Challenge
Clarksville, Virginia is a community home to many industries, such as candy manufacturer Russel-Stover. When the aerated lagoon – used to pre-treat wastewater – became overloaded, the town turned to Evoqua for solutions.
While the effluent wastewater is hardly hazardous to your health, it is a very common problem for candy manufacturers as it contains a very high proportion of Biochemical Oxygen Demand (BOD) and Total Suspended Solids (TSS). When combined with the effluent from other industries, it can overload a small to medium sized municipal wastewater treatment system's capacity to process these wastes and meet stringent regulatory standards.
A case in point centers on the municipal system in Clarksville, Virginia, with a population of approximately 2,000 people. This community is located on the shore of Buggs Island Lake, a large, man-made recreational water resource along the Virginia-North Carolina border. Among the industries in the area is Russell-Stover Candy Manufacturing.
Russell-Stover initially discharged into the town sewer, but the high strength organic waste severely overloaded the town's treatment plant. In the mid-70s, Russell-Stover constructed an aerated lagoon—which converted the high organic loading to biological solids—to pre-treat their wastewater prior to discharge into the town's sewer system. Even with the pretreatment system in place, the town's treatment plant was still overloaded, especially with solids, and was unable to produce a satisfactory effluent.
Solution
In 1986-87, on the advice of B&B Consultants, Inc., of South Hill, VA, the aerated lagoon was converted to an activated sludge system with nutrient additions, an aerobic digester and an Evoqua filter press.
In this process, 30% ammonium nitrate and 35% phosphoric acid are added to the raw waste. The aeration basin is equipped with four 14hp pumps and four 25hp blowers. The pumps pump 2,500 gallons per minute, while the blowers push 740 cubic feet of air per minute.
The sludge is wasted from the activated sludge process to the aerobic sludge digester tank. This sludge is pumped into a flocculator along with the addition of a polymer. The resulting floc is the aggregate of the suspended particulates in the wastewater and must be dewatered prior to disposal.
The innovative part of this system has been the incorporation of a filter press to dewater the sludge floc. The filter press recommended by the engineering consultants is a J-Press, manufactured by Evoqua Water Technologies of Holland, Michigan. The J-Press is a liquid/solids filtration and separation device widely used in this country by a variety of industries faced with wastewater treatment requirements. Most importantly, this type of filter press yields high dry solids content in the filter cake and an extremely high degree of clarity of the filtrate effluent.
The particular model of J-Press in use at the Clarksville satellite treatment plant is a J-1000, 30 cu. ft. equipped with non-gasketed recessed chamber, membrane plates. This type of press is particularly easy to maintain, especially important since this plant operates with only one full-time employee. The type of press chosen is unique in that it mechanically squeezes the filter cake after the cake has been partially formed. This achieves a dry filter cake from a typically difficult to dewater slurry. Membrane plates are constructed similarly to the standard recessed chamber plates; however, the drainage surfaces on the face of the plates are actually polypropylene (or other elastomeric material) diaphragms. After filtration, when the chambers are filled with sludge and while the J-Press is still sealed, air or water pressure is exerted behind the diaphragms, which in turn flex outward against the filter cake, squeezing them to reduce the amount of remaining moisture prior to cake discharge.
Results
The results that the operation achieves are an impressive 20 cu. ft. or 600 lbs of dry solids per daily cycle that requires three hours to complete. This is 1/3 less volume than what could be achieved with a standard recessed chamber plate press. That combined with the virtually contaminant free wastewater effluent has reduced the overload on the main system while also exceeding the requirements necessary to comply with the regulatory standards.
Previously, the effluent BOD count ranged from 3,000-15,000 ppm. The effluent from the satellite wastewater treatment plant incorporating the J-Press averages a BOD count of 25 ppm and the percent solids of the filter cake is 28-30%, which exceeds the minimum 20% solids concentration requirement of most landfills in order to dump.