Wastewater treatment plant progress


Explanation and terms

This application contains wastewater pollutant loads for select pollutants.
The reported values on Discharge Monitoring Reports (DMRs) are the basis for permit compliance.

Estimated and observed pollutant load calculations

Loading values are a mix of observed data and values estimated based on previously reported values. The loads are considered accurate but based on calculations and not raw data. Loads are derived by multiplying the monthly average concentration and monthly total flow. The resulting loads may vary slightly from mass reported on DMRs due to calculation methods. Calculated loads are used for research and planning purposes.

Total suspended solids (TSS) is a measure of the material suspended in water or wastewater. TSS can cause interference with light penetration, buildup of sediment, and potential degradation of aquatic habitat. Suspended solids also carry nutrients causing algal blooms that are harmful to fish and other aquatic life.

Oxygen demand is the amount of oxygen required to break down organic wastes introduced into water. A high oxygen demand reduces the concentration of oxygen in the receiving waters, deteriorating water quality and impacting fish, insects, and other aquatic life. Untreated domestic wastes and many industrial wastes have high concentrations of organic materials. Microorganisms consume oxygen while decomposing the waste and this is measured with the biochemical oxygen demand (BOD) or carbonaceous biochemical oxygen demand (CBOD). Both BOD and CBOD are indicators of the strength of wastewater effluent and the effectiveness of treatment..

Municipal wastewater treatment facility effluent measurements are expressed as CBOD and industrial dischargers typically report BOD. This report uses CBOD for load calculations because it provides a more complete data set for municipal facilities. Industrial facilities are not included in this calculation because there are too few observations to confidently estimate concentrations. The complete BOD/CBOD load could be significantly higher than the currently reported values because industrial flow accounts for nearly half of the flow within the state.

Total phosphorus (TP) is the primary pollutant associated with increased algae growth in Minnesota’s lakes and streams. Excess phosphorus from human activities causes algal blooms and reduced water transparency, making water unsuitable for swimming and other activities. Phosphorus is released from both point and nonpoint sources of pollution. Minnesota has had point source effluent limitations for phosphorus since the early 1970s.