Box-Behnken design and life cycle assessment for nickel oxide nanoparticles application in biomethane production

[Display omitted] •NiONPs enhanced biogas and biomethane production from green algae C. linum.•The Box-Behnken design was applied to define the optimum biomass and NiONPs levels.•The supreme biomethane generation (94.86 mL/g VS) was achieved by the addition of NiONPs.•LCA was used to estimate the environmental influence of NiONPs on biogas generation. The optimization of the three parameters process was assessed as a controlling factor for the optimum generation of biogas and biomethane by Response Surface Methodology (RSM) using green algae Cheatomorpha linum (C. linum) as the substrate. The three factors, biomass amount, Nickel oxide nanoparticles (NiONPs) dosage and digestion time, were assessed and optimized by RSM using Box-Behnken design (BBD) to define their optimum level. The effectiveness of NiONPs with different concentrations as an improver for biogas and biomethane generation from C. linum was studied. BET, FTIR, TGA, XRD, and TEM were used to characterize the NiONPs. To evaluate the sustainability of using NiONPs for biomethane production, the environmental influences accompanying the process were computed from a life cycle assessment (LCA) perspective. Furthermore, the energy balance of biogas generation via co-digestion of C. linum and cow-manure using different dosages of NiONPs was estimated. The kinetic investigation proved that the modified Gompertz model fit the working results satisfactorily, with R2 ranging between 0.983 and 0.995 and 0.837 to 0.972 for biogas and biomethane production, respectively. The results recommended that adding NiONPs at doses of 5 mg/L and 15 mg/L to C. linum (1 and 1.5 g) gives rise to a significant increase in biogas yield compared to all other treatments (384 and 380 mL/g VS). The maximum biomethane generation (94.86 mL/g VS) was achieved by the addition of NiONPs at doses of 15 mg/L to C. linum (1.5 g). LCA and energy analysis results showed that incorporating NiONPs with cow manure and C. linum remarkably reduced the negative environmental impacts, including global warming potential (GWP), and enhanced energy recovery compared to the case without NiONPs.