Reduction of S0 deposited on electroactive biofilm under an oxidative potential

Alternating current-powered bioelectrode for enhanced sulfide removal from sulfide-rich organic effluent

Conventional biological wastewater treatments often struggle with efficient sulfide removal. This study presents an innovative and sustainable approach using an alternating current (AC)-powered bioelectrode to facilitate periodic microbial oxidation and reduction for sulfide removal from sulfide-rich organic effluents. The AC bioelectrode addressed the drawbacks of conventional direct current (DC) systems, demonstrating 93.2 % sulfide removal, 64.5 % elemental sulfur production and 75.8 % chemical oxygen demand removal, coupled with a 25 % decrease in energy consumption. AC stimulation mitigated elemental sulfur accumulation on the electrode surface, promoted biofilm colonization, and enhanced bidirectional electrocatalytic activity, thereby elevating active biomass and electron utilization efficiency. Additionally, AC bioelectrode enriched functional microbiomes capable of sulfur-oxidizing, sulfur-reducing, and electron-transport capacities, as confirmed by enzyme gene expression profiling. This study offers an efficient, resource-efficient, and sustainable solution to treating sulfide-rich organic effluents.

Dual-purpose elemental sulfur for capturing and accelerating biodegradation of petroleum hydrocarbons in anaerobic environment

Hydrophobic organic pollutants in aqueous environments are challenging to biodegrade due to limited contact between microorganisms, the pollutants and the electron acceptor, particularly under anaerobic or anoxic conditions. Here, we propose a novel strategy that uses inexpensive, dual-function elemental sulfur (S0) to enhance biodegradation. Using petroleum hydrocarbons as the target pollutants, we demonstrated that hydrophobic and nonpolar S° can concentrate hydrocarbons while simultaneously serving as an electron acceptor to enrich hydrocarbon-degrading bacteria. The permeable reactive barrier filled with S0 effectively removed petroleum hydrocarbons. In addition to rapid adsorption, we discovered, for the first time, that petroleum hydrocarbons underwent efficient biodegradation through the reduction of S0. Specifically, n-alkanes were degraded by 80 % to 90 % and polycyclic aromatic hydrocarbons by 40 % to 95 %. These degradation rates were 17 % to 30 % and 26 % to 43 % higher, respectively, compared to those observed without S0. Consecutive subcultures combined with untargeted metabolomics analysis revealed that bacteria capable of dissimilatory sulfur reduction enhanced the fermentation process. These bacteria provided electrons to the metabolic network, which facilitated the mineralization of petroleum hydrocarbons. Our findings highlight the significant potential of S° for removing hydrophobic organic pollutants in oxygen-free environments, demonstrate the feasibility of integrating adsorption, biodegradation, and electron supply to enhance pollutant removal.

Understanding the Tail Current Behavior of Electroactive Biofilms Realizes the Rapid Measurement of Biochemical Oxygen Demand

The use of microbial electrochemical sensors, with electroactive biofilms (EABs) as sensing elements, is a promising strategy to timely measure the biochemical oxygen demand (BOD) of wastewater. However, accumulation of Coulombic yield over a complete degradation cycle is time-consuming. Therefore, understanding the correlation between current output and EAB metabolism is urgently needed. Here, we recognized a tail stage (TS) on a current-time curve according to current increase rate─a period with the least electron harvesting efficiency. EAB adopted a series of metabolic compensation strategies, including slow metabolism of residual BOD, suspended growth, reduced cell activity, and consumption of carbon storage polymers, to cope with substrate deficiency in TS. The supplementary electrons provided by the decomposition of glycogen and fatty acid polymers increased the Coulombic efficiencies of TS to >100%. The tail current produced by spontaneous metabolic compensation showed a trend of convergent exponential decay, independent of BOD concentration. Therefore, we proposed the TS prediction model (TSPM) to predict Coulombic yield, which shortened BOD measurement time by 96% (to ∼0.5 h) with deviation <4 mg/L when using real domestic wastewater. Our findings on current output in TS give insights into bacterial substrate storage and consumption, as well as regulation in substrate-deficient environment, and provide a basis for developing BOD sensors.