Harnessing cactus biomass for biogas and biofertilizer production under temporal fermentation strategies

Some cactus species are invasive, requiring innovative strategies for control. We evaluated the potential and optimization strategies of cactus (Opuntia spp.) for biogas production. Treatments included: (1) cattle dung + cactus on day 0, (2) cattle dung + cactus on day 0 + cactus replacement with cattle dung once a cactus starting on day 21 + cactus replacement with cattle dung once a week, (5) pre-fermented cattle dung + cactus starting on day 42, (6) pre-fermented cattle dung + cactus starting on day 42 + cactus replacement with cattle dung once a week, and (7) cactus only and (8) cattle dung only controls. Treatments were allocated to a randomized complete block design (RCBD) with three replicates for 20 weeks. Effluent from treatments 5 through 8 were applied at 0, 9.5, 18.9, and 28.4 g DM pot-1 in a RCBD with three replicates to evaluate ryegrass (Lolium multiflorum) growth in a greenhouse. Cattle dung pre-fermentation combined with weekly cactus replacement maintained pH within the optimal 6.5-7.7 range for methanogens and produced the greatest cumulative CH4 (102 g). Ryegrass shoot and root biomass were not different among the effluents from pre-fermented cattle dung, but were greater than those of cactus-only and control.