Impacts of iron oxide and titanium dioxide nanoparticles on biogas production: Hydrogen sulfide mitigation, process stability, and prospective challenges.

Anaerobic digestion for biogas production is one of the most used technology for bioenergy. However, the adoption of nanoparticles still needs further studies. Therefore, this study was designed to examine the effect of metal oxide nanoparticles (MONPs) at four different concentrations in two different combinations, 20 (R1) and 100 (R2) mg/L for Fe2O3, 100 (R3) and 500 (R4) mg/L for TiO2, and a mixture of Fe2O3 and TiO2 at rates of 20, 500 (R5) and 100, and 500 (R6), on hydrogen sulfide (H2S) mitigation, biogas, and methane (CH4) yield during the anaerobic digestion of cattle manure (CM) using an anaerobic batch system. The results showed that H2S production was 2.13, 2.38, 2.37, 2.51, 2.64, and 2.17 times lower than that of the control (R0), respectively, when the CM was treated by the aforementioned MONPs. Additionally, biogas and CH4 production were 1.09 and 1.105, 1.15 and 1.191, 1.07 and 1.097, 1.17 and 1.213, 1.10 and 1.133, and 1.13 and 1.15 times higher than those of R0 when R1, R2, R3, R4, R5, and R6 were supplemented with MONPs, respectively. The highest specific production of biogas and CH4 was 336.25 and 192.31 mL/gVS, respectively, which was achieved by R4 supplemented with 500 mg/L TiO2 NPs, while the corresponding values in the case of R0 were 286.38 and 158.55 mL/gVS.

Prospects for biogas production and H2S control from the anaerobic digestion of cattle manure: The influence of microscale waste iron powder and iron oxide nanoparticles.

Improving the quality and quantity of biogas usually requires pre-treatment to maximize methane yields and/or post-treatment to remove H2S, which involves considerable energy consumption and higher costs. Therefore, this study proposes a cost-effective method for the enhanced anaerobic digestion (AD) of dairy manure (DM) without pre/post-treatment by directly adding waste iron powder (WIP) and iron oxide nanoparticles (INPs) to batch digesters. The results showed that the addition of iron in the form of microscale WIP (generated from the laser cutting of iron and steel) at concentrations of 100 mg/L, 500 mg/L, and 1000 mg/L improved methane yields by 36.99%, 39.36%, and 56.89%, respectively. In comparison, the equivalent dosages of INPs improved yields by 19.74%, 18.14%, and 21.11%, respectively. Additionally, the highest WIP dose (1000 mg/L) achieved the maximum improvement in the rate of hydrolysis (k), which was 1.25 times higher than in control reactions, and a maximum biomethane production rate (Rmax) of 0.045 L/gVS/d according to kinetic analysis models (i.e., first-order and the Gompertz kinetic models). The rate of H2S production was also significantly reduced (by 45.20%, 58.16%, and 77.24%) using the three WIP concentrations in comparison with INPs (which achieved reductions of 33.59%, 46.30%, and 53.52%, respectively). Therefore, the direct mixing of WIP with cattle manure is proposed as a practical and economical means of addressing complex and high-cost pre- and post-treatments that are otherwise required in the digestion process.

Potential of biogas production from manure of dairy cattle fed on natural soil supplement rich in iron under batch and semi-continuous anaerobic digestion.

This study provides a novel method for improving the anaerobic digestion (AD) of Holstein dairy manure (HDM) by the direct addition of Mineraso (MnS), a natural soil-derived supplement, to the feed of Holstein dairy cattle (HDC). MnS is chiefly composed of approximately 69.08% Fe3O4 and was supplemented at rates of 0 (F1), 25 (F2), and 50 (F3) g/head of HDC/d for two months. The HDM was then examined for non-absorbed iron prior to the batch and semi-continuous bench AD experiments. The results revealed that MnS enhanced CH4 generation in F2 and F3 by 25% and 42%, respectively, in the batch experiments compared to that of F1. Additionally, the gas yield improved in F2 and F3 by 45% and 66%, respectively, over the control after 7 d in the bench experiments. Therefore, supplementing animals with MnS represents a sustainable and economic approach to enhancing CH4 yields.