Life cycle assessment and life cycle costing of advanced anaerobic digestion of organic fraction municipal solid waste

The aim of this study is the evaluation of the environmental sustainability by means of Life Cycle Assessment (LCA) and economic profitability through Life Cycle Costing (LCC) of the 18 anaerobic digestion (AD) configurations carried out on Organic Fraction Municipal Solid Waste (OFMSW) at three Substrate Inoculum (S:I) ratios (1:2, 1:1 and 2:1) for three different inoculum incubation times (0, 5 and 10 d). The adopted approach was the eco-efficiency perspective, coming from the combination of technical, environmental (LCA) and economic (LCC) perspectives. The main findings of the study were that increasing both the S:I ratio and the inoculum incubation time (5 and 10 d) the environmental impacts decreased, and economic profitability increased. The lowest values of Climate Change were achieved by the AD performed with both inocula WAS and CAS for 10 d at S:I equal to 2:1: 28.67 and 27.72 kg CO2 eq respectively. The minimum AD plant size for which all the 18 AD configurations was economically profitable after 5 y of amortization was 30,000 t/y of OFMSW. Capital and operational costs decreased by increasing the incubation time of the inoculum and the S:I ratio, since higher specific biogas rate was reached, and smaller AD bio-reactor volume were adopted because hydraulic retention time decreased. The AD plant size, for which maximal revenues and minimal capital and operational costs were detected, was 50,000 t/y OFMSW. Among all the AD configurations, the environmental sustainability and economic profitability were reached by test perfomed with inocula WAS and CAS incubated for 5 and 10 d at the highest S:I ratio 2:1.

Automated summary

Increasing the substrate inoculum ratio and incubation time decreases environmental impacts and increases economic profitability in anaerobic digestion configurations. The most economically profitable plant size is 30,000 tons/year of OFMSW, while the optimal size for maximal revenues and minimal costs is 50,000 tons/year. The highest environmental sustainability and economic profitability were achieved with incubated inocula WAS and CAS at the highest S:I ratio of 2:1.