A. Adamiec, L. Przywara
University of Bielsko-Biala, Faculty of Materials, Civil and Environmental Engineering, Bielsko-Biala, PL


Efficiency of wastewater treatment depends not only on the applied technology of wastewater treated, but also on processing problems and management of sludge leachates. Currently, treatment plants do not use methods of separate treatment of leachate generated during the processing of sludge and such residues are returned to the beginning of technological process of treatment. Sludge leachates due to the content of non-biodegradable organic matter can affect the efficiency of the purification process. Therefore, it is important not only to determine the overall content of organic compounds in wastewater, but also the specific characteristics of organic substances, by determining of COD fractions. In this study, fractional composition of organic matter during wastewater treatment in the subsequent stages of mechanical and biological wastewater treatment was analyzed. The wastewater used originated from the plant using integrated removal of organic and biogenic compounds. The circulation of leachate formed during dewatering of sediments on gravity thickeners, resulted in an increase in the concentration of the hardly-biodegradable organic matter. During mechanical/biological phase of wastewater treatment, the proportions of Si, Ss, Xi, Xs fractions were completely changed. The dominant fraction in purified effluents was a fraction of dissolved and non-biodegradable compounds Si. In total, Si and Xi inert fractions in purified effluent accounted for 70% of the total COD. The fraction of Xi, in purified effluent, in case of processes not influenced by recirculated sludge leachates, amounted for 10% of the total COD. This shows that the cleaning processes occurs with high effectiveness.

Keywords: organic matter, COD fractions, reject water