Photocatalytic and electrocatalytic degradation of bisphenol A in the presence of graphene/graphene oxide-based nanocatalysts: A review.

Bisphenol A (BPA), a widely recognized endocrine disrupting compound, has been discovered in drinking water sources/finished water and domestic wastewater influent/effluent. Numerous studies have shown photocatalytic and electrocatalytic oxidation to be very effective for the removal of BPA, particularly in the addition of graphene/graphene oxide (GO)-based nanocatalysts. Nevertheless, the photocatalytic and electrocatalytic degradation of BPA in aqueous solutions has not been reviewed. Therefore, this review gives a comprehensive understanding of BPA degradation during photo-/electro-catalytic activity in the presence of graphene/GO-based nanocatalysts. Herein, this review evaluated the main photo-/electro-catalytic degradation mechanisms and pathways for BPA removal under various water quality/chemistry conditions (pH, background ions, natural organic matter, promotors, and scavengers), the physicochemical characteristics of various graphene/GO-based nanocatalysts, and various operating conditions (voltage and current). Additionally, the reusability/stability of graphene/GO-based nanocatalysts, hybrid systems combined with ozone/ultrasonic/Fenton oxidation, and prospective research areas are briefly described.

Adsorption of uranyl ion on hexagonal boron nitride for remediation of real U-contaminated soil and its interpretation using random forest.

Acid leaching has been widely applied to treat contaminated soil, however, it contains several inorganic pollutants. The decommissioning of nuclear power plants introduces radioactive and soluble U(VI), a substance posing chemical toxicity to humans. Our investigation sought to ascertain the efficacy of hexagonal boron nitride (h-BN), an highly efficient adsorbent, in treating U(VI) in wastewater. The adsorption equilibrium of U(VI) by h-BN reached saturation within a mere 2 h. The adsorption of U(VI) by h-BN appears to be facilitated through electrostatic attraction, as evidenced by the observed impact of pH variations, acidic agents (i.e., HCl or H2SO4), and the presence of background ions on the adsorption performance. A reusability test demonstrated the successful completion of five cycles of adsorption/desorption, relying on the surface characteristics of h-BN as influenced by solution pH. Based on the experimental variables of initial U(VI) concentration, exposure time, temperature, pH, and the presence of background ions/organic matter, a feature importance analysis using random forest (RF) was carried out to evaluate the correlation between performances and conditions. To the best of our knowledge, this study is the first attempt to conduct the adsorption of U(VI) generated from real contaminated soil by h-BN, followed by interpretation of the correlation between performance and conditions using RF. Lastly, a. plausible adsorption mechanism between U(VI) and h-BN was explained based on the experimental results, characterizations, and a. comparison with previous adsorption studies on the removal of heavy metals by h-BN.

Ultrasonic treatment of dye chemicals in wastewater: A review.

The existence of pollutants, such as toxic organic dye chemicals, in water and wastewater raises concerns as they are inadequately eliminated through conventional water and wastewater treatment methods, including physicochemical and biological processes. Ultrasonic treatment has emerged as an advanced treatment process that has been widely applied to the decomposition of recalcitrant organic contaminants. Ultrasonic treatment has several advantages, including easy operation, sustainability, non-secondary pollutant production, and saving energy. This review examines the elimination of dye chemicals and categorizes them into cationic and anionic dyes based on the existing literature. The objectives include (i) analyzing the primary factors (water quality and ultrasonic conditions) that influence the sonodegradation of dye chemicals and their byproducts during ultrasonication, (ii) assessing the impact of the different sonocatalysts and combined systems (with ozone and ultraviolet) on sonodegradation, and (iii) exploring the characteristics-based removal mechanisms of dyes. In addition, this review proposes areas for future research on ultrasonic treatment of dye chemicals in water and wastewater.

Photocatalytic boron nitride-based nanomaterials for the removal of selected organic and inorganic contaminants in aqueous solution: A review.

Boron nitride (BN) coupled with various conventional and advanced photocatalysts has been demonstrated to exhibit extraordinary activity for photocatalytic degradation because of its unique properties, including a high surface area, constant wide-bandgap semiconducting property, high thermal-oxidation resistance, good hydrogen-adsorption performance, and high chemical/mechanical stability. However, only limited reviews have discussed the application of BN or BN-based nanomaterials as innovative photocatalysts, and it does not cover the recent results and the developments on the application of BN-based nanomaterials for water purification. Herein, we present a complete review of the present findings on the photocatalytic degradation of different contaminants by various BN-based nanomaterials. This review includes the following: (i) the degradation behavior of different BN-based photocatalysts for various contaminants, such as selected dye compounds, pharmaceuticals, personal care products, pesticides, and inorganics; (ii) the stability/reusability of BN-based photocatalysts; and (iii) brief discussion for research areas/future studies on BN-based photocatalysts.

Review of adsorption-membrane hybrid systems for water and wastewater treatment.

Adsorption is an effective method for the removal of inorganic and organic contaminants and has been commonly used as a pretreatment method to improve contaminant removal and control flux during membrane filtration. Over the last two decades, many researchers have reported the use of hybrid systems comprising various adsorbents and different types of membranes, such as nanofiltration (NF), ultrafiltration (UF), and microfiltration (MF) membranes, to remove contaminants from water. However, a comprehensive evaluation of the removal mechanisms and effects of the operating conditions on the transport of contaminants through hybrid systems comprising various adsorbents and NF, UF, or MF membranes has not been performed to date. Therefore, a systematic review of contaminant removal using adsorption-membrane hybrid systems is critical, because the transport of inorganic and organic contaminants via the hybrid systems is considerably affected by the contaminant properties, water quality parameters, and adsorbent/membrane physicochemical properties. Herein, we provide a comprehensive summary of the most recent studies on adsorption-NF/UF/MF membrane systems using various adsorbents and membranes for contaminant removal from water and wastewater and highlight the future research directions to address the current knowledge gap.

Catalytic non-thermal plasma treatment of endocrine disrupting compounds, pharmaceuticals, and personal care products in aqueous solution: A review.

Contaminants of emerging concerns such as endocrine-disrupting compounds (EDCs) and pharmaceuticals/personal-care products (PPCPs) constitute a problem since they are not completely eliminated by traditional water and wastewater treatment methods. Non-thermal plasma (NTP) is considered as one of the most favorable treatment methods for the removal of organic contaminants in water and wastewater. The degradation of selected EDCs and PPCPs of various classes was reviewed, based on the recent literature, to (i) address the effect of the main NTP treatment parameters (water quality and NTP conditions: pH, initial concentration, temperature, background common ion, NOM, scavenger, gas type/flow rate, discharge/reactor type, input power, and energy efficiency/yield) on the degradation of contaminants and their intermediates, (ii) assess the influences of different catalysts and hybrid systems on degradation, (iii) describe EDC and PPCP degradation along with their properties, and (iv) evaluate mineralization, pathway, and degradation mechanism of selected EDCs and PPCPs for different cases studied. Furthermore, areas of potential research in NTP treatment for the degradation of EDCs and PPCPs in aqueous solutions are recommended. It could be reasonably predicted that this review is valid for developing our understanding of the fundamental scientific principles concerning the catalytic NTP of EDCs and PPCPs, providing helpful and practical references for researchers and designers on the effective removal of EDCs/PPCPs and the optimized operation of catalytic NTP systems.

Effect of single and multilayered Ti3C2TX MXene as a catalyst and adsorbent on enhanced sonodegradation of diclofenac and verapamil.

Single and multilayered Ti3C2TX MXene (referred to as SLM and MLM in this study, respectively) was applied as catalysts in the ultrasonic (US) process to treat selected pharmaceutical compounds including diclofenac and verapamil (VRP). Due to solid surface, elemental composition, and functional groups of Ti3C2TX MXene, the free OH• production was increased by 48.8% for the US treatment with SLM and 59.8% for the US treatment with MLM compared with the US-only treatment. Additionally, adsorption affected the performance during the US treatment in the presence of the catalyst. Thus, the US treatment in the presence of Ti3C2TX MXene had an enhanced performance not only because of increased oxidation but also because of adsorption, particularly between positively charged VRP and negatively charged Ti3C2TX MXene. Moreover, although the degradation of the performance was higher for SLM (85.1%) than for MLM (81.8%), by improving the dispersion and reducing the size via sonication, the US treatment in the presence of MLM showed the highest synergy effect. In other words, the US treatment in the presence of MLM showed higher performance than the simple sum of oxidation and adsorption. These findings confirm that the US treatment in the presence of MLM may be a promising technology to treat various pharmaceuticals as a more degradable, strongly reusable, and less toxic process.

Characterization of marine dissolved organic matter and its effect on ozonation.

As the marine industry develops, the importance of seawater treatment process is increasing. To treat seawater, oxidation processes have primarily been used, such as ballast water treatment systems, aquaculture farm operations, aquarium management, and seawater desalination. However, dissolved organic matter in seawater, whose characteristics vary spatially and seasonally, affects the efficiency of oxidation processes. Therefore, in this study, seawater samples were acquired from various locations in the Republic of Korea to understand the spatio-temporal patterns of marine dissolved organic matter. It was reported that the characterization of marine dissolved organic matter using liquid chromatography-organic carbon detector and excitation-emission matrix-parallel factor modeling. Furthermore, the effects of marine dissolved organic matter were evaluated on ozonation, an oxidation process. The results demonstrate that marine dissolved organic matter varies in its aquagenic, pedogenic, and intermediate characteristics based on region and season. These variations affect ozonation by influencing the consumption of oxidants (e.g., bromine). As a result, it was concluded that characterizing marine dissolved organic matter can help improve the effectiveness of oxidation processes, particularly ozonation.

Photocatalytic degradation of dissolved organic matter under ZnO-catalyzed artificial sunlight irradiation system.

This study investigates the photocatalytic degradation of dissolved organic matter (DOM) under ZnO-assisted artificial sunlight system at various conditions (ZnO dosage, pH, and the presence of Cl-, SO42-, and HCO3-). The results show that the degradation of DOM follows a pseudo-first-order kinetics. Fluorescence excitation-emission matrices coupled with parallel factor (EEM-PARAFAC) analysis decomposes DOM into two fluorophores (C1 and C2). The total removals and photodegradation rates calculated with DOC, UV254, and the Fmax of C1 are similar, increasing with higher ZnO dosages and being highest in pH 7 and lowest in pH 4. ZnO dosage has a similar effect on DOM degradation when assessed using C2, as with C1, but pH effect is not consistent. As for the anions, HCO3- shows the strongest inhibition for DOC, UV254 and C1 while Cl- has the strongest facilitation effect for C2. The total removal and photodegradation rates calculated with the Fmax of C1 and C2 are higher than those calculated using DOC and UV254. This study demonstrates that the successful application of EEM-PARAFAC analysis in addition to traditional parameters can provide further insight into the photocatalytic degradation mechanisms associated with DOM in conjunction with a ZnO catalyst under artificial sunlight.

Tungsten Trioxide (WO3)-assisted Photocatalytic Degradation of Amoxicillin by Simulated Solar Irradiation.

This study investigates the photocatalytic degradation of amoxicillin (AMO) by simulated solar irradiation using WO3 as a catalyst. A three-factor-three-level Box-Behnken design (BBD) consisting of 30 experimental runs is employed with three independent variables: initial AMO concentration, catalyst dosage, and pH. The experimental results are analyzed in terms of AMO degradation and mineralization, the latter of which is measured using dissolved organic carbon (DOC). The results show that the photocatalytic degradation of AMO follows pseudo-first-order kinetics. AMO degradation efficiency and the pseudo-first-order rate constants decrease with increasing initial AMO concentration and pH and increase with increasing catalyst dosage. Though AMO degradation is almost fully complete under the experimental conditions, DOC removal is much lower; the highest DOC removal rate is 35.82% after 180 min. Using these experimental results, second-order polynomial response surface models for AMO and DOC removal are constructed. In the AMO removal model, the first-order terms are the most significant contributors to the prediction, followed by the quadratic and interaction terms. Initial AMO concentration and pH have a significant negative impact on the photocatalytic degradation of AMO, while catalyst dosage has a significant positive impact. In contrast, in the DOC removal model, the quadratic terms make the most significant contribution to the prediction and the first-order terms the least. The optimal conditions for the photocatalytic degradation of AMO are found to be an initial AMO concentration of 1.0 µM, a catalyst dosage of 0.104 g/L, and a pH of 4, under which almost complete removal of AMO is achieved (99.99%).

Characteristics of intracellular algogenic organic matter and its reactivity with hydroxyl radicals.

The aim of this study was to investigate the reactivity of intracellular algogenic organic matter (IOM) with hydroxyl radicals (·OH), a key reaction species in advanced oxidation processes. IOM was extracted from two green algae, Chlamydomonas reinhardtii and Scenedesmus sp., and two blue-green algae, Anabaena sp. and Microcystis aeruginosa using a freeze-thaw method. The second-order rate constants of the extracted IOM with ·OH were determined as 7.95 × 108 MC-1 s-1 (Chlamydomonas reinhardtii), 6.71 × 108 MC-1 s-1 (Scenedesmus sp.), 4.02 × 108 MC-1 s-1 (Anabaena sp.), and 4.45 × 108 MC-1 s-1 (Microcystis aeruginosa). These rate constants were significantly higher than values reported for dissolved organic matter in various water sources. This implies that IOM formation during algal bloom season could change the ·OH water matrix demand and adversely affect the performance of advanced oxidation processes. To investigate the physical and chemical composition characteristics of IOM and their relationship to the rate constants determined for the reaction between IOM and ·OH, liquid chromatography-organic carbon detection (LC-OCD) and fluorescence excitation-emission matrix & parallel factor analysis (FEEM-PARAFAC) were used. The IOM mainly consisted of low molecular weight (LMW) matter and protein-related compounds, as evidenced LMW neutrals (38-65%), biopolymers (7-19%), and tryptophan-like compounds (74-94%). Based on the composition characteristics of IOM, it was concluded that the molecular weight and the presence of nitrogen-containing compounds are influential parameters for determining the reactivity of IOM with ·OH.

Characteristics and fate of natural organic matter during UV oxidation processes.

Advanced oxidation processes (AOPs) are widely used in water treatments. During oxidation processes, natural organic matter (NOM) is modified and broken down into smaller compounds that affect the characteristics of the oxidized NOM by AOPs. In this study, NOM was characterized and monitored in the UV/hydrogen peroxide (H2O2) and UV/persulfate (PS) processes using a liquid chromatography-organic carbon detector (LC-OCD) technique, and a combination of excitation-emission matrices (EEM) and parallel factor analysis (PARAFAC). The percentages of mineralization of NOM in the UV/H2O2 and UV/PS processes were 20.5 and 83.3%, respectively, with a 10 mM oxidant dose and a contact time of 174 s (UV dose: approximately 30,000 mJ). Low-pressure, Hg UV lamp (254 nm) was applied in this experiment. The steady-state concentration of SO4- was 38-fold higher than that of OH at an oxidant dose of 10 mM. With para-chlorobenzoic acid (pCBA) as a radical probe compound, we experimentally determined the rate constants of Suwannee River NOM (SRNOM) with OH (kOH/NOM = 3.3 × 108 M-1s-1) and SO4- (kSO4-/NOM = 4.55 × 106 M-1s-1). The hydroxyl radical and sulfate radical showed different mineralization pathways of NOM, which have been verified by the use of LC-OCD and EEM/PARAFAC. Consequently, higher steady-state concentrations of SO4-, and different reaction preferences of OH and SO4- with the NOM constituent had an effect on the mineralization efficiency.

Thermochemical destruction of asbestos-containing roofing slate and the feasibility of using recycled waste sulfuric acid.

In this study, we have investigated the feasibility of using a thermochemical technique on ∼17% chrysotile-containing roofing sheet or slate (ACS), in which 5N sulfuric acid-digestive destruction was incorporated with 10-24-h heating at 100°C. The X-ray diffraction (XRD) and the polarized light microscopy (PLM) results have clearly shown that raw chrysotile asbestos was converted to non-asbestiform material with no crystallinity by the low temperature thermochemical treatment. As an alternative to the use of pricey sulfuric acid, waste sulfuric acid discharged from a semiconductor manufacturing process was reused for the asbestos-fracturing purpose, and it was found that similar removals could be obtained under the same experimental conditions, promising the practical applicability of thermochemical treatment of ACWs. A thermodynamic understanding based on the extraction rates of magnesium and silica from a chrysotile structure has revealed that the destruction of chrysotile by acid-digestion is greatly influenced by the reaction temperatures, showing a 80.3-fold increase in the reaction rate by raising the temperature by 30-100°C. The overall destruction is dependent upon the breaking-up of the silicon-oxide layer - a rate-limiting step. This study is meaningful in showing that the low temperature thermochemical treatment is feasible as an ACW-treatment method.

Characterization of soluble microbial products and their fouling impacts in membrane bioreactors.

Membrane bioreactor (MBR) fouling is not only influenced by the soluble microbial products (SMP) concentration but by their characteristics. Experiments of separate producing biomass associated products (BAP) and utilization associated products (UAP) allowed the separation of BAP and UAP effects from sludge water (SW). Thus, filtration of individual SMP components and further characterization becomes possible. Unstirred cell filtration was used to study fouling mechanisms and liquid chromatography--organic carbon detection (LC-OCD) and fluorescence excitation--emission matrix (EEM) were used to characterize the foulant. Generally, the SMP exhibiting characteristics of higher molecular weight, greater hydrophilicity and a more reduced state showed a higher retention percentage. However, the higher retention does not always yield higher fouling effects. The UAP filtration showed the highest specific cake resistance and pore blocking resistance attributed to their higher percentage of low molecular weight molecules, although their retention percentage was lower than the SW and BAP filtration. The UAP produced in the cell proliferation phase appeared to have the highest fouling potential.

Impact of wastewater treatment processes on organic carbon, organic nitrogen, and DBP precursors in effuent organic matter.

Unintentional, indirect wastewater reuse often occurs as wastewater treatment plant (WWTP) discharges contaminate receiving waters serving as drinking-water supplies. A survey was conducted at 23 WWTPs that utilized a range of treatment technologies. Samples were analyzed for typical wastewater and drinking-water constituents, chemical characteristics of the dissolved organic matter (DOM), and disinfection byproduct (DBP) precursors present in the effluent organic matter (EfOM). This was the first large-scale assessment of the critical water quality parameters that affect the formation of potential carcinogens during drinking water treatment relative to the discharge of upstream WWTPs. This study considered a large and wide range of variables, including emerging contaminants rarely studied at WWTPs and never before in one study. This paper emphasizesthe profound impact of nitrification on many measures of effluent water quality, from the obvious wastewater parameters (e.g., ammonia, biochemical oxygen demand) to the ones specific to downstream drinking water treatment plants (e.g., formation potentialsfor a diverse group of DBPs of health concern). Complete nitrification reduced the concentration of biodegradable dissolved organic carbon (BDOC) and changed the ratio of BDOC/DOC. Although nitrification reduced ultraviolet absorbance (UVA) at 254 nm, it resulted in an increase in specific UVA (UVA/DOC). This is attributed to preferential removal of the less UV-absorbing (nonhumic) fraction of the DOC during biological treatment. EfOM is composed of hydrophilic and biodegradable DOM, as well as hydrophobic and recalcitrant DOM, whose proportions change with advanced biological treatment. The onset of nitrification yielded lower precursor levels for haloacetic acids and nitrogenous DBPs (haloacetonitriles, N-nitrosodimethylamine). However, trihalomethane precursors were relatively unaffected by the level of wastewater treatment Thus, one design/operations parameter in wastewater treatment, the decision to have a long enough solids retention time to get reliable nitrification, affected much beyond its immediate goal of ammonium oxidation.

Fate of effluent organic matter and DBP precursors in an effluent-dominated river: a case study of wastewater impact on downstream water quality.

The impact of treated wastewater discharges on downstream water quality was evaluated in an effluent-dominated stream in the Southwest USA. The fate and transport of effluent organic matter (EfOM) and disinfection by-product (DBP) precursors was studied. Nitrification and biodegradation were important mechanisms. Changes in DBP formation potential along the river appeared to correlate with dissolved organic carbon (DOC) and organic nitrogen concentrations and specific ultraviolet absorbance. The mean oxidation state of carbon (MOC) decreased in value along the river. MOC decreases paralleled decreases in the biodegradability of residual DOC (i.e., lower biodegradable DOC/DOC ratio). The EfOM was biodegradable by up to 40 percent, both in the stream and in a laboratory reactor, and many DBP precursors (e.g., haloacetonitriles, certain nitrosamines) decreased in concentration. Alternatively, the DBP yields for trihalomethanes or haloacetic acids either remained the same or increased slightly, suggesting that these precursors were part of the recalcitrant organic matter (OM).

Differentiation of wastewater effluent organic matter (EfOM) from natural organic matter (NOM) using multiple analytical techniques.

Using three analytical techniques of size exclusion chromatography (SEC), fluorescence excitation-emission matrix (EEM), and dissolved organic nitrogen (DON) measurement, differentiating characteristics of effluent organic matter (EfOM) from natural organic matter (NOM) have been investigated. SEC reveals a wide range of molecular weight (MW) for EfOM and high amount of high MW polysaccharides, and low MW organic acids compared to NOM. Clear protein-like peaks using fluorescence EEM were a major feature of EfOM distinguishing it from NOM. Fluorescence index (FI), an indicator to distinguish autochthonous origin from allochthonous origin, differentiated EfOM from NOM by exhibiting higher values, indicating a microbial origin. In EfOM samples, DON present in higher amounts than NOM.

Kinetics and mechanisms of the sonolytic destruction of non-volatile organic compounds: investigation of the sonochemical reaction zone using several OH* monitoring techniques.

This study investigates the sonolytic degradation mechanism of non-volatile organic compounds and reaction sites for its degradation using various tools that allow OH* to be monitored, such as: the spin-trapping method of OH* detection using non-volatile nitrone trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), the hydrogen peroxide analytical methods and the p-chlorobenzoic acid (pCBA)-probe method. These methods can successfully monitor OH* produced during sonochemical processes, and identify the major reaction sites involving OH* of the three proposed reaction zones--within the cavity, in the bulk solution, and at the gas-liquid interfacial (shell) region. The patterns of hydrogen peroxide accumulation under the various conditions suggest that peroxides pre-form at the interfacial region, but the self-scavenging reaction by hydrogen peroxide simultaneously takes place in the same region. The simultaneously measured peroxide concentration, in the absence and presence of DMPO, and that of the DMPO-OH adduct indicated the peroxide production and DMPO-OH adduct formation reaction occur at the shell region. The sonolytic destruction efficiency of ultrasound coupled with Fe(II) has been also investigated. The coupled Fe(II)/ultrasound process was found to enhance the OH* production rate by 70% compared to the ultrasound process alone due to the reaction of Fe(II) with sonochemically produced hydrogen peroxide (Fenton's reaction). This accelerated reaction was also found to occur at the shell region rather than in the bulk solution. The enhancement effect of Fe(II)/ultrasound was also examined using pCBA as a probe. 2.8-fold and 3.6-fold increases of the pCBA degradation rate were observed at Fe(II) concentrations of 10 and 20 microM, respectively.