Regulation of the autochthonous microbial community in excess sludge for the bioconversion of carbon dioxide to acetate without exogenic hydrogen

A novel strategy to promote sludge solubilization and short-chain fatty acid production by coupling thermal hydrolysis and sodium thiosulfate pretreatment

Thermal hydrolysis (TH) technology is promising for sludge pretreatment, but the high cost and the generation of refractory substances limit its application. In this study, sodium thiosulfate (STS) was innovatively combined with TH pretreatment to improve the anaerobic fermentation efficiency of sludge. TH-STS pretreatment (140 °C, 0.132 g/g TSS) increased sludge solubility by 33.4 % and increased short-chain fatty acid (SCFA) production to 1.86 times that of the control group. TH effectively stripped the extracellular polymeric substances, and STS subsequently lysed the cells through its reducing power. TH-STS pretreatment promoted SCFA accumulation by increasing the activity of key enzymes and enriching hydrolyzing and acidifying bacteria. In addition, TH-STS pretreatment increased the activity of the electron transport system, which positively promoted the biotransformation of SCFAs. This study reveals that STS and TH pretreatment have a synergistic effect, providing an effective method for improving sludge pretreatment and resource recycling.

Enhanced corrosion of 2205 duplex stainless steel by Acetobacter aceti through synergistic electron transfer and organic acids acceleration

Acetobacter aceti is a microbe that produces corrosive organic acids, causing severe corrosion of industrial equipment. Previous studies have focused on the organic acid corrosion of A. aceti, but neglected the possibility that it has electron transfer corrosion. This study found that electron transfer and organic acids can synergistically promote the corrosion of 2205 duplex stainless steel (DSS). Electrochemical measurement results showed that corrosion of 2205 DSS was more severe in the presence of A. aceti. Surface analysis indicated a thick biofilm formed on the steel surface, with low pH and dissolved oxygen concentrations under the biofilm. Corrosion intensified when A. aceti lacked a carbon source, suggesting that A. aceti can corrode metals by using metallic substrates as electron donors, in addition to its acidic by-products.

Enhancement of nitrate reduction in microbial fuel cells by acclimating biocathode potential: Performance, microbial community, and mechanism

The enhancement of nitrate reduction in microbial fuel cells (MFCs) by acclimating biocathode potential was studied. An MFC system was started up, and measured by cyclic voltammetry to determine a suitable potential region for acclimating biocathode. The experimental results revealed that potential acclimation could efficiently improve denitrification performance by relieving the phenomenon of nitrite accumulation, and optimum performance was obtained at -0.4 V with a total nitrogen removal efficiency of 87.4 %. Subsequently, the characteristics of electron transfer behaviors were measured, suggesting that a positive correlation between nitrate reduction and the contribution of direct electron transfer emerged. Furthermore, a denitrification mechanism was proposed. The results indicated that potential acclimation was conducive to enhancing denitrifying enzyme activity and that the electron transport system activity could be increased by 5.8 times. This study provides insight into the electron transfer characteristics and denitrification mechanisms in MFCs for nitrate reduction at specific acclimatization potentials.

Integrated biogas upgrading and medium-chain fatty acids production for more efficient resource recovery

The conversion of carbon dioxide (CO2) from biogas into medium-chain fatty acids (MCFAs) represents an eco-friendly resource recovery approach to reduce dependence on fossil fuels and combat global climate change. This study presented the novel concept of integrated resource recovery by coupling biogas upgrading and MCFAs production for the first time. Initially, the impact of different initial ethanol concentrations on chain elongation was examined, determining that an ethanol concentration of 160 mmol/L maximized MCFAs yield at 45.7 mmol/L. Subsequently, using this optimal ethanol supply, the integrated strategy was implemented by connecting two bioreactors in series and maintaining continuous operation for 160-day. The results were noteworthy: upgraded bio-methane purity reached 97.6 %, MCFAs production rate and carbon-flow distribution reached 24.5 mmol/L d-1 and 76.1 %, respectively. In summary, these promising outcomes pioneer a resource recovery approach, enabling the high-value utilization of biogas and the conversion of CO2 into valuable bio-chemicals.