Water Quality/Mid-Atlantic: Land Application Protects Chesapeake Water Quality

Challenge:
Anne Arundel County, Md., sits on the shores of the Chesapeake Bay, one of the largest and most environmentally sensitive estuaries in the United States. With concern about water quality increasing in the region, the county’s six wastewater treatment facilities have been challenged to meet their effluent discharge limits, particularly since the early 1980s. At that time, the county was experiencing severe operational constraints, including design problems and equipment breakdowns, and lack of sufficient offsite storage space for the treated biosolids was hindering further development of the county’s land application program.

Solution:
In 1984, Anne Arundel County officials decided to obtain private-sector capabilities to help address these deficiencies. After competitive bidding, the county selected Synagro Technologies, Inc. to design, build and operate dewatering and post-lime treatment at the county’s treatment facilities and manage the land application of all treated biosolids generated by these plants.

When this project began, few treatment facilities incorporated dry lime to disinfect dewatered biosolids; thus, the Anne Arundel County project provided an opportunity to establish methods for successfully operating this technology. Currently, advanced technology provides for polymer conditioning of the biosolids using chemical metering pumps, mixing tanks and mixers. Belt press dewatering follows this conditioning process, and screw augers meter lime from on-site storage silos into the dewatered cake biosolids. The treated biosolids are briefly stored onsite in closed-top metal containers before they are removed for transport to land application sites.

Currently, all six treatment plants produce undigested solids that are lime stabilized to Class B pathogen reduction levels following belt press dewatering. Year-round biosolids land application is accomplished through prudent use of a double-lined storage lagoon located at a farm participating in the program. This storage facility can hold up to 100 days’ volume of biosolids production during periods when weather or other constraints prevent land application.

Agronomic application is the backbone of the program. To date, more than 30,000 acres of farmland in nine Maryland counties participate. These farms produce crops such as corn, soybeans, grain and hay, as well as turf. Agronomic application at nitrogen-based rates generally ranges from 3 to 5 dry tons per acre. A weighted average of plant-available nitrogen is the basis for the application rates regulated by the Maryland Department of the Environment (MDE). Regulated metal concentrations are analyzed monthly and reported to MDE.

The program also includes sand and gravel surface mines that use the biosolids to reclaim depleted soils. Such sites offer operational flexibility by complementing the timing of typical farming operations. They also provide the opportunity to enhance soil properties by replacing depleted organic matter, which protects the area's water quality by reducing soil erosion.

Results:
The program is an outstanding example of a sustained effort involving the county’s wastewater treatment plant team, area farmers, and local public and governmental interests. The success of the program began with the enthusiasm of farmers over the crop yields and cost savings they achieved through the biosolids program, and it continues to maintain the support of local communities. The program has the approval of elected officials in all nine participating counties, and early meetings explaining the program to community associations and other neighbors have led to continued support.

The program now is in its 16th year of operation for 100 percent of the county's daily output of approximately 33 dry tons of biosolids. All Anne Arundel County wastewater treatment facilities have repeatedly been recognized by the Association of Metropolitan Sewerage Agencies with peak performance awards given annually for exemplary compliance with National Pollutant Discharge Elimination System effluent limits. In 2001, EPA recognized the county with its annual National Exemplary Biosolids Management Award. The county received the 1st-place award for operating projects greater than 5 dry tons/day.

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