Environmental Technology

He, Qiongqiong; Huang, Jun; Gao, Ruize; Xiang, Pengxu; Wu, Xiaoqi; Miao, Zhenyong

doi: 10.1080/09593330.2025.2587900pmid: 41264926

Coal chemical wastewater, characterized by high toxicity, salinity, and refractory organics (e.g. phenols), poses significant environmental challenges. An innovative system integrating micro-nano bubbles (MNBs) and acclimated bacterial consortia (DP-1) was developed in this study. It was designed to achieve efficient phenol degradation and chemical oxygen demand (COD) removal. DP-1 was domesticated under MNBs aeration, high phenol (up to 400 mg/L), and high-salt (1–15 g/L) conditions, exhibiting remarkable adaptability. The MNBs@DP-1 system achieved 100% phenol degradation and 88.9% COD removal within 24 h at 600 mg/L phenol, demonstrating robust performance across a wide pH range (6–9) and salinity (1–15 g/L). Notably, in a sequencing batch biofilm reactor (MNB-AR), long-term treatment of actual coal chemical wastewater (COD: 1300–1600 mg/L) yielded a stable average COD removal of 76.2% with <1.6% fluctuation. Microbial community analysis revealed Proteobacteria (99.1%) dominance post-acclimation, with Acinetobacter (65.7%) and Comamonas (29.7%) as key functional genera driving phenol mineralization. Comparative studies confirmed the superior efficacy of MNBs@DP-1 over conventional aeration systems, attributing enhanced degradation to MNBs-induced bacterial activity and biofilm stability. This work provides a scalable strategy for achieving ‘zero discharge’ in coal chemical wastewater treatment by synergizing bubble technology and microbial acclimation.

Shao, Linan; Li, Yonghui; Wang, Tianning

doi: 10.1080/09593330.2025.2588498pmid: 41241966

Aqueous contamination by arsenic and antimony has become a significant concern due to its prevalence in smelting activities. Nowadays, adsorption stands out as an effective method for the removal of these heavy metal ions from water, particularly when the goal is to achieve high levels of purification and ensure safety. However, the complex nature of smelting wastewater often leads to a decrease in the selectivity and salt resistance of adsorbents under industrial conditions. In this study, we introduce a novel designated composite-resin material (KYE003), which is tailored for the deep purification of arsenic and antimony. By precisely adjusting the synthesis ratios, we have controlled the intrinsic kinetics of material synthesis, enabling the in-situ loading of ferric oxide onto the resin surface, coupled with organic functional groups (–COOH and –SH). The resin's inherent porous structure not only promotes the nucleation and growth of amorphous iron oxide but also establishes a quantitative basis for nano-scale binding sites. Further surface characterisation analysis indicates that interfacial functional groups, including (–COOH, –SH, and –OH), are instrumental in the complexation of arsenic and antimony. The synergistic interactions, such as –O–As/Sb, –COO–As/Sb, and –S–As/Sb, demonstrate that the hybridisation of these groups restructures the interfacial electronic state, thereby enhancing the adsorption performance. The KYE003 material exhibits exceptional adsorptive selectivity and chemical stability under complex conditions, capable of maintaining arsenic concentrations in the effluent below 20 µg·L−1 until the bed volumes ratio surpasses 6240. This research presents a new perspective for the deep purification of heavy metal ions.

Zwaan, Ramon; Sorokin, Dimitry Y.; Stouten, Gerben R.; van Loosdrecht, Mark C.M.; Wilfert, Philipp

doi: 10.1080/09593330.2025.2588499pmid: 41277589

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.

Pan, Hongzhong; Wei, Kexin; Zhu, Xianbin; Wang, Dan; Yao, Huaming; Zhong, Wen

doi: 10.1080/09593330.2025.2588720pmid: 41264929

Extracellular polymeric substances (EPS) play a vital role in forming microbial aggregates such as biofilms, flocs, and granules. However, standardised methods for extracting EPS from the activated sludge across different wastewater treatment processes remain elusive. The anaerobic-anoxic-oxic (A2O) process, widely used in wastewater treatment, was selected to investigate EPS extraction from its activated sludge. This study compared twenty-five physicochemical methods for EPS extraction from the activated sludge collected from the secondary sedimentation basin of an A2O reactor, evaluating EPS yield, composition, and cell lysis. The results show that combined chemical-physical extraction methods, particularly NaOH/heat treatment, achieved higher extraction rates while preserving EPS characteristics. This method yielded higher concentrations of proteins (PN) and polysaccharides (PS) with reduced cell lysis compared to other techniques. In most methods, protein content exceeded polysaccharides content, with PN/PS ratios ranging from 0.005 to 4.17 g/g. Higher PN/PS ratios were associated with smoother, more uniform EPS morphology. Particle size distribution of the treated sludge showed minimal variation between methods. Fourier transform infrared (FTIR) and excitation emission matrix (EEM) fluorescence spectroscopy confirmed the presence of proteins, polysaccharides, and DNA in EPS, with NaOH/heat treatment more effectively preserving functional groups. Optimisation tests identified 45 min as the ideal heating duration for maximum EPS extraction. Overall, this study provides a systematic evaluation of EPS extraction methods from the activated sludge in A2O systems, offering methodological insights for future wastewater treatment research.

Shaeyan, Masumeh; Nosrati, Mohsen; Rasekh, Behnam; Dastgheib, Seyed Mohammad Mehdi; Zamir, Seyed Morteza

doi: 10.1080/09593330.2025.2589528pmid: 41277605

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.

Zhang, Xiushuang; Wang, Ying; Wu, Di; Liang, Hongwang; Ma, Litong

doi: 10.1080/09593330.2025.2589944pmid: 41308695

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.

Ferro Orozco, Ana Micaela; Contreras, Edgardo Martín

doi: 10.1080/09593330.2025.2590639pmid: 41277610

The volumetric oxygen mass transfer coefficient ( $k_La$ k L a ) is a critical parameter in the design, scale-up, and operation of bioreactors. In this study, a fully automated dynamic method was developed for determining $k_La$ k L a , eliminating manual intervention and ensuring reproducible and reliable estimates. The approach includes a probe response-time correction and was validated under different operational conditions in an aerated stirred system. The influence of two representative pollutants was evaluated: phenol and benzalkonium chloride (BAC). While phenol produced a small enhancement (≈18%) of the overall $k_La$ k L a , BAC caused a reduction in $k_La$ k L a , mainly due to its pronounced effect on the surface mass transfer coefficient ( $k_La_S$ k L a S ). To the best of our knowledge, this work provides the first experimental evidence of BAC effects on oxygen transfer in bioreactors. These results expand the current understanding of how pollutants can simultaneously act as metabolic inhibitors and as modifiers of gas–liquid mass transfer, with significant implications for optimising aeration strategies in biological wastewater treatment.

Han, Yang; Zhao, Xing-Ming; Cheng, Hao-Yi; Nawab, Said; Wang, Hong-Cheng; Song, Hao; Yong, Yang-Chun

doi: 10.1080/09593330.2025.2592738pmid: 41308691

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.

Rai, Vaibhav Kumar; Yadav, Sudeep; Saifi, Gulnaz; Tiwari, Himanshu; Singh, Ram Sharan

doi: 10.1080/09593330.2025.2592739pmid: 41348578

Nowadays, the presence of triazine-based azo dyes like Reactive Red 120 (RR 120) in textile wastewater poses a significant hazardous environmental impact, deteriorating the aquatic biota and requiring an effective treatment method. Compared to conventional energy-intensive and secondary waste-generating physicochemical methods, biological methods, especially microbial biodegradation, offer a sustainable, eco-friendly, and cost-effective alternative for the treatment of effluents containing dye-laden wastewater. This study evaluated the efficacy of Bacillus tequilensis MCC2908 for biodegradation and detoxification of RR 120 using a continuously Packed Bed Bioreactor (PBBR). The experimental findings revealed an optimum range of ILR within 75–85 mg/L.day, achieving 94.2 ± 2.71% RE and 24.1 ± 1.205 mg/L.day EC, avoiding limitations imposed by mass transfer and bioreaction, and maintaining a robust and efficient bioreactor system. Crystal Violet staining test confirmed the quantitative assessment of biofilm growth, while SEM images made it observable on the polyurethane bio-carrier. The FTIR spectra confirmed the biodegradation of RR 120, showing significant changes in the functional groups. The detoxification was demonstrated using bacterial and phytotoxicity, validating the toxicity reduction, further duly supported by photosynthetic pigment analysis. The Monod model and the Andrew-Haldane kinetics significantly described microbial growth under non-inhibitory and inhibitory conditions, respectively. Nevertheless, the present findings not only highlighted the potential of biofilm-based PBBR but also delivered an eco-friendly, sustainable solution for the remediation of textile wastewater. Future studies may explore the scaling up of this biotechnological solution for the mitigation of industrial challenges and establish hybrid approaches to further enhance biodegradation efficiency. Highlights PBBR significantly achieved efficient biodegradation and detoxification of RR 120. An optimum ILR of 75–85 mg/L.day exhibited the best operating conditions for PBBR. Microbial biomass and biofilm formation were quantified using the Crystal Violet Staining method. Phytotoxicity, photosynthetic pigment analysis, and bacterial toxicity unveiled the RR 120 detoxification. Moderate Ki and low Ks values depicted the resilience and high microbial activity for RR 120.

Xu, Jinlan; Chen, Tingyu; Dai, Jianan; Liu, Chuanyu; Zhou, Rankang; Wang, Jiayi; Zhai, Xin; Guan, Huiwen

doi: 10.1080/09593330.2025.2592740pmid: 41348583

This study aims to enhance biogenic elemental sulfur (S0 bio) recovery efficiency in Simultaneous Nitrogen and Sulfur Removal (SNSR) processes for dual environmental and economic benefits. The addition of thiosulfate to redirect reaction pathways in a Thiobacillus denitrificans-augmented SNSR system elucidates its regulatory mechanism on S0 bio yield and stability. Under low sulfide loading (100 mg/L S2-), 30 mg/L S2O3 2− amendment achieved peak S0 bio yield of 69.85% at 36 h, with sulfur conversion efficiency 3.03-fold higher than the high-loading non-inhibited group (NI). The target pathway (S2−→ S0 bio) intensity increased by 0.53–1.05-fold, while the competing pathway (S2−→ S2O3 2-) was inhibited (0.10–0.28-fold reduction). Thiosulfate enabled the S0 bio generation pathway to dominate over S2−→ SO4 2−during early-stage low-sulfide SNSR, reaching a maximum contribution of 55.32%. Additionally, the fluorescence intensity contribution of soluble microbial products (SMP) reached a peak of 49.81%, while concurrent measurements showed significant increases in viable cell count and viability (averaging 2.17-fold and 3.18-fold higher than those in the non-thiosulfate-amended groups, respectively). Thiosulfate synergistically drives efficient S0 bio stabilization through dual mechanisms: (1) enhancing Thiobacillus denitrificans bioactivity to intensify key reaction kinetics; (2) optimizing sulfur speciation transformation to establish target-pathway dominance. This work provides technical insights for resource recovery from sulfur-laden wastewater and stable S0 bio reclamation. Highlights Early-stage inhibition boosts S0 bio yield to 69.85% at low sulfide loading with thiosulfate amendment. 3.03× higher sulfur conversion efficiency versus high-loading controls via pathway redirection to S0 bio generation. Dual regulation: Synergistically enhances Thiobacillus denitrificans activity (↑1.22× viability) and redirects sulfur flux toward S2-→S0 bio (55.32% dominance), suppressing competing pathways. Resource recovery strategy enabling stable S0 bio reclamation from sulfur-laden wastewater.