How collection efficiency and legal constraints on digestate management can affect the effectiveness of anaerobic digestion of bio-waste: An analysis of the Italian context in a life cycle perspective

Abstract

The influence of collection efficiency and of legal regulations on both the technology and the effectiveness of energy and fertilizer recovery from the anaerobic digestion (AD) of bio-waste was investigated in a life cycle perspective for the Italian context. Concerning collection efficiency, some correlation was detected to both the AD technology and the amount of energy and fertilizer recovered. Nine out of 31 CE plants were based on solid anaerobic digestion batch located in those areas with collection efficiency <65%, recovering about 100 kg and 125 kWh of fertilizer and electricity, respectively, per Mg of bio-waste. The 17 plants adopting wet technologies were implemented in areas with collection efficiency ranging from 50% up to >85% able to recover on average about 130 kg of fertilizer and 275 kWh of electricity per each Mg of bio-waste. Wet AD was also the only adopted for larger size plants from 60,000 Mg/year up to 600,000 Mg/year. Legal constraint on the direct use on land of the digestate caused an average increase of main impacts such as global warming (kgCO_2eq), freshwater eutrophication (kgP_eq) and human health (DALY) of about 300%. The effect of the quality of the bio-waste returned after the collection showed lower incidence on the overall impacts of about 20%, and mainly limited to global warming (kgCO_2eq) and photochemical ozone formation (kgNMVOC_eq).

Keywords: Anaerobic digestion; Bio-waste; Digestate recovery; Life cycle assessment; Separated collection.