Enhanced bioremediation of BTEX contaminated groundwater in pot-scale wetlands

Fate of wastewater trace organic chemicals in vegetated biofiltration systems

Vegetated biofiltration system (VBS) is an effective green technology for urban stormwater and greywater treatment. However, VBS is yet to be optimised for effective treatment of wastewater, particularly if it contains trace organic chemicals (TrOCs). The effect of plant species has not been addressed under TrOC wastewater loading. This study tested and evaluated the effectiveness of VBS over a one-year period in removing six TrOCs commonly found in wastewater, namely Caffeine (CAF), Paracetamol (PCM), Sulfamethoxazole (SMX), N diethyl‑meta-toluamide (DEET), Bisphenol A (BPA) and Ibuprofen (IBU). Eleven VBS configurations were tested in a year-long laboratory column study to explore the role of seven different plant species (with differing characteristic), varied soil media depths, and soil characteristics, on the fate of TrOCs in the systems. The effect of different operational conditions (e.g., dosing volume and regime) on removal efficiency was investigated. The results indicated VBS was able to maintain a high removal rate (>95 %) of CAF, BPA, and IBU throughout the experiment, followed by PCM (>79 %), SMX (50 %-80 %), and DEET (<12 %). Plant species significantly impacted the removal of SMX and DEET (p<0.05), with C. indica as the best performer. Reducing hydraulic loading rate and decreasing daily dosing volume and frequency contributed positively to the PCM, SMX, and DEET removal rates. Noticeable accumulations of SMX, DEET, and BPA (8.2, 43.1, and 54.5 ng·g-1, respectively) were detected in the filter media, particularly within the saturated zone. Higher chemical concentrations (i.e., CAF and DEET) were found in plant root tissue than in plant shoot tissue. This study offers valuable insights into VBS's design and operational aspects for removing TrOCs.

Sustainable refinery waste management through biotechnological interventions: Health impacts, historical successes, and emerging solutions

In today's highly competitive and interconnected global market, economic achievement and prosperity are essential needs for every individual. However, in recent years, the "science of sustainability" has gained popularity due to mounting evidence of the damaging impacts of environmental issues. Lately, the expansion of petroleum industries and refineries has led to a substantial rise in the production of refinery oily waste. The treatment of such waste presents significant environmental challenges, necessitating the development of sustainable solutions. This review explores the latest advancements in biological processes for treating it, focusing on their efficacy and limitations. These processes are still facing challenges such as slow degradation rates, nutrient availability, and pollutant toxicity, which can hinder efficiency. To address these, efforts are being made to develop more viable biological treatments including exploration of microbial strains, optimizing process conditions, bioreactor systems, and integrating advanced bioremediation techniques. Potential applications of these processes across different contaminated sites are discussed along with commercially available technologies. Drawbacks related to bioprocess scale-up, cost-effectiveness, and regulatory constraints are also addressed. Additionally, it incorporates pertinent case studies that serve as illustrations of successful implementations of biological strategies. Ultimately, this sets the stage for practical bioremediation implementation as a solution for refinery waste management.

Optimizing nano-sized oxygen bubble application for prolonged aerobic degradation of BTEX in contaminated groundwater

This study investigates the use of nano-sized oxygen bubbles (NOBs) to enhance BTEX (benzene, toluene, ethylbenzene, xylene) biodegradation in groundwater. Optimized NOBs, averaging 155 nm and at a concentration of 6.59 × 10⁸ bubbles/mL, were found to provide sustained oxygen release with a half-life of approximately 50 days. Laboratory column experiments demonstrated that NOBs released up to 380% more oxygen than initially injected, significantly boosting BTEX degradation. The repeated injection of NOBs increased the volume of trapped bubbles within soil pores, enhancing long-term oxygen release efficiency by expanding the available gas phase within the porous matrix. NOB treatment resulted in markedly lower effluent BTEX concentrations and elevated gene expression linked to BTEX-degrading enzymes. This mechanism supports the sustainability of NOBs as an oxygen source, maintaining aerobic conditions over extended periods. Compared to traditional oxygen sources, NOBs improve oxygen solubility without introducing secondary pollutants, offering a novel in situ remediation strategy for urban groundwater contamination, thereby supporting long-term monitored natural attenuation (MNA).

Absorption, translocation, and metabolism of atrazine, carbamazepine, and sulfamethoxazole by the macrophyte Orange King Humbert canna lily (Canna × generalis L.H. Bailey (pro sp.) [glauca × indica])

Canna × generalis L.H. Bailey (pro sp.) [glauca × indica] (common name: Orange King Humbert canna lily) has been reported as a promising plant species that can effectively remove contaminants of emerging concern (CECs), such as atrazine (ATZ), carbamazepine (CBZ), and sulfamethoxazole (SMX), from contaminated surface water. In the present study, absorption, translocation, and metabolism of such CECs in canna were examined using carbon-14-labeled ([¹⁴C]) analogues of each contaminant to understand the removal of each. Uptake/adsorption of the [¹⁴C]-CECs increased over time and was > 47.5% at the end of the 14-day study. The root-shoot translocation of [¹⁴C]-ATZ in canna was the greatest at 49.9-78.8%, followed by [¹⁴C]-CBZ (1.9-44.7%) and [¹⁴C]-SMX (3.3-6.0%). The cumulative transpiration of canna was correlated with absorption (R² > 0.95) and root-shoot translocation (R² > 0.97) magnitudes of [¹⁴C]-CECs in canna. Radiographic results revealed significant conversion of parent [¹⁴C]-CECs into other metabolites during the 14-day study. Metabolism of [¹⁴C]-ATZ and [¹⁴C]-CBZ occurred mainly in the shoots, whereas metabolism of [¹⁴C]-SMX occurred in the roots. Taken together, root-shoot redistribution and metabolism of CECs absorbed into canna can vary by transpiration volume as well as chemical properties.

Phytoremediation, Bioaugmentation, and the Plant Microbiome

Understanding plant biology and related microbial ecology as a means to phytoremediate soil and groundwater contamination has broadened and advanced the field of environmental engineering and science over the past 30 years. Using plants to transform and degrade xenobiotic organic pollutants delivers new methods for environmental restoration. Manipulations of the plant microbiome through bioaugmentation, endophytes, adding various growth factors, genetic modification, and/or selecting the microbial community via insertion of probiotics or phages for gene transfer are future areas of research to further expand this green, cost-effective, aesthetically pleasing technology─phytoremediation.

Enhanced dissipation of trace level organic contaminants by floating treatment wetlands established with two macrophyte species: A mesocosm study

This study evaluated removal efficiencies of six contaminants of emerging concern (CECs) in floating treatment wetland (FTW) mesocosms established with either Japanese Sweetflag (Acorus gramineus Sol. ex Aiton) or canna lilies (Canna Hybrida L. 'Orange King Humbert'). The CECs included: acetaminophen (APAP), atrazine (ATZ), carbamazepine (CBZ), perfluorooctanoic acid (PFOA), sulfamethoxazole (SMX), and 17β-estradiol (E2). Each treatment was planted with different numbers of plants (i.e., 0, 10, 15, and 20), and the experiments lasted for 17 weeks. Dissipation of CECs was greater in planted treatments than in non-planted controls, and the planting number had little effect on dissipation of CECs. All residues of APAP and E2 dissipated rapidly within 2 weeks in all planted treatments. At the end of the experiment, residues of ATZ and SMX completely dissipated in the canna treatments, but not in the sweetflag treatments (75.8-87.6% and 96.3-97.1%, respectively). During the 17 week study, moderate dissipation of CBZ was observed in treatments including cannas (79.5-82.6%) and sweetflag (69.4-82.3%), while less dissipation was observed for PFOA (9.0-15.0% with sweetflag and 58.4-62.3% with cannas). Principal component analysis indicates that aqueous persistency of CECs and species of plants used influenced the dissipation of CECs in FTWs. Of the two species evaluated, canna was the most promising plant species for FTW systems designed to remove these CECs from surface water.

Applications of chitosan in environmental remediation: A review

Environmental biotechnology is the use of biotechnology to develop and regulate biological systems for the remediation of environmental contamination. Nature has gifted ample material for remediation of its resources, among which chitosan is one of the most important and largely available biomaterial globally. Chitosan is a biopolymer obtained by deacetylation of chitin extracted from marine waste and its applications from drug delivery to food additives are broadly available. Chitosan exhibit several properties such as availability, low cost, high biocompatibility, and biodegradability. These properties make it biologically and chemically acceptable for use in various fields. Due to some limitations of pure chitosan, there has been a growing interest in modifying the chitosan in order to improve the original properties and widen the applications of pure phase chitosan. Various modified forms of chitosan and their associated applications are reviewed here with emphasis on their use in environmental remediation. The demand of chitosan in the global industrial market is growing which is briefly explained in this paper. Chitosan is used for water purification since a long time and still progress is going on for making it more efficient in the removal process. It can be used as a flocculent and coagulant, as an adsorbent for removing the contaminants like heavy metals, dyes, pesticides, antibiotics, biological contaminants from wastewater. Soil remediation using chitosan material is explained in this review. Various other applications such as drug delivery, food additives, tissue engineering are thoroughly reviewed.

Potential use of floating treatment wetlands established with Canna flaccida for removing organic contaminants from surface water

Surface water bodies worldwide may be contaminated with various organic contaminants. In many cases, the actual toxicity thresholds to nontarget organisms are unknown, thus presenting unknown risks. This study evaluated the potential use of floating treatment wetlands (FTWs) planted with Canna flaccida (common name: Canna) for removing two pharmaceuticals (acetaminophen and carbamazepine) and one herbicide (atrazine) from contaminated water. Triplicate FTWs with varying plant densities were established in 378 L mesocosms. After dosing the mesocosms with the contaminants, water samples were collected over a 12-week period for analysis. The planted FTWs showed differing abilities for removing acetaminophen, atrazine, and carbamazepine. Plant densities on the FTWs did not affect dissipation of acetaminophen or atrazine, but did carbamazepine. All acetaminophen residues were removed from the water within 2 weeks, while all atrazine residues were removed within 12 weeks. Approximately, 79-92% of these residues removed were associated with the FTWs. In contrast, all of the carbamazepine was not removed after 12 weeks, at which time only 29-36.7% of the total removed was associated with the FTWs. Overall results suggest that FTWs established with C. flaccida are promising for removing trace concentrations of acetaminophen, atrazine, and carbamazepine from surface water.

Application of magnesium peroxide (MgO2) nanoparticles for toluene remediation from groundwater: batch and column studies

In the present study, magnesium peroxide (MgO₂) nanoparticles were synthesized by electro-deposition process and characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The batch experiments were conducted to evaluate the MgO₂ half-life (600 mg/L) in groundwater under various temperatures (4, 15, and 30 °C) and initial pH (3, 7, and 12). The effect of Fe²⁺ ions (enhanced oxidation) on the toluene remediation by MgO₂ was also investigated. Nanoparticles were injected to sand-packed continuous-flow columns, and toluene removal (50 ppm) was studied within 50 days at 15 °C. The results indicated that the half-life of MgO₂ at pH 3 and 12 were 5 and 15 days, respectively, in comparison to 10 days at the initial pH 7 and 15 °C. The nanoparticles showed 20 and 7.5 days half-life at 4 and 30 °C temperatures, respectively. Injection of Fe²⁺ ions indicated an impressive effect on toluene removal by MgO₂, and the contaminant was completely removed after 5 and 10 days, in the batch and column experiments, respectively. Confocal laser scanning microscope (CLSM) analysis indicated that the attached biofilm had a significant role in the decontamination of groundwater. Comparison of bioremediation and enhanced oxidation resulted in a considerable insight into the application of magnesium peroxide in groundwater remediation. Graphical abstract ᅟ.

Performance evaluation of duplex constructed wetlands for the treatment of diesel contaminated wastewater

A duplex constructed wetland (duplex-CW) is a hybrid system that combines a vertical flow (VF) CW as a first stage with a horizontal flow filter (HFF) as a second stage for a more efficient wastewater treatment as compared to traditional constructed wetlands. This study evaluated the potential of the hybrid CW system to treat influent wastewater containing diesel range organic compounds varying from C₇ - C₄₀ using a series of 12-week practical and numerical experiments under controlled conditions in a greenhouse (pH was kept at 7.0 ± 0.2, temperature between 20 and 23° C and light intensity between 85 and 100-μmol photons m^-2 sec^-1 for 16 h d^-1). The VF CWs were planted with Phragmites australis and were spiked with different concentrations of NH₄⁺-N (10, 30 and 60 mg/L) and PO₄^3--P (3, 6 and 12 mg/L) to analyse their effects on the degradation of the supplied petroleum hydrocarbons. The removal rate of the diesel range organics considering the different NH₄⁺-N and PO₄^3--P concentrations were simulated using Monod degradation kinetics. The simulated results compared well with the observed database. The results showed that the model can effectively be used to predict biochemical transformation and degradation of diesel range organic compounds along with nutrient amendment in duplex constructed wetlands.

Airborne toluene removal for minimizing occupational health exposure by means of a trickle-bed biofilter

The paper presents the experimental results on a biotrickling pilot plant, with a water scrubber as pre-treatment, finalized to the treatment of an airborne toluene stream in a working place. The air stream was characterized by a very high variability of the inlet concentrations of toluene (range: 4.35-68.20 mg Nm(-3)) with an average concentrations of 16.41 mg Nm(-3). The pilot plant has proved its effectiveness in toluene removal, along a 90-day experimentation period, in steady-state conditions. The scrubbing pre-treatment has achieved an average removal efficiency of 69.9 %, but in particular it has proven its suitability in the rough removal of the toluene peak concentrations, allowing a great stability to the following biological process. The biotrickling stage has achieved an additional average removal efficiency of 75.6 %, confirming the good biodegradability of toluene. The biofilm observation by a scanning confocal laser microscope has evidenced a biofilm thickness of 650 μm fully penetrated by toluene degrading bacteria. Among the micro-population Pseudomonas putida resulted the dominant specie. This bacterium can therefore be considered the responsible for most of the toluene degradation. The whole experimented process has determined an average 92.7 % for toluene removal efficiency. This result meets the most stringent limits and recommendations for occupational safety, given by authoritative organizations in the USA and EU; it also meets the odorous threshold concentration of 11.1 mg Nm(-3).