Surface properties of activated sludge-derived biochar determine the facilitating effects on Geobacter co-cultures

Abstract

Biochar has been reported to facilitate direct interspecies electron transfer (DIET) in co-cultures between Geobacter metallireducens and Geobacter sulfurreducens, a model defined co-culture system. In this study, the biochar derived from the activated sludge with different pyrolysis temperature was added to the co-cultures, the ethanol metabolism rates (Re) and succinate production rates (Rs) of co-culture with biochar-800 were 1.05- and 1.42-fold higher than that without addition. The results suggested that the conductivity of the biochar did not correlate with the facilitating effect of the biochar on the co-culture metabolism. Furthermore, the surface functional group and surface charge of biochar may also influence the facilitating effect on the interspecies electron transfer between the two Geobacter cells. Based on these results, it supported that the electron transfer depending on the charging and discharging process of the surface functional groups might play a major role in facilitating the direct electron transfer process by the biochar derived from activated sludge here. This study could shed light on the better understanding of the bacteria-biochar electron transfer system and the potential utilization of the biochar in the environmental wastewater treatments.

Extracellular Electron Uptake by TwoMethanosarcinaSpecies

“…However, similar to previous reports (Zhang et al, 2018), Geobacter could partially convert ethanol to acetate using GAC as insoluble electron acceptor (Fig. S5; Van Der Zee et al, 2003; Zhang et al, 2018), likely until it reaches its maximum capacitance of 40 F/g (Zhang et al, 2009). Co-cultures of G. metallireducens and M. horonobensis could not carry interspecies H 2 transfer because G. metallireducens is a strict respiratory microorganism which cannot ferment ethanol to generate H 2 (Shrestha et al, 2013) and because M. horonobensis is unable to use H 2 as electron donor for their metabolism (Shimizu et al, 2010).…”

Extracellular Electron Uptake by Two Methanosarcina Species

“…Single species controls with GAC showed that ethanol could not be converted to methane by the methanogen or the syntroph alone ( Figure 6C and Figure S5). However, similar to previous reports (Zhang P. et al, 2018b), Geobacter could partially convert ethanol to acetate using GAC as insoluble electron acceptor ( Figure S5 ;Van Der Zee et al, 2003;Zhang P. et al, 2018b), likely until it reaches its maximum capacitance of 40 F/g (Zhang et al, 2009). Co-cultures of G. metallireducens and M. horonobensis could not carry interspecies H 2 transfer because G. metallireducens is a strict respiratory microorganism which cannot ferment ethanol to generate H 2 (Shrestha et al, 2013) and because M. horonobensis is unable to use H 2 as electron donor for their metabolism (Shimizu et al, 2010).…”

Multi-walled carbon nanotubes accelerate interspecies electron transfer between Geobacter cocultures

“…3, Fig. S3, S4, S5 and S6) further revealed that Geobacter cells were distributed on the MWCNTs aggregate surface rather than forming Geobacter aggregates as previously reported [18], yielding similar results to granular activated carbon (GAC), carbon cloth, and biochar added in the cocultures for accelerating DIET [12,17,21,22]. DIET enhancement effect of these materials was due to their excellent conductivity that supports electron transfer.…”

“…Protein concentrations were determined by BCA method according to the manufacturer's protocol (Solarbio, China). Conductivity of the MWCNTs was determined with the four-probe method by a powder resistivity tester (ST2722, Suzhou Jingge, China) [17].…”

“…Direct contact between bacteria with the capacity for extracellular electron transfer and MWCNTs is precondition for promoting IET. Cells in the cocultures exist in one of two types: planktonic, freely existing in the solution, and sessile, attached to the surface of MWCNTs [17]. Thus, we compared the total biomass concentration at the end of the incubation to determine protein concentration.…”