The characterisation and treatment of food waste for improvement of biogas production during anaerobic digestion - A review

Abstract

Anaerobic digestion is one of the major biological-based technologies for converting organic waste to energy. The end-product of the process is the production of biogas that can be harvested as renewable energy and a nutrient-rich digestate that can be transformed as biofertiliser. Food waste varies seasonally and geographically, leading to a variation of biogas potential among different studies. There is still a lack of study on the relationship among the variation of food waste characteristic, its effect on the operational parameters and their inhibition value and its effect on the efficiency of the methods for improving biogas production. This paper reviews the anaerobic digestion of food waste in three sections: the characteristic of food waste reported in the literature, mono-digestion of food waste and co-digestion of food waste with other feedstocks. This review aims to relate the characteristics of food waste to biogas potential and to propose process improvement for enhanced biogas production. Food waste showed variation in terms of bromatological analysis, where the carbohydrates was reported to be around 11.8–74%, protein was 13.8–18.1% and lipid was 3.78–33.72%. The biogas yield for mono-digestion of food waste was 0.27–0.642 m3 CH4/kg VS and for the co-digestion of food waste with other substrates was 0.272–0.859 m3 CH4/kg VS. It has been concluded that the variation in the characteristic of food waste, in terms of physical and biochemical properties, can affect the efficiency of the applied treatment for process improvement, including nutrient balance, mechanical treatment, thermal treatment and two-stage configuration. Co-digestion remains an effective method for biogas production from food waste. Thermal treatment can significantly increase biogas production but excessive treatment can reduce the biodegradability of food waste. Mechanical treatment is more effective in treating waste rich in cellulosic material.