The promotion of the atrazine degradation mechanism by humic acid in a soil microbial electrochemical system.

The enhancing effects of anodes on the degradation of the organochlorine pesticide atrazine (ATR) in soil within microbial electrochemical systems (MES) have been extensively researched. However, the impact and underlying mechanisms of soil microbial electrochemical systems (MES) on ATR degradation, particularly under conditions involving the addition of humic acids (HAs), remain elusive. In this investigation, a soil MES supplemented with humic acids (HAs) was established to assess the promotional effects and mechanisms of HAs on ATR degradation, utilizing EEM-PARAFAC and SEM analyses. Results revealed that the maximum power density of the MES in soil increased by 150%, and the degradation efficiency of ATR improved by over 50% following the addition of HAs. Furthermore, HAs were found to facilitate efficient ATR degradation in the far-anode region by mediating extracellular electron transfer. The components identified as critical in promoting ATR degradation were Like-Protein and Like-Humic acid substances. Analysis of the microbial community structure indicated that the addition of HAs favored the evolution of the soil MES microbial community and the enrichment of electroactive microorganisms. In the ATR degradation process, the swift accumulation of Hydrocarbyl ATR (HYA) was identified as the primary cause for the rapid degradation of ATR in electron-rich conditions. Essentially, HA facilitates the reduction of ATR to HYA through mediated bonded electron transfer, thereby markedly enhancing the efficiency of ATR degradation.

Fulvic acid more facilitated the soil electron transfer than humic acid.

Humus substances (HSs) participate in extracellular electron transfer (EET), which is unclear in heterogeneous soil. Here, a microbial electrochemical system (MES) was constructed to determine the effect of HSs, including humic acid, humin and fulvic acid, on soil electron transfer. The results showed that fulvic acid led to the optimal electron transfer efficiency in soil, as evidenced by the highest accumulated charges and removal of total petroleum hydrocarbons after 140 days, with increases of 161% and 30%, respectively, compared with those of the control. However, the performance of MES with the addition of humic acid and humin was comparable to that of the control. Fulvic acid amendment enhanced the carboxyl content and oxidative state of dissolved organic matter, endowing a better electron transfer capacity. Additionally, the presence of fulvic acid induced an increase in the abundance of electroactive bacteria and organic degraders, extracellular polymeric substances and functional enzymes such as cytochrome c and NADH synthesis, and the expression of m tr C gene, which is responsible for EET enhancement in soil. Overall, this study reveals the mechanism by which HSs stimulate soil electron transfer at the physicochemical and biological levels and provides basic support for the application of bioelectrochemical technology in soil.

Combined phyto-microbial-electrochemical system enhanced the removal of petroleum hydrocarbons from soil: A profundity remediation strategy.

The soil contaminated by petroleum hydrocarbons has been a global environmental problem and its remediation is urgent. A combined phyto-microbial-electrochemical system (PMES) was constructed to repair the oil-contaminated soil in this study. During the 42-day operation time, a total petroleum hydrocarbons (TPHs) of 18.0 ± 3.0% were removed from PMES, which increased by 414% compared with the control group (CK1). The supervision of physicochemical properties of pore water in soil exhibited an enhanced microbial consumption of the total organic carbon (TOC) and N source under the applied potential with the generation of bio-current. The microbial succession indicated that the Dietzia, Georgenia and Malbranchea possibly participated in the degradation and current output in PMES. And a collaborative network of potential degrading microorganisms including unclassified norank_f__JG30-KF-CM45 (in Chloroflexi), Dietzia and Malbranchea was discovered in PMES. While the functional communities of microorganism were re-enriched with the reconstructed interactions in the system which was started with the sterilized soil (S+MEC). The superiority of TPHs degradation in S+MEC compared to P + CK2 (removing the electrochemical effect relative to CK1) revealed the key role of external potential in regulating the degradation microflora. The study provided a strategy of the potential regulated phyto-microbial interaction for the removal of TPHs.