Anaerobic co-digestion of dairy cow manure and high concentrated food processing waste

Anaerobic co-digestion of dairy manure (DM) and concentrated food processing wastes (FPW) under thermophilic (55 °C) and mesophilic (35 °C) temperatures, and fertilizer value of the effluent were investigated in this study. Two types of influent feedstock were utilized: 100 % DM and a 7:3 mixture (wet weight basis) of DM and FPW. The contents of the FPW, as feedstock were 3:3:3:1 mixture of cheese whey, animal blood, used cooking oil and residue of fried potato. Four continuous digestion experiments were carried out in 10 L digesters. Co-digestion under thermophilic temperature increased methane production per digester volume. However, co-digestion at 35 °C was inhibited. Total Kjeldahl nitrogen (N) recovered after digestion ranged from 73.1 to 91.9 %, while recoveries of ammonium nitrogen (NH₄-N) exceeded 100 %. The high recovery of NH₄-N was attributed to mineralization of influent organic N. The mixture of DM and FPW showed greater recoveries of NH₄-N after digestion compared to DM only, reflecting its greater organic N degradability. The ratios of extractable to total calcium, phosphorus and magnesium were slightly reduced after digestion. These results indicate that co-digestion of DM and FPW under thermophilic temperature enhances methane production and offers additional benefit of organic fertilizer creation.