Synthesis, characterization, optimization and application of Pisum sativum peels S and N-doping biochars in the production of biogas from Ulva lactuca

This study assessed the usefulness of Pea Pisum sativum peels S-modified biochar (PPB–S) and Triethylenetetramine (TETA)-modified biochar (PPB-T) as improvers for biogas generation from green algae Ulva lactuca either individually or co-digested with Pea peels (PPs). BET, FTIR, TGA, XRD, XPS, SEM coupled with EDX were used to characterize the PPB-S and PPB-T biochars. EDX, FTIR, and XPS analyses proved the formation of sulphur and nitrogen groups on the surface of PPB-S and PPB-T. The kinetic study confirmed that the modified Gompertz model fits the experimental data satisfactorily, with R2 ranging between 0.948 and 0.991. The results suggested that adding 50 mg/L of PPB-S significantly increased the biogas production yield compared to all other studied treatments, either individually or in co-digestion with PPs. The extreme biogas production (498 mL/g VS) was formed when 50 mg/L of PPB-S was added to U. lactuca. According to Response surface methodology (RSM), the maximum biogas production among all experiments is 460.91 (ml/g VS), achieved for U. lactuca and PPB-S treatment corresponds to 54 days contact time and 50 mg/L of PPB-S dose. The direct electron transfer mechanism has been investigated in detail, and it is confirmed that conductive PPB-S can support electron transfer and promote methane production, as proved by the XPS and FTIR analyses, which the creation of sulphur groups on the PPB-S surface may propose. In this study, the use of PPB-S in biogas production aligns with the principles of a circular economy.