Pollution load assessment in the form of TSS and COD emitted from an urbanized catchment in the aspect of administrative pollutant discharge fees on the example of the activity of the J1 CSO in Lodz (Poland)

The article presents the possibility of reducing fees for wastewater discharge from combined sewer overflows (CSOs) into the aquatic environment by minimizing the load emission of total suspended solids (TSS) and chemical oxygen demand (COD). The analysis was conducted based on limiting the wastewater volume discharged to the receiving water by one of the viable options, i.e., raising the overflow crest. The assessment was made on the example of the functioning J1 CSO in Lodz (in Polish: Łódź) in the years 2013–2015. An analysis of rainfall recorded in the J1 catchment area was also performed for this period. For the determination of the TSS and COD load emitted to the receiver, a predictive model based on rainfall parameters and the volume of discharged wastewater was used. To determine the wastewater volume emitted during individual activations of the J1 overflow, the model of the sewer network serving this catchment was calibrated in the EPA SWMM software. Simulations were conducted, considering different heights of the weir crest (static change). The results of the analyzes showed that raising the crest by 5 cm reduced the total fee for the J1 activity by 35% compared to its existing height in 2013 and about 40% for 2015. Raising the crest by 10 cm in 2015 enabled, for example, the J1 overflow activity to be in accordance with the applicable law. Reducing the amount of wastewater discharged to the receiver by using the overflow crest height adjustment method presented in the article may bring measurable financial and ecological benefits.