Evaluating the environmental and economic sustainability of energy from anaerobic digestion of different feedstocks in Turkey

Anaerobic digestion (AD) of organic wastes is recognised as a promising solution to reduce GHG emissions owing to its multiple functions, such as energy supply, waste treatment and production of organic fertiliser. Being the 7th largest country for agricultural production, Turkey produces large amounts of agricultural wastes and livestock manure, most of which is underutilised or managed in unsustainable ways causing adverse effects on the environment. Thus, this study aims to evaluate the environmental and economic sustainability of heat and power cogenerated through AD of different types of waste in Turkey. For this purpose, life cycle assessment (LCA) and life cycle costing (LCC) have been carried out for biogas plants utilising animal manure (cattle and chicken), organic wastes (vegetable and slaughterhouse wastes) and crop maize silage. Using feedstocks with high solid content and biogas yield (i.e., organic wastes and chicken manure) leads to lower environmental impacts than for the current energy systems (heat from natural gas and electricity from the grid) in 15 out of 17 categories considered, including climate change. On the other hand, due to the lower organic-matter content and biogas yield, bioenergy from cattle slurry (with or without maize silage co-digestion) has 40–70 % higher impacts than the current energy systems for climate change, photochemical oxidants formation and particulates, in addition to a much higher acidification and marine eutrophication (>4 times), but still performing better in nine environmental categories. The digestate application is the main hotspot for the majority of impacts for all feedstocks. However, the credits from the displacement of mineral fertilisers offset most of these impacts fully, providing net savings in eight impacts. The LCC are net-negative, ranging from −$6.1 to −$15.3 per MWhe+th for all the feedstocks due to the incentives for electricity. Levelised costs of energy conversion are also substantially lower than that of natural-gas heat and grid electricity, except electricity generated via the AD of cattle slurry (with or without maize silage). At the national level, if all available chicken manure and 60 % of cattle manure are co-digested with organic wastes for heat and electricity production, this could potentially save 12.2 Mt CO2 eq./yr (or 2.5 %) of annual GHG emissions and $1.3 bn (or 10 %) of fossil-fuel import costs.