Watertown Repurposes Building to Reduce Biosolids

Challenge: A study was conducted for the City of Watertown that looked at the feasibility of continuing land application of liquid biosolids. The land application process was very cost-effective; however, nearby land used for biosolids disposal was becoming limited, and the City had concerns about the future availability of land. The City asked if HR Green’s wastewater team to evaluate three options: 1) the potential to transition from liquid land application to mechanical dewatering of biosolids with landfill disposal, 2) the continued use of City equipment, or 3) contractor hauling liquid biosolids, and identify areas the current program could be more efficient and cost-effective.

Solution: The study determined land application was not a long-term option for the City of Watertown. Recommendations included adding a screw press into the wastewater treatment facility process to handle dewatering the liquid biosolids into a dewatered cake, which would ultimately be disposed of at the local landfill.

The project consisted of design and construction services to repurpose a decommissioned pretreatment building into a solids dewatering building. HR Green evaluated several different screw press manufacturers and layouts to install a screw press and leave room for a future second screw press with little structural modifications to the existing building. HR Green also identified cost savings to the City by reusing the existing conveyor belt with minimal modifications.

Three aging sludge pumps were replaced with new high-efficiency rotary lobe pumps along with VFDs. Yard piping was added to intercept the existing liquid sludge piping to redirect sludge to the solids dewatering building but also allow for sludge to be redirected to the existing sludge storage tank.

Benefit: The project provides the City of Watertown with a low-maintenance, long-term solution for processing and handling the liquid biosolids while also allowing for the disposal of the biosolids that no longer require the City to rely on the availability of farmland. The project also saved the City significant money by designing the new equipment and layout to allow for repurposing a decommissioned building and reusing some existing equipment.