Anaerobic digestion of waste wafer material from the confectionery production

This paper presents results of semi-continuous mesophilic anaerobic digestion of waste wafer materials at high loadings. The digestion was carried out in a partially mixed horizontal fermenter. A model digestion was conducted in a way that the volume of the fermenter reached a high intensity of methane production at a low production of digestate without the addition of trace elements. For this reason, the waste was fed in a concentrated form. The intensity of dry biogas production was 6.44 mN3 m−3 d−1 with the average methane content of 55.1 vol% at the average load of 8.23 kgVS m−3 d−1 during 203 days and the average hydraulic retention time of 148 days. The process was running stably at C:N ratio 5.3:1, at pH between 7.5 and 8.2, at the average temperature 39.7 °C and the ratio of total inorganic carbonate to the sum of lower fatty acids about 1:1. The specific biogas yield from waste wafer material was 0.703 mN3 kg−1. The digestate contained 13.4 wt% of total dry matter in average with the loss on ignition of 75.4 wt% for the whole process. The dry matter of digestate contained 10 wt% of lipids and to 3.5 wt% of lower fatty acids.