Określenie potencjalnych możliwości usuwania związków organicznych w sieci kanalizacyjnej

The sewerage is an often skipped element of the wastewater treatment system. Because of its high retention capacity and relatively long flow time, it has to be considered that processes affecting wastewater composition and their vulnerability to biological treatment may occur in the sewerage. Changing hydraulic conditions in collectors and numerous side influents providing new portions of wastewater diversified in quantity and quality cause difficulties in a precise description of biochemical transformations occuring during wastewater flow in gravity sewers. The authors conducted research on changes in organic compounds (expressed as total COD) and their dissolved form (soluble COD) in wastewater, during their flow through the laboratory model of a gravity collector. The model is constructed as a cascade of five basins made from acrylic glass, 1.12 L each. Wastewater flowed through the model continuously with the rate of 0.5 L/h. It allowed to achieve the flow time of 11 hours, which is 2-3 times longer than flow times occuring in a typical large sewer network and enabled to take samples in the collector profile. Reaeration process, pH and temperature, as well as the psychro and mezophilic bacteria were also taken into account in the analysis. The results of two research series were presented in the article, i.e. where wastewater flowed continuously through the model for 17 and 33 days, respectively. It was proven that during flow in a collector, a number of processes takes place, including sedimentation, washing out of solid contaminations, removal of dissolved organic compounds and enzymatic hydrolysis of slowly biodegradable organic matter. Biomass growth in bulk wastewater and on the model wall proved that biological processes occur there. There are significant differences between research series, mainly caused by the temperature. It was observed that the amount of biofilm was rather small and did not exceed 5% of total biomass. Removal of total COD was in the range of 28.8-80.3 mg O2/(L h) and soluble COD from 8.5 to 11.5 mg O2/(L h). In the last part of the model, the rate od COD removal decreased due to the lack of substrate, which is in accordance with data given by other researchers.