Case Studies: Headworks/Biosolids

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Improved capacity and space savings

Problem

The 3.15 mgd (design) treatment plant in Marseilles, Ill., averaged 1.25 mgd and produced 55 dry tons of biosolids per year. Increased solids production taxed the capacity of the drying beds, which took two to six months to dry in ideal conditions. Aerobic cake averaged 17 to 19 percent solids and anaerobic 20 to 24 percent. “The cake had to be stored for three years before land-applying it,” says Don Christensen, wastewater superintendent. “We were running out of storage options and needed more dewatering capacity, but had no extra space for it.”

 

Solution

The city installed a 900/2000CV two-channel expandable rotary press from Fournier Industries. Biosolids are fed at low pressure into a 36-inch channel between two parallel filters. As water drains away, solids collect against the outlet gate. The slow rotation produces enough backpressure to dewater the remaining solids and extrude dry cake. More dewatering modules can be added as the need arises. The press is low maintenance and energy efficient.

 

Result

The plant now uses the drying beds for storage. “The press has improved our biosolids process by leaps and bounds,” says Christensen. “The best thing is, once we start the press, we can leave it unattended. It automatically adjusts to changes in the material.” 418/423-4241; www.rotary-press.com.

 

Frontline protection

Problem

To meet regulatory limits for total nitrogen and phosphorus, the Borough of Mifflinburg, Pa., asked the engineering firm of Herbert, Rowland & Grubic to evaluate upgrades for its aging wastewater treatment plant. A membrane bioreactor was selected and new screening equipment would be required to ensure successful operation.

 

Solution

Effective screening is a concern with MBRs as membrane fouling from suspended solids can damage membranes, decrease efficiency, and dramatically increase lifecycle costs. A dual-stage screening system was designed and installed that included one Mahr bar screen with 6 mm openings and two Eliminator band screens with 2 mm openings from Headworks Inc. The dual-stage process prevents the buildup of materials on the fine screens, since larger solids are removed in the first step. Ultimately, there are two lines of defense at the head of the plant. Screenings from both systems are compressed by two Screwpactor units. A shafted screw feeds material into the sieve zone, which allows free water to drain. Solids then move through a wash zone to reduce organic content before being compacted and sent through a discharge tube for additional dewatering.

 

Result

“The screens affect the efficiency of the entire facility,” says Steve Benner, Borough Project Manager. “Their overall performance has been stellar.” 713/647-6667; www.headworksusa.com.

 

Energy recovery system

Problem

The Buffalo (Minn.) Wastewater Treatment Facility faced rising costs to manage aerobically stabilized biosolids, odor issues, and an increase in volume through population growth. Plans to upgrade the plant included a more efficient way to meet the EPA 503 Class A biosolids standards within a limited footprint.

 

Solution

The facility chose the BioCon dual-belt biosolids dryer and energy recovery system (ERS) from Kruger. The unit uses convection temperatures of 175 to 350 degrees F to evaporate water from biosolids, reducing the mass by 95 percent. The solids are then fed into a furnace that returns 80 percent of the heat to the drying process.

 

Result

The system increased the facility’s biosolids capacity to 1,850 tons of dry solids per year, fit in a small footprint, and met Class A requirements. 919/677-8310; www.krugerusa.com.

 

Confined-space screen solution

Problem

A malfunctioning comminutor in the influent pump station of the Oostburg (Wis.) Wastewater Treatment Plant caused clogging throughout the treatment process. The narrow building has a short inlet channel with the comminutor pit in the middle. Screenings are lifted 20 feet to the operating floor for disposal. The comminutor underwent frequent repairs, and the city wanted to replace it with a fine-screening device.

 

Solution

The engineering consultant considered stair screens, band screens, climber screens, and in-channel drum screens, but none fit without major modifications to the structure. He finally found the ROTAMAT RoK 4 screen from Huber Technology, which occupied one square yard in the comminutor pit. The unit vertically lifts the screenings while washing and dewatering them, then compacts and deposits the material in a continuous plastic bagger to eliminate odors. The screen is cleaned automatically.

 

Result

The plant has had no further clogging problems. 704/949-1010; www.huber-technology.com.

 

Enhanced performance and odor control

Problem

The York (Pa.) Wastewater Treatment Plant needed to expand its sludge thickening capabilities before anaerobic digestion but was concerned about odor control and meeting York City Sewer Authority requirements.

 

Solution

The engineer specified two thickeners, each processing 240 gpm at 2 to 3 percent dry solids. Polymer was restricted to 8 pounds neat per ton of dry solids, and the thickened sludge was to be 4 to 6 percent solids. York purchased two enclosed GSCE Gravabelt gravity belt thickeners from Komline-Sanderson. Polymer-conditioned material diluted 0.5 to 1.0 percent is introduced at the feed end of a moving horizontal filter belt. The Roto-Kone high-rate drainage system holds back the solids while causing constant movement throughout the sludge blanket, allowing optimal drainage of free water. The discharged material is pumpable.

 

Result

When the system went online, the primary and waste activated sludge were at 1.1 percent solids. This, and limiting downstream capabilities, forced operators to adjust the units to thickened sludge at 6 percent dry solids at a feed rate of 195 gpm using 1.1 pounds of neat polymer per ton of dry solids. The system enhanced performance and odor control. 800/225-5457; www.komline.com.

 

Deragging solution

Problem

The Arbennie Pritchett Water Reclamation Facility in Okaloosa County, Fla., installed Aqua Guard perforated plate Model PF bar screens with 0.25-inch openings from Parkson Corp. The self-cleaning, in-channel fine screens automatically removed suspended solids from the flow, but soon after their implementation, the paddle blade mixers in the oxidation ditches began accumulating rags and tripping out on overload. Operators had to clean the blades daily.

 

Solution

When contacted by the contractor, Parkson sent a team to investigate how the material entered the plant. They discovered that the fibrous components in large rags were small enough to slip through the openings in the plates. The team modified the screen’s sealing mechanism to optimize it, then added a variable-frequency drive control to capture the tiny fibers. Parkson controls experts also designed a strategy based on ultrasonic differential level measurements. The system started the screens at 20 Hz, one-third the normal speed, then slowly ramped up speed as demand increased.

 

Result

The plate screen captured the small fibrous components, eliminated a scum layer in the headworks channel, and ended the rag problem. 954/935-6237; www.parkson.com.

 

Cleaning dewatering belts

Problem

Clogging belts on the two gravity belt thickeners at the Cowlitz County (Wash.) Three Rivers Wastewater Treatment Plant extended run times, reduced machine efficiency and belt life, and increased maintenance costs. Operators washed the belts to restore function and occasionally removed them for high-pressure cleaning to dislodge materials, but the fix was only temporary.

 

Solution

The facility tested the Belt Blaster spray system from GillTrading.com. Within the first few revolutions of the belt, the waterjet removed all materials, and operators saw the spray penetrating the fabric. The cake was consistent and within the anticipated range. When the system was turned off, the belt fouled after a few revolutions with water flowing over it.

 

Result

The spray system optimized liquid removal, increased belt longevity, and eliminated manual belt cleaning. 866/447-2496; www.gilltrading.com.

 

Cold-weather composting

Problem

The Ishpeming (Mich.) Area Joint Wastewater Treatment Authority faced increasing costs to landfill biosolids. Land application of Class B biosolids is limited in Michigan’s Upper Peninsula. Because of the cold and snowy weather, the authority turned to in-vessel composting to make a Class A biosolids product.

 

Solution

Engineered Compost Systems (ECS) provided an SV Composter stationary in-vessel system. It provides automated aeration control, monitoring and data recording, insulated concrete vessels and doors, leachate and condensate collection, and biofiltration of all process gases for odor and VOC reduction. The company worked with the authority’s consulting engineers to fast-track construction.

 

Result

The facility was finished in February 2010, and the first batch of finished product was sold to commercial and residential customers that spring. With few glitches, the authority went from a costly landfill problem to saving money and providing a valuable product to the community. 206/634-2625; www.compostsystems.com.

 

Increased solids handling capacity

Problem

The 13.8 mgd (design) Gloversville-Johnstown (N.Y.) Joint Wastewater Treatment Facility treats domestic flows as well as numerous industrial waste streams. These streams contribute to high influent BOD and have been growing for five years, increasing the solids to process and dewater, according to George Bevington, plant manager. Solids have been difficult to handle and dewater because of high concentrations of dairy whey. A pair of 2-meter belt presses could not keep up.

 

Solution

Two model 3DP Belt Presses from BDP Industries replaced the 2-meter units and dramatically increased solids throughput and capture. The 2.5-meter units use an independent gravity belt and a vertical pressure zone to optimize dewatering. Open construction simplifies maintenance and operation. A pair of 2.5-meter gravity belt thickeners from BDP thicken waste activated sludge before the anaerobic digesters and extend solids residence time in the digesters.

 

Result

The belt presses dewater 150,000 and 230,000 gpd of 3 percent solids material, resulting in 100 wet tons of biosolids. The previous presses were limited to 38 to 40 gpm per meter of belt width. Each new press handles 55 to 60 gpm per meter of belt width, or up to a dry ton per hour. Higher solids throughput and improved solids capture reduce the solids “recycled” back through the process, improving the performance of the entire plant. The thickeners have boosted solids concentration to the digesters, improving their efficiency. 518/695-6851; www.bdpindustries.com.

 

Dewatering in a small footprint

Problem

Drying beds were not keeping up with demand at the 5.75 mgd Lancaster (S.C.) Wastewater Treatment Plant, and the storage area reached capacity in 1.5 months. Haulers transported 6 million gallons of liquid biosolids in 1,200 trailer loads for land application. The facility needed a dewatering option that did not require a full-time operator and could handle a plant expansion to 7.5 mgd.

 

Solution

The city bought a rotary fan press from Prime Solution. Conditioned sludge feeds into the enclosed slow-moving (less than 1 rpm) dewatering channel between two rotating circular parallel stainless steel wedge wire screens. A pressure drop forces liquids through the filter openings. The dewatering process intensifies as the cake advances toward the tapered outlet, where a pneumatic restriction plate controls pressure. The compression from the plate, the backpressure from incoming biosolids, and the frictional force of the screens condense the cake to release additional filtrate.

 

Result

The press runs constantly with minimal supervision and is less labor intensive than the drying beds. Cake is 16 to 22 percent solids, allowing Lancaster to store six months of production. Paying $22 per cubic yard for transportation instead of 3.5 cents per gallon saves the facility thousands of dollars annually. 269/673-9559; www.psirotary.com.

 

Pumps decrease downtime

Problem

The Kelowna (B.C.) Wastewater Treatment Plant used progressive cavity pumps to pump dewatered biosolids at 21 percent solids from two centrifuges 260 feet to ports discharging into trucks. The material, 132,000 pounds per day, was incinerated. Maintaining and replacing the pumps twice a year was not cost-efficient, and downtime stopped the process for three or four hours at a time.

 

Solution

Schwing Bioset engineers suggested two KSP 45V(HD)L sludge pumps and an SD 250 screw feeder. They also decided to keep the existing Schwing Bioset KSP 17V(K) in operation, playing a backup role for the new pumps.

 

Result

The decrease in downtime saved the plant time and money. It now ships Class B biosolids to the OgoGrow Production Facility to become a soil conditioner. 715/247-3433; www.schwingbioset.com.

 

Continuous-feed biosolids dryer

Problem

In 2006, the 2 mgd advanced secondary treatment Sanford (Fla.) South Water Resource Center added a natural-gas-heated batch process dryer to produce Class A biosolids. When the price of natural gas rose to historic highs, the agency considered cost-effective alternative solutions that allowed for projected growth.

 

Solution

MaxWest Environmental Systems in Sanford installed an IC 5400 Bio-Scru dryer from Therma-Flite. The fully automated dryer has a true continuous-flow process, feeding 77 to 89 wet tons per day and discharging 1,080 to 2,077 pounds of dry solids per hour and 6,480 to 7,477 pounds of water per hour. The screw rotor design maximizes thermal efficiency by dewatering the material through the drying process. The solids are then burned in a 10 MMBtu heater, fueling the drying process and replacing natural gas. A programmable logic controller ensures uninterrupted operation with minimal operator attention, while continuously meeting federal 503 Class A requirements.

 

Result

The technology reduced the plant’s overall costs and will capture an estimated $12 million in savings over the life of the contract. 707/747-5949; www.therma-flite.com.



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