Aeration and mixing unit helps plant keep up with increasing demand

Problem: The Big Park Domestic Wastewater Improvements District in Arizona built a 500,000 gpd wastewater treatment system in 1997. As it aged it could not keep up with increasing demand.

Solution: The district engaged Sunrise Engineering, which partnered with Aeration Industries International to upgrade the plant’s equalization basin and the sludge digester and thickener. To upgrade without interrupting operations, Aire-O2 equalization basin and digester systems were installed. The Aire-O2 Triton units enable aeration and mixing with one device easily accessed from the surface. When oxygen demand is low, the control system turns the equipment off to save energy. Digestion and thickening occur in one basin. For decanting, the system is turned off and the solids settle to the bottom.

Result: The equalization basin and digestion/thickening systems have made it possible to reduce maintenance and free up time to optimize treatment. 800/328-8287; www.aireo2.com

Related: Case Study: Case Studies: Headworks/Biosolids

Bar screen helps reduce manpower and maintenance costs

Problem: Four years ago, Mendocino City (California) Community Services District administrators saw a need to improve the headworks at the 1 mgd wastewater treatment plant. “It would reduce some solids to a smaller size but would pass everything through,” says representative Steve Acker. Nonbiodegradable materials had to be manually removed to keep them from accumulating elsewhere in the facility.

Solution: A Screentec vertical screen from Aqualitec matched the plant’s technical requirements and footprint constraints, accommodating a 12-foot-deep headworks serviced by way of an 8-foot manhole.

Result: Waste accumulation dropped to a fraction of its former level. Personnel no longer had to manually fish out solids, saving labor and reducing exposure to hazardous conditions. The unit has required no servicing. 855/650-2214; www.aqualitec.com

Related: Headworks and Biosolids

Composting agitator installed in odor-sensitive area

Problem: The town of Fairfield (Connecticut) Biosolids Compost Facility is next to the town’s water pollution control facility and within 500 feet of dense residential areas on multiple sides. Odors need to be minimized.

Solution: The town selected an enclosed, agitated-bay compost system with agitators from BDP Industries. The technology is designed to contain and treat odors and produce a compost product after 21 days that is stable enough to store outdoors without significant odor.

Result: The compost facility was started in 1989 and performed well for 15 years. In 2006, the facility underwent a major overhaul, including a new and more efficient compost agitator to replace the two original units. 518/695-6851; www.bdpindustries.com

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Digester heater uses biogas, saving natural gas costs

Problem: The Washington/East Washington (Pennsylvania) Wastewater Treatment Plant used a hot-water boiler and heat exchanger to heat its anaerobic digester. In winter the boiler ran continuously; natural gas fuel cost up to $3,000 per month. Although digester gas was available, the boiler required a minimum pressure that kept it from fully using that fuel.

Solution: An Envirex Heater and Heat Exchanger from Evoqua Water Technologies replaced the previous system. This integral unit with a boiler and tube-in bath heat exchanger is more efficient and has a smaller footprint that separate boiler and heat exchanger. The unit can operate at a pressure of 2 inches of water column, maximizing use of biogas.

Result: Digester heating is now highly efficient and cost-effective. The unit runs almost exclusively on biogas, saving some $20,000 a year. www.evoqua.com

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Rotary press helps city save big on disposal

Problem: Canal Winchester, Ohio, operates a conventional activated sludge plant with aerobic digestion and once relied on liquid injection of biosolids. That was costly and time-consuming, and material had to be stored over winter.

Solution: The facility installed a Fournier Industries rotary press with four dewatering channels and capability to add two more channels later. The press typically runs unattended.

Result: Biosolids are dewatered continuously in alternating weeks, Monday through Friday. The press receives material at 0.8 to 1.2 percent solids and discharges cake at 15 to 17 percent. Biosolids hauling costs have declined by 75 percent. “A quality piece of equipment you can trust makes all the difference in the world,” says Steve Smith, superintendent. 418/423-4241; www.rotary-press.com

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Large-bubble mixing works to suspend post-grit tank solids

Problem: An Indianapolis Southport Advanced Water Treatment Facility post-grit-removal junction structure needed mixing to move fine minerals and organic wastes to downstream treatment. The material had to be lifted 25 feet to pass over weirs and into distribution channels. Removing the structure from service for manual cleaning was not an option.

Solution: The design engineer selected a Sequential Large-Bubble Vertical Mixer from Pulsed Hydraulics to create the lift needed to keep material from accumulating in the post-grit tank. The 36-inch-diameter pulsed air masses each create over 900 pounds of buoyant force through each bubble-forming plate on the tank floor. Only two to four pulses per minute per plate are necessary. The mixing energy requires only a 20 hp rotary-vane compressor operating at two-hour intervals for 30 minutes per interval.

Result: Solids no longer accumulate on the tank floor, and grease and other materials that could cause odors do not accumulate on the water’s surface. The vertical mixing system minimizes maintenance and uses minimal energy. 800/641-1726; www.phiwater.com


Screw press helps create cleaner, more efficient dewatering

Problem: Seneca (South Carolina) Light & Water operates a 20 mgd water treatment facility that used alum as a coagulant. Waste alum was dewatered to 24 percent solids on plate-and-frame presses that ran batches; the process was labor-intensive and not clean.

Solution: The utility successfully pilot-tested a Schwing Bioset screw press that yielded 28 to 32 percent solids.

Result: A fully automated FSP 503 screw press was designed into a dewatering building. The dewatered sludge is hauled to the nearby wastewater treatment plant, mixed with dewatered biosolids and hauled to landfill. The press yields up to 34 percent and 30 percent on average. 715/247-3433; www.schwingbioset.com


Plant optimizes grit system performance and maintenance

Problem: Grit removal was a problem at the Shamokin Coal Township (Pennsylvania) Joint Sewer Authority. An Archimedes screw device augered grit from two chamber wells. During wet weather, grit included sediment and other fine particles harmful to pumps and processes. The older system could not remove the large amount of grit entering during those events, requiring costly multiday clean-outs four times a year.

Solution: The authority chose the PISTA 360 grit system with V-FORCE BAFFLE from Smith & Loveless for its particle removal efficiency, ability to handle surge events, high turndown and low life-cycle cost. The hydraulic design with integral flow-control baffle maintains the ideal velocity during low-flow and surge events, ensuring consistent and efficient grit removal.

Result: The upgraded plant was commissioned in 2015. The PISTA 360 has provided dependable grit removal with minimal maintenance. “It’s removing 99 percent of the grit pre-storm and during storm events,” says Paul Petrovich, general manager. “We don’t see any grit downstream, including in the motors, where grit can tear them up.” 800/898-9122; www.smithandloveless.com


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