Influence of Combined Mechanical, Chemical, and Thermal Pretreatment Methods and Concentration Control on Biomethane Production from Opuntia ficus-indica Waste

The waste by the pruning Opuntia ficus-indica (OFI) cactus crop is considered a substrate for generating biogas. However, the physicochemical composition and the lignocellulosic fibers, difficulty the anaerobic digestion (AD) process, which generates biogas with a low yield of CH4. The present study implemented the application of combined pretreatments techniques: the mechanical (wet grinding), chemical (alkaline), thermal (modified basic hydrolysis), and organic load control in the OFI waste to control the parameters that influence AD are particle size, pH, residue solubility, and organic load control to evaluate the increase of the biogas. An orthogonal Taguchi L-8 design experimental was employed to test the biochemical potential methane (BMP) assay. The better combination of pretreatments was mechanical level 1 (M-1 = 0.5-0.8 mm), chemical level 2 (pH(2) = 8.5), thermal level 1 (T-1 = 30 degrees C), and concentration level 2 (C-1 = 30 gCODL(-1)) resulted in the most significant increase of CH4 in the biogas with a production of 755.31 NmLCH(4). The results show that the combined pretreatments in the OFI waste increased by 160% the methane production with a yield of 201.04 NmLCH(4)gVS(-1) higher than the waste OFI without pretreatment (21.77 NmLCH(4)gVS(-1)). The equivalent energy potential of the waste was 5.96 GJton(-1) and 33.98 GJ ha(-1) yr(-1) OFI waste. The combined pretreatments in the OFI waste improve the quality of the biogas and solve the environmental problem that is the inadequate management of the waste.