Economic and environmental life cycle assessment of organic waste treatment by means of incineration and biogasification. Is source segregation of biowaste justified in Germany?

Abstract

In the realm of the German scope, four different waste treatment options for the Organic Fraction of Municipal Solid Waste (OFMSW) were evaluated against the environmental and economic background: (i) anaerobic digestion followed by composting, (ii) incineration of OFMSW, (iii) incineration of separately pre-dried OFMSW and (iv) a cascaded treatment system, which couples anaerobic digestion with incineration (i.e. incineration of digestate). Environmental life cycle assessment (eLCA) and a calculation of the levelized costs of exergy (LCOE) were performed to map the sustainability aspects of the different product systems. Within a hybrid approach, consisting of literature data evaluation, theoretical modelling, the conduct of lab-scaled experiments and a substrate analysis, a comprehensive assessment was compiled. Within the eLCA, the main drivers of the total environmental impact were the categories global warming potential (GWP) and the fossil depletion potential (FDP). (i) Anaerobic digestion followed by composting and (ii) incineration were hereby characterized by the fewest environmental impacts. With regards to the base case, the GWP was calculated to ~500 g CO₂-Eq/kWh exergy for these options. The FDP was <0.05 kg oil-Eq/kWh exergy for anaerobic digestion and ~0.075 kg oil-Eq/kWh exergy for incineration. The other examined treatment options were characterized by a significantly higher GWP and FDP. The economic assessment showed median LCOE of 27 ct/kWh exergy for anaerobic digestion followed by composting and thus outcompeted incineration (median: 55 ct/kWh Exergy). Separate pre-drying prior to incineration increased the economic burdens marginally. Anaerobic digestion followed by incineration showed the highest economic expenses (89 ct/kWh exergy). In conclusion, anaerobic digestion followed by composting was marked by an overall preferential environmental and economic constellation and source segregation is thereof justified and should further be maintained.

Keywords: Anaerobic digestion; Cascaded waste treatment; Environmental life cycle assessment; Incineration; Organic fraction of municipal solid waste.