SUMMARY
Anaerobic digestion (AD) is a mature technology commonly used for manure treatment, both for the stabilisation of waste and for the production of energy. The introduction of new incentives could represent an opportunity for biogas production, when the current feed-in-tariffs, which improved the financial feasibility of AD plants producing electricity will end. This paper examines the feasibility of reconverting an existing AD biogas production plant into a biomethane production plant. The AD plant, in this case study, is a two-stage reactor situated in the centre of Italy and mainly fed with livestock manure from both cows and buffaloes. The economic analysis of two hypotheses is provided: i) continuing the electricity production from biogas after the end of the current incentives (2025); ii) considering the new incentives program for the biomethane and reconverting the plant, using hollow-fibre membranes for the purification of the raw biogas (SEPURAN® Green modules, EnviTec). For this purpose, investment and operating costs, based on plant monitoring data (2105.3 m3 d–1, Biogas production; 4432.9 kWh d–1, electricity production) as well as on market analysis for costs evaluation were considered. The mean biogas production for the considered year was about 30% less than the expected production, indicated by producer, highlighting the need for the optimisation of the management of the reactors. Moreover, based on the averaged methane production (June 2017-June 2018), results show that: i) plant conversion for the biomethane production is not suitable for small-scale plants, due to the high investment costs of upgrading technology (1.2 M€); ii) when current incentives end, the electricity production from biogas in the current plant may not be self-sufficient, due to the highly expensive operating costs. This paper provides a first analysis of the possible fate of the biogas plants under the new incentives.