Less Volume, Less Cost

An enzyme formulation helps a small Washington treatment plant reduce biosolids volume and cut hauling costs substantially
Less Volume, Less Cost
Audrey Charles, laboratory technician II, empties a 2.2-pound package of BiOWiSH-Aqua FOG biocatalyst into the mixing drum.

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The Mission Beach Wastewater Treatment Plant in Marysville, Wash., spent more than $100,000 per year transporting biosolids every few days to the Class A compost facility at the La Conner Wastewater Treatment Plant.

“It’s a 60-mile round trip, fuel averages $114 per day, and the fee is $330 per load,” says plant manager Cliff Jones. “We own the 3,300-gallon tanker and it’s our driver, but the trips take him away from his other duty of pumping septic tanks.”

The plant has a dewatering screw press from Somat Co., but the fees for delivering cake to facilities near Everett or Seattle were two and three times higher. “We can’t land-apply because we’re not set up for 503 regulations,” says Jones. “Furthermore, the plant is on Tulalip Tribal lands, and the tribal membership told us that biosolids must be removed from the reservation.”

Looking for ways to minimize biosolids production, Jones turned to BiOWiSH-Aqua FOG, a biocatalyst distributed by Green Bio Solutions. The company agreed to provide all materials for a four-month pilot project — the product’s first test at a wastewater treatment plant.

“In 2010, a year before the project, we hauled 148 loads of biosolids,” says Jones. “Using BiOWiSH, we expect to haul 100 to 105 loads for 2011.”

 

Add water and mix

Opened in 1993, the 616,000 gpd (design) activated sludge treatment plant has an average flow of 200,000 gpd from 3,200 residential customers. Effluent discharges to Puget Sound. Sludge is wasted to an aerated digester tank for decanting and removal.

BiOWiSH, a blend of enzymes and cofactors that assist in biochemical transformations, acts like a catalyst, accelerating the breakdown of organic material and reducing odors. The enzymes digest solids, reducing them to nitrogen and oxygen.

Green Bio Solutions delivered two 55-gallon drums, set up at the headworks. One drum lid held an aquarium aerator and the other a 1/30 hp peristaltic dosing pump. No advance preparation was necessary. “The startup dose was two 2.2-pound packages of product per day for a week,” says Jones. “After that, it was one pack per day.”

Audrey Charles, laboratory technician II, prepared the mixtures. She emptied the packets of freeze-dried enzymes into a drum, filled it with water, put on the lid with the aerator, and allowed the solution to mix for 24 hours. The core water temperature, 45 to 50 degrees F, was too cold for the enzymes, so Lee suggested wrapping barrel heaters around the drums to keep the liquid at 60 to 70 degrees.

The pump on the second drum dosed a few cubic centimeters of solution into the oxidation ditch with each pulse, distributing 55 gallons over 24 hours. “At startup, we kept the mixed liquor suspended solids at 2,200 to 4,500 mg/l to provide enough activity to jump-start the process,” says Jones. “Now we try to keep it at 2,700 to 3,300 mg/l.”

 

Minimal maintenance

During the first three weeks of the project, Jones watched TSS numbers edge toward the plant’s limit. “The rise in turbidity scared me,” he says. “Our fecal coliform also increased, from zeros and ones to nine and 10 CFU per 100 ml. Then all of a sudden at the end of the third week, the numbers began going back down.”

Jones assumed that the spike was due to enzymes attacking the accumulated grease in the plant and sending it downstream. When the aquarium aerator wore out, Jones upgraded to a Gast air compressor rated for 24-hour operation at 0.2 cfm/10 psi.

Based on savings recorded to date, Jones projects savings of $20,000 to $30,000 annually through reduced biosolids volume, resulting in a 12-month payback. “We never expected to make major dollars at the end of the year,” he says. “The whole idea was to save a little bit over a long time. When you extend those savings over 10 years, that’s a substantial amount for our small operation.”



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