Assessment of AOPs as a polishing step in the decolourisation of bio-treated textile wastewater: Technical and economic considerations

Bibliometric analysis of Advanced Oxidation Processes studies with a focus on Life Cycle Assessment and Costs

Advanced oxidation processes (AOPs) are wastewater treatment technologies that stand out for their ability to degrade Contaminants of Emerging Concern (CECs). The literature has extensively investigated these removal processes for different aqueous matrices. Once technically mature, some of these systems have become accredited to be applied on a large scale, and therefore, their systemic performances in the environmental and cost spheres have also become essential requirements. This study proposed corroborating this trend, analyzing the available literature on the subject to verify how experts in the AOP area investigated this integration during 2015-2023. For this purpose, a sample of publications was treated by applying the Systematic Review (SR) methodology. This resulted in an extract of 83 studies that adopted life-cycle logic to estimate environmental impacts and process costs or evaluated them as complementary to the technical dimension of each treatment technology. This analysis found that both dimensions can be used for selecting or sizing AOPs at the design scale. However, the appropriate choice of the impact categories for the environmental assessment and establishing a methodology for cost analysis can make the approach still more effective. In addition, a staggering number of processes would broaden the reality and applicability of the estimates, and adopting multicriteria analysis methodologies could address essential aspects of decision-making processes during the design of the arrangements. By meeting the original purposes, the study broadened the requirements for designing AOPs and disseminating their use in mitigating the discharge of CECs.

Decontamination of wastewater containing contaminants of emerging concern by electrooxidation and Fenton-based processes - A review on the relevance of materials and methods

In recent years, there has been an increasingly growing interest regarding the use of electrochemical advanced oxidation processes (EAOPs) which are considered highly promising alternative treatment techniques for addressing environmental issues related to pollutants of emerging concern. In EAOPs, electrogenerated oxidizing agents, such as hydroxyl radical (HO^•), can react non-selectively with a wide range of organic compounds, degrading and mineralizing their structures to unharmful molecules like CO₂, H₂O, and inorganic ions. To this date, a broad spectrum of advanced electrocatalysts have been developed and applied for the treatment of compounds of interest in different matrices, specifically aiming at enhancing the degradation performance. New combined methods have also been employed as alternative treatment techniques targeted at circumventing the major obstacles encountered in Fenton-based processes, such as high costs and energy consumption, which still contribute significantly toward inhibiting the large-scale application of these processes. First, some fundamental aspects of EAOPs will be presented. Further, we will provide an overview of electrode materials which have been recently developed and reported in the literature, highlighting different anode and cathode structures employed in EAOPs, their main advantages and disadvantages, as well as their contribution to the performance of the treatment processes. The influence of operating parameters, such as initial concentrations, pH effect, temperature, supporting electrolyte, and radiation source, on the treatment processes were also studied. Finally, hybrid techniques which have been reported in the literature and critically assess the most recent techniques used for evaluating the degradation efficiency of the treatment processes.

A critical analysis of sono-hybrid advanced oxidation process of ferrioxalate system for degradation of recalcitrant pollutants

The emerging contaminants in wastewater discharged from numerous chemical process industries, pharmaceutical industries, textile, and wineries have attracted the attention of the scientific community due to their toxicity and persistence in the environment. The conventional techniques are incompetent to treat many of such recalcitrant toxic pollutants. To achieve high mineralization, advanced oxidation processes (AOPs) are found to be more efficient for the degradation of these organic pollutants without producing secondary pollutants with no/less amount of sludge. The primary oxidation agents for AOPs are in-situ generated free radicals, which are highly reactive and effective oxidants for degrading any type of organic molecules present in the wastewater. In the past decades, the combination of AOPs or simultaneous application of more than one AOP has been investigated extensively for wastewater treatment and these hybrid-AOPs have been reported to be beneficial for high-level mineralization of organic pollutants. This paper presented the characteristics, properties and influence of parameters in sono-photo-ferrioxalate system. The primary operating parameters in sono-photo-ferrioxalate system that affect the kinetics are defined as the solution pH, temperature, molar ratio of Fe³⁺/C₂O₄^2-, H₂O₂ concentration, source of light, ultrasound intensity, dissolved gases, and size of cavitation bubble. In this process, several oxidizing radicals are generated such as HO^•, HO₂^•, C₂O₄^•-, CO₂^•- and O₂^•- which are also responsible for degradation. In this review, we have mainly addressed the degradation of recalcitrant pollutants using the sono-photo-ferrioxalate system and a critical analysis of process parameters that influence mineralization efficiency.

Facile fabrication of hybrid titanium(IV) isopropoxide/pozzolan nanosheets (TnS-Pz) of high photocatalytic activity: characterization and application for Cr(VI) reduction in an aqueous solution

This paper presents the synthesis of a hybrid material through the use of natural pozzolan and titanium(IV) isopropoxide using the sol-gel method and its application in the photocatalytic hexavalent chromium reduction. The characterization data indicated a mesoporous material possessing a surface area of 271.7 m² g^-1. The morphology studies (SEM and TEM) showed nanosheet hybrid structures. The analysis of DRUV, FTIR, XRD, and Mössbauer spectroscopy provides a different electronic structure of the synthetized material when compared with the originals, proving the hybridization process between pozzolan and titanium(IV) isopropoxide. The photocatalytic reduction of Cr(VI) to Cr(III) using the hybrid material showed a better performance than conventional photocatalysts (precursor and TiO₂-P25). Operational conditions such as chromium initial concentration (0.02-0.20 mM), solution pH (3-6), and type of scavenger (citric or tartaric acid) were evaluated in order to determine the best experimental conditions for the Cr(VI) photoreduction. At their optimum (catalyst load of 15 mg L^-1, tartaric acid as scavenger, [scavenger]₀/[Cr(VI)]₀ M ratio = 3:1, pH 3, and 25 °C), the total photoreduction of 0.20 mM Cr(VI) was achieved in 180 min. The novel hybrid materials synthesized from pozzolan and titanium(IV) isopropoxide showed to be a potential catalyst for the Cr(VI) reduction in aqueous solution. Graphical abstract.

Nickel ferrite nanoenabled graphene oxide (NiFe2O4@GO) as photoactive nanocomposites for water treatment

Nanocomposite materials can enhance the capabilities of water treatment processes such as photocatalysis. In this work, novel light-driven nanocatalysts were synthesized by using nickel ferrite (NiFe₂O₄) to nanoenable graphene oxide (GO) substrates. GO is an emerging 2D nanomaterial with high conductivity and adsorption properties. Moreover, the electric properties of GO improve photocatalytic performance by promoting charge carrier separation. Results of the characterization of the nickel ferrite nanoenabled graphene oxide (NiFe₂O₄@GO) nanocomposites demonstrate that homogeneous and stable photocatalysts were produced. The as-synthesized nanocatalysts enabled complete decolorization of the colored water matrix in short irradiation times of 150 min using minimal catalyst loading at 0.5 g L^-1. The selective hook and destroy mechanism reduced the competitive effect of co-existing ions in solution. Furthermore, the use of specific scavengers helped to elucidate the degradation mechanisms of organic dye methylene blue by NiFe₂O₄@GO nanocomposites.

A tube-in-tube membrane microreactor for tertiary treatment of urban wastewaters by photo-Fenton at neutral pH: A proof of concept

This work presents a disruptive approach to promote highly-efficient photo-Fenton process at neutral pH under continuous mode operation. The system consists of a tube-in-tube membrane reactor designed for continuous-flow titration of low iron doses to the annular reaction zone (ARZ). A concentrated acidic ferrous ion (Fe²⁺) solution is fed by the lumen-side of the membrane, permeating through the membrane pores (inside-out mode), being dosed and uniformly delivered to the membrane shell-side. Polluted water, containing amoxicillin (AMX) and oxidant (H₂O₂), flows continuously in the reactor annulus (space between the membrane shell-side and an outer quartz tube). The catalyst radial dispersion is enhanced by the helicoidal movement of water around the membrane shell-side, efficiently promoting its contact with H₂O₂ and UV light. The efficiency of photochemical and photocatalytic oxidation was evaluated as a function of catalyst dose, catalyst injection mode (radial permeation vs injection upstream from the reactor inlet), light source (UVA vs UVC) and aqueous solution matrix (synthetic vs real wastewater). At steady-state, photo-Fenton reaction with Fe²⁺ radial addition, driven by UVC light, showed the highest AMX removal for synthetic (∼65%, removal rate of 44 μM_AMX/min, using [Fe²⁺]_ARZ = 2 mg/L and [H₂O₂]_inlet = 10 mg/L) and real municipal wastewaters (∼45%, removal rate of 31 μM_AMX/min, with [Fe²⁺]_ARZ = 5 mg/L and [H₂O₂]_inlet = 40 mg/L), with a residence time of only 4.6 s.

Quantitative structure-activity relationship in the photodegradation of azo dyes

The photolysis characteristics of azo dyes are critically important in environmental pollution control, dye-sensitized solar cells, and dyeing-related industries. However, there is still lack of quantitative relationship between the structures of azo dyes and their photolysis characteristics. To address this issue, the photolysis of 22 azo dyes were conducted side by side at three pH (4.0, 6.0, 9.0). The obtained pseudo-first order photodegradation rate constants (k₁) were processed with meta-analysis. Statistically, the hydrazone tautomer had a smaller excitation energy and was easier to undergo photolysis than the azo tautomer. The ortho-substituted sulfonate groups had an obvious protective effect on the photostability of azo dyes. The softness (s), the most positive and negative partial charge on a carbon atom (qC⁺, qC^-) were found to be crucial descriptors in the establishment of QSAR models for the photostability of azo dyes. The QSAR model at pH 9.0 was robust for predicting the photostability of azo dyes under UV irradiation. N₂-purging experiments and quantum chemical computation verified that the cleavage of azo bond was not a result of direct photolysis but was caused by the attack of photoinduced reactive oxygen species. The results here are helpful for the design of more stable azo dyes or the selection of suitable approaches for the treatment of dye-contaminated water bodies.

Niobium Oxide Catalysts as Emerging Material for Textile Wastewater Reuse: Photocatalytic Decolorization of Azo Dyes

Niobium-based metal oxides are emerging semiconductor materials with barely explored properties for photocatalytic wastewater remediation. Brazil possesses the greatest reserves of niobium worldwide, being a natural resource that is barely exploited. Environmental applications of solar active niobium photocatalysts can provide opportunities in the developing areas of Northeast Brazil, which receives over 22 MJ m2 of natural sunlight irradiation annually. The application of photocatalytic treatment could incentivize water reuse practices in small and mid-sized textile businesses in the region. This work reports the facile synthesis of Nb2O5 catalysts and explores their performance for the treatment of colored azo dye effluents. The high photoactivity of this alternative photocatalyst makes it possible to quickly obtain complete decolorization, in less than 40 min of treatment. The optimal operational conditions are defined as 1.0 g L−1 Nb2O5 loading in slurry, 0.2 M of H2O2, pH 5.0 to treat up to 15 mg L−1 of methyl orange solution. To evaluate reutilization without photocatalytic activity loss, the Nb2O5 was recovered after the experience and reused, showing the same decolorization rate after several cycles. Therefore, Nb2O5 appears to be a promising photocatalytic material with potential applicability in wastewater treatment due to its innocuous character and high stability.

Combined photocatalytic and biological process for textile wastewater treatments

Azo dyes, common in textile wastewater, have high photolytic and chemical stabilities, which make them difficult to be removed using conventional treatments. This study aims to evaluate a combined process using heterogeneous photocatalysis, with ZnO/UV or TiO₂ /UV (0.6 g catalyst L^-1 solution/2-hr UV radiation), and a biological process for textile wastewater treatment. After the proposed treatments, the color and organic matter removals from synthetic wastewater (SW) and industrial wastewater (IW) were evaluated. For SW, the coupled photocatalytic (ZnO/UV or TiO₂ /UV)-biological system promoted a high extent of color removal (98%) and total organic carbon (TOC) reduction (>80%). Promising results were obtained with IW using combined photocatalytic (TiO₂ /UV)-biological treatments, reaching 97% and 63% of color and TOC removal, respectively. This process, coupling heterogeneous photocatalysis and a bioprocess, has proved to be a good alternative for the treatment of textile wastewater, not only for color removal but also for dye mineralization purposes. PRACTITIONER POINTS: A combined process using heterogeneous photocatalysis (ZnO/UV or TiO₂ /UV) and biological process was evaluated for synthetic (SW) and industrial (IW) textile wastewaters treatment. For SW, coupled process promoted high extent of colour and organic matter removals. For IW, promising results were obtained with TiO₂ /UV-biological treatment (97% of colour and 63% of organic matter removals).

Biodegradation of tannery dye effluent using Fenton's reagent and bacterial consortium: A biocalorimetric investigation

The impact caused by dye effluent discharge on the environment is well known. The study explores a hybrid method of combining Fenton oxidation with biological treatment by a defined bacterial consortium for the biodegradation of an effluent containing toxic azo dye (acid blue 113). In actual treatment process, the fluctuation in toxic load and presence of other dyeing chemical inhibits the activity of the bacterial consortium. An effective pre-treatment of effluent would ensure the optimal degradation irrespective of its initial load. The pre-treatment of dye effluent with Fenton (H₂O₂ & Fe²⁺), considerably reduced the dye concentration by 40% and a maximum dye degradation of 85% (i.e., 45% by biodegradation) was achieved in shake flask. The biodegradation process was investigated in a bioreaction calorimeter (BioRc1e), the heat profile, bioenergetics data along with CER (Carbon dioxide emission rate) and OUR (Oxygen uptake rate) provided vital information for the effective commercial scale up. Enhanced degradation of up to 97% was achieved in BioRc1, the CER and OUR profile follows the power-time profile alluding that the heat generated is the resultant effect of bacterial metabolic activity. In real dye bath effluent the Fenton pre-oxidized biodegradation reaction showed a degradation efficacy of 89.5% and considerable COD reduction of 93.7%. Fluorescence-activated cell sorting (FACS) analysis revealed a better bacterial cell proliferation in pre-treated experiment and gas chromatography and mass spectrum analysis were used for prediction of metabolites. The unique combination of Fenton and the microbial consortia is a competitive technology for industrial effluent treatment processes.

A Rapid Fenton treatment of bio-treated dyeing and finishing wastewater at second-scale intervals: kinetics by stopped-flow technique and application in a full-scale plant

A rapid Fenton treatment at second-scale intervals was investigated for further removal of organic compounds in the effluent of bio-treated dyeing and finishing wastewater (BDFW). The decolorization kinetics was studied using a stopped-flow spectrophotometer (SFS) at second-scale intervals. A combined first-order model was found to fit well for the decrease of both methylene blue and rhodamine B in SFS as well as SCOD (soluble chemical oxygen demand) and DOC (dissolved organic carbon) in real BDFW in batch test during Fenton oxidation. A full-scale plant with treatment capacity of 400,000 m³·d⁻¹ was designed and has been run continuously based on the results of the stopped-flow study to treat the effluent of BDFW using Fenton oxidation in 16 pipeline reactors, each with a volume of 6.9 m³ and 24 s of reaction time since 2014. The COD, SCOD and DOC decreased from 140, 110 and 35 mg·L⁻¹ to 77, 71 and 26 mg·L⁻¹ respectively, which can meet the latest strict discharge limitations. The natural fluorescent substances detected in the BDFW were completely removed. The main organic pollutants in the BDFW can be significantly reduced using both gas chromatography-mass spectrometry and ultrahigh-performance liquid chromatography-hybrid quadrupole time-of-flight mass spectrometry. The rapid Fenton reaction applied in pipeline reactors at second intervals has several advantages over the conventional Fenton’s process such as much shorter reaction time at second scale intervals, no need to build extra pH adjustment or reaction tanks, simple operation, low capital cost, etc.

An innovative photoreactor, FluHelik, to promote UVC/H2O2 photochemical reactions: Tertiary treatment of an urban wastewater

An innovative photoreactor, FluHelik, was used to promote the degradation of contaminants of emerging concern (CECs) by a photochemical UVC/H₂O₂ process. First, the system was optimized for the oxidation of a model antibiotic, oxytetracycline (OTC), using both ultrapure water (UPW) and a real urban wastewater (UWW) (collected after secondary treatment) as solution matrices. Following, the process was evaluated for the treatment of a UWW spiked with a mixture of OTC and 10 different pharmaceuticals established by the Swiss legislation at residual concentrations (∑CECs <660 μg L^-1). The performance of the FluHelik reactor was analyzed both at lab and pre-pilot scale in multiple and single pass flow modes. The efficiency of the FluHelik photoreactor, at lab-scale, was evaluated at different operational conditions (H₂O₂ concentration, UVC lamp power (4, 6 and 11 W) and flow rate) and further compared with a conventional Jets photoreactor. Both photoreactors exhibited similar OTC removal efficiencies at the best conditions; however, the FluHelik reactor showed to be more efficient (1.3 times) in terms of mineralization when compared with the Jets reactor. Additionally, the efficiency of the UVC/H₂O₂ photochemical system using the FluHelik photoreactor in reducing the toxicity of the real effluent containing 11 pharmaceuticals was evaluated through zebrafish (Danio rerio) embryo toxicity bioassays. FluHelik scale-up from laboratory to pre-pilot to promote UVC/H₂O₂ photochemical process proved to be feasible.

Cryptosporidium-contaminated water disinfection by a novel Fenton process

Three novel modified advanced oxidation process systems including ascorbic acid-, pro-oxidants- and ascorbic acid-pro-oxidants-modified Fenton system were utilized to study the disinfection efficiency on Cryptosporidium-contaminated drinking water samples. Different concentrations of divalent and trivalent iron ions, hydrogen peroxide, ascorbic acid and pro-oxidants at different exposure times were investigated. These novel systems were also compared to the classic Fenton system and to the control system which comprised of only hydrogen peroxide. The complete in vitro mechanism of the mentioned modified Fenton systems are also provided. The results pointed out that by considering the optimal parameter limitations, the ascorbic acid-modified Fenton system decreased the Cryptosporidium oocytes viability to 3.91%, while the pro-oxidant-modified and ascorbic acid-pro-oxidant-modified Fenton system achieved an oocytes viability equal to 1.66% and 0%, respectively. The efficiency of the classic Fenton at optimal condition was observed to be 20.12% of oocytes viability. The control system achieved 86.14% of oocytes viability. The optimum values of the operational parameters during this study are found to be 80mgL^-1 for the divalent iron, 30mgL^-1 for ascorbic acid, 30mmol for hydrogen peroxide, 25mgL^-1 for pro-oxidants and an exposure time equal to 5min. The ascorbic acid-pro-oxidants-modified Fenton system achieved a promising complete water disinfection (0% viability) at the optimal conditions, leaving this method a feasible process for water disinfection or decontamination, even at industrial scales.

Souza SMA. Photochemical UVC/H2O2 oxidation system as an effective method for the decolourisation of bio-treated textile wastewaters: towards onsite water reuse

A photochemical UVC/H₂O₂ oxidation system was applied for the decolourisation of two real textile wastewaters collected after biological oxidation from two different textile wastewater treatment plants.