Sorption determination of phenols and polycyclic aromatic hydrocarbons in a multiphase constructed wetland system by solid phase microextraction

The Partial Contribution of Constructed Wetland Components (Roots, Gravel, Microorganisms) in the Removal of Phenols: A Mini Review

Constructed wetlands (CW) have attracted growing interest in wastewater treatment research in the last 20 years, and have been investigated intensively worldwide. Many of the basic processes occurring in CWs have been qualitatively established; however, much quantitative knowledge is still lacking. In this mini review, the proportionate contributions of the different system components to removal of contaminants are examined. The main objective of this mini review is to provide a more in-depth assessment of the interactions between the porous bed, plants, and microorganisms during the removal of organic contaminants from the water in a subsurface flow CW system. In addition, a unique technique to study the partial contribution to the total removal of contaminants in a CW is described. Future studies in this field will expand our knowledge of any synergistic or antagonistic interactions between the components and facilitate improved CW construction and operation. Here, phenol will be used as a model industrial organic contaminant to illustrate our current understanding of the contributions of the different components to total removal. I will also discuss the various factors influencing the efficacy of bacteria, whether planktonic or as biofilm (on porous bed or plant roots), in subsurface flow CWs.

Application of constructed wetlands in the PAH remediation of surface water: A review

Polycyclic aromatic hydrocarbons (PAHs) pose adverse risks to ecosystems and public health because of their carcinogenicity and mutagenicity. As such, the extensive occurrence of PAHs represents a worldwide concern that requires urgent solutions. Wastewater treatment plants are not, however, designed for PAH removal and often become sources of the PAHs entering surface waters. Among the technologies applied in PAH remediation, constructed wetlands (CWs) exhibit several cost-effective and eco-friendly advantages, yet a systematic examination of the application and success of CWs for PAH remediation is missing. This review discusses PAH occurrence, distribution, and seasonal patterns in surface waters during the last decade to provide baseline information for risk control and further treatment. Furthermore, based on the application of CWs in PAH remediation, progress in understanding and optimising PAH-removal mechanisms is discussed focussing on sediments, plants, and microorganisms. Wetland plant traits are key factors affecting the mechanisms of PAH removal in CWs, including adsorption, uptake, phytovolatilization, and biodegradation. The physico-chemical characteristics of PAHs, environmental conditions, wetland configuration, and operation parameters are also reviewed as important factors affecting PAH removal efficiency. Whilst significant progress has been made, several key problems need to be addressed to ensure the success of large-scale CW projects. These include improving performance in cold climates and addressing the toxic threshold effects of PAHs on wetland plants. Overall, this review provides future direction for research on PAH removal using CWs and their large-scale operation for the treatment of PAH-contaminated surface waters.

A review on treatment of petroleum refinery and petrochemical plant wastewater: A special emphasis on constructed wetlands

Petroleum refinery and petrochemical plants (PRPP) are one of the major contributors to toxic and recalcitrant organic polluted water, which has become a significant concern in the field of environmental engineering. Several contaminants of PRPP wastewater are genotoxic, phytotoxic, and carcinogenic, thereby imposing detrimental effects on the environment. Many biological processes were able to achieve chemical oxygen demand (COD) removal ranging from 60% to 90%, and their retention time usually ranged from 10 to 100 days. These methods were not efficient in removing the petroleum hydrocarbons present in PRPP wastewater and produced a significant amount of oily sludge. Advanced oxidation processes achieved the same COD removal efficiency in a few hours and were able to break down recalcitrant organic compounds. However, the associated high cost is a significant drawback concerning PRPP wastewater treatment. In this context, constructed wetlands (CWs) could effectively remove the recalcitrant organic fraction of the wastewater because of the various inherent mechanisms involved, such as phytodegradation, rhizofiltration, microbial degradation, sorption, etc. In this review, we found that CWs were efficient in handling large quantities of high strength PRPP wastewater exhibiting average COD removal of around 80%. Horizontal subsurface flow CWs exhibited better performance than the free surface and floating CWs. These systems could also effectively remove heavy oil and recalcitrant organic compounds, with an average removal efficiency exceeding 80% and 90%, respectively. Furthermore, modifications by varying the aeration system, purposeful hybridization, and identifying the suitable substrate led to the enhanced performance of the systems.

Implementing a superhydrophobic substrate in immersed solvent-supported microextraction as a novel strategy for determination of organic pollutants in water samples

In this research, a new approach for extraction and determination of polycyclic aromatic hydrocarbons from sea and rain water samples was developed by implementing a superhydrophobic substrate and consuming the least amount of solvent. This version of solvent-supported microextraction enabled us to perform the procedure in the immersion mode with the slightest troubles arising from water leakage into the gas chromatography. The superhydrophobic property leads to the fixation of extracting solvent on the substrate surface during water sampling. To prepare a superhydrophobic substrate, a piece of melamine foam was coated by tannic acid and silica nanoparticles using methyltrimethoxysilane and tetramethyl orthosilicate. The morphology of the prepared foams was studied by scanning electron microscopy. The developed solvent-supported microextraction method in combination with gas chromatography-mass spectrometry was applied to the isolation and determination of some typical polycyclic aromatic hydrocarbons from aquatic media. Influential parameters such as substrate nature, extractive solvent, eluting solvent and its quantity and extraction time were investigated. The limits of detection and quantification of the method under the optimized conditions were 0.01-0.11 µg L^-1 and 0.03-1.01 µg L^-1, respectively. The relative standard deviations at the concentration level of 20 µg L^-1 were between 3% and 14% (n = 3). The linearity of calibration curves ranged from 0.03 to 60 µg L^-1. The implementation of the solvent-supported method to the analysis of real water samples was quite successful and the relative recoveries were between 88% and 107%.

Removal of dimethylphenols and ammonium in laboratory-scale horizontal subsurface flow constructed wetlands

Phenolic compounds in industrial wastewaters are toxic pollutants and pose a threat to public health and ecosystems. More recently, focus is being directed toward combining the treatment of these compounds with a cost-effective and environmentally sound technology. The removal efficiency of dimethylphenol and ammonium nitrogen was studied, for the first time, in three different laboratory-scale horizontal subsurface flow constructed wetlands planted with Juncus effusus. Two of the wetlands used were filled with gravel. One of these was planted and the second left without vegetation. The third wetland was a hydroponic system. It was found that the removal efficiencies of dimethylphenol was dependent on the inflow loading of the contaminant and was higher in the planted systems. Both planted systems yielded 99% removal efficiency up to loads of 240 mg/d, compared to only 73% for the unplanted constructed wetland. Factors and processes such as redox dynamics, methanogenesis, reduction of ammonium and low nitrate and nitrite concentrations imply simultaneous aerobic and anaerobic dimethylphenol transformations. A significant surplus of organic carbon was detected in the planted wetlands, which may originate from intermediates of the dimethylphenol transformation processes and/or organic plant root exudates. The present study demonstrates that horizontal subsurface flow constructed wetlands are a promising alternative system for the treatment of effluents contaminated with dimethylphenol isomers.

A flow-through aqueous standard generation system for thin film microextraction investigations of UV filters and biocides partitioning to different environmental compartments

In this paper problems associated with preparation of aqueous standard of highly hydrophobic compounds such as partial precipitation, being lost on the surfaces, low solubility in water and limited sample volume for accurate determination of their distribution coefficients are addressed. The following work presents two approaches that utilize blade thin film microextraction (TFME) to investigate partitioning of UV filters and biocides to humic acid (dissolved organic carbon) and sediment. A steady-state concentration of target analytes in water was generated using a flow-through aqueous standard generation (ASG) system. Dialysis membranes, a polytetrafluoroethylene permeation tube, and a frit porous (0.5 μm) coated by epoxy glue were basic elements used for preparation of the ASG system. In the currently presented study, negligible depletion TFME using hydrophilic-lipophilic balance (HLB) and octadecyl silica-based (C18) sorbents was employed towards the attainment of free concentration values of target analytes in the studied matrices. Thin film geometry provided a large volume of extraction phase, which improved the sensitivity of the method towards highly matrix-bound analytes. Extractions were performed in the equilibrium regime so as to prevent matrix effects and with aims to reach maximum method sensitivity for all analytes under study. Partitioning of analytes on dissolved organic carbon (DOC) was investigated in ASG to facilitate large sample volume conditions. Binding percentages and DOC distribution coefficients (Log K_DOC) ranged from 20 to 98% and 3.71-6.72, respectively. Furthermore, sediment-water partition coefficients (K_d), organic-carbon normalized partition coefficients (Log K_OC), and DOC distribution coefficients (Log K_DOC) were investigated in slurry sediment, and ranged from 33 to 2860, 3.31-5.24 and 4.52-5.75 Lkg^-1, respectively. The obtained results demonstrated that investigations utilizing ASG and TFME can yield reliable binding information for compounds with high log K_OW values. This information is useful for study of fate, transport, and ecotoxicological effects of UV filters and biocides in aquatic environment.

A review on the application of constructed wetlands for the removal of priority substances and contaminants of emerging concern listed in recently launched EU legislation

The presence of organic pollutants in the aquatic environment, usually found at trace concentrations (i.e., between ng L^-1 and μg L^-1 or even lower, known as micropollutants), has been highlighted in recent decades as a worldwide environmental concern due to their difficult elimination by conventional water and wastewater treatment processes. The relevant information on constructed wetlands (CWs) and their application for the removal of a specific group of pollutants, 41 organic priority substances/classes of substances (PSs) and 8 certain other substances with environmental quality standards (EQS) listed in Directive 2013/39/EU as well as 17 contaminants of emerging concern (CECs) of the Watch List of Decision 2015/495/EU, is herein reviewed. Studies were found for 24 PSs and 2 other substances with EQS: octylphenol, nonylphenol, perfluorooctane sulfonic acid, di(2-ethylhexyl)phthalate, trichloromethane, dichloromethane, 1,2-dichloroethane, pentachlorobenzene, benzene, polychlorinated dibenzo-p-dioxins, naphthalene, fluoranthene, trifluralin, alachlor, isoproturon, diuron, tributyltin compounds, simazine, atrazine, chlorpyrifos (chlorpyrifos-ethyl), chlorfenvinphos, hexachlorobenzene, pentachlorophenol, endosulfan, dichlorodiphenyltrichloroethane (or DDT) and dieldrin. A few reports were also published for 8 CECs: imidacloprid, erythromycin, clarithromycin, azithromycin, diclofenac, estrone, 17-beta-estradiol and 17-alpha-ethinylestradiol. No references were found for the other 17 PSs, 6 certain other substances with EQS and 9 CECs listed in EU legislation.

The use of halophytic plants for salt phytoremediation in constructed wetlands

This research studied the use of constructed wetlands (CWs) to reduce water salinity. For this purpose, three halophytic species of the Chenopodiaceae family (Salicornia europaea, Salsola crassa, and Bienertia cycloptera) that are resistant to saline conditions were planted in the CWs, and experiments were conducted at three different salinity levels [electrical conductivity (EC)∼2, 6, 10 dS/m]. EC and concentrations of calcium (Ca), magnesium (Mg), sodium (Na), and chlorine (Cl) were measured before and after phytoremediation with a retention time of 1 week. The results suggested that these plants were able to grow well and complete their life cycles at all the salinity levels within this study. Moreover, these plants reduced the measured parameters to acceptable levels. Therefore, these plants can be considered good options for salt phytoremediation.

Removal of phenol, bisphenol A, and 4-tert-butylphenol from synthetic landfill leachate by vertical flow constructed wetlands

Lab-scale vertical flow constructed wetlands (CWs) were used to remove phenol, bisphenol A (BPA), and 4-tert-butylphenol (4-t-BP) from synthetic young and old leachate. Removal percentages of phenolic compounds from the CWs were in the following order: phenol (88-100%)>4-t-BP (18-100%)≥BPA (9-99%). In all CWs, phenol was removed almost completely from leachate. Results show that BPA and 4-t-BP were removed more efficiently from CWs planted with Phragmites australis than from unplanted CWs, from old leachate containing lower amounts of acetate and propionate as easily degradable carbon sources than from young leachate, and in the dry season mode with long retention time than in the wet season mode with short retention time. Adsorption by initial removal and subsequent biodegradation processes might be major removal processes for these phenolic compounds. The presence of plant is beneficial for enrichment of BPA-degrading and 4-t-BP-degrading bacteria and for the carbon source utilization potential of microbes in CWs.

Hydrothermal carbonization of poly(vinyl chloride)

Poly(vinyl chloride) (PVC) was subjected to hydrothermal carbonization in subcritical water at 180-260 °C. Dehydrochlorination increased with increasing reaction temperature. The release of chlorine was almost quantitative above ∼235 °C. The fraction of organic carbon (OC) recovered in the hydrochar decreased with increasing operating temperature from 93% at 180 °C to 75% at 250 °C. A wide array of polycyclic aromatic hydrocarbons (PAHs) could be detected in the aqueous phase, but their combined concentration amounted to only ∼140 μg g(-1) PVC-substrate at 240 °C. A pathway for the formation of cyclic hydrocarbons and O-functionalized organics was proposed. Chlorinated hydrocarbons including chlorophenols could only be identified at trace levels (low ppb). Polychlorinated dibenzodioxins (PCDDs) and dibenzofurans (PCDFs) could not be detected. The sorption potential of the hydrochar turned out to be very low, in particular for polar organic pollutants. Our results provide strong evidence that hydrothermal carbonization of household organic wastes which can be tied to co-discarded PVC-plastic residues is environmentally sound regarding the formation of toxic organic products. Following these findings, hydrothermal treatment of PVC-waste beyond operating temperatures of ∼235 °C to allow complete release of organic chlorine should be further pursued.

Characterization of biocoals and dissolved organic matter phases obtained upon hydrothermal carbonization of brewer's spent grain

The wet biomass brewer's spent grain was subjected to hydrothermal carbonization to produce biocoal. Mass balance considerations indicate for about two thirds of the organic carbon of the input biomass to be transferred into the biocoal. The van Krevelen plot refers to a high degree of defunctionalization with decarboxylation prevailing over dehydration. Calorific data revealed a significant energy densification of biocoals as compared to the input substrate. Sorption coefficients of organic analytes covering a wide range of hydrophobicities and polarities on biocoal were similar to those for dissolved humic acids. Data from GC/MS analysis indicated that phenols and benzenediols along with fatty acids released from bound lipids during the hydrothermal process constituted abundant products. Our findings demonstrate that the brewer's spent grain by-product is a good feedstock for hydrothermal carbonization to produce biocoal, the latter offering good prospects for energetic and soil-improving application fields.