Enhanced benzofluoranthrene removal in constructed wetlands with iron- modified biochar: Mediated by dissolved organic matter and microbial response

Anaerobic treatment of groundwater co-contaminated by toluene and copper in a single chamber bioelectrochemical system

Addressing the simultaneous removal of multiple coexisting groundwater contaminants poses a significant challenge, primarily because of their different physicochemical properties. Indeed, different chemical compounds may necessitate establishing distinct, and sometimes conflicting, (bio)degradation and/or removal pathways. In this work, we investigated the concomitant anaerobic treatment of toluene and copper in a single-chamber bioelectrochemical cell with a potential difference of 1 V applied between the anode and the cathode. As a result, the electric current generated by the bioelectrocatalytic oxidation of toluene at the anode caused the abiotic reduction and precipitation of copper at the cathode, until the complete removal of both contaminants was achieved. Open circuit potential (OCP) experiments confirmed that the removal of copper and toluene was primarily associated with polarization. Analogously, abiotic experiments, at an applied potential of 1 V, confirmed that neither toluene was oxidized nor copper was reduced in the absence of microbial activity. At the end of each experiment, both electrodes were characterized by means of a comprehensive suite of chemical and microbiological analyses, evidencing a highly selected microbial community competent in the biodegradation of toluene in the anodic biofilm, and a uniform electrodeposition of spherical Cu2O nanoparticles over the cathode surface.

Interaction of reed litter and biochar presences on performances of constructed wetlands

Constructed wetlands (CWs) are frequently used for effective biological treatment of nitrogen-rich wastewater with external carbon source addition; however, these approaches often neglect the interaction between plant litter and biochar in biochar-amended CW environments. To address this, we conducted a comprehensive study to assess the impacts of single or combined addition of common reed litter and reed biochar (pyrolyzed at 300 and 500 °C) on nitrogen removal, greenhouse gas emission, dissolved organic matter (DOM) dynamics, and microbial activity. The results showed that combined addition of reed litter and biochar to CWs significantly improved nitrate and total nitrogen removal compared with biochar addition alone. Compared to those without reed litter addition, CWs with reed litter addition had more low-molecular-weight and less aromatic DOM and more protein-like fluorescent DOM, which favored the enrichment of bacteria associated with denitrification. The improved nitrogen removal could be attributed to increases in denitrifying microbes and the relative abundance of functional denitrification genes with litter addition. Moreover, the combined addition of reed litter and 300 °C-heated biochar significantly decreased nitrous oxide (30.7 %) and methane (43.9 %) compared to reed litter addition alone, while the combined addition of reed litter and 500 °C-heated biochar did not. This study demonstrated that the presences of reed litter and biochar in CWs could achieve both high microbial nitrogen removal and relatively low greenhouse gas emissions.

Construction of an effective method combining in situ capping with electric field-enhanced biodegradation for treating PAH-contaminated soil at abandoned coking sites

The simultaneous application of in situ capping and electro-enhanced biodegradation may be a suitable method for ensuring the feasibility and safety of reusing abandoned coking sites. However, the capping layer type and applied electric field pattern may affect the efficiency of sequestering and removing pollutants. This study investigated changes in electric current, soil moisture content and pH, polycyclic aromatic hydrocarbon (PAH) concentration, bacterial number, and microbial community structure and metabolic function during soil remediation at abandoned coking plant sites under different applied electric field patterns and barrier types. The results indicated that polarity-reversal electric field was more conducive to maintaining electric current, soil properties, resulting in higher microbial number, community diversity, and functional gene abundance. At 21d, the mean PAH concentrations in contaminated soil, the capping layer's clean soil and barrier were 78.79, 7.56, and 1.57 mg kg-1 lower than those with a unidirectional electric field, respectively. The mean degradation rate of PAHs in the bio-barrier was 10.12 % higher than that in the C-Fe barrier. In the experiment combining a polarity-reversal electric field and a bio-barrier, the mean PAH concentrations in contaminated soil and the capping layer were 706.68 and 27.15 mg kg-1 lower than those in other experiments, respectively, and no PAHs were detected in the clean soil, demonstrating that the combination of the polarity-reversal electric field and the bio-barrier was effective in treating soil at abandoned coking plant sites. The established method of combining in situ capping with electro-enhanced biodegradation will provide technical support for the treatment and reuse of heavily PAH-contaminated soil at abandoned coking plant sites.

In-situ reactivation and reuse of micronsized sulfidated zero-valent iron using SRB-enriched culture: A sustainable PRB technology

Sulfidated zero-valent iron (S-ZVI) is an attractive material of permeable reactive barriers (PRBs) for the remediation of contaminated groundwater. However, S-ZVI is prone to be passivated due to the oxidation of reactive and conductive iron sulfide (FeSx) shell and the formation of inactive and non-conductive ferric (hydr)oxides, which serve as electron transfer barriers to hinder the electron flow from Fe° core to contaminants. This study thus proposed a novel approach for in-situ reactivation and reuse of micronsized S-ZVI (S-mZVI) in PRB using sulfate-reducing bacteria (SRB) enriched culture to realize long-lasting remediation of Cr(VI)-contaminated groundwater. S-mZVI were passivated after reactions with Cr(VI) due to the formation of electron transfer barriers (mainly inactive and non-conductive Fe(III) (hyd)oxides, which increased the polarization resistance from 16.38 to 27.38 kΩ cm2 and hindered the electron transfer from the Fe° core. Interestingly, the passivated S-mZVI was efficiently reactivated by providing the SRB-enriched culture and organic carbon within 12 h, and the Cr(VI) removal capacity of S-mZVI in the three use cycles increased to 37.4 mg Cr/g, which was 2.1 times higher than that of the virgin S-mZVI. After biological reactivation, the Rp of reactivated S-mZVI decreased to 12.30 kΩ cm2. SRB-mediated reactivation removed the electron transfer barriers via biotic and abiotic reduction of Fe(III) (hyd)oxides. Especially, the microbial Fe(III) reduction mediated by FmnA-dmkA-fmnB-pplA-ndh2-eetAB-dmkB protein family enhanced the Fe2+ release from the surface and the subsequent re-formation of reactive and conductive FeSx shell. A long-term PRB column test further demonstrated the feasibility of in-situ biological reactivation and reuse of S-mZVI for enhanced Cr(VI)-contaminated groundwater remediation. Within 64 days, the Cr(VI) removal capacity of S-mZVI in the four use cycles increased by 3.2 times, compared to the virgin one. The bio-reactivation using the SRB-enriched culture and sulfate locally-available in groundwater will reduce the chemical and maintenance costs associated with the frequent replacement of reactive ZVI-based materials. The PRB technology based on the bio-renewable S-mZVI can be a sustainable alternative to the conventional PRBs for the long-lasting and low-cost remediation of groundwater contaminated by oxidative pollutants.

Characteristics of polycyclic aromatic hydrocarbons (PAHs) removal by nanofiltration with and without coexisting organics

Polycyclic aromatic hydrocarbons (PAHs) are contaminants of great concern owing to their persistence, toxicity, and bioaccumulation in aquatic environments. In this study, nanofiltration (NF) was used to investigate the removal of naphthalene (NAP) and phenanthrene (PHE) using three membranes of NF270, NF90, and DK. Subsequently, we examined the effects of coexisting organics on PAHs removal. Based on the results, DK was determined to be the optimal membrane for removing PAHs by comparing the membrane flux and pollutant rejection. The membrane flux reached 34.32 L/m2·h, and the NAP and PHE rejections were 92.21% and 97.85%, respectively, at transmembrane pressure (TMP) of 5 bar using DK. Coexisting organics decreased the membrane fluxes of NF270 and DK in the following order: protein > glucose > humic acid. The NAP and PHE rejections were obviously improved using NF270 in the following order: humic acid > protein > glucose. The PHE rejection was slightly improved using DK. A low concentration of organics could reduce the NAP rejection using DK; however, the NAP rejection could be restored at high concentrations of organics, except for humic acid. Coexisting organics could cause severe membrane fouling. The order of the effect of different coexisting organics on membrane fouling was protein > humic acid > glucose. The total investment and operating costs were about 1.47 and 0.187 million dollars, respectively, for treating PAHs solution using DK when the feed flow was 300 m3/d.

Releasing and Assessing the Toxicity of Polycyclic Aromatic Hydrocarbons from Biochar Loaded with Iron

Iron (Fe)-loaded biochar has garnered attention for its potential applications in recent years. However, the pyrolysis process of Fe-loaded biochar generates polycyclic aromatic hydrocarbons (PAHs), which can have adverse effects on both human health and the environment. This study explored the correlation between Fe loading and PAH production in Fe-loaded biochar. The results indicate that increasing Fe loading in biochar reduces the PAH concentration, with the most significant decrease observed in naphthalene (0.02-0.08 mg/kg). This reduction can be attributed to the decrease in precursor compounds (e.g., C2H2), substitution of the C=O bond by Fe-O, and a decrease in the dissolved organic matter concentration (3.19-10.76 mg/L) with Fe loading. When Fe loading increased from 0 to 10%, the ecological toxicity of biochar increased by 33.48% due to an elevated production of dibenzo[a,h]anthracene, which poses a significant risk to human health. Therefore, it is imperative to take into consideration the ecological risk of PAHs prior to the application of Fe-loaded biochar. This study presents a comprehensive risk assessment of Fe-loaded biochar and provides valuable insights into the optimization of its production and safe application.

Bioremediation of PBDEs and heavy metals co-contaminated soil in e-waste dismantling sites by Pseudomonas plecoglossicida assisted with biochar

Biochar-assisted microbial remediation has been proposed as a promising strategy to eliminate environmental pollutants. However, studies on this strategy used in the remediation of persistent organic pollutants and heavy metals co-contaminated soil are lacking, and the effect of the combined incorporation of biochar and inoculant on the assembly, functions, and microbial interactions of soil microbiomes are unclear. Here, we studied 2,2',4,4'-tetrabrominated diphenyl ether (BDE-47) degradation and heavy metal immobilization by and biochar-based bacterial inoculant (BC/PP) in an e-waste contaminated soil, and corresponding microbial regulation mechanisms. Results showed that BC/PP addition was more effective in reducing Cu and Pb availability and degrading BDE-47 than inoculant alone. Notably, BC/PP facilitated bound-residue formation of BDE-47, reducing the ecological risk of residual BDE-47. Meanwhile, microbial carbon metabolism and enzyme activities (related to C-, N-, and P- cycles) were enhanced in soil amended with BC/PP. Importantly, biochar played a crucial role in inoculant colonization, community assembly processes, and microbiome multifunction. In the presence of biochar, positive interactions in co-occurrence networks of the bacterial community were more frequent, and higher network stability and more keystone taxa were observed (including potential degraders). These findings provide a promising strategy for decontaminating complex-polluted environments and recovering soil ecological functions.