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Economical assessment of BIOGASNET at full-scale

One of the objectives of the LIFE BIOGASNET project was to assess the technical-economical feasibility of full-scale anoxic desulfurization of biogas. The report is based on the experience gained from operating the pilot-scale prototype installed at the Miramundo-Los Hardales environmental complex in Cádiz, Spain.
The pilot plant in Cádiz consisted of two main pieces of equipment: (i) a nitrification bioreactor that was fed with landfill leachate (which had a high ammonium concentration), and (ii) a washing tower coupled to a stirred tank bioreactor that was fed with the nitrified effluent and biogas from landfill wells. It was possible to nitrify the landfill leachate, obtaining a nitrate-rich effluent and achieving high H2S removal efficiencies from the landfill biogas. However, due to unfavorable site conditions, such as the high salinity of the leachate and the low concentrations of H2S in the biogas (<150 ppmv), was not the ideal scenario. Nevertheless, the experience gained from this study, along with previous studies, leads us to the conclusion that this process is possible under more favourable conditions. Therefore, the process can be implemented in a location with a biogas effluent flow rate of 6,200 m3 h-1 and an H2S concentration of 3,360 ppmv. The effluent to be nitrified is centrate from anaerobic digestion digestate, which will contain an ammonium concentration of 1,230 mg N-NH4+ L-1. The desulfurized biogas will be used to generate electricity and heat in a combined heat and power plant. This feasibility study shows that such a biogas plant has an electrical capacity of 14 MW.

Four different scenarios were evaluated to determine the economic viability of the project. Scenarios 1 to 3 involve desulfurizing biogas using the same BIOGASNET technology described above, but they differ in the way ammonium is treated. In scenario 1 (Sc.1), ammonium is completely converted to nitrate in the nitrification system (complete nitrification). In scenario 2 (Sc.2), all ammonium is transformed into nitrite through partial nitrification. In scenario 3 (Sc.3), there is no nitrification system since the effluent is already nitrified. Scenario 4 (Sc.4) studies a chemical method (chemical scrubber) to compare with the biological scenarios.
The total initial investment required for all scenarios would be between 657,637€ and 957,164€, with revenue inflow of €8.5M. The biggest difference among the four scenarios lies in the operating costs, where Sc.4 presents high values of 4,923,724€/year, while Scenarios 1 to 3

remain below 630,900€/year. Another difference between the scenarios is observed in the profitability indicators (see table below). In terms of net present value (NPV), internal rate of return (IRR), payback period (PBP), and levelized cost of return (LCOE), the biological processes (Scenarios 1 to 3) demonstrate greater economic viability compared to the chemical system (Sc.4).