ACS ES&T engineering最新文献

The addition of soil amendments to facilitate plant-based remediation of soil contaminated with radioactive nuclides is considered a promising approach. Here, we tested different levels of biochar to help clean uranium-contaminated soil in the potted plants. Adding 1% biochar had the best results in deactivating uranium, increasing soil enzyme activity, and promoting ryegrass growth. Microbiological and metabolomic analysis further revealed that 1 wt % biochar significantly enhanced the abundance of microorganisms such as Actinobacteriota and Myxococcota and accelerated the production of differential metabolites such as lipids and lipid-like molecules, organic acids and derivatives, and organic oxygen compounds. The analysis of biological and nonbiological interaction networks indicates that the coordinated interaction between bacteria, enzymes, and metabolites significantly improves the expression level of the ABC transporter’s metabolic pathway. This enhances the resistance of living cells to uranium and maintains system homeostasis under uranium stress. This study provides an example of the application of biochar-assisted phytoremediation and offers theoretical guidance for the remediation of soil contaminated with radioactive nuclides.

Enzyme catalysis has shown its great power in dealing with global poly(ethylene terephthalate) (PET) waste. However, it is still challenging to design a super enzyme that can treat the sheer volume of worldwide PET waste. Without a complete understanding of the catalytic mechanism, it will be difficult to reach this important goal. Here, we systematically study the PET depolymerization mechanism catalyzed by structurally different hydrolases. The role of fleeting chiral intermediates was proved to be crucial. We observed different prochiral selectivities among these PET hydrolases. While most hydrolases favor Si-face binding, a few hydrolases (e.g., Humicola insolens cutinase) mainly adapt Re-face binding. Interestingly, we found that Si-face binding leads to higher activity than Re-face binding in all of the studied hydrolases. This Si-face selectivity originates from the difficulty of proton transfer from catalytic histidine residue to the substrate and the less stability of the oxyanion hole. Since the Si-face binding ratio ranges from 0 to 95%, we infer that all these hydrolases are not perfectly evolved to degrade PET. Our in silico results highlight that enlarging binding site residues (e.g., Leu66 and Asn69) will enhance enzymatic depolymerization, which was further confirmed by our in vitro experiments where both Leu66Phe and Asn69Phe show significantly increased PET hydrolysis activity. Hopefully, this work will aid the future rational design of super enzymes to fight PET pollution.

Nitridated zero-valent iron (N-ZVI) and its sulfidated counterpart (S–N-ZVI) are promising materials for groundwater remediation. The dechlorination performance of N-ZVI and S–N-ZVI is intricately linked to the specific N and S surface speciation, yet their roles in tuning the physicochemical characteristics, dechlorination reactivity, and electron selectivity of both particles remain unclear. In this study, we synthesized ZVIs using varied N and S agents, leading to the formation of different surface N species (iron nitrides (Fe_xN_y), pyridinic, and graphitic nitrogen) and sulfur species (FeS and FeS₂). The trichloroethylene (TCE) dechlorination rate showed a linear correlation with Fe_xN_y content, indicating Fe_xN_y-mediated ZVI dechlorination. Hydrogen production capacity was, however, linearly correlated with pyridinic N. Electron paramagnetic resonance (EPR) analysis revealed that pyridinic N enhanced proton transfer processes, thereby facilitating atomic hydrogen generation. This was further supported by the reduced H/D kinetic isotope effects (KIEs) in N-ZVI (2.07) and S–N-ZVI (∼1) compared to unmodified ZVI (3.06) and noticeable mitigation of surface passivation in N-ZVI and S–N-ZVI at pH 9. FeS and FeS₂ species minimized the hydrogen evolution reaction and removed the proton transfer limitation in TCE dechlorination. This magnifies the effect of Fe_xN_y and contributes to a synergistic interplay between nitridation and sulfidation in enhancing the dechlorination kinetics.

Ammonia inhibition often occurs during anaerobic digestion (AD) of the protein-rich substrate. Iron-containing substances were proved to be efficient in alleviating the ammonia stress. However, the mechanisms behind, especially the distinct impacts of different forms of iron materials, are not fully revealed. Here, the alleviating performances of FeCl₃ and Fe₃O₄ on AD systems under ammonia stress were investigated. Moreover, the mechanisms behind these were revealed and compared at the transcriptional level. Results showed that FeCl₃ and Fe₃O₄ additions with an equal amount of iron element content (1.29 mM) led to the increased cumulative biogas and methane yields under an ammonia concentration of 3 g/L. Furthermore, the addition of iron-containing substances alleviated the accumulation of volatile fatty acids (VFAs) and extracellular polymeric substances (soluble carbohydrates and protein) caused by ammonia stress, which also had an obvious positive effect on the electron transfer capability. Microbial analysis demonstrated that the microbes (e.g., orders Methanosarcinales, Clostridiales, and Syntrophobacterales) associated with direct interspecies electron transfer (DIET), syntrophic acetate oxidization, and degradation of organic compounds were enriched. Metatranscriptomic analysis showed that ammonia inhibited the AD process by disrupting cellular redox homeostasis, infecting the ATPase activity, affecting cellular energy supply, inhibiting methane-producing enzyme activity, and suppressing the expression of cell conductive structure genes. Meanwhile, the addition of FeCl₃ and Fe₃O₄ enhanced the cellular basal metabolism and energy supply, as well as microbial electron transfer and enzymic activities on methanogenesis. Metatranscriptomic analysis indicated that the addition of free iron species (FeCl₃) can relieve the ammonia stress on syntrophic propionate and acetate oxidizing bacteria, enhance DIET by stimulating the synthesis of c-type cytochrome, and thus promote methane production. Meanwhile, Fe₃O₄ may promote methane production by stimulating the expression of related genes and facilitating electron transfer in the AD system as a capacitor. Overall, the results demonstrated that ferric chloride and magnetite can alleviate the ammonia inhibition in the AD process of high-nitrogen waste through different mechanisms.

Recovering high-concentration and high-quality phosphorus (P) from municipal sludge presents significant technical challenges. Herein, an electrochemical phosphorus recovery system (EPRS) was developed to treat the anaerobically digested sludge (ADS), featuring a leaching unit for P leaching and a recovery unit for P separation. The leaching unit consistently reduced the ADS pH from 7.5 to 3.3 and elevated the dissolved ortho-P concentration from 65.7 ± 19.7 to an average of 215.2 ± 44.6 mg L^–1. The recovery unit achieved a P recovery efficiency of 74.8 ± 7.5% until reaching a maximum ortho-P concentration of ∼4040 mg L^–1 after 33 cycles. This maximum concentration could potentially be increased by adjusting the anolyte pH to 3–4 as predicted by a mechanistic model. Mass distribution analysis revealed that 54% of total P input was in the final anolyte of the recovery unit, which contained less than 1% of Mn, Al, Zn, Cu, Pb, Cd, and Ni that were in the ADS. However, 10% of total As was detected in the recovery unit anolyte, likely because of chemical speciation. The solid product from the EPRS consisted of struvite and magnesium phosphate. Although the leaching unit was the main energy and chemical consumer, it significantly reduced the total coliform levels that satisfied the USEPA Class A pathogen standards.