Enhanced Biogas Production from Nanoscale Zero Valent Iron-Amended Anaerobic Bioreactors

Abstract

Addition of nanoscale zero valent iron (NZVI) to anaerobic batch reactors to enhance methanogenic activity is described. Two NZVI systems were tested: a commercially available NZVI (cNZVI) slurry and a freshly synthesized NZVI (sNZVI) suspension that was prepared immediately before addition to the reactors. In both systems, the addition of NZVI increased pH and decreased oxidation/reduction potential compared with unamended control reactors. Biodegradation of a model brewery wastewater was enhanced as indicated by an increase in chemical oxygen demand removal with both sNZVI and cNZVI amendments at all concentrations tested (1.25-5.0 g Fe/L). Methane production increased for all NZVI-amended bioreactors, with a maximum increase of 28% achieved on the addition of 2.5 and 5.0 g/L cNZVI. Addition of bulk zero-valent iron resulted in only a 5% increase in methane, indicating the advantage of using the nanoscale particles. NZVI amendments further improved produced biogas by decreasing the amount of CO released from the bioreactor by approximately 58%. Overall, addition of cNZVI proved more beneficial than the sNZVI at equal iron concentrations, due to decreased colloidal stability and larger effective particle size of sNZVI. Although some have reported cytotoxicity of NZVI to anaerobic microorganisms, work presented here suggests that NZVI of a certain particle size and reactivity can serve as an amendment to anaerobic digesters to enhance degradation and increase the value of the produced biogas, yielding a more energy-efficient anaerobic method for wastewater treatment.

Comparison of enhancement of anaerobic digestion of waste activated sludge through adding nano-zero valent iron and zero valent iron

“…Such different effects of NZVI on CH 4 production were also reported in previous studies. Carpenter et al 33 reported that 1 g L À1 NZVI and 1.25 g L À1 NZVI dramatically stimulated methanogenesis compared with controls [a 3.7-fold (on day 21) and 10.7% increase in methane production, respectively]. However, adding NZVI at a high dosage could inhibit methanogenesis, 16,23 e.g., 69.0% reduction of methane production was observed on addition of 1.68 g L À1 NZVI to anaerobic sludge.…”

A review of the environmental implications of in situ remediation by nanoscale zero valent iron (nZVI): Behavior, transport and impacts on microbial communities

“…Thus, in addition to enhance CH 4 production, this process increases the quality and value of the biogas by fixing CO 2 . Although substantial enhancement in CH 4 production in the range of 28 to 61% (Carpenter et al, 2015; Hu et al, 2015; Su et al, 2013) is usually achieved in the presence of nZVI, one study showed that high concentration of nZVI could also be detrimental to methanogens. Indeed, at higher nZVI concentrations, the faster release of hydrogen gas increases the hydrogen gas partial pressure at levels that favor hydrogenotrophic anaerobic processes, such as homoacetogenesis, over methanogenesis.…”

“…Although applications of nZVI beyond surface and subsurface remediation are extremely limited, organic waste stabilization, odor abatement, and biogas production are also referenced (Carpenter et al, 2015; Su et al, 2013). In this section all applications of nZVI are considered in order to understand nZVI life cycle, and evaluate its potential routes from entrance points to untargeted environments (Mitrano et al, 2015; Nowack, 2009; Som et al, 2010).…”

“…More recently, its use for wastewater remediation (Fu et al, 2014; Grieger et al, 2010; Mueller et al, 2012), and anaerobic digestion process enhancement (Carpenter et al, 2015; Hu et al, 2015) has also received growing attention. Due to its reduced size, nZVI has a higher reactivity towards a broad range of contaminants, including halogenated compounds, nitrate, phosphate, polycyclic aromatic hydrocarbons, and heavy metals (Fu et al, 2014; Mueller et al, 2012; Tosco et al, 2014; Wei-xian, 2003), and a higher mobility compared to its microscale counterpart.…”

Upgrading continuous H2gas recovery from rice straw hydrolysate via fermentation process amended with magnetite nanoparticles

“…Nanoparticles (NPs) have diameter range from 1 to 100 nm surpassed larger scale at biological applications as a result of their higher surface area . Metal NPs provide slow releasing rate of metallic ions along AD process; the safe concentration of these ions valorizes bacterial reproduction.…”