What are the impacts from the City of Toledo overflow from sewage on algal blooms in Lake Erie?
Combined sewer overflows (CSOs) may discharge sewage directly into the lake and local tributaries when storm water overloads the capacity of storm drains designed to discharge through wastewater treatment plants (WWTPs). These overflows occur when storm water from rain events overloads the capacity of the sewer system. This combined sewer overflow contains the same pollutants as sewage: phosphorus, organics, metals and pathogens.
There are few direct measurements of phosphorus from CSOs. The Ohio Lake Erie Phosphorus Task Force estimated an annual total phosphorus load to Lake Erie from Ohio cities of approximately 90.4 metric tonnes (there are no available estimates for soluble phosphorus). Like many cities with CSOs, the City of Toledo has a Long Term Control Plan (LTCP) approved by USEPA to address their CSOs. The LTCP has a schedule of control projects, performance criteria and critical milestones to address the CSOs. The Plan will take many years to fully implement as it requires a significant investment in infrastructure with the majority of the costs borne by the ratepayers of Toledo.
Often older cities have sewage systems that combine the sanitary system (flow from our homes and buildings) with the flow from our road gutters and parking lots. These systems often cannot handle the volume of the flow when it rains. The most important part of the treatment process in most sewage treatment plants is a biological process in which we encourage the rapid growth of huge amounts of biological material (microorganisms). That growth removes nutrients (nitrogen, phosphorus, and potassium---N, P, K) from the water before it is discharged to a river or lake. If we allow too much water to flow through the treatment plant, we blow out the culture of living organisms in the treatment plant and it fails to operate correctly even at normal flows. Therefore, many sewage treatment plants have the capability to bypass the sewage treatment plant when the flow is too large. When this happens raw sewage (completely untreated sewage) flows directly into our rivers and lakes. Typically, this happens every time it rains. Pathogens in this sewage often close nearby swimming beaches for several days after a rain and cause odor problems in the vicinity of the sewage treatment plant. The nutrients (N, P, K) in the untreated sewage are much higher than in treated effluent and, because these algal blooms are caused by excessive nutrient concentrations, these overflows contribute to algal blooms in the Maumee River, Maumee Bay, and ultimately, all of Lake Erie.
Gail Hesse, Ohio EPA