Addition of iron ore tailings to increase the efficiency of anaerobic digestion of pig manure: A technical and economic analysis

Abstract Anaerobic digestion (AD) stands out as an option for treating, transforming pig manure into renewable energy in the form of biogas and providing an organic substrate for agricultural use. However, methane variability and high operational expenses make it difficult to implement this technology in Brazil. This study analyses using iron ore tailings (IOTs) to optimize AD processes for generating biogas from pig manure. Mineralogical and toxicological analyses were carried out for the mining waste (MW) to assess its applicability in the process. The manure was anaerobically digested in sequential batch reactors with varied IOTs dosages, ranging between 0 kg m and 3, 1.56 kg m-3, 3.12 kg m-3, and 4.69 kg m-3. The influence these additives had on the process was analysed through examination of the reductions in organic constituents, as well as the biogas production and composition. Furthermore, an economic feasibility analysis was conducted for the entire process using uncertainty analysis. The results indicated that the elements Fe, K, Si, Al, Mg, Ca, Na, and P are present in the additive. Maximum production was measured at 8.41 × 10-2 m3 CH4 kg-1 in the substrate. Moreover, there were reductions of 77% and 81.40% in the organic load (COD and BOD5,20) for the maximum applied dosage. The levelized cost of electricity (LCOE) ranged from 80 US$ to 90 US$ MWh-1 for scenarios with 50,000- and 200,000-head operations. A total of 742 and 10,135 scenarios for 200,000-head operations resulted in a decrease of 23.24% and 12.28% in relation to the maximum market value.