Techno-economic model to appraise the use of cattle manure in biodigesters in the generation of electrical energy and biofertilizer

Abstract

The increase in dependence on electrical energy has become critical during the last decades. This paper proposes a model to evaluate the technical and economic viability of electrical energy and biofertilizer generation from cattle manure in biodigesters. In the technical phase, the relevant aspects of this process were investigated, such as raw material (type and quantity), the influence of external temperature, the hydraulic retention time of the system, the amount of energy generated and the reduction of energy costs. In the first step of the economic phase, the Investment Projects (IPs) were ranked under the Net Present Value (NPV) criterion. Next, the deterministic Expanded Multi-Index Methodology (EMIM) was applied on the IPs with positive NPV. Finally, the IPs with high sensitivity were analyzed through Monte Carlo Simulation. We validated the model on a rural property in Southeast Parana state in Brazil. Three biodigester systems were compared under ten power levels: cattle manure mono-digestion (Project A), cattle manure/corn co-digestion (60:40 mixture - Project B) and cattle manure/grass co-digestion (60:40 mixture - Project C). The production of energy in the three evaluated systems presented economic advantages, as the size of the system increases due to the economy of scale. Therefore, the combination of system biodigester and power was essential to ensure the project viability.