In-situ methane enrichment in continuous anaerobic digestion of pig slurry by zero-valent iron nanoparticles addition under mesophilic and thermophilic conditions

Historical Perspective of the Addition of Magnetic Nanoparticles Into Anaerobic Digesters (2014-2021)

“…Other hypotheses point that responsible for methane improvement is not only the presence of iron but its state of oxidation, with can happen with magnetite but it is more evident when using zero valent iron NPs which is the most reduced oxidation state of iron. In this case, the effect of the reduction of organic matter to methane has been observed when using materials such as wastewater sludge (Barrena et al, 2021) and pig manure (Cerrillo et al, 2021). These studies highlight the iron state of oxidation as a key role in the enhancement of methane in the anaerobic digestion process, even at thermophilic conditions.…”

Enhancement of Anaerobic Digestion with Nanomaterials: A Mini Review

“…Cu and Fe oxides Biogas and methane increase Batch, iron and copper NPs were synthesized by hydrothermal treatment of corn straw [16] Co ferrate Biogas and methane increase Batch, NP addition enhanced H 2 /CO 2 methanogenesis pathway. Excess NPs revealed negative effects [17] Cu and Fe oxides Biogas and methane increase Batch, review of microbial mechanisms [18] Fe zero-valent Biogas increase and methane enrichment Continuous, increase in the biodegradability of fibers due to the presence of NPs [19] Zn oxide Biogas and methane increase Batch, inhibition observed at high ZnO NPs concentrations [20] Fe zero-valent Methane enrichment Continuous, increase in the methane content of biogas, under both thermophilic and mesophilic conditions [12] Ti and Fe oxides Biogas and methane increase Semicontinuous, NPs and salts boosted methane production for lignocellulosic materials [21] Fe zero-valent Methane enrichment Semicontinuous, the increase in the oxidation state of NPs seemed to be related to the loss of effect over time [11] Ti oxide Biogas increase and fast hydrolysis and acidogenesis Batch, hydrolysis and acidogenesis rates have been enhanced due to the addition of NPs [22] Fe oxide Biogas increase and inhibition of H 2 S production Batch, high rate of H 2 S production decrease (from 50 to 80%) [23] Fe zero-valent Methane increase and better stability Batch, NPs promoted the acidogenesis-acetogenesis without acidification [24] Table 2. Examples of studies using other nanomaterials and their effect on anaerobic digestion.…”

“…It is also hypothesized that the state of oxidation of iron NPs is a key parameter for biogas or methane increase. Some studies dealing with wastewater sludge [11] and pig manure [12], studied in detail in the oxidation state, highlighted the iron state of oxidation as a promoter for increasing methane in anaerobic digestion. A schematic drawing of the mechanisms of enhancement is presented in Figure 2.…”

“…In addition, it is evident that batch tests can only simulate mixed reactors [43] but not more complex anaerobic reactors [44]. This is the reason why most recent anaerobic digestion studies in which methane yields are used to reproduce full-scale reactors are performed in a continuous mode of operation [12,45,46]. Other possibilities of operation (for instance, semi-batch or fed-batch) are rarely used in pilot of full-scale anaerobic digesters.…”

“…On the one hand, most studies published in the batch mode report significant increases in biogas production, which is the typical way to interpret this effect [9,10]. However, several recent studies carried out in the continuous mode reported a similar production of biogas, with this biogas being considerably enriched in methane content when some NPs were added [11,12]. In times of a worldwide energy crisis, this result is particular interesting, as it supposes an in situ biogas upgrading (i.e., methane enrichment) that makes this renewable energy closer to the natural gas produced or obtained from fossil fuels.…”