Evaluation of advanced oxidation processes for water and wastewater treatment - A critical review

Sono-Fenton hybrid process on the inactivation of Microcystis aeruginosa: Extracellular and intracellular oxidation

For the first time, the inactivation of Microcystis aeruginosa using sono-Fenton process at low frequency high intensity (20 kHz, 0.42 W/mL) and high frequency low intensity (800 kHz, 0.07 W/mL) was investigated, respectively. 20 kHz sono-Fenton treatment successfully reduced cyanobacterial cell number from 4.19 × 10⁶ cells/mL to 0.45 × 10⁶ cells/mL within 5 min treatment. Alternatively, efficient performance of 800 kHz sono-Fenton process was observed to decrease Microcystis cell number to 2.33 × 10⁶ cells/mL after 5 min inactivation, with lower energy cost. It was found that powerful 20 kHz sonication induced pore formation on the cell wall, leading to extracellular damage, while 800 kHz irradiation with low intensity triggered intracellular uptake of chemicals, suggesting endocytosis effects. Furthermore, sono-Fenton Processes were found to be affected by the concentrations of Fenton's reagent, and pre-sonication time. Although solo Fenton treatment released microcystins in water, the degradation of microcystin-LR were achieved using 20 and 800 kHz sono-Fenton processes, respectively. The results of this work showed that severe extracellular oxidation is the vital inactivation mechanism of 20 kHz sono-Fenton process, while the internal oxidation caused by intracellularly delivered Fenton reagents is suggested to be the main cause of 800 kHz sono-Fenton inactivation, leading to much lower energy cost. This work provides alternative methods to control harmful cyanobacteria in water towards effective treatment.

The effect of inorganic salt in wastewater on the viscosity of coal water slurry

The preparation of coal water slurry (CWS) using wastewater, which contains inorganic and organic components, is one method of wastewater utilization. In this study, the effect of inorganic salts on the viscosity of CWS was examined. The results show that monovalent salts (NaCl, KCl) decreased the viscosity of CWS. The viscosity of CWS was not affected by bivalent salts (CaCl₂, MgCl₂). However, CWS combined with trivalent salt (AlCl₃) sharply increased the viscosity. The zeta potential of CWS with inorganic salts increased which can enhance the electric repulsion and beneficial to reduce the viscosity. The content of free water in CWS with trivalent salt decreased, and the freedom of the free water in CWS with trivalent salt decreased which were all bad to the viscosity and the adsorption of the dispersant on the particles. Compared with the surface polarity of the particles without inorganic salts, the surface polarity of the particles with divalent salts was similar to those without inorganic salts. Under the comprehensive influence, divalent salt has little effect on the viscosity of CWS.

Moving from the traditional paradigm of pathogen inactivation to controlling antibiotic resistance in water - Role of ultraviolet irradiation

Ultraviolet (UV) irradiation has proven an effective tool for inactivating microorganisms in water. There is, however, a need to look at disinfection from a different perspective because microbial inactivation alone may not be sufficient to ensure the microbiological safety of the treated water since pathogenic genes may still be present, even after disinfection. Antibiotic resistance genes (ARGs) are of a particular concern since they enable microorganisms to become resistant to antibiotics. UV irradiation has been widely used for disinfection and more recently for destroying ARGs. While UV lamps remain the principal technology to achieve this objective, UV light emitting diodes (UV-LEDs) are novel sources of UV irradiation and have increasingly been reported in lab-scale investigations as a potential alternative. This review discusses the current state of the applications of UV technology for controlling antibiotic resistance during water and wastewater treatment. Since UV-LEDs possess several attractive advantages over conventional UV lamps, the impact of UV-LED characteristics (single vs combined wavelengths, and operational parameters such as periodic or pulsed and continuous irradiation, pulse repetition frequencies, duty cycle), type of organism, and fluence response, are critically reviewed with a view to highlighting the research needs for addressing future disinfection challenges. The energy efficiency of the reported UV processes is also evaluated with a focus on relating the findings to disinfection efficacy. The greater experience with UV lamps could be useful for investigating UV-LEDs for similar applications (i.e., antibiotic resistance control), and hence identification of future research directions.

Treatments for color removal from wastewater: State of the art

It is evident from many recent papers that release of colored wastewater into the environment is source of pollution and this is a problem that particularly affect textile, dyeing and food industries. The review: (i) presents an analysis of various mechanisms involved in the different processes for color removal; (ii) describes conveniences and disadvantages that may exist in adopting one type of treatment in spite of another; (iii) reports the results of approximately 180 experimental tests. Both examples of treatments already widely applied to the real scale and still in the experimental phase are reported. This work focuses on different types of chemical/physical, chemical, electrochemical and biological processes applied in the field of color removal from industrial wastewater. Common chemical/physical treatments such as coagulation/flocculation, adsorption and membrane filtration as well as chemical-type processes are discussed, both those that exploit the traditional oxidizing chemical agents such as Ozone, H₂O₂ and reactive based on chlorine and those based on the principle of advanced chemical oxidation. In particular, both Hydroxyl radical based Advanced Oxidation Processes (AOPs) and Sulfate radical based AOPs are reported. The most commonly used Electrochemical processes for the removal of color are also presented as well as biological treatments. Based on more than 200 papers, this review provides important information on the use, effectiveness, advantages and downsides of the various treatments aimed at removing the color from the wastewater with a look at the technologies still under development.

Sonocatalytic degradation of butylparaben in aqueous phase over Pd/C nanoparticles

In the present work, the sonocatalytic degradation of butylparaben was investigated using Pd immobilized on carbon black as the sonocatalyst. The presence of 25 mg/L 10Pd/C significantly increased the removal rate of butylparaben and the observed kinetic constant increased from 0.0126 to 0.071 min^-1, while the synergy index between sonolysis and adsorption was 70.7%. The BP degradation followed pseudo-first-order kinetics with the apparent kinetic constant decreased from 0.071 to 0.030 min^-1 when the initial concentration of butylparaben increased from 0.5 to 2 mg/L. The process was being favored slightly under alkaline conditions. The presence of organic matter (20 mg/L humic acid) reduced the apparent kinetic constant more than two times. The addition of chlorides up to 250 mg/L did not significantly reduce the rate of reaction, while the presence of 250 mg/L bicarbonates reduced the observed kinetic constant from 0.071 to 0.0472 min^-1. The prepared catalyst retains the efficiency after five subsequent experiments since the apparent kinetic constant was only slightly decreased from 0.071 to 0.059 min^-1.

What you extract is what you see: Optimising the preparation of water and wastewater samples for in vitro bioassays

The assessment of water quality is crucial for safeguarding drinking water resources and ecosystem integrity. To this end, sample preparation and extraction is critically important, especially when investigating emerging contaminants and the toxicity of water samples. As extraction methods are rarely optimised for bioassays but rather adopted from chemical analysis, this may result in a misrepresentation of the actual toxicity. In this study, surface water, groundwater, hospital and municipal wastewater were used to characterise the impacts of common sample preparation techniques (acidification, filtration and solid phase extraction (SPE)) on the outcomes of eleven in vitro bioassays. The latter covered endocrine activity (reporter gene assays for estrogen, androgen, aryl-hydrocarbon, retinoic acid, retinoid X, vitamin D, thyroid receptor), mutagenicity (Ames fluctuation test), genotoxicity (umu test) and cytotoxicity. Water samples extracted using different SPE sorbents (Oasis HLB, Supelco ENVI-Carb+, Telos C18/ENV) at acidic and neutral pH were compared for their performance in recovering biological effects. Acidification, commonly used for stabilisation, significantly altered the endocrine activity and toxicity of most (waste)water samples. Sample filtration did not affect the majority of endpoints but in certain cases affected the (anti-)estrogenic and dioxin-like activities. SPE extracts (10.4 × final concentration), including WWTP effluents, induced significant endocrine effects that were not detected in aqueous samples (0.63 × final concentration), such as estrogenic, (anti-)androgenic and dioxin-like activities. When ranking the SPE methods using multivariate Pareto optimisation an extraction with Telos C18/ENV at pH 7 was most effective in recovering toxicity. At the same time, these extracts were highly cytotoxic masking the endpoint under investigation. Compared to that, extraction at pH 2.5 enriched less cytotoxicity. In summary, our study demonstrates that sample preparation and extraction critically affect the outcome of bioassays when assessing the toxicity of water samples. Depending on the water matrix and the bioassay, these methods need to be optimised to accurately assess water quality.

Capturing the oxic transformation of iopromide - A useful tool for an improved characterization of predominant redox conditions and the removal of trace organic compounds in biofiltration systems?

The biological degradation of many trace organic compounds has been reported to be strongly redox dependent. The traditional characterization of redox conditions using the succession of inorganic electron acceptors such as dissolved oxygen and nitrate falls short in accurately describing the critical transition state between oxic and suboxic conditions. Novel monitoring strategies using intrinsic redox tracers might be suitable to close that gap. This study investigated the potential use of the successive biological transformation of the iodinated contrast medium iopromide as an intrinsic tracer of prevailing redox conditions in biofiltration systems. Iopromide degradation in biofiltration systems was monitored by quantifying twelve known biological transformation products formed under oxic conditions. A novel dimensionless parameter (T_IOP) was introduced as a measure for the successive transformation of iopromide. A strong correlation between the consumption of dissolved oxygen and iopromide transformation emphasized the importance of general microbial activity on iopromide degradation. However, results disproved a direct correlation between oxic (>1 mg/L O₂) and suboxic (<1 mg/L O₂) conditions and the degree of iopromide transformation. Results indicated that besides redox conditions also the availability of biodegradable organic substrate affects the degree of iopromide transformation. Similar behavior was found for the compounds gabapentin and benzotriazole, while the oxic degradation of metoprolol remained stable under varying substrate conditions.

Degradation of Phenol Using Peroxymonosulfate Activated by a High Efficiency and Stable CoMgAl-LDH Catalyst

In this study, we report on an active and stable CoMgAl layered double hydrotalcite (LDH) catalyst for phenol degradation by heterogeneous activation of peroxymonosulfate (PMS). The CoMgAl-LDH catalyst was synthesized by hydrothermal method. The PMS/CoMgAl-LDH system overcomes the drawbacks of traditional Fenton processes. Various effects, e.g., scavengers, chloride ion, catalyst dosage, PMS concentration, temperature, and pH, were also inspected to evaluate the system. The results indicated that the PMS/CoMgAl-LDH system had extremely high efficiency for phenol degradation; 0.1 mM phenol could be completely degraded by 0.3 g/L catalyst and 3 mM PMS within 60 min at 30 °C. The CoMgAl-LDH catalyst appeared to possess outstanding reusability and stability. After four rounds of recycling, nearly 100% of the phenol was removed within 80 min by the PMS/CoMgAl-LDH system, with only 0.05 mg/L Co2+ leaching. A sulfate radical was the main oxidation species in the PMS/Co-LDH system. The degradation rate of phenol was influenced by temperature, and the activation energy was 65.19 kJ/mol. These advantages proved the PMS/CoMgAl-LDH system is an effective strategy for the treatment of organic contaminants.

Heterogeneous Fenton reaction for elimination of Acid Yellow 36 in both fluidized-bed and stirred-tank reactors: Computational fluid dynamics versus experiments

Heterogeneous Fenton process is a kind of advanced oxidation processes (AOPs) that is significant for wastewater treatment. In the first part of this study, acid yellow 36 (AY36) degradation process has occurred in two kinds of reactors: fluidized-bed and stirred-tank reactors. Performances of these two semi-pilot reactors are compared by evaluating the removal ratio of the dye and pH changes during the process. Pyrite has been used as a heterogeneous catalyst. For obtaining the characteristics of pyrite, XRD, SEM, and FT-IR analysis have been carried out. In the second part of this study, a modified computational fluid dynamics (CFD) method has been utilized to solve the momentum and mass balances for heterogeneous Fenton process in both reactors. In AOPs, free radicals are reactive and have a short lifetime, so that turbulence mixing would be a limiting factor for the reactions that radicals are involved. By introducing a new parameter, named turbulence mixing rate, as a reaction rate for reactive species like hydroxyl radicals, the results of removal ratio and pH changes during the process showed a good agreement between the experiments and the CFD simulations, compared with not including the mixing rate in the CFD simulations (conventional kinetic modeling). In addition, the results revealed the high performance of the fluidized-bed reactor for this process in both experiments and CFD simulation.

Simulated solar driven photolytic ozonation for the oxidation of aqueous recalcitrant-to-ozone tritosulfuron. Transformation products and toxicity

This work reports the combination of ozone and solar radiation as an advanced oxidation process to remove the herbicide tritosufuron (TSF) in water. Firstly, the recalcitrance of TSF has been assessed, obtaining an ozonation second order rate constant of 5-154 M^-1 min^-1 in the range of pH from 5 to 8; while the rate constant with HO was found to be (1.8-3.1)·10⁹ M^-1 s^-1. Secondly, the simultaneous application of simulated solar radiation in between 300 and 800 nm and ozone resulted positive in the oxidation rate of TSF. Mineralization extent was also higher. Less effective oxidation was achieved after limiting the radiation to the range 360-800 nm or 390-800 nm; also completely inappropriate for mineralization. Thirdly, the detected transformation products (TPs) demonstrated the vulnerability of TSF molecule to be attacked by HO in the sulfonylurea bridge. The combination of ozone and radiation of 300-800 nm led to the most effective removal of the TPs. Finally, after the photolytic ozonation treatment toxicity was also evaluated in terms of phytotoxicity towards the germination and root elongation of Lactuca Sativa seeds, and toxicity by immobilization tests of Daphnia Magna.

Total coliform inactivation in natural water by UV/H2O2, UV/US, and UV/US/H2O2 systems

The presence of pathogens in drinking water can seriously affect human health. Therefore, water disinfection is needed, but conventional processes, such as chlorination, result in the production of dangerous disinfection by-products. In this regard, an alternative solution to tackle the problem of bacterial pollution may be the application of advanced oxidation processes. In this work, the inactivation of total coliforms, naturally present in a Colombian surface water by means of UV/H₂O₂, UV/US, and the UV/US/H₂O₂ advanced oxidation processes, was investigated. Under the investigated conditions, complete bacterial inactivation (detection limit equal to 1 CFU 100 mL^-1) was found within 5 min of treatment by UV/H₂O₂ and UV/US/H₂O₂ systems. UV/US oxidation process also resulted in total bacterial load elimination, but after 15 min of treatment. Bacterial reactivation after 24 h and 48 h in the dark was measured and no subsequent regrowth was observed. This phenomenon could be attributed to the high oxidation capacity of the evaluated oxidation systems. However, the process resulting in the highest oxidation potential at the lowest operating cost, in terms of energy consumption, was UV/H₂O₂ system. Therefore, UV/H₂O₂ advanced oxidation system can be used for disinfection purposes, enabling drinking water production meeting the requirements of regulated parameters in terms of water quality, without incurring extremely high energy costs. Nonetheless, further researches are required for minimizing the associated electric costs.

A mini review of activated methods to persulfate-based advanced oxidation process

Persulfate-based advanced oxidation has been widely applied in environmental remediation for degrading contaminants. In recent years, numerous kinds of organic analytes including pesticides, dyes and pharmaceuticals, have emerged and related researches on the activation methods, the mechanism and the application have been performed. The activation is critical in persulfate-based advanced oxidation because the persulfate alone has a weaker oxidation potential to degrade these organic pollutants. Hence various activation methods have been extensively investigated to achieve a higher oxidation efficiency. These novel methods are gradually expanding the applicability and practicality. This review focuses on the classification of the different activation methods based on whether it is related to the substances or not. The effect of the environmental conditions (solution pH, dosage and the co-existing substance) on the oxidation capacity are also discussed.

Morphology-tunable WMoO nanowire catalysts for the extremely efficient elimination of tetracycline: kinetics, mechanisms and intermediates

The presence of antibiotics in aquatic environments has attracted global concern. The Fenton system is one of the most popular methods for eliminating antibiotics in aquatic environments, but the existing Fenton system is limited due to the potential for secondary pollution, and the narrow pH range (∼3-5). In this study, we report that the bottlenecks for high-strength tetracycline (TC) wastewater treatment under neutral conditions can be tackled well by a class of mixed-valence W/Mo containing oxides (WMoO-x) with tunable morphologies. Triethanolamine was selected as a structure-directing agent to control the morphologies of the catalysts going from ultrathin nanowires (UTNWs) to wire-tangled nanoballs (WTNBs). As a proof of concept, the most efficient catalyst in the batch samples, WMoO-1 ultrathin nanowires, was employed as a model material for TC degradation, in which the coordinatively unsaturated metal atoms with oxygen defects serve as the sites for TC chemisorption and electron transfer. As a result, 91.75% of TC was degraded in 60 min for the initial TC concentration of 400 μM. Furthermore, LC-MS analysis confirmed that the TC could be degraded to nontoxic by-products without benzene rings, and finally mineralized to CO2 and H2O. ICP-MS and cycle experiments showed the good stability and reusability of WMoO-1 UTNWs in the Fenton-like system. The findings of this work provide fresh insights into the design of nanoscale catalyst morphology and reaffirm the versatility of doping in tuning catalyst activity, extending the range of the optimal pH values to neutral conditions. This is significant for the expansion of the heterogeneous Fenton-like family and its application in the field of water treatment.

Nitrate Removal via a Formate Radical-Induced Photochemical Process

Removal of excess nitrate is critical to balance the nitrogen cycle in aquatic systems. This study investigated a novel denitrification process by tailoring photochemistry of nitrate with formate. Under UV light irradiation, short-lived radicals (i.e., HO^•, NO₂^•, and CO₃^•-) generated from nitrate photolysis partially oxidized formate to highly reductive formate radical (CO₂^•-). CO₂^•- further reduced nitrogen intermediates generated during photochemical denitrification (mainly NO^•, HNO, and N₂O) to gas-phase nitrogen (i.e., N₂O and N₂). The degradation kinetics of total dissolved nitrogen was mainly controlled by the photolysis rates of nitrate and nitrite. The distribution of final products was controlled by the reaction between CO₂^•- and N₂O. To achieve a simultaneous and complete removal of dissolved nitrogen (i.e., nitrate, nitrite, and ammonia) and organic carbon, the formate-to-nitrate stoichiometry was determined as 3.1 ± 0.2 at neutral pH in deionized water. Solution pH impacted the removal rates of nitrate and nitrite but not that of total dissolved nitrogen or formate. The presence of dissolved organic matter at levels similar to those in groundwater had a negligible impact on the photochemical denitrification process. A high denitrification efficiency was also achieved in a synthetic groundwater matrix. Outcome from this study provides a potential denitrification technology for decentralized water treatment and reuse facilities to abate nitrate in local water resources.

Iron(ii) tetrafluoroborate complexes of new tetradentate C-scorpionates as catalysts for the oxidative cleavage of trans-stilbene with H2O2

Iron(ii) complexes of two new tetradentate C-scorpionate ligands are characterized. Both catalyze stilbene cleavage using either H₂O₂ or a O₂/photocatalyst oxidant.

Removal of refractory organics in dinitrodiazophenol industrial wastewater by an ultraviolet-coupled Fenton process

A significant amount of biorefractory organic wastewater is generated during the production of dinitrodiazophenol (DDNP). In this study, ultraviolet light (254 nm) that was coupled with the Fenton (UV-Fenton) process was applied to treat refractory organics in DDNP industrial wastewater. The effects of key parameters (i.e., H₂O₂ dose, Fe²⁺ dosage, and initial pH) on the treatment efficacy for DDNP industrial wastewater by the UV-Fenton process was investigated systematically. Alcohol quenching experiments were carried out to identify reactive oxygen species in the UV-Fenton process. The treatment efficacy and degradation characteristics of refractory organics were studied and compared by using control experiments. Increasing H₂O₂ and Fe²⁺ doses could lead to improved treatment results to a different extent. A more intense reaction and better treatment results were achieved by using the UV-Fenton process at lower pH conditions. Under optimal conditions of H₂O₂ dose = 7.5 mL L⁻¹, Fe²⁺ dosage = 0.05 mM, and initial pH = 5.0, the pseudo-first order constants k for chemical oxygen demand removal and color number removal were 0.18 min⁻¹ and 1.24 min⁻¹, and the chemical oxygen demand and color number removal efficiencies were 74.24% and 99.94%, respectively. The treatment results for the UV-Fenton process were better than other processes under the same conditions, and a significant synergetic effect was observed for the UV-Fenton process. Alcohol quenching experiments indicated that the predominant reactive oxygen species in the UV-Fenton process was the hydroxyl radical (·OH). Because more ·OH was produced, the UV-Fenton process exhibited a much better treatment performance in degrading and destroying organic structures (i.e., benzene rings, –NO₂, and –N Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> N–). Furthermore, the biodegradability indicated by the biological oxygen demand/chemical oxygen demand ratio was improved considerably to 0.48 from 0.054. The good treatment performance by UV-Fenton allowed for a more efficient electrical energy consumption compared with the UV and UV-H₂O₂. This study provides a theoretical reference for DDNP industrial wastewater treatment by using the UV-Fenton process.

In this study, ultraviolet-Fenton process was applied to degrade refractory organics in dinitrodiazophenol industrial wastewater. In addition, the treatment efficiency and reaction mechanism were systematically investigated.

Disinfection performance using a UV/persulfate system: effects derived from different aqueous matrices

The disinfectant power of UV combined with a persulfate salt has been assessed. The results obtained suggest this system as an attractive alternative to other photochemical processes currently in use for seawater treatment.

The construction of a Fenton system to achieve in situ H2O2 generation and decomposition for enhanced photocatalytic performance

A photo-Fenton system combining Ni_xFe_yO₄–BiOBr with the in situ generation and decomposition of H₂O₂ was constructed for efficient organic compound degradation.

Highly stable binder free CNTs/rGO aerogel electrode for decolouration of methylene blue & palm oil mill effluent via electro-Fenton oxidation process

In this study, single wall carbon nanotubes (CNTs)/reduced graphene oxides (rGO) aerogels were prepared by a one-pot hydrothermal process without using a binder.

Assessment of Sulfate Radical-Based Advanced Oxidation Processes for Water and Wastewater Treatment: A Review

High oxidation potential as well as other advantages over other tertiary wastewater treatments have led in recent years to a focus on the development of advanced oxidation processes based on sulfate radicals (SR-AOPs). These radicals can be generated from peroxymonosulfate (PMS) and persulfate (PS) through various activation methods such as catalytic, radiation or thermal activation. This review manuscript aims to provide a state-of-the-art overview of the different methods for PS and PMS activaton, as well as the different applications of this technology in the field of water and wastewater treatment. Although its most widespread application is the elimination of micropollutants, its use for the disinfection of wastewater is gaining increasing interest. In addition, the possibility of combining this technology with ultrafiltration membranes to improve the water quality and lifespan of the membranes has also been discussed. Finally, a brief economic analysis of this technology has been undertaken and the different attempts made to implement it at full-scale have been summarized. As a result, this review tries to be useful for all those people working in that area.

Enhanced photocatalytic activity of BiVO4 powders synthesized in presence of EDTA for the decolorization of rhodamine B from aqueous solution

Bismuth vanadate (BiVO₄) powders were successfully synthesized in presence of EDTA via microwave irradiation and used as photocatalysts in the oxidation reaction of rhodamine B (rhB) under visible light. Different concentrations of EDTA (0.5 to 10%) to chelate Bi³⁺ ions were employed on the BiVO₄ synthesis. Under the presence of EDTA, a monoclinic crystalline structure was obtained, whereas a mixture of monoclinic and tetragonal phases was observed in the absence of EDTA. In addition, the use of different EDTA concentrations promoted the formation the different shapes of particles. The BiVO₄ sample synthesized with low concentration of EDTA (0.5%) exhibited about 85% of rhB decolorization in 300 min at pH 7.5. Therefore, this high efficiency can be attributed to a combination of intrinsic properties such as the morphology type and monoclinic structure of BiVO₄ particles.

Removal of trace organic chemicals in wastewater effluent by UV/H2O2 and UV/PDS

In this study, we comparatively investigated the degradation of 12 trace organic chemicals (TOrCs) during UV/H₂O₂ and UV/peroxydisulfate (PDS) processes. Second-order rate constants for the reactions of iopromide, phenytoin, caffeine, benzotriazole, and primidone with sulfate radical (SO₄^•-) were determined for the first time. Experiments were conducted in buffered pure water and wastewater effluent with spiked TOrCs. UV/PDS degraded all TOrCs more efficiently than UV/H₂O₂ in buffered pure water due to the higher yield of SO₄^•- than that of hydroxyl radical (^•OH) at the same initial molar dose of PDS and H₂O₂, respectively. UV/PDS showed higher selectivity toward TOrCs removal than UV/H₂O₂ in wastewater effluent. Compounds with electron-rich moieties, such as diclofenac, venlafaxine, and metoprolol, were eliminated faster in UV/PDS whereas UV/H₂O₂ was more efficient in degrading compounds with lower reactivity to SO₄^•-. The fluence-based rate constants ( [Formula: see text] ) of TOrCs in wastewater effluent linearly increased as a function of initial H₂O₂ dose during UV/H₂O₂, possibly due to the constant scavenging impact of the wastewater matrix on ^•OH. However, exponential increase of k_obs-UV/PDS with increasing PDS dose was observed for most compounds during UV/PDS, suggesting the decreasing scavenging effect of the water matrix (electron-rich site of effluent organic matter (EfOM)) after initial depletion of SO₄^•- at low PDS dose. Fulvic and humic-like fluorophores appeared to be more persistent during UV/H₂O₂ compared to aromatic protein and soluble microbial product-like fluorophores. In contrast, UV/PDS efficiently degraded all identified fluorophores and showed less selectivity toward the fluorescent EfOM components. Removal pattern of TOrCs during pilot-scale UV/PDS was consistent with lab-scale experiments, however, overall removal rates were lower due to the presence of higher concentration of EfOM and nitrite.

High-silica zeolites for adsorption of organic micro-pollutants in water treatment: A review

High-silica zeolites have been found to be effective adsorbents for the removal of organic micro-pollutants (OMPs) from impaired water, including various pharmaceuticals, personal care products, industrial chemicals, etc. In this review, the properties and fundamentals of high-silica zeolites are summarised. Recent research on mechanisms and efficiencies of OMP adsorption by high-silica zeolites are reviewed to assess the potential opportunities and challenges for the application of high-silica zeolites for OMP adsorption in water treatment. It is concluded that the adsorption capacities are well-related to surface hydrophobicity/hydrophilicity and structural features, e.g. micropore volume and pore size of high-silica zeolites, as well as the properties of OMPs. By using high-silica zeolites, the undesired competitive adsorption of background organic matter (BOM) in natural water could potentially be prevented. In addition, oxidative regeneration could be applied on-site to restore the adsorption capacity of zeolites for OMPs and prevent the toxic residues from re-entering the environment.

Degradation of geosmin and 2-methylisoborneol in water with UV/chlorine: Influencing factors, reactive species, and possible pathways

Geosmin (GSM) and 2-methylisoborneol (2-MIB) are two common odor compounds in drinking water. In this paper, the performance of UV/chlorine was compared with that of chlorine and UV to degrade GSM (100 ng L^-1) and 2-MIB (100 ng L^-1) in water. UV/chlorine was further exploited, and a steady-state kinetic model was used to conduct a detailed study on efficiency, rate, reactive species and pathway. The results showed that UV/chlorine greatly could improve the removal ratio to 90% within 5 min, from approximately 20% with only UV or dark chlorine in 60 min. The removal ratio and rate depended on UV light intensity, free chlorine dosage, reaction time and water quality parameters (e.g. pH, concentrations of HCO₃^- and Cl^-). Among these factors, the first two obviously could accelerate the rate and increase the ratio. The degradation was also significantly improved in an acidic condition, while alkaline conditions and HCO₃^- had inhibitory effects, and Cl^- created no difference. Contributions of OH and Cl to the degradation of 2-MIB and GSM were further revealed, and OH was found to be the most important reactive species. In the UV/chlorine process, 6 degradation byproducts of 2-MIB, including 1 alcohol, 2 ketones, and 3 olefins, were identified, and 14 degradation byproducts of GSM, including 6 ketones, 1 aldehyde, 2 alcohols, 3 naphthenes, and 2 olefins, were found by using solid-phase microextraction coupled to gas chromatography-mass spectrometry. The possible degradation pathways of GSM and 2-MIB in UV/chlorine thus were proposed.

The use of steel slags in the heterogeneous Fenton process for decreasing the chemical oxygen demand of oil refinery wastewater

The Fenton process is a useful and inexpensive type of advanced oxidation process for industrial wastewater treatment. This study was performed with the aim of using the steel slag as a catalyst in the heterogeneous Fenton process in order to reduce the chemical oxygen demand (COD) of oil refinery wastewater. The effects of various parameters including the reaction time (0.5, 1.0, 2.0, 3.0 and 4.0 h), pH (2.0, 3.0, 4.0, 5.0, 6.0 and 7.0), the concentration of steel slag (12.5, 25.0 and 37.5 g/L), and H₂O₂ concentration (100, 250, 400 and 500 mg/L) on the Fenton process were investigated. Furthermore, the effect of microwave irradiation on the process efficiency was studied by considering the optimum conditions of the mentioned parameters. The results showed that using 25.0 g/L of steel slag and 250 mg/L H₂O₂, at pH = 3.0, could reduce COD by up to 64% after 2.0 h. Also, microwave irradiation decreased the time of the process from 120 min to 25 min in the optimum conditions, but it consumed a high amount of energy. It could be concluded that steel slags had a high potential in the treatment of oil refinery wastewater through the Fenton process.

Photocatalytic Degradation of Diclofenac by Hydroxyapatite⁻TiO₂ Composite Material: Identification of Transformation Products and Assessment of Toxicity

Diclofenac (DCF) is one of the most detected pharmaceuticals in environmental water matrices and is known to be recalcitrant to conventional wastewater treatment plants. In this study, degradation of DCF was performed in water by photolysis and photocatalysis using a new synthetized photocatalyst based on hydroxyapatite and TiO₂ (HApTi). A degradation of 95% of the target compound was achieved in 24 h by a photocatalytic treatment employing the HApTi catalyst in comparison to only 60% removal by the photolytic process. The investigation of photo-transformation products was performed by means of UPLC-QTOF/MS/MS, and for 14 detected compounds in samples collected during treatment with HApTi, the chemical structure was proposed. The determination of transformation product (TP) toxicity was performed by using different assays: Daphnia magna acute toxicity test, Toxi-ChromoTest, and Lactuca sativa and Solanum lycopersicum germination inhibition test. Overall, the toxicity of the samples obtained from the photocatalytic experiment with HApTi decreased at the end of the treatment, showing the potential applicability of the catalyst for the removal of diclofenac and the detoxification of water matrices.

Ozonation of nursing home wastewater pretreated in a membrane bioreactor

Nursing home (NH) wastewater was pretreated in an ultrafiltration membrane bioreactor (MBR) and subsequently ozonated in a pilot plant in order to evaluate the elimination of pharmaceutically active compounds (PhACs). Dosing of the pre-treated wastewater with 5 mg ozone (O₃) L^-1 led to the elimination of >50% for nearly all investigated PhACs in the ozonation plant, whereas dosing 10 mg O₃ L^-1 increased elimination to >80%. A total hydraulic retention time of 12.8 min proved sufficient for PhAC elimination. Specific ozone consumption and influent dissolved organic carbon (DOC) (8.2-9.5 mg L^-1) were in similar ranges for all three performed trials. Combining the MBR with subsequent ozonation at a dosage of 5 mg O₃ L^-1 achieved elimination of >90% and effluent concentrations below 250 ng L^-1 for nearly all the investigated PhACs. Influent concentrations of the MBR were comparable to those found in municipal wastewater. Thus, the recommended dosage for PhAC elimination of 5 mg O₃ L^-1 (i.e. a specific consumption of 0.6 g O₃*(g DOC)^-1) is in the same range as for municipal wastewater. However, due to a smaller plant size, the specific costs for treating NH wastewater would significantly exceed those of treating municipal wastewater.

Using Natural Biomacromolecules for Adsorptive and Enzymatic Removal of Aniline Blue from Water

The present study investigated the adsorptive and enzymatic removal of aniline blue dye (AB) from aqueous solution using waxy riceprocessing waste (RW), peanut shell (PS), microbial waste of Aspergillus niger (MW) as low cost adsorbents, and laccase (Lac) as a biocatalyst. Commercial activated carbon (AC) was also employed to compare the adsorption performance with the three adsorbents. Dye removal was examined under various parameters in batch experiments. It was found that dye removal by RW and Lac was 89–94% noticeably better than that by MW and PS (20–70%). In any cases, AC produced the highest dye removal among the tested materials. The kinetics, isotherms, and thermodynamics were then analyzed to elucidate the adsorption process by the four adsorbents. The pseudo-second order kinetic was superior to the pseudo first order kinetic model in describing adsorption for all adsorbents. The Langmuir model fitted the adsorption process very well, indicating monolayer coverage of dyes on a solid surface. A thermodynamic analysis of enthalpy (ΔH°), entropy (ΔS°), and Gibbs free energy (ΔG°) classified the adsorption as a nonspontaneous and endothermic process. The results reveal diverse natural materials (e.g., processing waste RW) as novel substitutes for traditional activated carbon, as well as laccase as a green catalyst for the treatment of dye wastewater.