An overview of chlorophenols as contaminants and their removal from wastewater by adsorption: A review

Occurrence and fate of Adsorbable Organic Halogens (AOX) in two WWTPs from Romania

Absorbable organic halogens (AOX) are a global parameter which refers to a group of chemical compounds that contain one or more chlorine, bromine or iodine atoms in their molecule and can easily adsorb on activated carbon. The global concern related to the occurrence of the AOX compounds in the environment is due to their toxic and mutagenic effects on aquatic organisms and their potential role as inhibitors of microorganism growth, even at AOX low concentrations. The purpose of this study was to analyze the presence, occurrence and composition of absorbable organic halogens in wastewater and sewage sludge. In addition, their genotoxicity effect on the environment was tested on a bacterial biological model. Daily mass loading, mass emission and fate of AOX parameter were investigated in two wastewater treatment plants (wastewater and sewage sludge samples) from Romania, Galati and Iasi. Their AOX daily mass loadings (151 and 55.4 g/day/1000people) and mass emissions into the environment (47.8 and 23.5 g/day/1000 people) for both locations were correlated with the concentration level of volatile organic compounds, chlorophenols, organochlorine pesticides and polychlorinated biphenyls from both wastewater and sewage sludge, respectively. Concentration levels of detected halogenated organic compounds (regulated by current standards) accounted only for a small percentage (3.70-14.5%) from the total AOX amount. An exception was observed in the case of dehydrated sludge samples where the identified compounds accounted for 80% of the AOX content from Iasi WWTP and 53% for Galati. Evaluating the genotoxic activity of AOX in sludge samples showed that genotoxicity was not induced up to 100 µg/mL dehydrated sludge.

Estimation of 2,4-dichlorophenol photocatalytic removal using different artificial intelligence approaches

Photocatalytic degradation is one of the effective methods to remove various pollutants from domestic and industrial effluents. Several operational parameters can affect the efficiency of photocatalytic degradation. Performing experimental methods to obtain the percentage degradation (%degradation) of pollutants in different operating conditions is costly and time-consuming. For this reason, the use of computational models is very useful to present the %degradation in various operating conditions. In our previous work, Fe3O4/TiO2 nanocomposite containing different amounts of silver nanoparticles (Fe3O4/TiO2/Ag) were synthesized, characterized by various analytical techniques and applied to degradation of 2,4-dichlorophenol (2,4-DCP). In this work, a series of models, including stochastic gradient boosting (SGB), artificial neural network (ANN), adaptive neuro-fuzzy inference system (ANFIS), the improvement of ANFIS with genetic algorithm (GA-ANFIS), and particle swarm optimization (PSO-ANFIS) were developed to estimate the removal percentage of 2,4-DCP. The model inputs comprised of catalyst dosage, radiation time, initial concentration of 2,4-DCP, and various volumes of AgNO3. Evaluating the developed models showed that all models can predict the occurring phenomena with good compatibility, but the PSO-ANFIS and the SGB models gave a high accuracy with the coefficient of determination (R 2) of 0.99. Moreover, the relative contributions, and the relevancy factors of input parameters were evaluated. The catalyst dosage and radiation time had the highest (32.6%), and the lowest (16%) relative contributions on the predicting of removal percentage of 2,4-DCP, respectively.

Magnetic adsorbent developed with alkali-thermal pretreated biogas slurry solids for the removal of heavy metals: optimization, kinetic, and equilibrium study

Discharge of effluents containing heavy metal without adequate treatment causes contamination of water resources and creates environmental and health issues. Adsorption could be applied to remediate heavy metals from wastewater effectively. In this study, a low-cost adsorbent was prepared by magnetic modification of pretreated biogas slurry solids (BSS) to remove heavy metals such as Cu²⁺, Cd²⁺, and Pb²⁺. The temperature (423 K) and time (1.5 h) of pretreatment, the BSS to KOH ratio (1:10 w/v), and the ratio of magnetic iron nanoparticle (MIN) to pretreated BSS (PSS) (1:2 w/w) were optimized for the preparation of adsorbent. The magnetically modified pretreated biogas slurry solid (MMPSS) adsorbent was characterized by BET isotherm, FTIR, XRD, FESEM, VSM, and EDX analysis. MMPSS attained equilibrium at 60 min and showed an adsorption capacity of 26.84 mg/g, 24.79 mg/g, and 23.86 mg/g with removal percentages 89.46%, 82.63%, and 79.54% for Cu²⁺, Cd²⁺, and Pb²⁺, respectively, at 310 K and pH 6 with an initial concentration of 150 mg/L. The adsorption process followed a pseudo second-order model with an R² value above 0.9 for all metals with a well-approaching equilibrium pattern. The good fit of experimental data by the Langmuir isotherm model implied monolayer adsorption. The metal ions adsorbed onto MMPSS were able to desorb effectively in the presence of HCl and retained 83.01%, 84.66%, and 81.83% of the initial adsorption capacity for Cu²⁺, Cd²⁺, and Pb²⁺ respectively after 5 consecutive cycles.

Graphene oxide functionalized with cobalt ferrites applied to the removal of bisphenol A: ionic study, reuse capacity and desorption kinetics

A new adsorbent material based on graphene oxide (GO) functionalized with magnetic cobalt ferrite nanoparticles (γCoFe₂O₄) was synthesized via ultrasonication to remove the endocrine-disrupting-chemical bisphenol A (BPA) from aqueous solutions. The synthesized material (GO-γCoFe₂O₄) was characterized by TEM, SEM, DRX and FTIR analysis. Magnetization measures proved that the adsorbent had superparamagnetic characteristics that facilitated its separation from the aqueous solution. The maximum adsorption capacity obtained was 30 mg g^-1 with adsorbent concentration of 1 g L^-1, temperature of 55°C and natural pH of the solution. The experimental data were better adjusted to the kinetic models of pseudo-second-order and Langmuir isotherm. The thermodynamic parameters showed that the BPA adsorption on GO-γCoFe₂O₄ was spontaneous, exothermic and thermodynamically favourable. Desorption kinetics was performed using 50% ethanol as solvent, resulting in an equilibrium time of 4 h with better adjustment to the pseudo-second order kinetic model. The adsorbent showed a high regeneration capacity maintaining adsorptive capacity above 75% after 6 cycles of reuse.

Combined Analytical Study on Chemical Transformations and Detoxification of Model Phenolic Pollutants during Various Advanced Oxidation Treatment Processes

Advanced oxidation processes (AOPs) have been introduced to deal with different types of water pollution. They cause effective chemical destruction of pollutants, yet leading to a mixture of transformation by-products, rather than complete mineralization. Therefore, the aim of our study was to understand complex degradation processes induced by different AOPs from chemical and ecotoxicological point of view. Phenol, 2,4-dichlorophenol, and pentachlorophenol were used as model pollutants since they are still common industrial chemicals and thus encountered in the aquatic environment. A comprehensive study of efficiency of several AOPs was undertaken by using instrumental analyses along with ecotoxicological assessment. Four approaches were compared: ozonation, photocatalytic oxidation with immobilized nitrogen-doped TiO₂ thin films, the sequence of both, as well as electrooxidation on boron-doped diamond (BDD) and mixed metal oxide (MMO) anodes. The monitored parameters were: removal of target phenols, dechlorination, transformation products, and ecotoxicological impact. Therefore, HPLC–DAD, GC–MS, UHPLC–MS/MS, ion chromatography, and 48 h inhibition tests on Daphnia magna were applied. In addition, pH and total organic carbon (TOC) were measured. Results show that ozonation provides by far the most suitable pattern of degradation accompanied by rapid detoxification. In contrast, photocatalysis was found to be slow and mild, marked by the accumulation of aromatic products. Preozonation reinforces the photocatalytic process. Regarding the electrooxidations, BDD is more effective than MMO, while the degradation pattern and transformation products formed depend on supporting electrolyte.

Modelling the cathodic reduction of 2,4-dichlorophenol in a microbial fuel cell

This work presents a simplified mathematical model able to predict the performance of a microbial fuel cell (MFC) for the cathodic dechlorination of 2,4-dichlorophenol (2,4-DCP) operating at different cathode pH values (7.0 and 5.0). Experimental data from previous work were utilized for the fitting of the model. The MFC modelled consisted of two chambers (bioanode and abiotic cathode), wherein the catholyte contained 300 mg L⁻¹ of 2,4-DCP and the anolyte 1000 mg L⁻¹ of sodium acetate. The model considered two mixed microbial populations in the anode compartment using sodium acetate as the carbon source for growth and maintenance: electrogenic and non-electrogenic biomass. 2,4-DCP, its intermediates of the reductive process (2-chlorophenol, 2-CP and 4-chlorophenol, 4-CP) and protons were considered in the model as electron acceptors in the electrogenic mechanism. The global process rate was assumed to be controlled by the biological mechanisms and modelled using multiplicative Monod-type equations. The formulation of a set of differential equations allowed to describe the simultaneous evolution of every component: concentration of sodium acetate in the anodic compartment; and concentration of 2,4-DCP, 2-CP, 4-CP, phenol and chloride in the cathode chamber. Current production and coulombic efficiencies were also estimated from the fitting. It was observed that most of the organic substrate was used by non-electrogenic mechanism. The influence of the Monod parameters was more important than the influence of the biomass yield coefficients. Finally, the model was employed to simulate different scenarios under distinct experimental conditions.

A review on recent trends in the removal of emerging contaminants from aquatic environment using low-cost adsorbents

Emerging contaminants (ECs), a class of contaminants with low concentrations but significant harm, have received a lot of attention in recent times. ECs comprises of various chemicals that enter the environment every day. In today's modern lifestyle, we use many chemical-based products. These persist in wastewater and ultimately enter the water bodies, causing serious problems to the human and aquatic ecosystem. This is because the conventional wastewater treatment methods are inefficient in identifying and removing such contaminants. Aiming for a long-term, effective solution to this issue, Adsorption was proposed. Although several adsorbents are already present in the market, which have proved beneficial in removing such ECs, not all are affordable. This article reviews replacing costly adsorbents with agriculture-based biomass that are abundant, inexpensive, and biodegradable and possess excellent adsorption capacity. The objectives of this article is to look at adsorption as a viable treatment option for emerging pollutants, as well as sophisticated and cost-effective emerging contaminants treatment options.

Construction of imine-linked covalent organic framework as advanced adsorbent for the sensitive determination of chlorophenols

Food safety is a great concern of the general public. Chlorophenols (CPs) as organic pollutant can be found in drinking water and foods, causing serious harm to human health. Herein, imine-linked covalent organic frameworks (COFs), named as TAPT-AN-COF, was synthesized by aniline modulation strategy through condensation of 1,3,5-triformylphoroglucinol and 4,4',4''-(1,3,5-Triazine-2,4,6-triyl)trianiline with aniline as modulator. The prepared TAPT-AN-COF possesses good crystallinity and regular morphology, displaying excellent adsorption capability towards CPs pollutants. Thus, the TAPT-AN-COF was used as novel adsorbent for off-line solid-phase extraction of four CPs (2-CP, 3-CP, 2,3-CPs, 2,4-CPs) from bottled water, tea drink and honey samples before high performance liquid chromatography-ultraviolet detection. Under optimal conditions, wide linear range, low detection limits and satisfactory extraction recovery were gained. The π-stacking and hydrophobic interactions between the TAPT-AN-COF and the analytes played an important role in the adsorption. The established method has a great potential in determining other hydrophobic aromatic compounds.

Environmentally Friendly Polyvinyl Alcohol-Alginate/Bentonite Semi-Interpenetrating Polymer Network Nanocomposite Hydrogel Beads as an Efficient Adsorbent for the Removal of Methylene Blue from Aqueous Solution

Hazardous chemicals like toxic organic dyes are very harmful to the environment and their removal is quite challenging. Therefore there is a necessity to develop techniques, which are environment friendly, cost-effective and easily available in nature for water purification and remediation. The present research work is focused on the development` and characterization of the ecofriendly semi-interpenetrating polymer network (semi-IPN) nanocomposite hydrogels composed of polyvinyl alcohol (PVA) and alginate (Alg) hydrogel beads incorporating natural bentonite (Bent) clay as a beneficial adsorbent for the removal of toxic methylene blue (MB) from aqueous solution. PVA-Alg/Bent nanocomposite hydrogel beads with different Bent content (0, 10, 20, and 30 wt%) were synthesized via external ionic gelation method. The designed porous and steady structure beads were characterized by the use of Fourier transform infrared spectroscopy (FTIR), energy-dispersive X-ray spectroscopy (EDX), and scanning electron microscopy (SEM). The performance of the beads as MB adsorbents was investigated by treating aqueous solutions in batch mode. The experimental results indicated that the incorporation of Bent (30 wt%) in the nanocomposite formulation sustained the porous structure, preserved water uptake, and increased MB removal efficiency by 230% compared to empty beads. Designed beads possessed higher affinity to MB at high pH 8, 30 °C, and fitted well to pseudo-second-order kinetic model with a high correlation coefficient. Moreover, the designed beads had good stability and reusability as they exhibited excellent removal efficiency (90%) after six consecutive adsorption-desorption cycles. The adsorption process was found be combination of both monolayer adsorption on homogeneous surface and multilayer adsorption on heterogeneous surface. The maximum adsorption capacity of the designed beads system as calculated by Langmuir isotherm was found to be 51.34 mg/g, which is in good agreement with the reported clay-related adsorbents. The designed semi-IPN PVA-Alg/Bent nanocomposite hydrogel beads demonstrated good adsorbent properties and could be potentially used for MB removal from polluted water.

Algae-mediated processes for the treatment of antiretroviral drugs in wastewater: Prospects and challenges

The prevalence of pharmaceuticals (PCs), especially antiretroviral (ARV) drugs in various aquatic ecosystems has been expansively reported, wherein wastewater treatment plants (WWTPs) are identified as the primary point source. Consequently, the occurrence, ecotoxicity and treatment of ARV drugs in WWTPs have drawn much attention in recent years. Numerous studies have shown that the widely employed activated sludge-based WWTPs are incapable of removing ARV drugs efficiently from wastewater. Recently, algae-based wastewater treatment processes have shown promising results in PCs removal from wastewater, either completely or partially, through different processes such as biosorption, bioaccumulation, and intra-/inter-cellular degradation. Algal species have also shown to tolerate high concentrations of ARV drugs than the reported concentrations in the environmental matrices. In this review, emphasis has been given on discussing the current status of the occurrence of ARV drugs in the aquatic environment and WWTPs. Besides, the current trends and future perspectives of PCs removal by algae are critically reviewed and discussed. The potential pathways and mechanisms of ARV drugs removal by algae have also been discussed.

Bioremediation of lignin derivatives and phenolics in wastewater with lignin modifying enzymes: Status, opportunities and challenges

Lignin modifying enzymes from fungi and bacteria are potential biocatalysts for sustainable mitigation of different potentially toxic pollutants in wastewater. Notably, the paper and pulp industry generates enormous amounts of wastewater containing high amounts of complex lignin-derived chlorinated phenolics and sulfonated pollutants. The presence of these compounds in wastewater is a critical issue from environmental and toxicological perspectives. Some chloro-phenols are harmful to the environment and human health, as they exert carcinogenic, mutagenic, cytotoxic, and endocrine-disrupting effects. In order to address these most urgent concerns, the use of oxidative lignin modifying enzymes for bioremediation has come into focus. These enzymes catalyze modification of phenolic and non-phenolic lignin-derived substances, and include laccase and a range of peroxidases, specifically lignin peroxidase (LiP), manganese peroxidase (MnP), versatile peroxidase (VP), and dye-decolorizing peroxidase (DyP). In this review, we explore the key pollutant-generating steps in paper and pulp processing, summarize the most recently reported toxicological effects of industrial lignin-derived phenolic compounds, especially chlorinated phenolic pollutants, and outline bioremediation approaches for pollutant mitigation in wastewater from this industry, emphasizing the oxidative catalytic potential of oxidative lignin modifying enzymes in this regard. We highlight other emerging biotechnical approaches, including phytobioremediation, bioaugmentation, Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-based technology, protein engineering, and degradation pathways prediction, that are currently gathering momentum for the mitigation of wastewater pollutants. Finally, we address current research needs and options for maximizing sustainable biobased and biocatalytic degradation of toxic industrial wastewater pollutants.

Treatment of industrial contaminants with zero-valent iron- and zero-valent aluminium-activated persulfate: a case study with 3,5-dichlorophenol and 2,4-dichloroaniline

Zero-valent iron (ZVI)- and zero-valent aluminium (ZVA)-activated persulfate (PS) oxidation procedure was applied to remove the industrial pollutants 3,5-dichlorophenol (3,5-DCP; 12.27 µM) and 2,4-dichloroaniline (2,4-DCA; 12.34 µM) from aqueous solutions. The effects of PS concentration and pH were investigated to optimize heterogeneous treatment systems. Negligible removals were obtained for both pollutants by individual applications of nanoparticles (1 g/L) and PS (1.00 mM). PS activation with ZVI resulted in 59% (1.00 mM PS; 1 g/L ZVI; pH 5.0; 120 min) and 100% (0.75 mM PS; 1 g/L ZVI; pH 5.0; 80 min) 3,5-DCP and 2,4-DCA removals, respectively. The ZVA/PS treatment system gave rise to only 31% 3,5-DCP (1.00 mM PS; 1 g/L ZVA; pH 3.0; 120 min) and 47% 2,4-DCA (0.25 mM PS; 1 g/L ZVA; pH 3.0; 120 min) removals. The pH decreases from 5.0 to 3.0 and from 3.0 to 1.5 enhanced contaminant removals for ZVI/PS and ZVA/PS treatments, respectively. Pollutant removal rates were in correlation with the consumption rates of the oxidants. Metal ion (Al, Fe) release increased in the presence of PS and with decreasing pH.

Zeolitic imidazolate framework-8/ fluorinated graphene coated SiO2 composites for pipette tip solid-phase extraction of chlorophenols in environmental and food samples

In this work, a novel composite adsorbent was successfully prepared by zeolite imidazolate framework-8/fluorinated graphene layer-by-layer covalently bonded on SiO₂ microspheres, and followed to be packed into micro pipette tip for extraction of trace chlorophenols prior to their detection by high performance liquid chromatography (HPLC). The morphology and structure of adsorbent material was characterized by field emission scanning electron microscopy with energy dispersive spectrometer, X-ray diffraction, and N₂ adsorption. The parameters including the amount of adsorbent, sampling volume, sampling rate, sample pH, and desorption solvent affected the extraction performance was systematically investigated by pipette tip solid-phase extraction (PT-SPE) coupled with HPLC analysis. Under the optimized condition, the linearity of this method ranged from 20 to 2000 ng mL^-1 for chlorophenols (CPs) with determination coefficient higher than 0.99. The limit of detection (at a signal-to-noise ratio of 3) were in the range 2-20 ng mL^-1 for tap water and black tea drinks, 0.2-2 μg g^-1 for honey. The relative recoveries of the CPs from spiked samples ranged from 71.8% to 104.7%, with relative standard deviations less than 6.2%. The filled extraction tube exhibited good stability and reproducibility. The proposed method has been successfully used to detect CPs in water and drinks with satisfactory recoveries.

Synergistic catalysis of BiOIO3 catalyst for elimination of organic pollutants under simultaneous photo-irradiation and ultrasound-vibration treatment

Development of efficiently catalytic strategy for oxidative purification of organic pollutants is of great significance. Photocatalysis has become one of the most important technologies in the past half a century, but the inefficiency of photocatalysts drastically suppresses its practical application. This work proposes a synergistic photopiezocatalysis of BiOIO₃ under simultaneous photo-irradiation and ultrasound-vibration treatment to degrade various organic pollutants. Different from the high recombination of photo-excited charges in photocatalysis, the ultrasound-induced stress deforms the pyroelectric BiOIO₃ to form a piezoelectric potential that drives photo-/thermo-generated free electrons and holes in catalyst to diffuse along opposite directions. In comparison with the single photocatalysis and piezocatalysis, the photopiezocatalysis possesses a synergistic effect, presenting evidently enhanced catalytic performance for decomposing a variety of organic dyes and a persistent organic pollutant 2,4-DCP. No apparent decrease in activity during successive five runs demonstrates that the photopiezocatalysis of BiOIO₃ has a high stability and reusability. Finally, a plausible photopiezocatalysis mechanism is proposed based on the determination of active species produced on catalyst and intermediates during pollutant degradation. Our findings provide a new insight to promote charge separation and meanwhile develop an efficient synergistic photopiezocatalysis for environment remediation.

New insight into increased toxicity during ozonation of chlorophenol: The significant contribution of oxidizing intermediates

Biological safety evaluation and toxic by-products identification are critical issues in the partial oxidation process. Previous studies have shown that the whole toxicity increased in the effluent of an ozonation process for chlorophenols removal. Here, this study systematically investigated the changes of acute toxicity during the ozonation of 3-chlorophenol under four key operational conditions, including initial 3-chlorophenol concentration (20-60 mg/L), ozone concentration (14-42 mg/L), reaction pH (3-10) and ozonation time (0-50 min). The results found that the ozonation process induced a significant increase in the acute toxicity, followed by its gradual decrease. The observation of higher acute toxicity increase generally happened at higher initial 3-chlorophenol concentration, lower ozone concentration and lower reaction pH. At the toxicity peaks, the oxidizing intermediates posed acute toxicity equal to 65.8%-96.3% of the whole toxicity. Among them, free active chlorine (FAC) contributed 21.4%-51.6%, and its concentrations significantly correlated to the acute toxicity change. Therefore, two possible FAC generation pathways initiated by ozone molecule were proposed: (i) bond breaking of the oxychloride complex formed by the combination of chloride ion and zwitterion; or (ii) hydrolysis of ozonides formed by the electrophilic reaction of ozone molecule. Together, these results firstly revealed the significant toxicity contribution of oxidizing intermediates during the ozonation of chlorophenols, supporting further development of safe and effective ozone-based water treatment schemes.

Para-Chlorophenol (4-CP) Removal by a Palladium-Coated Biofilm: Coupling Catalytic Dechlorination and Microbial Mineralization via Denitrification

Rapid dechlorination and full mineralization of para-chlorophenol (4-CP), a toxic contaminant, are unfulfilled goals in water treatment. Means to achieve both goals stem from the novel concept of coupling catalysis by palladium nanoparticles (PdNPs) with biodegradation in a biofilm. Here, we demonstrate that a synergistic version of the hydrogen (H₂)-based membrane biofilm reactor (MBfR) enabled simultaneous removals of 4-CP and cocontaminating nitrate. In situ generation of PdNPs within the MBfR biofilm led to rapid 4-CP reductive dechlorination, with >90% selectivity to more bioavailable cyclohexanone. Then, the biofilm mineralized the cyclohexanone by utilizing it as a supplementary electron donor to accelerate nitrate reduction. Long-term operation of the Pd-MBfR enriched the microbial community in cyclohexanone degraders within Clostridium, Chryseobacterium, and Brachymonas. In addition, the PdNP played an important role in accelerating nitrite reduction; while NO₃^- reduction to NO₂^- was entirely accomplished by bacteria, NO₂^- reduction to N₂ was catalyzed by PdNPs and bacterial reductases. This study documents a promising option for efficient and complete remediation of halogenated organics and nitrate by the combined action of PdNP and bacterial catalysis.

Lactic acid separation and recovery from fermentation broth by ion-exchange resin: A review

Lactic acid has become one of the most important chemical substances used in various sectors. Its global market demand has significantly increased in recent years, with a CAGR of 18.7% from 2019 to 2025. Fermentation has been considered the preferred method for producing high-purity lactic acid in the industry over chemical synthesis. However, the recovery and separation of lactic acid from microbial fermentation media are relatively complicated and expensive, especially in the process relating to second-generation (2G) lactic acid recovery. This article reviews the development and progress related to lactic acid separation and recovery from fermentation broth. Various aspects are discussed thoroughly, such as the mechanism of lactic acid production through fermentation, the crucial factors that influence the fermentation process, and the separation and recovery process of conventional and advanced lactic acid separation methods. This review's highlight is the recovery of lactic acid by adsorption technique using ion-exchange resins with a brief focus on the potential of in-site separation strategies alongside the important factors that influenced the lactic acid recovery process by ion exchange. Apart from that, other lactic acid separation techniques, such as chemical neutralization, liquid-liquid extraction, membrane separation, and distillation, are also thoroughly reviewed.

Risk assessment and the adsorptive removal of some pesticides from synthetic wastewater: a review

Background

The need for environmental protection and remediation processes has been an increasing global concern. Pesticides are used as biological agents, disinfectants, antimicrobials, and also in a mixture of some chemical substances. Their modes of application are through selective dispensing and attenuation processes which act upon any pest that compete with the production, processing, and storage of foods and also in agricultural commodes. The pests might comprise weeds, insects, birds, fish, and microbes.

Main body

Pesticides are commonly found in water surface, landfill leachate, ground water, and wastewater as pollutant. An overview of recently studied adsorption processes for the pesticide elimination from polluted water has been reported in this study utilizing activated carbon, clay materials, biomass materials, metal organic frame work, graphene, and carbon-based materials as well as agricultural wastes as adsorbents. The risk assessment and cost analysis of adsorbents were also provided.

Conclusion

Evidences from literature recommend modified adsorbent and composite materials to have a prospective use in pesticide removal from wastewater. The adsorption data obtained fitted into different isotherm and kinetic models and also the thermodynamic aspect have been discussed.

Graphical abstract

Husk of Agarwood Fruit-Based Hydrogel Beads for Adsorption of Cationic and Anionic Dyes in Aqueous Solutions

Hydrogel beads based on the husk of agarwood fruit (HAF)/sodium alginate (SA), and based on the HAF/chitosan (CS) were developed for the removal of the dyes, crystal violet (CV) and reactive blue 4 (RB4), in aqueous solutions, respectively. The effects of the initial pH (2–10) of the dye solution, the adsorbent dosage (0.5–3.5 g/L), and contact time (0–540 min) were investigated in a batch system. The dynamic adsorption behavior of CV and RB4 can be represented well by the pseudo-second-order model and pseudo-first-order model, respectively. In addition, the adsorption isotherm data can be explained by the Langmuir isotherm model. Both hydrogel beads have acceptable adsorption selectivity and reusability for the study of selective adsorption and regeneration. Based on the effectiveness, selectivity, and reusability of these hydrogel beads, they can be treated as potential adsorbents for the removal of dyes in aqueous solutions.

Investigation of chlorinated phenols sorption mechanisms on different layers of the Danube alluvial sediment

The characteristics of the Danube river alluvial sediment are of great importance in assessing the risk for transport of pollutants to drinking water sources. Characterization of the sediment column layers has shown that the alluvial sediment, sampled near the city of Novi Sad, is a mesoporous sandy material with certain differences in the properties of individual layers. In order to investigate the sorption mechanisms of four chlorinated phenols (CPs) on the alluvial deposit, static sorption experiments were performed at pH 4, 7 and 10. The results of sorption experiments, confirmed by principal components analysis sugest different mechanisms govern the sorption process at different pH conditions. This can be attributed to the molecular characteristics of CPs, geosorbent properties and to variations in the surface charge of the sorbent at different pH conditions.

Palladium nanoparticle loaded β-cyclodextrin monolith as a flow reactor for concentration enrichment and conversion of pollutants based on molecular recognition

This study reports pollutant remediation by a catalyst-loaded, β-cyclodextrin cross-linked polymer monolith. The monolith enabled removal of the pollutant to a residual concentration with no environmental effect and conversion of the adsorbed pollutant into useful compounds with enriched concentration, allowing for the adsorption capacity regeneration.

Sorption behavior of selected chlorophenols onto polyurethane foam treated with iron(III): kinetics and thermodynamic study

An efficient, selective, and inexpensive method for complete elimination of chlorophenols (CPs) from water has been established. The proposed procedure was based upon the use of n-tributyl phosphate (TBP)-plasticized iron(III) physically immobilized polyurethane foam (PUF) solid sorbent for complete removal of CPs from aqueous media at pH close to 0. The interaction of the complex ion [Fe(C₆H₅O)₆]^3- with protonated ether oxygen of the PUF sorbent forms ternary ion associate on/in the PUFs. The retention of 4-chlorophenol (4-C) and 2,4,6-trichlorophenol (TCP) by the TBP-treated iron(III)-immobilized PUF fitted well with the pseudo-second-order kinetic model with a rate constant (k) of 0.04 and 0.15 g (mg min)^-1, respectively. The sorption of 4-CP was endothermic whereas the uptake of TCP was favorable at low temperature approving the exothermic and non-spontaneous characteristics of its uptake. The ΔS value for 4-CP reveals good affinity of the ion [Fe(C₆H₅O)₆]^3- towards the PUF sorbent.

A strategy for the efficient removal of chlorophenols in petrochemical wastewater by organophilic and aminated silica@alginate microbeads: Taguchi optimization and isotherm modeling based on partition coefficient

Through in situ encapsulation of cetyltrimethylammonium bromide (CTAB) and urea-functionalized SiO₂ nanoparticles in alginate hydrogel, two types of new functionalized microbeads, CTAB-SiO₂@alginate (organophilic) and urea-SiO₂@alginate (aminated), were produced. Their adsorption behavior toward multiple chlorophenols (CPs: e.g., 4-chlorophenol (MCP), 2,4-dichlorophenol (DCP), and 2,4,6-trichlorophenol (TCP)) in petrochemical wastewater was assessed with the aid of Taguchi's L9 orthogonal array at three levels. In terms of the partition coefficient (PC: μmol/g·μM (or L/g)), the use of three-parameter models (hybrid Langmuir-Freundlich and Redlich-Peterson) yielded the best fit (R² ≈ 1). Furthermore, the performance evaluation in terms of PC metric indicated that CTAB-SiO₂@alginate (7.85 L/g) was better to treat total CPs than urea-modified SiO₂@alginate microbeads (3.83 L/g). The enhanced performance of the former reflects the significant contribution of CTAB functionality (sp² carbon tail and quaternary amine (N⁺) cationic head sites) for accelerating uptake of molecular (or suspended) and ionizable CPs molecules (e.g., with the aid of salting-out effect at a high initial CPs concentration and salinity) via hydrophobic/electrostatic interactions. The high performance of the CTAB-SiO₂@alginate was demonstrated against petroleum hydrocarbons, CPs, and phenol contaminants using real petrochemical wastewater (up to three reusable cycles).

Monitoring of priority pollutants chlorophenols in water and milk by headspace solid-phase microextraction based on electrospun polycaprolactam nanofibers decorated with cadmium oxide-carbon nanotubes

Priority pollutants chlorophenols are broadly used chemicals that are persistent in the environment and causing serious human health hazards. The current study introduces a novel adsorbent for the extraction of chlorophenols from river water, surface water, and milk by headspace solid-phase microextraction coupled with gas chromatography. The adsorbent composite was prepared by blending polycaprolactam (nylon-6) mat and newly synthesized carbon nanotubes decorated with cadmium oxide nanoparticles followed by electrospinning technique to produce based nanofiber. The proposed nanofiber was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction techniques. The main parameters that affect extraction efficiency, including ionic strength, extraction time, desorption time, and extraction temperature, were investigated and optimized. The linear range was 0.05-5 ng/mL; the limits of detection (signal/noise=3) were 0.02-0.04 ng/mL. The relative recoveries for real samples (river water, surface water, and milk) were in the range of 84-114%.

Examination of Photocatalyzed Chlorophenols for Sequential Photocatalytic-Biological Treatment Optimization

Given the known adverse effect of chlorophenols for the aquatic environments which they can reach, the development of efficient methods both technically and economically to remove them has gained increasing attention over time. The combination of photocatalytic oxidation with biological treatment can lead to high removal efficiencies of chlorophenols, while reducing the costs associated with the need to treat large volumes of aqueous solutions. Therefore, the present paper had as its main objective the identification of the minimum photocatalytic oxidation period during which the aqueous solutions of 4-chlorophenol and 2,4-dichlorophenol can be considered as readily biodegradable. Thus, the results of photocatalytic oxidation and biodegradability tests showed that, regardless of the concentration of chlorophenol and its type, the working solutions become readily biodegradable after up to 120 min of irradiation in ultraviolet light. At this irradiation time, the maximum organic content of the aqueous solution is less than 40%, and the biochemical oxygen demand and chemical oxygen demand (BOD/COD) ratio is much higher than 0.4. The maximum specific heterotrophic growth rate of activated sludge has an average value of 4.221 d−1 for 4-chlorophenol, and 3.126 d−1 for 2,4-dichlorophenol. This irradiation period represents at most half of the total irradiation period necessary for the complete mineralization of the working solutions. The results obtained were correlated with the intermediates identified during the photocatalytic oxidation. It seems that, working solutions initially containing 4-chlorophenol can more easily form readily biodegradable intermediates.

Fully automated identification and quantification of five polar pesticides in groundwater by isotope dilution-online solid phase extraction coupled with high-performance liquid chromatography-quadrupole Orbitrap high-resolution mass spectrometry

A fully automated method for identification and quantification of five polar pesticides in groundwater by isotope dilution-online solid-phase extraction (SPE) coupled with high-performance liquid chromatography-quadrupole Orbitrap high-resolution mass spectrometry was developed. After one step of filtration, an aliquot of a 7.5-ml water sample was automatedly preconcentrated and purified on a turbulent Cyclone SPE column. The analytes were eluted in backflush mode, then separated on an analytical column and acquired by full MS/dd-MS2 scan in negative and positive ions mode. The major parameters for sample loading, cleanup, and elution were optimized in detail. Preconcentration and ionization efficiency were highly improved by using 0.1% acid solution in the mobile phase. The method provided good linearity of calibration coefficients (R2 > 0.995), sensitive method limits of detection (0.5-10.0 ng/L), accurate mass spectra (within 5 ppm error), satisfactory matrix spiking recoveries (98.4% to 109%), and high precision (intraday/interday relative standard deviations 1.57-8.90%). The method was successfully applied to analyze large batch groundwater of National Groundwater Monitoring Project and suspect screening of potential pesticides in groundwater. The study provided a practical alternative for a simple, robust, sensitive, and accurate identification and qualification of five polar pesticides in groundwater.

Adsorption of Phenol and Chlorophenols by HDTMA Modified Halloysite Nanotubes

The adsorption of phenol, 2-, 3-, 4-chlorophenol, 2-, 4-dichlorophenol and 2-, 4-, 6-trichloro-phenol on halloysite nanotubes modified with hexadecyltrimethylammonium bromide (HDTMA/halloysite nanocomposite) was investigated in this work by inverse liquid chromatography methods. Morphological and structural changes of the HDTMA/halloysite nanocomposite were characterized by scanning and transmission electron microscopy (SEM, TEM), Fourier-transform infrared spectrometry (FT-IR) and the low-temperature nitrogen adsorption method. Specific surface energy heterogeneity profiles and acid base properties of halloysite and HDTMA/halloysite nanocomposite have been determined with the inverse gas chromatography method. Inverse liquid chromatography methods: the Peak Division and the Breakthrough Curves Methods were used in adsorption experiments to determine adsorption parameters. The obtained experimental adsorption data were well represented by the Langmuir multi-center adsorption model.

A comprehensive review on contaminants removal from pharmaceutical wastewater by electrocoagulation process

The pharmaceuticals are emergent contaminants, which can create potential threats for human health and the environment. All the pharmaceutical contaminants are becoming enormous in the environment as conventional wastewater treatment cannot be effectively implemented due to toxic and intractable action of pharmaceuticals. For this reason, the existence of pharmaceutical contaminants has brought great awareness, causing significant concern on their transformation, occurrence, risk, and fate in the environments. Electrocoagulation (EC) treatment process is effectively applied for the removal of contaminants, radionuclides, pesticides, and also harmful microorganisms. During the EC process, an electric current is employed directly, and both electrodes are dissoluted partially in the reactor under the special conditions. This electrode dissolution produces the increased concentration of cation, which is finally precipitated as hydroxides and oxides. Different anode materials usage like aluminum, stainless steel, iron, etc. are found more effective in EC operation for efficient removal of pharmaceutical contaminants. Due to the simple procedure and less costly material, EC method is extensively recognized for pharmaceutical wastewater treatment over further conventional treatment methods. The EC process has more usefulness to destabilize the pharmaceutical contaminants with the neutralization of charge and after that coagulating those contaminants to produce flocs. Thus, the review places particular emphasis on the application of EC process to remove pharmaceutical contaminants. First, the operational parameters influencing EC efficiency with the electroanalysis techniques are described. Second, in this review emerging challenges, current developments and techno-economic concerns of EC are highlighted. Finally, future recommendations and prospective on EC are envisioned.

Production of Reactive Oxygen Species by the Reaction of Periodate and Hydroxylamine for Rapid Removal of Organic Pollutants and Waterborne Bacteria

Periodate (PI, IO₄^-) can be activated by hydroxylamine (HA), resulting in the rapid removal of organic pollutants within seconds. While the previous studies on PI-based advanced oxidation processes (AOPs) have proposed iodate radical (^•IO₃) as the major reactive species, no evidence of ^•IO₃ production was found in the present PI/HA system. Reactive oxygen species (ROS) including ^•OH, HO₂^•, and ¹O₂ are proposed to be the main oxidants of the PI/HA system, which is supported by various tests employing the scavengers, chemical probes, and spin-trapping electron paramagnetic resonance (EPR) technique. To minimize the risk of toxic iodinated byproduct formation caused by reactive iodine species such as HOI and I₂, the molar ratio of HA/PI was optimized at 0.6 to achieve the stoichiometric conversion of IO₄^- to iodate (IO₃^-), a preferred nontoxic sink of iodine species. The PI/HA system also efficiently inactivated both Gram-positive and -negative bacteria with producing ¹O₂ as the dominant disinfectant. The mechanism of ROS production was also investigated and is discussed in detail. This work offers a simple and highly efficient option for PI activation and ROS production which might find useful applications where urgent and rapid removal of toxic pollutants is needed.

Microcrystalline cellulose (MCC) based materials as emerging adsorbents for the removal of dyes and heavy metals - A review

In an attempt to overcome such threats posed by water pollution, various processes ranging from physical, chemical as well as biological were applied to get rid of wastewater pollutants. The simplicity, high efficiency and cheapness of an adsorption process make it the most widely used among various other processes. Adsorbents with different properties were used in the adsorption process but this paper was focused on reviewing various articles published by numerous researchers on the isolation of microcrystalline cellulose (MCC), a popular carbohydrate polymer from lignocellulosic biomass and utilization of MCC based materials as effective adsorbents for the successful removal of dyes and heavy metals from synthetic wastewater. The sudden interest on MCC and MCC-based materials as adsorbents cannot be separated from their excellent properties such as renewability, biodegradability, biocompatibility, economic value, non-toxicity, high mechanical properties and surface area. Upon comparison with established adsorbents reported from literature, MCC-based materials performed excellently well in the adsorption of dyes and heavy metals with Langmuir isotherm and pseudo-second order reported mostly as the best fit models for the generated equilibrium and kinetic data, respectively pointing at the distribution of adsorption sites to be homogeneous as well as the formation of monolayer adsorbate on their surfaces. The various thermodynamic studies reported further revealed the adsorption processes of both dyes and heavy metals onto MCC-based materials to be entropy driven processes, spontaneous, and endothermic. Finally, future research was suggested to focus on optimization to enhance the performance of the MCC-based adsorbents, carrying out the adsorption on real wastewater instead of synthetic ones as well as expanding the range of adsorbates to include other contaminants such as chlorophenols, herbicides, pesticides and others in addition to dyes and heavy metals.

Multiple draft tubes airlift loop membrane bioreactor as an efficient system for acidic 7-amino cephalosporanic acid (7-ACA) wastewater treatment

In this study, a lab-scale multiple draft tubes airlift loop membrane bioreactor (Mt-ALMBR) was used for treating acidic 7-amino cephalosporanic acid (7-ACA) wastewater under different pHs (3.54-6.20) and hydraulic retention time (HRT) (48 h, 36 h, 24 h and 16 h). During about 200 days operation, under HRT of 48 h and pH condition about 6.0, the optimum average COD and BOD₅ removal rates were reach to 84.4 ± 2.1% and 94.9 ± 0.8%, and the highest 7-ACA removal rate also observed as 77.6%. Biodegradation, membrane rejection, hydrolysis and sludge adsorption were the four main pathways of 7-ACA removal. With the increase of pH, biodegradation, membrane rejection and hydrolysis had significant positive impacts on 7-ACA removal, while adsorption had a negative impact. Moreover, mathematical models for 7-ACA removal rate and pH were calculated to guide the operation of Mt-ALMBR. Biodegradation was the main pathway to remove 7-ACA when pH was >4.17.

Construction of novel microbial consortia CS-5 and BC-4 valued for the degradation of catalpa sawdust and chlorophenols simultaneously with enhancing methane production

This study might be the first to explore the novel constructed microbial consortia CS-5 and BC-4 for enhancing methane (CH₄) production during anaerobic digestion (AD) with simultaneous degradation of catalpa sawdust and chlorophenols (CPs). Significant reduction in cellulose, hemicellulose and lignin contents was achieved after the biodegradation of catalpa sawdust for 15 days by CS-5 and BC-4, with a total weight loss of 69.2 and 56.3%, respectively. The synergistic microbial consortia enhanced cumulative biogas and CH₄ yields by 76.3 and 64.3%, respectively higher than the corresponding control at the end of AD. More than 90% of CH₄ was produced within 18 days of AD as a result of microbial pretreatment of catalpa sawdust. These consortia resulted in remarkably higher energy conversion efficiency of 44.3% (218.1 L_N CH₄/kg TS) over the control. CS-5 and BC-4 removed more than 69 and 77% of the total amount of CPs tested after 15 days.

Sorption of Organic Pollutants by Humic Acids: A Review

Humic acids (HA) are promising green materials for water and wastewater treatment. They show a strong ability to sorb cationic and hydrophobic organic pollutants. Cationic compounds interact mainly by electrostatic interaction with the deprotonated carboxylic groups of HA. Other functional groups of HA such as quinones, may form covalent bonds with aromatic ammines or similar organic compounds. Computational and experimental works show that the interaction of HA with hydrophobic organics is mainly due to π-π interactions, hydrophobic effect and hydrogen bonding. Several works report that sorbing efficiency is related to the hydrophobicity of the sorbate. Papers about the interaction between organic pollutants and humic acids dissolved in solution, in the solid state and adsorbed onto solid particles, like aluminosilicates and magnetic materials, are reviewed and discussed. A short discussion of the thermodynamics and kinetics of the sorption process, with indication of the main mistakes reported in literature, is also given.

Adsorptive and Reductive Removal of Chlorophenol from Wastewater by Biomass-Derived Mesoporous Carbon-Supported Sulfide Nanoscale Zerovalent Iron

Chlorinated compounds in a water environment pose serious threats to humanity. A nanoscale zerovalent iron (nZVI) has desirable properties for water dichlorination, but its reactivity is still limited by agglomeration and oxidation. In this study, the mesoporous carbon (MC) derived from biomass waste was prepared for immobilizing nZVI, and the nZVI@MC was further modified by sulfur (S-nZVI@MC) to relieve surface oxidation. The synergistic effect between nZVI and surface modification, the reaction conditions and the removal mechanism were investigated systematically. The characterization results showed nZVI was successfully loaded on the surface of MC, and the aggregation of nZVI was prevented. Moreover, sulfidation modification resulted in the formation of FeS on the surface of nZVI, which effectively alleviated surface oxidation of nZVI and promoted the electron transfer. Batch experiments demonstrated S-nZVI@MC had greatly enhanced reactivity towards 2,4,6-trichlorphenol (TCP) as compared to MC and nZVI, and the removal rate could reach 100%, which was mainly attributed to the significant synergistic effect of MC immobilization and sulfidation modification. Furthermore, the TCP removal process was well described by a Langmuir adsorption model and pseudo-second-order model. The possible mechanism for enhanced removal of TCP is the fast adsorption onto S-nZVI@MC and effective reduction by S-nZVI. Therefore, with excellent reducing activity and antioxidation, S-nZVI@MC has the potential as a pollutant treatment.