Biogas and digestate production from food waste: a case study of dome digester in Morocco

Food wastes are characterized by high contents of biodegradable materials, which have negative effects on the environment. For instance, 24 tons of food wastes are rejected annually by the canteen of the Training Institute for Renewable Energies and Energy Efficiency of Oujda (East of Morocco). Anaerobic digestion is one of the most important processes which may be implemented to valorize this organic waste. However, literature shows limited research works on anaerobic digestion of food wastes using small-scale biogas plants in Morocco. The aims of this work were to evaluate (i) the biogas production from food wastes and (ii) the effect of liquid digestate on open field crops. In this study, food wastes and cattle manure were co-digested in the 20 m3 dome digester over a period of eight months. The production and composition of biogas were monitored during the anaerobic digestion. During the experimental period, a total amount of 4000 kg of food waste was treated generating a cumulative biogas production of 92 m3. The average daily biogas production was 0.9 m3/day with an organic loading rate of 0.4 kg VS/m3/day and biogas specific production of 0.2 m3/kg VS. Overall, the liquid digestate was non-toxic to plants because the germination index was 168%. Moreover, the liquid digestate improved the yields of lettuce (+ 65% and + 33% respectively for the diluted and raw digestate), maize (+ 40% for the raw digestate), and potato (+ 33% for the raw digestate) for all fertilization treatments based on liquid digestate in comparison to the non-fertilized treatments.