Economic and environmental implications of the development of <scp>UASB</scp> reactors in Mexico for sustainable industrial wastewater treatment

Abstract The objective of this work is to demonstrate that the inclusion of an up‐flow anaerobic sludge bed (UASB reactor) within an industrial wastewater treatment plant reduces the plant's investment and operating costs compared to a system based solely on conventional complete‐mix activated sludge (CMAS), operating under the same design principles within the Mexican standards. Furthermore, the economic feasibility of using biogas as an energy source is estimated based on the biogas flow rate produced and the H 2 S content that must be eliminated. Coupled anaerobic–aerobic processes increase energy efficiency in wastewater treatment compared to a purely aerobic plant. Results show that the advantages offered by this process arrangement, compared to the CMAS system for the highest COD concentration scenario, are the decrease in operation and maintenance costs (61%), lower investment (46%), and a decrease in excess sludge production (both in volume by 54% and in mass by 45%). Biogas production increases depending on the applied organic load. For a concentration of 4000 mg COD/l, biogas production was 178 m 3 /h ( T = 23°C, p = 0.8 atm) with a methane concentration of 68%. Therefore, if an internal combustion engine is incorporated, an electrical power production of 392 kW‐h/h is estimated which could cover the entire electrical demand of the plant (requiring 48 kW‐h/h) and have an energy surplus of 344 kW‐h/h, achieving negative carbon emissions. It is worth noting that using biogas as an energy source is not always feasible, as this depends on the payback time and, consequently, on the daily biogas production.