In the paper the suitability of the bakery and confectionery waste (OPC) as a substrate for biogas production has been analyzed. The co-fermentation process of OPC with the primary sludge was carried out in the model of the digester chamber. The parameters of leachate obtained from OPC to determine their potential utility as an external organic carbon source supporting denitrification process were also examined. The study takes into account the impact of mold on the measured parameters. The results show that solutions of the OPC, even after a significant contamination of the mold, may be used for the anaerobic digestion process. The fermentation mixture obtained a twofold increase of biogas production in relation to the fermentation of the primary sludge from waste water treatment. The COD value and a high rate of COD: N predestines tested leachate as external carbon source in the processes of denitrification.