Comparison of biomethane production process using two different types of reactors from dairy wastewater

The production of biomethane (Bio-CH4) from dairy wastewater was evaluated using two types of reactors: an upflow anaerobic sludge blanket (UASB) reactor and a batch reactor, using dairy wastewater, anaerobic sludge (as inoculum), and Opuntia imbricata (as biomass substrate). The latter is a cactus known as coyonoxtle and is considered an invasive plant in northern Mexico. The wastewater was characterized in accordance with NOM-001-SEMARNAT-2021. The UASB reactor having a capacity of 4.5 L, was charged with 350 mL of sludge, 24 g of Opuntia imbricata, and 3.5 L of dairy wastewater (20.1 g/L of O2) at pH 7.0. Batch reactors with a volume of 120 mL, were charged with 72 mL of dairy wastewater (20.1 g/L of O2), 8 mL of sludge, and 3 pieces of O. imbricata. The results of the UASB reactor: Total specific production was 21.2 mmol of Bio-CH4 and an efficiency in the degradation of organic matter of 70.7%, with a hydraulic retention time of 4.8 h and a total duration of 720 h. For the batch reactors: Total specific production was 11.6 mmol of Bio-CH4 and 97.95% efficiency in the removal of organic matter, with a total duration of 192 h. The results showed an economic, efficient and sustainable way of producing Bio-CH4.