Use of hairy roots extracts for 2,4-DCP removal and toxicity evaluation by Lactuca sativa test

2,4-Dichlorophenol (2,4-DCP) is widely distributed in wastewaters discharged from several industries, and it is considered as a priority pollutant due to its high toxicity. In this study, the use of different peroxidase extracts for 2,4-DCP removal from aqueous solutions was investigated. Tobacco hairy roots (HRs), wild-type (WT), and double-transgenic (DT) for tomato basic peroxidases (TPX1 and TPX2) were used to obtain different peroxidase extracts: total peroxidases (TPx), soluble peroxidases (SPx), and peroxidases ionically bound to the cell wall (IBPx). All extracts derived from DT HRs exhibited higher peroxidase activity than those obtained from WT HRs. TPx and IBPx DT extracts showed the highest catalytic efficiency values. The optimal conditions for 2,4-DCP oxidation were pH 6.5, H₂O₂ 0.5 mM, and 200 U mL^?1 of enzyme, for all extracts analyzed. Although both TPx extracts were able to oxidize different 2,4-DCP concentrations, the removal efficiency was higher for TPx DT. Polyethylene glycol addition slightly improved 2,4-DCP removal efficiency, and it showed some protective effect on TPx WT after 2,4-DCP oxidation. In addition, using Lactuca sativa test, a reduction of the toxicity of post removal solutions was observed, for both TPx extracts. The results demonstrate that TPx extracts from both tobacco HRs appear to be promising candidate for future applications in removing 2,4-DCP from wastewaters. This is particularly true considering that these peroxidase sources are associated with low costs and are readily available. However, TPx DT has increased peroxidase activity, catalytic efficiency, and higher removal efficiency than TPx WT, probably due to the expression of TPX1 and TPX2 isoenzymes.     

Evolutions of microbial degradation pathways for parent xenobiotic and for its metabolites follow different schemes

Background and purposes

The pathways used by microorganisms for the metabolism of every xenobiotic substrate are specific. The catabolism of a xenobiotic goes through a series of intermediate steps and lower intermediates (metabolites) appear in sequence. The structure of the metabolites can be similar to the parents due to kinship. The purposes of this study were to examine if the degradation pathways that were developed for a parent xenobiotic are effective to degrade the parent??s lower metabolites, and if the reverse is true.

Materials and methods

The xenobiotic substrates, 2,4-dichlorophenoxyacetic acid (2,4-D, the parent xenobiotic) and its metabolite 2,4-dichlorophenol (2,4-DCP), were independently subjected to acclimation and degradation tests by the biomasses of mixed-culture activated sludge and a pure culture of Arthrobacter sp.

Results

Activated sludge and Arthrobacter sp. that were acclimated to 2,4-D effectively degraded 2,4-D and the lower metabolites of 2,4-D, typically 2,4-DCP. During the degradation of 2,4-D, accumulations of the lower metabolites of 2,4-D were not found. The degradation pathways acquired from acclimation to 2,4-D are effective for all the metabolites of 2,4-D. However, pathways acquired from acclimation to 2,4-DCP are not effective in the degradation of the parent 2,4-D.

Conclusions

Microorganisms acclimated to 2,4-D evolve their degradation pathways by a scheme that is different from the scheme the microorganisms employ when they are acclimated to the metabolites of 2,4-D.     

A tiered ecological risk assessment of three chlorophenols in Chinese surface waters

Introduction

The ecological risks posed by three chlorophenols (CPs), 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TCP), and pentachlorophenol (PCP) in Chinese surface waters were assessed.

Materials and methods

This was achieved by applying a tiered ecological risk assessment (ERA) approach ranging from deterministic methods to probabilistic options to measured concentrations of CPs in surface water of seven major watersheds and three drainage regions in China and the chronic toxicity data for indigenous Chinese species.

Results and discussion

The results show that the risks of three chlorophenols are ranked PCP>2,4-DCP??2,4,6-TCP. PCP posed little ecological risk while 2,4-DCP and 2,4,6-TCP posed negligible or de minimis risk in Chinese surface water. However, the risks varied with different river basins, for example, PCP posed some ecological risk in the Yangtze, Huaihe, and Pearl Rivers. The magnitude of 2,4-DCP and 2,4,6-TCP pollution in North China was more serious than that in South China.

Conclusion

The probabilistic risk assessment approach, which can provide more information for risk managers and decision makers, was favored over the screening-level single-value estimate method. However, the results from all tiers of the ERA methods in the framework were consistent with each other.     

Oxidative degradation of chlorophenol derivatives promoted by microwaves or power ultrasound: a mechanism investigation

Background, aim, and scope

Phenols are the most common pollutants in industrial wastewaters (particularly from oil refineries, resin manufacture, and coal processing). In the last two decades, it has become common knowledge that they can be effectively destroyed by nonconventional techniques such as power ultrasound (US) and/or microwave (MW) irradiation. Both techniques may strongly promote advanced oxidation processes (AOPs). The present study aimed to shed light on the effect and mechanism of US- and MW-promoted oxidative degradation of chlorophenols; 2,4-dichlorophenoxyacetic acid (2,4-D), a pesticide widespread in the environment, was chosen as the model compound.

Materials and methods

2,4-D degradation by AOPs was carried out either under US (20 and 300 kHz) in aqueous solutions (with and without the addition of Fenton reagent) or solvent-free under MW with sodium percarbonate (SPC). All these reactions were monitored by gas chromatography–mass spectrometry (GC–MS) analysis and compared with the classical Fenton reaction in water under magnetic stirring. The same set of treatments was also applied to 2,4-dichlorophenol (2,4-DCP) and phenol, the first two products that occur a step down in the degradation sequence. Fenton and Fenton-like reagents were employed at the lowest active concentration.

Results

The effects of US and MW irradiation were investigated and compared with those of conventional treatments. Detailed mechanisms of Fenton-type reactions were suggested for 2,4-D, 2,4-DCP, and phenol, underlining the principal degradation products identified. MW-promoted degradation under solvent-free conditions with solid Fenton-like reagents (viz. SPC) is extremely efficient and mainly follows pyrolytic pathways. Power US strongly accelerates the degradation of 2,4-D in water through a rapid generation of highly reactive radicals; it does not lead to the formation of more toxic dimers.

Discussion

We show that US and MW enhance the oxidative degradation of 2,4-D and that a considerable saving of oxidants and cutting down of reaction times is thereby achieved. The results support the interpretation of previously published data and improve the understanding of the factors of direct degradation along different pathways.

Conclusions

Oxidative pathways for 2,4-D, 2,4-DCP, and phenol were proposed by a careful monitoring of the reactions and detection of intermediates by GC–MS.

Recommendations and perspectives

The understanding of the factors that affect chlorophenols degradation along different pathways may facilitate the optimization of the treatment. Type of energy source (US or MW), power, and frequency to be applied could be designed in function of the operative scenario (amount of pollutant in soil, water, or oils).     

Characteristics of an aerobic denitrifier that utilizes ammonium and nitrate simultaneously under the oligotrophic niche

Introduction

An aerobic denitrifier was isolated from the Hua-Jia-Chi pond in China and identified as Pseudomonas mendocina 3-7 (Genbank No. HQ285879). This isolated strain could express periplasmic nitrate reductase which is essential for aerobic denitrification occurred when the dissolved oxygen (DO) level maintains at 3?C10?mg?L^?1.

Methods

To determine whether the ability of isolated strain is exhibited in the bioremediation of polluted drinking source water, the heterotrophic nitrification and aerobic denitrification characteristics of P. mendocina 3-7 under different cultural conditions such as oxygen level, nitrate and organic concentrations were studied from the nitrogenous balance in the paper.

Results and conclusions

By measuring the nitrogen balance in all experiments under different culture conditions, the removal of total organic carbon and ammonium was positively correlated with total nitrogen removal, especially under high substrate level. With substrate concentration decreasing, ammonium and nitrate removal occurred separately, and ammonium was completely utilized first under low substrate concentration. Compared to that under high substrate level, the specific growth rate of P. mendocina 3-7 was not low under the low substrate level and the pollutant removal efficiencies remained high, which implies the stronger nitrogen removal and acclimatization capacities of the strain in oligotrophic niches.     

Evaluation of substrate removal kinetics for UASB reactors treating chlorinated ethanes

Purpose

Lack of focus on the treatment of wastewaters bearing potentially hazardous pollutants like 1,1,2 trichloroethane and 1,1,2,2 tetrachloroethane in anaerobic reactors has provided an impetus to undertake this study. The objective of this exercise was to quantify the behavior of upflow anaerobic sludge blanket reactors and predict their performance based on the overall organic substrate removal.

Methods

The reactors (wastewater-bearing TCA (R2), and wastewater-bearing TeCA (R3)) were operated at different hydraulic retention times (HRTs), i.e., 36, 30, 24, 18, and 12?h corresponding to food-to-mass ratios varying in the range of 0.2?C0.7?mg chemical oxygen demand (COD) mg^?1 volatile suspended solids day^?1. The process kinetics of substrate utilization was evaluated on the basis of experimental results, by applying three mathematical models namely first order, Grau second order, and Michaelis-Menten type kinetics.

Results

The results showed that the lowering of HRT below 24?h resulted in reduced COD removal efficiencies and higher effluent pollutant concentrations in the reactors. The Grau second-order model was successfully applied to obtain the substrate utilization kinetics with high value of R ² (>0.95). The Grau second-order substrate removal constant (K ₂) was calculated as 1.12 and 7.53?day^?1 for reactors R2 and R3, respectively.

Conclusion

This study demonstrated the suitability of Grau second-order kinetic model over other models, for predicting the performance of reactors R2 and R3, in treating wastewaters containing chlorinated ethanes under different organic and hydraulic loading conditions.     

Effect of C/N ratios on the performance of earthworm eco-filter for treatment of synthetics domestic sewage

Purpose

The performances of filter systems that use earthworms and plants, combined with earthworm eco-filter (EE) systems in treating synthetic domestic sewage (SDS) with different C/N ratios, were investigated for a 9-month period.

Methods

The effects of the combination of filters, earthworms, plants, as well as the combination of earthworms and plants on SDS nutrient removal efficiency were separately investigated to select the optimum system for treating SDS. The results of the current study could be used to determine how treatment performance responds to different C/N ratios and to explain and predict the performance of an operating EE system.

Results

EE systems with earthworms and plants (EP groups) consistently performed better than the other types of systems (CK, E, and P; that is, without earthworms and without plants, with earthworms and without plants, and without earthworms and with plants, respectively) under all C/N ratios. The highest removal efficiencies of chemical oxygen demand, total nitrogen, total phosphorus, and total organic carbon were achieved under C/N ratios of 6:1, 6:1, 6:1, and 9:1, respectively. The optimum nutrient removal efficiency was achieved at C/N?=?6, and the contribution order for nutrient removal was EP > P > E > CK.

Conclusions

Influent C/N ratios, the time of year, and the synergetic effects of earthworm behavior and microorganisms significantly affected nutrient removal efficiencies. Considering the removal of all nutrients, EE systems with plants and earthworms achieved optimum removal effects in July when the influent C/N ratio was controlled at 6. Appropriate control of carbon and nitrogen source concentrations permitted the achievement of optimal nutrient removal effects.     

Biofilm formation and microbial community analysis of the simulated river bioreactor for contaminated source water remediation

Background, aim, and scope

The start-up pattern of biofilm remediation system affects the biofilm characteristics and operating performances. The objective of this study was to evaluate the performances of the contaminated source water remediation systems with different start-up patterns in view of the pollutants removal performances and microbial community succession.

Methods

The operating performances of four lab-scale simulated river biofilm reactors were examined which employed different start-up methods (natural enrichment and artificial enhancement viadischarging sediment with influent velocity gradient increase) and different bio-fillers (Elastic filler and AquaMats? ecobase). At the same time, the microbial communities of the bioreactors in different phases were analyzed by polymerase chain reaction, denaturing gradient gel electrophoresis, and sequencing.

Results and discussion

The pollutants removal performances became stable in the four reactors after 2 months?? operation, with ammonia nitrogen and permanganate index (COD_Mn) removal efficiencies of 84.41?C94.21% and 69.66?C76.60%, respectively. The biomass of mature biofilm was higher in the bioreactors by artificial enhancement than that by natural enrichment. Microbial community analysis indicated that elastic filler could enrich mature biofilm faster than AquaMats?. The heterotrophic bacteria diversity of biofilm decreased by artificial enhancement, which favored the ammonia-oxidizing bacteria (AOB) developing on the bio-fillers. Furthermore, Nitrosomonas- and Nitrosospira-like AOB coexisted in the biofilm, and Pseudomonas sp., Sphaerotilus sp., Janthinobacterium sp., Corynebacterium aurimucosum were dominant in the oligotrophic niche.

Conclusion

Artificial enhancement via the combination of sediment discharging and influent velocity gradient increasing could enhance the biofilm formation and autotrophic AOB enrichment in oligotrophic niche.     

Efficient biosorption of chromium(VI) ion by dry Araucaria leaves

Background

In this paper, batch removal of hexavalent chromium from aqueous solutions by Araucaria heterophylla leaves was investigated. The batch experiments were conducted to study the adsorption of metal species and effect of different pH, contact time, metal concentration, biosorbent concentration, and adsorption capacity.

Method

Freundlich and Langmuir??s isotherm model were used to describe the adsorption behavior, and the experimental results fitted Freundlich model well.

Results

The adsorption efficiency observed for all chromium concentrations, i.e., 1, 3, 5, and 10?mg/L was 100% and the equilibrium was achieved in 30?min for 1 and 3?mg/L, whereas for 5 and 10?mg/L, it was less than 60?min. FTIR spectra was taken to identify functional groups involved in the biosorption.

Conclusion

Thus, Araucaria leaves can be considered as one of the cheap and efficient biosorbent for toxic hexavalent chromium removal from natural or wastewaters.     

Isolation and characterization of 3-nitrophenol-degrading bacteria associated with rhizosphere of Spirodela polyrrhiza

Introduction

The accelerated biodegradation of 3-nitrophenol (3-NP) in the rhizosphere of giant duckweed (Spirodela polyrrhiza) was investigated.

Materials and methods

Biodegradation of 3-nitrophenol in the rhizosphere of a floating aquatic plant, S. polyrrhiza, was investigated by using three river water samples supplemented with 10?mg?l^?1 of 3-NP. Isolation and enrichment culture of 3-NP-degrading bacteria were performed in basal salts medium containing 3-NP (50?mg?l^?1). The isolated strains were physiologically and phylogenetically characterized by using an API20NE kit and 16S rRNA gene sequencing.

Results and discussion

Accelerated removal of 3-NP (100%) was observed in river water samples with S. polyrrhiza compared with their removal in plant-free river water. Also, 3-NP persisted in an autoclaved solution with aseptic plants, suggesting that the accelerated 3-NP removal resulted largely from degradation by bacteria inhabiting the plant rather than from adsorption and uptake by the plant. We successfully isolated six and four strains of 3-NP-degrading bacteria from the roots of S. polyrrhiza and plant-free river water, respectively. Phylogenetic analysis based on 16S rRNA gene divided the 3-NP-degrading bacteria into two taxonomic groups: the genera Pseudomonas and Cupriavidus. The strains belonging to the genus Cupriavidus were only isolated from the roots of duckweed. All strains isolated from the roots utilized 3-NP (0.5?mM) as a sole carbon and energy source, indicating that they could have contributed to the accelerated degradation of 3-NP in the rhizosphere of S. polyrrhiza.

Conclusions

The rhizoremediation using S. polyrrhiza and its rhizosphere bacteria can be an effective strategy for cleaning up the 3-NP-contaminated surface waters.     

Removal of arsenate from groundwater by electrocoagulation method

Purpose

Arsenic, a toxic metalloid in drinking water, has become a major threat for human beings and other organisms. In the present work, attempts have been made to remove arsenate from the synthetic as well as natural water of Ballia district, India by electrocoagulation method. Efforts have also been made to optimize the various parameters such as initial arsenate concentration, pH, applied voltage, processing time, and working temperature.

Method

Electrocoagulation is a fast, inexpensive, selective, accurate, reproducible, and eco-friendly method for arsenate removal from groundwater. The present paper describes an electrocoagulation method for arsenate removal from groundwater using iron and zinc as anode and cathode, respectively.

Results

The maximum removal of arsenate was 98.8% at 2.0?mg?L^?1, 7.0, 3.0?V, 10.0?min, and 30°C as arsenate concentration, pH, applied voltage, processing time, and working temperature, respectively. Relative standard deviation, coefficient of determination (r ²), and confidence limits were varied from 1.50% to 1.59%, 0.9996% to 0.9998%, and 96.0% to 99.0%, respectively. The treated water was clear, colorless, and odorless without any secondary contamination. The developed and validated method was applied for arsenate removal of two samples of groundwater of Ballia district, U.P., India, having 0.563 to 0.805?mg?L^?1, arsenate concentrations.

Conclusions

The reported method is capable for the removal of arsenate completely (100% removal) from groundwater of Ballia district. There was no change in the groundwater quality after the removal of arsenate. The treated water was safe for drinking, bathing, and recreation purposes. Therefore, this method may be the choice of arsenate removal from natural groundwater.     

Isolation and characterization of a Rhodococcus strain with phenol-degrading ability and its potential use for tannery effluent biotreatment

Introduction

Wastewater derived from leather production may contain phenols, which are highly toxic, and their degradation could be possible through bioremediation technologies.

Materials, methods and results

In the present work, microbial degradation of phenol was studied using a tolerant bacterial strain, named CS1, isolated from tannery sediments. This strain was able to survive in the presence of phenol at concentrations of up to 1,000?mg/L. On the basis of morphological and biochemical properties, 16S rRNA gene sequencing, and phylogenetic analysis, the isolated strain was identified as Rhodococcus sp. Phenol removal was evaluated at a lab-scale in Erlenmeyer flasks and at a bioreactor scale in a stirred tank reactor. Rhodococcus sp. CS1 was able to completely remove phenol in a range of 200 to 1,000?mg/L in mineral medium at 30 ± 2?°C and pH 7 as optimal conditions. In the stirred tank bioreactor, we studied the effect of some parameters, such as agitation (200?C600 rpm) and aeration (1?C3?vvm), on growth and phenol removal efficiency. Faster phenol biodegradation was obtained in the bioreactor than in Erlenmeyer flasks, and maximum phenol removal was achieved at 400?rpm and 1 vvm in only 12?h. Furthermore, Rhodococcus sp. CS1 strain was able to grow and completely degrade phenols from tannery effluents after 9?h of incubation.

Conclusion

Based on these results, Rhodococcus sp. CS1 could be an appropriate microorganism for bioremediation of tannery effluents or other phenol-containing wastewaters.     

Removal of sulfamethoxazole from solution by raw and chemically treated walnut shells

Purpose

The sorption of sulfamethoxazole, a frequently detected pharmaceutical compound in the environment, onto walnut shells was evaluated.

Methods

The sorption proprieties of the raw sorbent were chemically modified and two additional samples were obtained, respectively HCl and NaOH treated. Scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric (TG/DTG) techniques were applied to investigate the effect of the chemical treatments on the shell surface morphology and chemistry. Sorption experiments to investigate the pH effect on the process were carried out between pH?2 and 8.

Results

The chemical treatment did not substantially alter the structure of the sorbent (physical and textural characteristics) but modified the surface chemistry of the sorbent (acid?Cbase properties, point of zero charge??pH_pzc). The solution pH influences both the sorbent??s surface charge and sulfamethoxazole speciation. The best removal efficiencies were obtained for lower pH values where the neutral and cationic sulfamethoxazole forms are present in the solution. Langmuir and Freundlich isotherms were applied to the experimental adsorption data for sulfamethoxazole sorption at pH?2, 4, and 7 onto raw walnut shell. No statistical difference was found between the two models except for the pH?2 experimental data to which the Freundlich model fitted better.

Conclusion

Sorption of sulfamethoxazole was found to be highly pH dependent in the entire pH range studied and for both raw and treated sorbent.     

Enhanced degradation of azo dye alizarin yellow R in a combined process of iron–carbon microelectrolysis and aerobic bio-contact oxidation

Purpose

With the aim of enhanced degradation of azo dye alizarin yellow R (AY) and further removal of the low-strength recalcitrant matter (LsRM) of the secondary effluent as much as possible, our research focused on the combination of aerobic bio-contact oxidation (ABO) with iron/carbon microelectrolysis (ICME) process.

Materials and methods

The combined ABO (with effective volume of 2.4?l) and ICME (with effectively volume of 0.4?l) process were studied with relatively short hydraulic retention time (HRT) of 4 or 6?h.

Results

At the HRT of 6?h with the reflux ratio of 1 and 2, the AY degradation efficiency in the final effluent was >96.5%, and the total organic carbon (TOC) removal efficiency were 69.86% and 79.44%, respectively. At the HRT of 4?h and the reflux ratio of 2, TOC removal efficiency and AY degradation efficiency were 73.94% and 94.89%, respectively. The ICME process obviously enhanced the total AY removal and the generated micromolecule acids and aldehydes then that wastewater backflow to the ABO where they were further biodegraded.

Conclusion

The present research might provide the potential options for the advanced treatment azo dyes wastewater with short HRT and acceptable running costs.     

Occurrence and distribution of selected pharmaceuticals and personal care products in aquatic environments: a comparative study of regions in China with different urbanization levels

Purpose

We analyzed and compared the distributions of 13 target pharmaceuticals in different water samples from the Hangzhou metropolitan area and Linan County, Southeast China.

Methods

Sampling was conducted in five hospitals, two wastewater treatment plants (WWTPs), and Qiantang River. Samples were concentrated by solid-phase extraction and PPCP concentrations were determined by UPLC-MS/MS.

Results and discussion

Trimethoprim, erythromycin A dihydrate, norfloxacin, ofloxacin, diclofenac sodium, and atenolol were the most frequently detected pharmaceuticals in hospital effluents. Most of the pharmaceutical concentrations in hospital effluents were higher than those in the WWTP influents. Although both WWTPs adopt the anaerobic?Caerobic?Canoxic treatment process, the removal rates for pharmaceuticals, such as trimethoprim and diclofenac sodium, were completely different. Meanwhile, erythromycin A dihydrate, ofloxacin, penicillin-G, cephalexin, cefazolin, ibuprofen, and diclofenac sodium were detected in Qiantang River.

Conclusions

These results indicate that hospitals are more concentrated sources of pharmaceuticals than WWTPs, and the WWTPs are not the only route of entry of pharmaceuticals into aquatic environments in these two regions.     

Acute effect of benzo[a]anthracene on the biodegradation of peptone under aerobic conditions

Background

This study investigated the acute effect of benzo[a]anthracene, a significant compound among polycyclic aromatic hydrocarbons, on the biodegradation of a synthetic organic substrate??a peptone/meat extract mixture??under aerobic conditions.

Methods

A laboratory-scale sequencing batch reactor was sustained at steady state at a sludge age of 10?days with substrate feeding. Inhibition tests involved running a series of batch reactors initially seeded with the biomass obtained from the parent reactor. After the biomass seeding, the reactors were started with the peptone mixture and a range of initial benzo[a]anthracene concentrations between 0.5 and 88?mg/L. Experimental profiles of oxygen uptake rates and polyhydroxyalkanoates were evaluated by calibration of a selected model.

Results

Lower doses of benzo[a]anthracene had no effect on process kinetics. The noticeable acute impact was only observed with the addition of 88?mg/L of benzo[a]anthracene, but it was limited with the storage mechanism: the amount of organic substrate diverted to polyhydroxyalkanoates was significantly reduced with a corresponding decrease in the maximum storage rate, k _STO, from 2.7 down to 0.6?day^?1. Similarly, the maximum growth rate from internally stored polyhydroxyalkanoates was lowered from 2.3 to 1.0?day^?1.

Conclusion

Among the mechanisms for direct substrate utilization, only the hydrolysis rate was slightly reduced, but otherwise, the overall COD removal efficiency was not affected.     

Removal of hexavalent chromium of contaminated soil by coupling electrokinetic remediation and permeable reactive biobarriers

Purpose

In this study, a novel and ecological alternative have been developed to treat soils contaminated with hexavalent chromium coupling two well-known systems: electrokinetic remediation and permeable reactive biobarriers. The electric field promotes the electromigration of the hexavalent chromium oxyanions towards the anode. The biobarriers were placed before the anode electrode, in order to promote the reduction and retention of the chromium migrating in its direction. Thus, this technology provided a global treatment to soil removal without subsequent treatments of the contaminated effluents.

Methods

The electrokinetic system was coupled with two different permeable reactive biobarriers composed by Arthrobacter viscosus bacteria, supported either in activated carbon or zeolite. An electric field of 10?V was applied and two different treatment times of 9 and 18?days were tested.

Results

Removal values of 60% and 79% were obtained when electrokinetic treatment was coupled with zeolite and activated carbon biobarriers, respectively, for a test period of 18?day. The reduction of hexavalent chromium to trivalent chromium was around 45% for both systems.

Conclusions

In this work, two types of biobarriers were efficiently coupled to electrokinetic treatment to decontaminate soil with Cr(VI). Furthermore, the viability of the new coupling technology developed (electrokinetic?+?biobarriers) to treat low-permeability polluted soils was demonstrated.     

Synthesis of α-Fe2O3 nanofibers for applications in removal and recovery of Cr(VI) from wastewater

Purpose

Nanomaterials such as iron oxides and ferrites have been intensively investigated for water treatment and environmental remediation applications. The purpose of this work is to synthesize α-Fe₂O₃ nanofibers for potential applications in removal and recovery of noxious Cr(VI) from wastewater.

Methods

α-Fe₂O₃ nanofibers were synthesized via a simple hydrothermal route followed by calcination. The crystallographic structure and the morphology of the as-prepared α-Fe₂O₃ nanofibers were characterized by X-ray diffraction, scanning electron microscope, and transmission electron microscope. Batch adsorption experiments were conducted, and Fourier transform infrared spectra were recorded before and after adsorption to investigate the Cr(VI) removal performance and adsorption mechanism. Langmuir and Freundlich modes were employed to analyze the adsorption behavior of Cr(VI) on the α-Fe₂O₃ nanofibers.

Results

Very thin and porous α-Fe₂O₃ nanofibers have been successfully synthesized for investigation of Cr(VI) removal capability from synthetic wastewater. Batch experiments revealed that the as-prepared α-Fe₂O₃ nanofibers exhibited excellent Cr(VI) removal performance with a maximum adsorption capacity of 16.17 mg g^?1. Furthermore, the adsorption capacity almost kept unchanged after recycling and reusing. The Cr(VI) adsorption process was found to follow the pseudo-second-order kinetics model, and the corresponding thermodynamic parameters ΔG°, ΔH°, and ΔS° at 298 K were calculated to be ?26.60 kJ?mol^?1, ?3.32 kJ?mol^?1, and 78.12 J?mol^?1 K^?1, respectively.

Conclusions

The as-prepared α-Fe₂O₃ nanofibers can be utilized as efficient low-cost nano-absorbents for removal and recovery of Cr(VI) from wastewater.     

Occurrence of diarrheagenic Escherichia coli genes in raw water of water treatment plants

Purpose

The high incidences of waterborne diseases are frequently associated with diarrheagenic Escherichia coli (DEC). DEC may pose a health risk to people who contact surface water for recreation or domestic use. However, there is no published report on the monitoring of DEC in drinking water sources in Taiwan. In this study, the occurrence of DEC genes in raw water for water treatment plants in Taiwan was investigated.

Method

Raw water samples were taken from water treatment plants adjacent to the Kaoping River in southern Taiwan. Each water sample was treated with membrane filtration followed by DNA extraction from the concentrate and concentrate enrichment, respectively. The target genes for various DEC strains of genes were identified, including enteroaggregative E. coli (EAEC), enterohemorrhagic E. coli (EHEC), enteroinvasive E. coli (EIEC), enteropathogenic E. coli (EPEC), and enterotoxigenic E. coli (ETEC).

Results

Among 55 water samples analyzed, DEC genes were detected in 16 (29.1%) samples. Strain-specific genes for EAEC, EHEC, EIEC, and EPEC were found in the percentages of 3.6%, 10.9%, 9.1%, and 9.1%, respectively. The specific gene for ETEC is not detected in the study. By looking at the presence/absence of specific genes and water sample characteristics, water temperature was found to differ significantly between samples with and without EHEC gene. In addition, pH levels differed significantly for EHEC and EPEC presence/absence genes, and turbidity was significantly different for water with and without EPEC genes.

Conclusion

DEC genes were detected in 29.1% of the raw water samples in the study location. The potential health threat may be increased if the treatment efficiencies are not properly maintained. Routine monitoring of DEC in drinking water sources should be considered.