Possibility to Utilize Fish Processing By-Products in the Context of Management of Non-renewable Resources

Fish processing generates considerable amounts of waste which constitutes a potential threat to the environment. The aim of this paper was to assess the possibility to use processing waste for anaerobic digestion and to use the generated digestate for fertilization purposes. This research involved evaluation of chemical composition of waste from a carp processing plant and of the digestate after methane fermentation. The content of dry matter, organic carbon, nitrogen, and other macroelements was determined in the samples. Moreover, the content of trace elements was determined. Dry matter content in the studied waste was 40%. Nitrogen content was approximately 5.56%, phosphorus—1.758%, calcium—0.4%, whereas mean potassium content was 0.502 g kg⁻¹. As a result of conducting methane fermentation, a reduction in nitrogen content by about 50% and a considerable increase in quantity of almost all elements were observed. A high zinc content was recorded in the digestate, whereas concentration of other microelements was at a level close to the one in natural fertilizers. Concentrations of heavy metals did not exceed permissible values for organic fertilizers. The studied material can be a component for fertilizer production, and its fertilizing value depends mostly on nitrogen and phosphorus content.