Care Flo-MultiRake Fine bar screen with 1/4-inch bar spacing.

Result: The plant staff estimates the new screen is removing two and a half times more solids than the old coarse screen. “We had specified the bar screen to be a turnkey, plug-and-go setup,” says Walls. “When we got it, it was. We did the install ourselves and had an electrician run the conduit and wiring to code. The control panel was preprogrammed and only needed minor adjustments. The bar screen fit perfectly in the pre-existing channel.” 815/636-8306; www.enviro-care.com.

Dewatering press produces drier cake solids, runs more efficiently

Problem: The Chestnut Ridge Area Joint Municipal Authority in New Paris, Pennsylvania, required an upgrade from an aging belt press. High operation and maintenance requirements had to be as low as possible to keep life cycle costs down, and dry cake solids were critical to reducing disposal expenses even as plant throughput rose.

Solution: Doug Vitovitch, chief facility operator, personally sourced and supervised the installation of a Volute ES302 following the results of a free pilot study. PWTech and local representatives from EnviRep included all necessary pumps and polymer preparation equipment, and provided both remote and on-site installation assistance to enable Vitovitch to complete the entire municipal project from project inception to installation and successful startup in just over six months.

Result: Chestnut Ridge began realizing immediate operational cost savings as the Volute press can run unattended while producing drier cake than the old belt press. The 2 hp unit uses significantly less power and wash water. The first two-hour maintenance is scheduled for February 2020, if needed. 443/648-3300; www.pwtech.us.

Screw press helps plant add efficiency to dewatering process

Problem: For years, the Williamson (New York) Wastewater Treatment Plant had placed anaerobically digested biosolids from a contact stabilization treatment process into two drying beds or four reed bed lagoons. Typically, every five to seven years the town would allow the reed beds to dry and remove the deposited solids via shovels into trucks. The material was unloaded and bulldozed into the nearby property the plant owned. This was time-consuming and labor-intensive, and rain made matters worse. There was also concern about damaging the liners during the operation. Plant leaders decided on a permanent dewatering operation and in the short term hauled the dewatered material to a composting facility in nearby Ontario, New York.

Solution: BDP Industries conducted on-site demonstrations with its belt press and a screw press. For financial and operational reasons, town leaders chose the screw press. To save on installation costs, the unit was skid-mounted with all accessories and piped and wired at the BDP factory. The press offers a small footprint, low operation labor and expected lower maintenance costs due to few moving components.

Result: The 12-inch-diameter screw press has met performance expectations. Throughput averages 25 gpm at an average of 2.15 percent influent solids concentration, representing 260 pounds per hour of dry solids. It produces a cake averaging 17.3 percent solids. Williamson is now exploring its own composting operation. 518/527-5417; www.bdpindustries.com.

Screw press helps dewater biosolids quickly

Problem: The wastewater treatment plant in the Town of Middlebury, Indiana, treats an average daily flow of 0.99 mgd. The plant had been using beds of pea gravel to dry biosolids. This process yielded biosolids at 5 to 8 percent solids but was proving labor-intensive, costly and time consuming with the increasing plant flows.

Solution: The plant installed a Schwing Bioset Screw Press, selected by the town and a consulting engineer after it outperformed other equipment pilot trials. The feed pump draws material from the aerobic digesters and feeds it to the screw press under low pressure. A simple control system allows unattended operation, and the resulting cake exceeds 19 percent dry solids.

Result: The press has improved operations and accommodates increasing plant flows by allowing the plant to quickly dewater the material with less labor, reduced odors and lower hauling costs, all within a smaller footprint. 715/247-3433; www.schwingbioset.com.

Dewatering system decreases energy demand

Problem: A septage dewatering facility in California wanted to become more energy-efficient. Facility leaders decided to replace an aging vacuum filter, which had a high energy demand and required significant time and expense to keep operating.

Solution: They chose a 20-foot dewatering drum from In The Round Dewatering. A cement pad was poured outside the building under a roof overhang, which allows dewatering to take place outside. The process is similar to a gravity dewatering box, as with the box the material must be mixed with a polymer to achieve the waste stream floc. The inside of the drum is lined with interlocking PVC tiles. The difference is that once the drum is full, it rotates one turn every two hours, allowing all free liquids to filter out overnight. The drum is mounted on a roll-off frame and can be loaded on a roll-off truck for transport to the landfill. Once unloaded, it can be washed out quickly with a garden hose and is ready to be filled again.

Result: The facility can dewater 20,000 to 24,000 gpd with virtually no maintenance. The 1/4 hp motor creates large energy savings and eliminates the diatomaceous earth used in the old process. 317/539-7304; www.itrdewatering.com.

Reverse aeration evens out temperature differentials

Problem: The City of Arlington, Washington, population 18,000, shifted its biosolids process to composting from land application to produce compost for city road improvements, ball fields, parks, a cemetery and a community garden. The challenge was to keep target temperatures within best management practice (BMP) range in the face of variable moisture content in the dewatered cake arriving at the facility, and variable moisture content in wood waste used as an amendment.

Solution: Arlington installed an Aeration Static Pile System (ASP) from Engineered Compost Systems (ECS). The system has automatically reversing aeration for primary and secondary composting and a biofilter to control odors. The facility produces eight batches of compost mix each weekday, or 40 batches a week, for a total of 2,100 cubic yards per year. Roughly 70 percent of the biosolids (800 cubic yards) are processed into Class A Exceptional Quality compost. The process takes five to six weeks.

Result: The reversing aeration system allows the operator to better control temperature and odor. Operator Kevin Bleeck says his ideal mix is 2 yards of biosolids cake, 3 yards wood waste and 2.5 to 3 yards of compost overs (larger wood particles that remain after product screening, providing porosity and a source of carbon). 206/634-2625; www.compostsystems.com.   


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