North Ridgeville, Ohio, has completed the first phase of a $4.5 million project that will expand the city's capacity for sludge handling. The expansion will enable the city - which already processes sludge from nearby communities and industries - to increase the amount of sludge it processes and boost wastewater treatment revenue.

For years, North Ridgeville has treated outside flow, including non-hazardous sludge and industrial waste; and, as a result, the city has been able to maintain stable rates for residential wastewater treatment. However, by 1999, the city's 20-year-old French Creek wastewater treatment plant needed major equipment overhauls, and Ridgeville officials had to choose between raising user fees or taking in more sludge to pay for the project.

The French Creek plant already had some sludge processing capabilities, but it was functioning at half of design capacity and with outdated equipment. A study conducted by Plant Superintendent Donald Daley showed that, by increasing the capacity from 3 mgd to 7.5 mgd, the city could boost revenue significantly. To do that, however, Ridgeville would have to expand storage space and add treatment and support facilities.

Working with H. B. Engineering, based in North Royalton, Ohio, the city finalized the project design. It wanted to add three aerobic digestion tanks, retrofit a concrete digester, add an ultraviolet system, expand the tertiary filter, expand the equalization basins and rehabilitate the drying beds.

Storage capacity - provided by digestion tanks - was critical to the profitability of a sludge-processing venture. North Ridgeville could have contracted to have the sludge hauled to a landfill or nearby farms, but those options would have cut into revenue. Instead, the city wanted to store the sludge and turn it into a dry Class A product for resale.

Storage also was critical to financing. "To have the money to purchase everything that we needed - and to afford subsequent phases - we would have to realize some of the profits on the project [this year]," Daley says. "We budgeted a $35,000 profit from this year's operation of the new storage component, and we factored that into the funding for the next phase of the project. It was almost a chicken-and-egg situation."

North Ridgeville hired Gateway Tank in nearby Sheffield Village to install the bolted steel digestion tanks. "The bolted tank assembly removed the weather variable that we would have had with concrete or welded tanks," Daley says.

Supplied by DeKalb, Ill.-based Engineered Storage Products, each of the tanks measures 119 feet in diameter by 19 feet in height, and each has a capacity of 1.34 million gallons. The tanks are situated above ground and have open tops, and stainless steel course bubble aeration systems and mechanical mixers are located inside.

The French Creek tanks began operating in August, allowing North Ridgeville to increase its sludge-handling revenue for 2000. The remainder of the expansion project is scheduled for completion next year.