Abstract
In the present study, three process parameters optimization were assessed as controlling factors for the biogas and biomethane generation from brown algae Cystoceira myrica as the substrate using RSM for the first time. The biomass amount, Co(3)O(4)NPs dosage, and digestion time were assessed and optimized by RSM using Box-Behnken design (BBD) to determine their optimum level. BET, FTIR, TGA, XRD, SEM, XPS, and TEM were applied to illustrate the Co(3)O(4)NPs. FTIR and XRD analysis established the formation of Co(3)O(4)NPs. The kinetic investigation confirmed that the modified model of Gompertz fit the research results satisfactorily, with R(2) ranging between 0.989-0.998 and 0.879-0.979 for biogas and biomethane production, respectively. The results recommended that adding Co(3)O(4)NPs at doses of 5 mg/L to C. myrica (1.5 g) significantly increases biogas yield (462 mL/g VS) compared to all other treatments. The maximum biomethane generation (96.85 mL/g VS) was obtained with C. myrica at (0 mg/L) of Co(3)O(4)NPs. The impacts of Co(3)O(4)NPs dosages on biomethane production, direct electron transfer (DIET) and reactive oxygen species (ROS) were also investigated in detail. The techno-economic study results demonstrate the financial benefits of this strategy for the biogas with the greatest net energy content, which was 2.82 kWh with a net profit of 0.60 USD/m(3) of the substrate and was produced using Co(3)O(4)NPs (5 mg/L).