The paper presents the research on how the effectiveness ofremoving organic substances is affected bythe use of polyurethane foam fillings characterized by a varied porosity and the temperature of the process of treating landfill leachate in a biological sequencing batch reactor. The information on the conversion of organic compounds during the operation of the reactor was obtained by measuring the absorbance for selected wavelengths to describe the process of humification. It was found that the technological conditions used in the experiment affected the effectiveness of reducing the COD, but did not affect the type or amount of the humic substances in the leachate treated. In all of the variants examined, the COD decreased the as the humification level increased, and yet this relation was not linear in character.