Wastewater Treatment Systems

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Increasing hydraulic capacity

Problem

The traveling bridge sand filters at the 80 mgd Donald C. Tillman Water Reclamation Plant in Van Nuys, Calif., had mechanical, structural, and performance degradation. Operators used chemicals and shock chlorination to maintain filter performance.

 

Solution

The plant retrofitted the sand filters with eight AquaDiamond filters from Aqua-Aerobic Systems. The units combine traveling bridge and cloth media filtration to achieve three times the flow capacity in the same footprint. Diamond laterals on the bed of the units are covered with 10 micron OptiFiber PES-13 cloth filtration media to handle 12.5 to 24 mgd. The filters run without continuous backwashing.

 

Result

The filters increased hydraulic capacity by 240 percent and produced reuse-quality effluent. Performance data includes effluent turbidity of 0.5 to 1.4 NTU and effluent TSS less than 2.0 mg/l. 815/654-2501; www.aqua-aerobic.com.

 

Core pneumatic-mixing technology

Problem

Submersible mechanical mixers rated at 15 hp stressed the operating budget of the 70 mgd (design) Mauldin Road Wastewater Treatment Plant in Greenville, S.C.

 

Solution

Renewable Water Resources (ReWa), a special purpose district, operates the Mauldin biological nutrient removal facility. Its engineers selected a 5 hp BioMix compressed pneumatic large-bubble mixing system from EnviroMix and installed it in an anoxic cell opposite a mechanical mixer in a parallel treatment train.

An air compressor fires short bursts of large bubbles through nozzles attached to the bottom of the process tank to agitate the mixed liquor without supplying significant oxygen. Components are housed in NEMA 4X enclosures or are non-clogging and self-cleaning within the tank. One compressor can mix more than 20 tanks. Programmable logic controllers in the control unit enable operators to optimize mixing to reduce air and power consumption.

 

Result

A study showed average effluent nitrate concentration for the gas-mixing system at 2.19 mg/l versus 2.39 mg/l for the mechanical mixer. Test data for TSS, DO, ORP and orthophosphate found no difference between the technologies. The gas system performs the same mixing function as the mechanical mixer with one-third the energy. 843/573-7510; www.enviro-mix.com.

 

Effective grit removal

Problem

The Soledad (Calif.) Wastewater Plant had aerated ponds, secondary ponds, and a polishing pond. An upgrade and expansion from 3.1 to 5.5 mgd included headworks, tertiary treatment, and residuals treatment. Plant solids would flow to stabilization basins for thickening, then to a screw press before the drying beds. Removing grit at the headworks was crucial.

 

Solution

Erin Brosnan, P.E., from Black & Veatch, specified the MectanV variable-angle grit removal system from John Meunier Inc., a subsidiary of Veolia Water Solutions & Technologies. Similar to a centrifuge, the circular chamber uses inflow velocity to swirl water, allowing heavier materials to collect in a well. A pump or airlift transfers grit to the clarifiers. The low-maintenance, compact unit operates with low head loss and is energy efficient.

 

Result

Field tests showed that the system removed more grit for each grit size analyzed than specifications required, especially in the finer particle size. 888/638-6437; www.johnmeunier.com.

 

Total treatment system

Problem

The Decatur (Ark.) Wastewater Treatment Plant could not meet total nitrogen and phosphorous limits with its activated sludge process, and high-strength wastewater from a poultry processor caused organic and hydraulic issues.

 

Solution

The city installed a three-train integrated surge anoxic mix (ISAM) unit from Fluidyne Corp. to treat 3 mgd, remove nutrients, and minimize sludge. Wastewater enters a covered anaerobic reactor for pretreatment and sludge thickening and destruction. Solids undergo hydrolysis to simpler soluble organics that pass to the surge anoxic mix tank. Besides regulating flow, the tank’s environment denitrifies recycled nitrates while stabilizing soluble organics.

The conditioned mixed liquor passes to the final aerobic tank for completion of BOD, nitrogen, and phosphorous removal and solids separation. A proprietary system controls the pace to provide tertiary-level water quality. The automated system also monitors dissolved oxygen and adjusts power usage. Jet aeration/mixing equipment provides high oxygen transfer and complete mixing to handle swings in organic loading.

 

Result

Effluent has less than 5 mg/l BOD and TSS, less than 8 mg/l TN, and less than 0.3 mg/l P. 319/266-9967; www.fluidynecorp.com.

 

Two-in-one reactor

Problem

The Yucaipa Valley (Calif.) Water District activated sludge treatment plant struggled to handle an increase in hydraulic loading and meet a new 6 mg/l total inorganic nitrogen limit. The District turned to Kruger engineers to design an upgrade.

 

Solution

The engineers selected the AnoxKaldnes hybrid biofilm with activated sludge (Hybas) process from Kruger. They retrofitted the first two aerobic reactors with the aeration system, K3 biofilm carrier elements, and wedge wire screens. After Hybas reactors nitrify the wastewater, a portion of the mixed liquor suspended solids is recycled to the circular anoxic reactors for denitrification. The process uses activated sludge biomass and fixed film in the same reactor.

 

Result

The upgrade increased the plant’s capacity from 4.5 to 8 mgd and reduced TIN levels to less than 5 mg/l. 919/677-8310; www.krugerusa.com.

 

Long-distance circulation technology

Problem

The 13.5 mgd Mebane Bridge treatment plant in Eden, N.C., ran 12 20-hp horizontal brush aerators in two aeration basins to meet 30 mg/l TSS requirements. Dissolved oxygen (DO) at 8 to 10 mg/l was higher than necessary, but reducing aeration would affect TSS. “We also had a mass of sludge on the bottom of the 13.5-foot-deep basins,” says superintendent Melinda Ward. Each basin has 1.74 surface acres.

 

Solution

Ward then installed one SB 10000v18 solar-powered circulation unit from SolarBee in the south basin and shut off the three closest aerators. “After activating the unit, solids rose to the top of the basin,” she says. “Later, we also saw better settling in the 90-foot-diameter clarifier, leading to reduced effluent TSS.” As the numbers improved, Ward deactivated three more brush aerators.

The unit’s long-distance circulation technology creates a near-laminar flow that completely mixes the water column, transporting 10,000 gpm to the surface. About 3,000 gpm rises through the intake hose; another 7,000 gpm rises around the hose. Water departs radially above and below the distribution dish, mixing with other surface currents across the treatment area. Sulfides convert to sulfate as they pass through the oxygenated layer, preventing the escape of odors.

 

Result

In one year, the plant’s electrical use declined by 1.7 million kWh, or 42 percent. Even with rising electric rates, the power bill decreased by $61,000 or 31 percent, providing an 11-month payback. 866/437-8076; www.solarbee.com.

 

Nutrient recovery

Problem

Stricter regulations required the York (Pa.) Wastewater Treatment Plant to reduce phosphorus levels to 0.8 mg/l. The biological nutrient removal facility also battled the buildup of struvite on pipes and valves, reducing flows, hurting efficiency, and requiring costly maintenance. Traditional solutions for removing struvite, such as chemical dosing, were cost-prohibitive.

 

Solution

The city installed the Pearl nutrient recovery process from Ostara to remove nitrogen, phosphorus, and other nutrients. The fluidized bed reactor uses a chemical reaction to reduce the phosphorus load returning to the liquid treatment train by 90 percent and the ammonia load by 20 percent. The recovered nutrient then mixes with magnesium chloride and caustic to form struvite pellets, which Ostara makes into Crystal Green slow-release commercial fertilizer, which provides revenue for the city.

 

Result

Ostara designed, built, and financed the facility for a monthly fee, less than what the city was spending on traditional nutrient removal methods. The plant is meeting permit limits and alleviating struvite. 604/408-6697; www.ostara.com.

 

Pulsating mixing

Problem

A shallow pump station in Darien, Conn., used a transducer to turn the pumps on and off and floats to back up the transducer. Grease caps sometimes more than 12 inches thick and hard enough to stand on fouled the equipment. Operators failed to remove it using chemicals and mechanical mixers. Pumping the grease cost $1,800 per episode.

 

Solution

The city installed a Hydro-Pulse PHi one-valve mixer from Pulsed Hydraulics, and an air compressor with receiver tank. The mixing technology pulses pressurized air through stainless steel plates on the bottom of the wet well. Beach-ball-size bubble masses rise to the surface, dragging tank contents along. The material rolls horizontally into a structural wall, or the next bubble mass forms a virtual wall. Either wall sends material down to the tank bottom, where it moves sideways, sweeping up settling solids. Pulsations use minimal energy to keep solids in suspension.

 

Result

The control system pulses the well once every minute, preventing the formation of grease caps. 800/641-1726; www.phiwater.com.

 

Aeration lagoon process

Problem

The three-cell aerated lagoon at the 792,000 gpd (design) Fayette (Mo.) Wastewater Treatment Facility could not meet new effluent ammonia permit limits of less than 4 mg/l in winter and 2 mg/l in summer.

 

Solution

The city selected the LemTec biological treatment process from Lemna Technologies. The system uses hydraulic baffles to divide the lagoon into four treatment cells to reduce short-circuiting. The cells are followed by an anaerobic settling zone and polishing reactor. A modular insulated cover over the lagoon enhances system kinetics, retains heat, controls odors, promotes solids digestion, and prevents algae growth. To meet permit requirements, the reactor provides tertiary treatment using fixed media for submerged attached-growth bacteria.

 

Result

During the past two winters, effluent levels were less than 10 mg/l BOD and TSS and less than 1 mg/l ammonia. 612/253-2000; www.lemnatechnologies.com.

 

Dual regenerative blowers

Problem

The three-cell, 6-foot-deep treatment lagoon at Concordia, Mo., struggled to meet 45 mg/l BOD and TSS limits. No matter the environmental conditions, dissolved oxygen never went higher than 7 ppm. In summer, a heavy, waxy algal cap emitted odors. In 2009, the state Department of Natural Resources told city administrators that the 28-acre system must meet 30 mg/l limits by the end of 2010.

 

Solution

The city hired an engineering firm that recommended installing four model WQA aerators from Reliant Water Technologies in the primary 18-acre cell and spreading more than 700 pounds of Sewper Rx in the three cells. Treatment began in June 2010.

The aeration system uses two 2 hp regenerative blowers. The first blower runs continuously, pushing water to eliminate the zero DO zone on the lagoon bottom. The second blower runs continually or automatically to provide additional DO. One 8-foot unit handles up to five acres of surface water. The Model WQA moves more than 9 mgd and adds up to 20 pounds of DO per hour.

Sewper Rx, a polymicrobial blend of enteric bacteria, reduces organic solids. When added to the 5.6-acre secondary and 3.2-acre final cells, it reduced BOD and TSS.

 

Result

In December 2010, the city met its permit with 12 mg/l BOD, 27 mg/l TSS, and DO often exceeding 20 ppm. 504/400-1239; www.reliantwater.us.com.

 

Coarse- and fine-bubble system

Problem

The 316,000 gpd Wasco (Ill.) Sanitary District treatment plant installed a pretzel-type aerator in two 24-foot-deep treatment lagoons. The fine-bubble system had high standard oxygen transfer efficiency, but insufficient turbulence to mix the liquid. Five feet of sludge accumulated in five years, causing 38 of 73 diffusers to clog and fail, and dissolved oxygen (DO) to drop below 1 mg/l. Clogging also created backpressure on the blower, raising the pressure by 3 psi. As effluent numbers exceeded permit levels and the lagoon turned septic, residents complained about the odor.

 

Solution

Plant engineers re-placed the diffusers with the MARS 3000 aeration system from Triplepoint Water Technologies. The 47 diffusers with Double Bubble technology produce 5 to 7 pounds of oxygen per horsepower hour (lb/hp-hr). Each diffuser has a flow range of 10 to 25 cfm and mixes 6,585 gpm. The diffusers have a central coarse-bubble tube surrounded by eight 9-inch fine-membrane bubble disc diffusers 16 inches above the lagoon floor. The 29-inch-high units have four weighted legs and clear the lagoon bottom by 10 inches.

Air enters the diffusers’ central static tube, creating a Venturi that circulates the water and liquefies sludge. Anticlogging technology prevents backflow. With coarse-bubble diffusion, 3- to 25-mm bubbles rise through the water column at 2 to 3 feet per second, causing turbulence and mixing. While suspended in the water column, the liquid mixes with fine bubbles — 1 to 2 mm in size and rising at less than 1 foot per second — from the self-cleaning membrane diffusers. The high surface-area-to-volume ratio of degraded debris and fine bubbles maximizes contact time and reduces BOD5.

 

Result

After one day of operation, the system was mixing solids, blower pressure dropped by 3 psi, DO levels rose to 4 mg/l, and odors subsided. Within days, the 2-foot-deep floating sludge mat disappeared, and effluent met permit levels. Over time, maintenance costs decreased by $12,000 annually. 630/208-0720; www.triplepointwater.com.



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