Madison Metropolitan Sewerage District recently shared the results of its Phase 2 sampling and analysis of PFAS, or per- and polyfluoroalkyl substances, in the local wastewater cycle.
The District has completed the first phase of its PFAS sampling and analysis plan, and the results are favorable.
The first phase of the plan tested for 33 PFAS compounds, as outlined by the Wisconsin Department of Natural Resources (WDNR). The District’s influent (incoming wastewater), effluent (outgoing, cleaned wastewater) and biosolids were tested. Struvite, a phosphorus-rich nutrient recovered from wastewater, and polymers, which are used in the treatment of biosolids, were also tested.
Samples were collected by a consultant, TRC, using lab-accepted collection methodologies. The samples were analyzed by Eurofins|TestAmerica, which is certified by WNDR to conduct PFAS testing.
Overall, the results of the District’s initial testing were as expected based on the characteristics of the 180-square-mile service area.
Sampling highlights are summarized below. Find the full 2021 report here.
Released September 30, 2021
Influent (Incoming wastewater)
The District tested influent from the five large sewer pipes, called forcemains, that aggregate wastewater from the service area and deliver it to the plant.
Examining all of the 33 compounds tested, the types of PFAS found in local wastewater is consistent with results from other municipal wastewater treatment plants in urbanized areas without significant industrial sources.
|PS08||PS18||PS07||PS11||PS02||Weighted Average, District||Median Concentration, Michigan Study**|
Percent of Total PFAS Attributed to Forcemain
*In the full report, numbers are reported as ng/L, which is the same as ppt, or parts per trillion. For context on ppt equivalents, see our About PFAS page.
**The Michigan Department of Environment, Great Lakes, and Energy conducted a statewide assessment of PFAS in 42 wastewater plants (WWTPs), which included the 20 largest WWTPs and 22 other WWTPs selected to represent different flow rates and treatment processes.
Effluent (Outgoing wastewater)
The District cleans wastewater to river-quality water and returns it to local watersheds via Badger Mill Creek and Badfish Creek.
The Department of Natural Resources approved surface water criteria for levels of PFOA and PFOS in Summer 2022. These criteria establish a threshold beyond which certain pollution minimization efforts must be undertaken. Our testing reveals PFOA and PFOS levels in the District’s effluent are lower than WDNR’s surface water criteria.
The waterways the District discharges to are not drinking water sources.
|District||WDNR Surface Water Criteria - Public Water Supply||WDNR Surface Water Criteria- all other surface waters|
|9.7 - 11||20||95|
The District produces two biosolids products. The primary product is Metrogro, a liquid class B biosolids product that is land applied to local farm fields as a valuable, nutrient-rich fertilizer. The District also produces a small amount of class A cake.
The amounts of PFOA and PFOS in the District’s biosolids are similar to data from other municipal wastewater treatment plants that do not, like Madison, accept industrial waste from major PFAS sources.
WDNR has not established PFAS standards or provided guidance for land application of biosolids, but Michigan offers proposed action levels in its interim guidance for comparison. The interim guidance specifies PFOS thresholds at which biosolids cannot be land applied (150 ppb); at which land application should be limited (50 ppb); and at which investigation of sources and sampling of effluent is recommended but land application is not restricted (20 ug/kg). The PFOS concentrations detected in both of the District’s biosolids samples are less than Michigan’s 50 ppb threshold for limited land application rates and also slightly less than the 20 ppb threshold for suggested source investigation and effluent sampling.
Land application of Metrogro is the most cost-effective and environmentally friendly way for the District to dispose of the solid waste recovered from wastewater. Alternatives such as landfilling or incineration are costly and have additional impacts on the environment and human health.
|Class B Liquid (Metrogro)||Class A Cake|
|1.2 - 1.6||16|
STRUVITE & POLYMERS
Polymer: The District uses polymer to help thicken biosolids. These polymers do not add any significant amount of PFAS to the waste stream. In fact, only two PFAS compounds were found, PFOS and PFBA, and both at less than 0.5 ppb. All other PFAS compounds were at a level below the laboratory method detection limit (MDL)*, which is considered zero.
Struvite: Struvite is a phosphorus-rich nutrient we recover from wastewater. Only one PFAS compound, PFHxA, was found in struvite at 0.06 ppb. All other PFAS compounds were at a level below the laboratory method detection limit*, which is considered zero.
Neither polymer nor struvite is a source of PFAS to the environment or waste stream.
|Polymer 1||Polymer 2||Polymer 3||Struvite|
|Less than MDL||Less than MDL||Less than MDL||Less than MDL|
|Less than MDL||Less than MDL||0.48||Less than MDL|
*According to the U.S. Environmental Protection Agency, method detection limit (MDL) is “the minimum measured concentration of a substance that can be reported with 99% confidence that the measured concentration is distinguishable from method blank results.”
Through 2022, the District was engaged in phase 2 of its PFAS sampling plan. This provides preliminary results for PFOA and PFOS, two PFAS compounds.
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