The impact of plastic bag residues on anaerobic digestion performance

Aim of the research: To test the suitability of a plastic bag material for separate collection of food waste prior to AD. Toxicity, biodegradability and biogas production of the polymer was assessed by comparison with other feedstocks as controls. 10 litre digesters were used with and without pretreatment of the plastic. Short summary: In this work we used 10 litre digesters to investigate the suitability of a polymer material for food waste collection plastic bags. The material needed to be robust, but also biodegradable. Digestion of the synthetic polymer was compared to natural polymers from maize and rice. Two controls were also used: cellulose (known for its high biodegradability) and sewage sludge (the most commonly used AD substrate). Parameters checked daily, included gas production and composition, CST and total and volatile solids of the digestate. Stability was assessed by Ripley’s ratio, VFA, ammonia and pH. Digester loading was 1.36 g VS/l/day at 60 day HRT. The experiment was in two halves with sewage sludge feed in the middle, as an internal control to check activity. In a second experiment the material was pre-treated according to the Animal By-product Regulations (Regulation, 2011) heating to 70oC for 1hr. The results show the material was completely inert.