Environmental Technology最新文献

Plastics represent a global environmental challenge due to their widespread use and persistent accumulation. This study is focused on the enzymatic depolymerization of non-pretreated household PET waste using two plastic-degrading esterases, LCC^ICCG and IsPETase^W159H/F229Y, leveraging the advantages of the extracellular expression in a Pichia pastoris system. The simple recovery and improved stability enabled by this expression system are crucial foundations in the development of biocatalytic remediation processes. Expression in batch cultures resulted in esterase activity levels of 86.3 ± 3.7 IU/mg for LCC^ICCG and 16.4 ± 0.3 IU/mg for IsPETase^W159H/F229Y after 48 hours of induction, and these enzymes kept their catalytic activity after at least 30 days at 4 and 25 °C. LCC^ICCG successfully degraded non-pretreated PET (87.6 ± 10.7 g_PET h^-1 g_enzyme^-1), while IsPETase^W159H/F229Y exhibited a tenfold increase in depolymerization efficiency over previous reports (1.71 ± 0.3 g_PET h^-1 g_enzyme^-1). LCC^ICCG exhibited enhanced activity at high temperatures, associated with the glycosylations introduced during expression in P. pastoris, making it a promising candidate for industrial applications requiring high-temperature operations. It is outstanding the specific space-time yield achieved by LCC^ICCG (183.1 mM_TAeq h^-1 mg_enzyme^-1), which results higher than those previously reported. These results encourage reducing both time and costs associated with conditioning pretreatments for non-pretreated household plastic wastes or biocatalyst downstream processing. They also underscore the potential of exploring a promising pathway towards large-scale, environmentally sustainable PET waste management.

This study investigated the efficacy and mechanisms of humic acid (HA)-loaded ferrihydrite (Fh) and magnetite (Mag) in suppressing phosphorus (P) release from sediment into the overlying water (OW) via direct capping, fabric-wrapped capping, and sediment amendment. The results showed that the direct capping, fabric-wrapped capping, and sediment amendment with HA-loaded ferrihydrite (HA-Fh) and magnetite (HA-Mag) effectively mitigated the sedimentary P migration into OW. Specifically, the average reduction efficiencies of soluble reactive phosphorus (SRP) in OW were 94.6%, 74.6%, and 45.0% for HA-Fh under direct capping, fabric-wrapped capping, and amendment conditions, respectively. For HA-Mag, the corresponding efficiencies were 83.9%, 71.1%, and 47.1%. Under HA-Fh and HA-Mag capping, P in the sediment continued to mobilise into the pore water through the microbial and sulphide-mediated chemical reduction of iron (III) (hydr)oxides. However, the capping layers significantly reduced the concentrations of pore water SRP and labile P measured by diffusive gradients in thin-films (DGT) in the upper sediment. This reduction was crucial for effectively intercepting the sedimentary P migration into OW by HA-Fh and HA-Mag. Our study demonstrates that HA-Fh and HA-Mag are effective capping materials for managing the sediment-derived internal P loading. In other words, even after HA aging treatment, Fh and Mag still remain effective sediment phosphorus release control materials. In addition, the direct capping methods using HA-Fh and HA-Mag are promising due to their high control efficiency and ease of application in preventing P release from sediment into OW.

This study investigates the use of constructed wetlands (CWs) with ceramsite derived from surplus sludge pyrolysis ash for acid mine drainage (AMD) remediation. The system, incorporating ceramsite, limestone, and gravel, used soybean wastewater as a microbial carbon source. Results showed that the ceramsite-based system effectively raised pH from 3.5 to 8.0, achieving removal rates of 99.96% for Fe, 96.53% for Mn, 94.84% for Cu, 99.26% for Zn, and 96.02% for total phosphorus. Metal ion removal was primarily through ceramsite adsorption, with minor plant-mediated adsorption. Microbial analysis revealed that pH and metal concentrations influenced bacterial composition, with dominant genera including Trichococcus, Clostridium_Sensu_Stricto_1, and Citrobacter. Sulfate-reducing bacteria such as Desulfovibrio and Desulfobulbus played crucial roles in sulfate reduction. This study demonstrates a sustainable AMD treatment method that not only improves metal ion removal but also addresses sludge disposal challenges, highlighting the environmental benefits of using waste-derived materials for pollution control and resource recovery.

To explore strategies for further reducing aeration energy consumption in the simultaneous nitrification and denitrification (SND) process, an SND reactor was constructed to treat low carbon-to-nitrogen (C/N) ratio domestic wastewater under ultra-low dissolved oxygen (DO) conditions (DO < 0.05 mg·L⁻¹). The effects of hydraulic retention time (HRT) and C/N ratio on nitrogen removal performance were systematically evaluated, and batch experiments were conducted to determine nitrification and denitrification rates. Under influent condition of 50.0 mg·L⁻¹ ammonia and a C/N ratio of 2.2, the reactor maintained stable ultra-low DO levels, achieved effluent ammonia concentrations below 5.0 mg·L⁻¹, and attained optimal SND efficiencies exceeding 80.0%. Although a shortened HRT destabilised performance, increasing the C/N ratio successfully restored nitrogen removal stability. Nitrification and denitrification rates ranged from 4.20-30.89 mg·L⁻¹·h⁻¹ and 1.57-21.92 mg·L⁻¹·h⁻¹, respectively, under C/N ratios from 2.2-8.0. High-throughput sequencing and metagenomic analysis revealed that heterotrophic nitrification and aerobic denitrification dominated nitrogen transformation, with microorganisms utilising low-energy nap and nirK enzymes to adapt to the ultra-low DO environment. These findings provide novel insights into energy-efficient nitrogen removal pathways under ultra-low oxygen conditions.

Microbial remediation of heavy metals (HMs) is an environmentally friendly and cost-effective approach to soil restoration. This study aimed to identify the endophytic bacterial strain with the highest capacity to mobilize cadmium (Cd) among four isolates from Paulownia fortunei root nodules. We conducted soil incubation experiments under four Cd contamination levels (10, 40, 80 and 300 mg kg^-1) and three inoculation treatments, and measured soil extractable Cd, microbial community composition, and diversity. Results indicated that strain S7 exhibited the greatest Cd activation capability, attributed to its production of siderophores, organic acids and extracellular polymeric substances (EPS). Analysis of variance showed that inoculation treatment, Cd level and their interaction had significant effects on the relative abundances of the phyla Actinobacteria, Firmicutes, Gemmatimonadota and Bacteroidetes, as well as on bacterial diversity indices (Shannon, ACE, Chao). These dominant phyla were strongly correlated with soil physicochemical properties. Structural equation modelling (SEM) revealed that strain S7 directly enhanced soil Cd mobilization through siderophore production, and indirectly by altering soil pH, bacterial richness (ACE index), and the abundance of Chloroflexi. This study provides new insights into the mechanisms by which endophytic bacteria facilitate Cd remediation and enhances our understanding of microbe-assisted environmental restoration.

The soil in reclaimed shale gas sites is compacted and suffers from issues like poor drainage, drought conditions, and nutrient deficiency, posing challenges for agricultural production. In this study, rare earth tailings were incorporated into biochar at different mass ratios (rare earth tailings: biochar = 1:1, 1:2, 1:3, 1:4). Subsequently, a series of rare earth tailings-doped biochar materials (REE-BC) were prepared by calcination at 700°C. The impact of REE-BC on the soil in reclaimed shale gas sites was evaluated by pot experiment. The results showed that the pH, moisture content, nutrients (N, P, K), organic matter, and enzyme activities in the treated soil were all increased, while the soil bulk density was decreased. At the same time, the chlorophyll, soluble sugar, soluble protein, and activities of antioxidant enzymes in Chinese cabbage were increased, while the malondialdehyde content was decreased. Additionally, FT-IR analysis detected an absorption peak at 550 cm^-1, indicating the successful loading of Ce onto the biochar. SEM-EDS and BET analyses showed that the biochar modified by secondary pyrolysis had a larger specific surface area and pore volume, which was conducive to increasing soil porosity and water retention. This study demonstrates the potential of REE-BC in improving soil properties and promoting Chinese cabbage growth, providing theoretical basis for novel approach for reclaiming shale gas-affected soils.

For the biological treatment of swine wastewater, accelerating the degradation of COD usually leads to increased microbial nitrification, resulting in a conflict between pollutant removal and nitrogen recycling. In this study, the addition of hematite-biochar mixture and the nitrification inhibitor dicyandiamide (DCD) was proposed and applied to simultaneously enhance COD removal and nitrogen recycling efficiency in a Myriophyllum aquaticum-based swine wastewater treatment process. The results showed that addition of hematite-biochar mixture achieved a 1 times increase on COD removal rate. Meanwhile, the addition of DCD effectively suppressed microbial nitrification but slightly increased nitrogen removal by enhancing nitrogen utilization with Myriophyllum aquaticum. Eventually, the addition of hematite-biochar and DCD simultaneously improved the COD removal and nitrogen recycling rate to 96.9% (vs. 46.6% for control) and 72.8% (vs. 39.9% for control), respectively. Furthermore, microbial community analysis indicated that the developed strategy enhanced the abundance of Firmicutes and the genus Comamonas (strengthening COD removal), while reducing the abundance of nitrifying bacteria (phylum Proteobacteria) (repressing the nitrification process). This work provided a practical approach to accelerate pollutants removal while preserving nitrogen for plant utilization, which would be a promising solution for nitrogen recycling from swine wastewater.

Lignite is not suitable as fuel due to its high moisture and ash content and low combustion efficiency. However, the high organic matter content of lignite makes it a potential raw material for microbial decomposition and hydrogen production. Hydrogen production has always been a technical challenge faced worldwide. This study used lignite as the reaction raw material to investigate the influencing factors of microbial hydrogen production, with a focus on the effect of fulvic acid, the main chemical component in lignite, on the microbial conversion of lignite for hydrogen production. By measuring the daily hydrogen production, total hydrogen production, and the content changes of humic acid and pyruvic acid in the reaction system of hydrogen produced by microorganisms in lignite, combined with spectral characteristic analysis, the mechanism of fulvic acid in hydrogen production from lignite was revealed. The research results show that the addition of fulvic acid can significantly improve the hydrogen production efficiency of lignite, especially when the addition amount is 100 mg/L, the promoting effect is the most obvious. The total hydrogen production reached 2.140 mL/g, which was 1.44 times that of the control group.

Biological desulfurization provides a sustainable and cost-effective alternative to conventional physicochemical methods for removing hydrogen sulfide (H₂S) from industrial gas streams, particularly in medium-scale applications. This study investigates the enrichment and application of an enriched sulfur-oxidizing bacterial (SOB) consortium, isolated from sulfur-rich natural environments in Iran, for the selective biological conversion of sulfide to elemental sulfur in a fed-batch airlift bioreactor. A Central Composite Design-Response Surface Methodology (CCD-RSM) was employed to statistically evaluate and optimize the effect of dissolved oxygen (DO), pH, and sulfide loading rate, aiming to maximize sulfur selectivity while minimizing by-product formation. Optimization results revealed that both DO concentration and sulfide loading rate significantly influenced sulfur selectivity. Notably, low DO levels enhanced the selective production of elemental sulfur, while higher pH and sulfide loading rates promoted thiosulfate formation. The optimal conditions determined were pH 8.5, DO concentration of 0.2 mg L^-1, and a sulfide loading rate of 97.2 mg L^-1 h^-1. Under these optimized fed-batch conditions, 71% of the inlet sulfide was selectively converted to elemental sulfur, with complete (100%) sulfide removal achieved across all experimental runs. These findings demonstrate the potential of using enriched SOB together with well-controlled process conditions can make biodesulfurization more efficient, selective, and environmentally friendly for industrial applications. Compared with conventional physicochemical methods, the optimized biological process operates under mild conditions, is more cost-effective and environmentally sustainable, while maintaining high sulfide removal and sulfur recovery.

A highly pure biomethane stream (≈97% CH₄) was produced continuously under halo-alkaline conditions (pH > 9, 0.6 M Na⁺) from complex alkaline organic waste residue originating from biopolymer extraction from sewage sludge. During the proof-of-concept operation, the substrate was degraded with similar efficiency (40% of the volatile solids, VS) compared to neutral conditions (36% of the VS). Operational data was utilised in a technical evaluation to identify bottlenecks for full-scale implementation at an early stage of process development and for comparison to conventional biogas upgrading using pressure swing and membranes. Initially identified bottlenecks for alkaline fermentation were related to overcautious assumptions, while others could be technically solved. Alkaline fermentation offers an attractive method for supplying increasingly needed high-purity biomethane using various recalcitrant substrates that have undergone alkaline pre-treatment. This is more feasible than the conventional ex-situ biogas upgrading. Next, upscaling steps for alkaline fermentation should be pursued. Strategies for integrated CO₂ sequestration and nutrient recovery are outlined, which will offer additional benefits in the future.