The biostimulation of anaerobic digestion with (semi)conductive ferric oxides: their potential for enhanced biomethanation

Abstract

The effect of biostimulation with ferric oxides, semiconductive ferric oxyhydroxide, and conductive magnetite on the anaerobic digestion of dairy wastewater was examined in a batch mode. The reactors supplemented with ferric oxyhydroxide (R2) and magnetite (R3) showed significantly enhanced biomethanation performance compared with the control (R1). The removal of chemical oxygen demand (COD) after 30 days was 31.9, 59.3, and 82.5% in R1, R2, and R3, respectively. The consumed COD was almost fully recovered as biogas in R2 and R3, while only 79% was recovered in R1. The total energy production as biogas was accordingly 32.2, 71.0, and 97.7 kJ in R1, R2, and R3, respectively. The reactors also differed in the acid formation profile with more propionate and butyrate found in R1 and more acetate found in R3. The enhanced biomethanation seems to be associated with variations in the bacterial community structure supposedly induced by the ferric oxides added. In contrast, no evident variation was observed in the archaeal community structure among the reactors. The potential electric syntrophy formed between Methanosaeta concilii-like methanogens and electroactive iron-reducing bacteria, particularly Trichococcus, was likely responsible for the enhanced performance. The stimulated growth of fermentative iron reducers may also have contributed by altering the metabolic characteristics of the bacterial communities to produce more favorable acidogenic products for methanogenesis. The overall results suggest the potential of biostimulation with (semi)conductive ferric oxides to enhance the rate and efficiency of the biomethanation of organic wastes. This seems to be potentially attractive, as increasing attention is being paid to the energy self-sufficiency of waste/wastewater treatment processes today.

Happy together: microbial communities that hook up to swap electrons

“…Promoting DIET might enhance the anaerobic digestion of organic wastes, one of the few proven, effective, large-scale bioenergy strategies. Many studies have now shown that adding materials known to facilitate DIET either to anaerobic digesters, or methanogenic enrichment cultures metabolizing important intermediates in anaerobic digestion, can accelerate the rate of methane production; increase the methane content of the gas produced; and/or stabilize the digestion to permit higher organic loading rates (Viggi et al, 2014;Baek et al, 2015;Li et al, 2015a, b;Xu et al, 2015;Yamada et al, 2015;Zhao et al, 2015;Zhuang et al, 2015a, b;Beckmann et al, 2016;Lee et al, 2016). None of these studies have directly demonstrated DIET with detailed studies of microbial metabolism, but DIET was inferred from enrichment of microorganisms known to participate in DIET and/or increased rates of methane production.…”

Carbon nanotubes accelerate methane production in pure cultures of methanogens and in a syntrophic coculture

“…Interestingly, it appears that conductive materials, including graphite particles (Kato et al ., ; Zhao et al ., ), granular activated carbon (Liu et al ., ; Rotaru et al ., ; Xu et al ., ; Dang et al ., ; Lee et al ., ), biochar (Chen et al ., ; Zhao et al ., ), graphene (Tian et al ., ), carbon nanotubes (CNT) (Li et al ., ; Zhang and Lu, ), carbon felt (Xu et al ., ) and carbon cloth (Chen et al ., ; Zhao et al ., ; Lei et al ., ), but also iron oxides as magnetite (Kato et al ., ; Cruz Viggi et al ., ; Baek et al ., ; Zhuang et al ., ; Yamada et al ., ; Tang et al ., ; Yang et al ., ; Yin et al ., ; Zhang and Lu, ; Jing et al ., ) may increase the rate of electron transfer and may affect metabolic pathways in anaerobic microbial processes by promoting DIET, between bacteria and methanogens. In general, these materials are highly stable, have large surface area, good adsorption capacity and high electric conductivity (Figueiredo et al ., ; Van der Zee and Cervantes, ; Pereira et al ., ).…”

Microorganisms meet solid minerals: interactions and biotechnological applications

“…In both cases, it is likely that these iron oxides facilitated direct IET (electric syntrophy) between methanogens and electroactive iron-reducing bacteria, thus resulting in more acidogenic substrates (e.g. volatile fatty acids) for methanogenesis (Baek et al 2015;Ma et al 2015).…”