City looks to oxygen for odor control

Problem: The city of Chestermere, Alberta, relies on Calgary municipal wastewater treatment plants. That requires extended force main for delivery. City leaders were concerned with odor control as Calgary maintained a hydrogen sulfide limit of 5 ppm at the monitoring station just upstream of its plants. The existing chemical odor-control program was expensive and required supply tanks and frequent truck deliveries, which sometimes bothered neighborhood residents. Untreated hydrogen sulfide levels exceed 300 ppm.

Solution: Anue Water Technologies provided a demonstration trailer in a successful pilot test of oxygen treatment. It eliminated the odors and involved no storage or delivery of chemicals. The pilot enabled the city to try out the oxygen-generation equipment, the effectiveness of oxygen infusion, and the software for on-site and remote monitoring and control while also validating the odor control solution on a full-flow force main test.

Result: The city purchased a permanent system after the demonstration project for installation in summer 2018. 760-727-2683; www.anuewater.com

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Metering pump resolves plant maintenance issues

Problem: West Valley Water District, serving 80,000 customers in Riverside County, California, was using a single diaphragm pump to inject 12.5 percent sodium hypochlorite to treat drinking water at two wells. During the suction phase, vapor lock caused loss of prime once or twice a month on average, requiring an operator to travel to the well site and manually relieve the pressure.

Solution: The district replaced the single diaphragm pumps with Blue-White Industries’ ProSeries-M MD-3 double diaphragm metering pumps. When the first diaphragm is in the suction phase, the second diaphragm is in the discharge phase. This allows fluid flow to occur almost continuously, preventing gas buildup and loss of prime.

Result: The pumps have experienced no loss of prime since installation in 2016. “The pumps have not been serviced since they were installed,” says Tony Lopez, production operator. 714-893-8529; www.blue-white.com

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Continuously cleaned bar screen solves ragging downstream

Problem: The perforated fine screen at the Bell County Water Control & Improvement District South Wastewater Treatment Plant in Killeen, Texas, was inadequate and needed excessive maintenance. Grease and rags that were passing through clogged the aeration basin and settled in the diffuser, even blocking valves. At the headworks, the screen “moved debris around — back and forth — rather than removing it,” says Bruce Sorenson, chief operator. The screen often overflowed at high flows.

Solution: Plant leadership chose Duperon’s FlexRake FPFS-M screen with 1/8-inch openings. It captures up to 37 percent more debris than 1/4-inch screening.

Result: We could see the difference right at startup,” Sorenson says. “The back side of the screen cleared up immediately; we could always see debris coming through before, but since the FlexRake was installed, we haven’t seen anything. It really catches everything.” Cleaning and maintenance downstream have been reduced. 800-383-8479; www.duperon.com

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Centrifuge helps district produce dryer solids and reduce polymer consumption

Problem: West Central Conservancy District in Avon, Indiana, had a belt press to dewater biosolids, but the system required a lot of man hours for maintenance and cleanup, and also used a high amount of polymer (4.5 to 5 gph at $16 per gallon) and had cake solids of only 12 to 14 percent.

Solution: The district installed a centrifuge system from Flottweg Separation Technology. The system automates feed pumps, grinders, polymer systems, conveyers and slide gates. The operator can easily control all of the equipment from one simple-to-use control panel. The centrifuges were also installed with Recuvanes, which recovers the centrifugal energy of the liquid phase and reduces power consumption.  

Result: The system saved the city money by producing much dryer solids (18 to 21 percent), significantly reducing disposal costs. It also saved on energy and maintenance. Polymer consumption was cut to 1.25 to 1.75 gph, saving $44 per hour on polymer, which is over $90,000 per year based on 40 weeks of operation. 859-448-2331; www.flottweg.com

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Grit removal technology upgraded during expansion

Problem: During a 2016 expansion, management at the Elkhart (Indiana) Wastewater Treatment Plant decided to replace outdated grit basins to improve efficiency and capacity.

Solution: The city chose PISTA VIO grit removal systems from Smith & Loveless. Chambers were installed inside existing aerated grit basins, increasing flows up to 40 mgd. Chamber internals are made of 304 stainless steel, preconstructed, and shipped complete with total grit handling equipment including pumping, conveying, concentration, and PLC controls. A circular forced vortex grit chamber allows design of the inlet and outlet channels at any variable angle up to 360 degrees, saves space. The system’s baffle system promotes a hydraulic vortex flow path that provides 95 percent grit removal efficiency across all flows for particles down to 100 microns.

Result: Use of the existing channels minimized new construction and concrete costs. Testing revealed that the systems removed 99 percent of grit down to 100 microns across all flows. 800-898-9122; www.smithandloveless.com

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City ends permit limit infringements with additive

Problem: The Southside Wastewater Treatment Plant in Tyler, Texas — a multitrain activated sludge plant — had seen sporadic effluent quality because of aeration limitations, compounded by low and unstable pH and insufficient influent alkalinity. The city’s recently commissioned water plant occasionally sent low-pH solids and process water to the facility. This led to intermittent permit limit infringement and potential for violations. Caustic soda was used to supply alkalinity and raise the pH, but great care was required to prevent pH spiking, and the amount of alkalinity supplied under the spiking limitations was marginal.

Solution: The city chose Thioguard Total System Treatment, a nonhazardous, nonpharmaceutical, technical-grade milk of magnesia to supply significantly more alkalinity in a biologically reactive form while shifting the pH into a bio-optimal range. The product also added divalent cations, improving the M/D ratio.

Result: Once on Thioguard and through a fully activated sludge age cycle, effluent BOD, TSS, and NH3 numbers dropped to well below permit limits and remained level. The city has used the product continuously ever since, withstanding random influent quality swings and aeration system upsets. 800-227-4287; www.thioguard.com

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Dewatering press allows industrial plant to meet concentration goal

Problem: The operators at a Wisconsin-based wastewater treatment facility for a cheese and yogurt plant had used a rotary-style press for dewatering. Anaerobic sludge at 1.9 to 3.4 percent solids was processed at 45 to 80 gpm. The existing dewatering equipment had difficulty achieving the desired 10 percent solids cake and filtrate quality.

Solution: The company chose Trident Processes to replace the outdated press with an MD 413 Dewatering Press that receives anaerobically digested biosolids after thickening with a membrane system. The flow to the press is controlled by a SEEPEX progressive cavity pump on a variable-frequency drive. The filtrate flows to a side tank and is sent to the aeration system by a small centrifugal pump on a variable-frequency drive. The press yields material at 15 to 20 percent solids.

Result: “The automation of this press allows us to make changes remotely; but even better, the trends allow us a window into the digester,” says the plant’s operations manager. “We have improved the cake dryness but have really improved on filtrate, allowing us to run the filtrate directly to the aeration system. And the automation package has made the operation much easier.” 800-799-3740; www.tridentprocesses.com