Technical and economic feasibility of polyester dyeing wastewater treatment by coagulation/flocculation and Fenton's oxidation

QSAR model and mechanism research on color removal efficiency of dying wastewater by FeCl3 coagulation

Coagulation is the most widely used method in the treatment of printing and dying wastewater. To better understand the relationship between the coagulation effect and dye molecular structures, quantitative structure activity relationship (QSAR) analyses were performed to elucidate the factors affecting the coagulation in ferric chloride (FeCl₃) coagulation process. First, the coagulation experiments on 38 dye molecules were conducted to determine their color removal rates (R_exp) by FeCl₃ under different pH conditions (i.e., pH = 4 and 10). The results showed that the average R_exp of dyes were 41.36% ± 2.40% at pH value of 4 and 55.70% ± 2.83% at pH value of 10. Subsequently, a multiple linear regression (MLR) method was used to construct QSAR models based on R_exp and 42 molecular parameters calculated by Gaussian 09, Materials Studio 7.0 and Multiwfn. The developed QSAR models exhibited excellent stability, reliability, and robustness with values of R² = 0.7950, 0.8170, Q²_INT = 0.6401, 0.7382, Q²_EXT = 0.5168, 0.5441, at pH values of 4 and 10, respectively. Through analysis of quantum parameter values, electrostatic adsorption and hydrogen bonding adsorption were primarily responsible for the coagulation process. Therefore, this study could be useful in providing critical information for evaluating the removal efficiency and a feasible way to predict the removal rate of dyes by FeCl₃ when no coagulation experiments were conducted.

Synergistic effects of oxidation, coagulation and adsorption in the integrated fenton-based process for wastewater treatment: A review

Fenton process is the most popular for wastewater treatment among all available advanced oxidation processes (AOPs). Numerous endeavors have been devoted to improving the oxidation efficiency of Fenton reaction in terms of promoting ·OH generation, accelerating iron redox cycle and extending applicable pH range. However, in addition to oxidation, coagulation and adsorption also simultaneously occur in the Fenton process, which play important role in the removal of pollutants. Rapid progress has revealed the synergistic effects of oxidation, coagulation and adsorption in the Fenton process, providing new ideas for the treatment of complex and refractory wastewater. Based on available studies, this review is the first to systematically summarize the research progress regarding the synergistic effects of oxidation, coagulation and adsorption in the integrated Fenton-based processes for wastewater treatment. The involved mechanism of the synergistic effects in different Fenton processes (homogeneous Fenton, heterogeneous Fenton and physical field-assistant Fenton coupling process) are critically reviewed. Furthermore, special attention has been paid to the representative applications of the synergistic effects in wastewater treatment (such as industrial organic wastewater, landfill leachate and heavy metal-organic complexes, etc.), particularly focusing on the operation parameters and removal performance. Finally, a conclusion of the review and subsequently, perspectives are given for possible research directions. We believe this review can provide useful information for researchers and end-users involved in the development and application of the Fenton process in wastewater treatment.

Can thermal intensification be considered a sustainable way for greening Fenton processes?

Life cycle assessment and kinetic modeling were used to elucidate the impact of thermal intensification (TI) on resource consumption and the techno-economic feasibility of a Fenton process at laboratory scale. Increasing temperature from 25 to 55 °C lowers treatment time (96.5%) and electricity use (67.8%) due to the positive impact of temperature on the reaction rate; however, beyond 50 °C no significant diminution in energy use, emissions, and operating cost was observed. The environmental footprint of the process is linked with energy use, operating pH, and the electricity share of the country; nevertheless, the impact of transport and infrastructure materials was lower. At 55 °C and pH of 2.8, emissions of precursors of freshwater and marine eutrophication, particulate matter formation, and ionizing radiation were reduced more than half; besides, in most of the midpoint categories, pondered by the ReCiPe-2016 method, emissions were lowered ca. 43.3%. The endpoint categories human health, ecosystem quality, and resource availability had a significant decline in disability-adjusted life years (46.0%), time-integrated species loss (42.0%), and surplus cost (33.1%). Harnessing the energy present in the wastewater itself decreased 41.9% global warming potential (GWP), but the use of steam for heating raised it 718.8%. In countries where electricity generation is dependent on fossil fuels, GWP could increase (2.0-20.0%) whereas GWP would decrease (8.8-9.4%) when renewable energy sources dominate. Operating at 55 °C and pH of 5.5 rose the reaction time (1835.5%), GWP (29.3%), particulate matter formation (44.3%), terrestrial acidification (21.8%), marine (48.9%), and freshwater eutrophication (66.7%). TI of Fenton processes could increase their treatment capacity with a small reduction in the quality of the effluent; furthermore, they can be made affordable for low-to-medium scale industries in emerging economies due to decreased resources consumption and emissions, leading to a lower treatment cost (US$0.49/m³).

Evaluation of the efficiency of coagulation/flocculation and Fenton process in reduction of colour, turbidity and COD of a textile effluent

The present study investigated the efficiency of physicochemical processes of coagulation and flocculation and Fenton advanced oxidative process in reducing the parameters of colour, turbidity and Chemical Oxygen Demand (COD) of a real effluent from a textile industry. During the physicochemical process, the efficiencies of different coagulants (aluminium polychloride (Polifloc 18), ferric chloride (Acquafloc FC40), aluminium sulphate combined with organic coagulant (AST) and aluminium sulphate) and nonionic (FX NS2), cationic (FX CS6 and FX CS7) and anionic (FX AS6 and AN905) flocculants were tested. After the tests, 72.60% of COD, 36.25% of colour and 98.59% of turbidity were removed, using aluminium polychloride coagulant and AN 905 flocculant. It was also evaluated the effect of Fenton advanced oxidative process application in removal of colour, COD and turbidity of the effluent previously treated through the physicochemical process. Removals of these parameters were analysed in two different pH ranges (pH 6.0 and 7.0). In both pH 6.0 and pH 7.0, reductions were observed in all analysed parameters, obtaining 170.78 mg O₂/L of COD, 22.19 mg/L of colour and 0.80 NTU of turbidity (at pH 6.0) and 151.80 mg O₂/L of COD, 26.73 mg/L of colour, 0.94 NTU of turbidity (at pH 7.0), which demonstrates the efficiency of this process in the reduction of parameters analysed.

Treatment of biodigested coffee processing wastewater using Fenton's oxidation and coagulation/flocculation

Biodigested coffee processing wastewater (CPW) presents a high organic load and does not meet the limits imposed by legislation (namely in Brazil) for discharge into water bodies. Anaerobic digestion generally cannot provide a satisfactory organic matter reduction in CPW as a significant fraction of recalcitrant compounds still persists in the treated effluent. So, this study aims to find alternative ways to remove refractory organic compounds from this wastewater in order to improve the biodegradability and reduce the toxicity, which will allow its recirculation back into the anaerobic digester. Three treatment approaches (Fenton's oxidation - Approach 1, Coagulation/flocculation (C/F) - Approach 2, and the combination of C/F with Fenton's process - Approach 3) were selected to be applied to the biodigested CPW in order to achieve that objective. The application of the Fenton process under the optimal operating conditions (initial pH = 5.0; T = 55 °C, [Fe³⁺] = 1.8 g L^-1 and [H₂O₂] = 9.0 g L^-1) increased the biodegradability (the BOD₅:COD ratio raised from 0.34 ± 0.02 in biodigested CPW to 0.44 ± 0.01 after treatment) and eliminated the toxicity (0.0% of Vibrio fischeri inhibition) along with moderate removals of organic matter (51.3%, 55.7% and 39.7% for total organic carbon - TOC, chemical oxygen demand - COD and biochemical oxygen demand - BOD₅, respectively). The implementation of a coagulation/flocculation process upstream from Fenton's oxidation, under the best operating conditions (pH 10-11 and [Fe³⁺] = 250 mg L^-1), also allowed to slightly increase the biodegradability (from 0.34 to 0.47) and reduce the toxicity, whereas providing a higher removal of organic matter (TOC = 76.2%, COD = 76.5 and BOD₅ = 66.3% for both processes together). Approach 1 and Approach 3 showed to be the best ones, implying similar operating costs (∼74 R$ m^-3/∼17 € m^-3) and constitute an attractive option for managing biodigested CPW.

Fenton treatment of bio-treated fermentation-based pharmaceutical wastewater: removal and conversion of organic pollutants as well as estimation of operational costs

The Fenton process is used as a tertiary treatment to remove organic pollutants from the effluent of bio-treated pharmaceutical wastewater (EBPW). The optimal and most appropriate Fenton conditions were determined by an orthogonal array test and single-factor experiments. The removal of chemical oxygen demand (COD) was influenced by the following factors in a descending order: H₂O₂/Fe(II) molar ratio > H₂O₂ dosage > reaction time. Under the most appropriate Fenton conditions (H₂O₂/Fe(II) molar ratio of 1:1, H₂O₂ dosage of 120 mg L^-1 and reaction time of 10 min), the COD and dissolved organic carbon (DOC) were removed with efficiencies of 62 and 53%, respectively, which met the national discharge standard (GB 21903-2008) for the Lake Tai Basin, China. However, the Fenton treatment was inadequate for removal of N compounds, and the removal of organic nitrogen led to an increment in N-NH₃ from 3.28 to 19.71 mg L^-1. Proteins and polysaccharides were completely removed, and humic acids (HAs) were partly removed with an efficiency of 55%. Three-dimensional excitation/emission matrix spectra (3DEEMs) indicated complete removal of fulvic acid-like substances and 90% reduction in the florescence intensity of humic acid-like substances. Organic pollutants with molecular weights (MW) > 10 kDa were completely removed, MW 5-10 kDa were degraded into smaller MW ones, and some low molecular weight acids (MW 0.1-1 kDa) were mineralized during the Fenton process. Some species, including pharmaceutical intermediates and solvents were detected by gas chromatography-mass spectrometry (GC-MS). The operational costs of the Fenton's treatment were estimated to be 0.58 yuan RMB/m³ EBPW based on reagent usage and iron sludge treatment and disposal.

Parametric study of a dyeing wastewater treatment by modified sericite

The aim of this study was to investigate color, suspended solids (SS), chemical oxygen demand (COD) and biological oxygen demand (BOD) removal using modified sericite with magnesium (Mg-Sericite) flocculants in dyeing wastewater. Mg-Sericite flocculants successfully removed >95% of color, SS. COD and BOD in dyeing wastewater at the following optimal conditions: Mg-Sericite dosage of 40 mg/L, pH of 11, Mg/Sericite ratio of 1.5, settling time of 20 min, mixing time of 10 min and mixing rate of 100 rpm. The bioflocculant, Mg-Sericite, can be a promising flocculants due to its high efficiency and low dose requirements in dyeing wastewater treatment. In addition, Mg-Sericite does not contaminate treated wastewater, which can be recycled to reduce not only the cost and the demand for water but also the extra operational costs for reusing wastewater.

Treatment of sugarcane vinasse by combination of coagulation/flocculation and Fenton's oxidation

The efficiency of individual and integrated processes applied to organic matter reduction and biodegradability improvement of a biodigested sugarcane vinasse wastewater was assessed. Strategies considered were Fenton's oxidation (Strategy 1), coagulation/flocculation (Strategy 2) and the combination of both processes (coagulation/flocculation followed by Fenton's reaction) - Strategy 3. It was found that Fenton's oxidation per se allowed reducing the organic matter, increasing the wastewater biodegradability and a non-toxic effluent was generated; however the cost of treatment was very high (86.6 R$/m(3) - 21.2 €/m(3)). Under optimized conditions, coagulation/flocculation provided a slight increase in effluent's biodegradability, toxicity towards Vibrio fischeri was also eliminated and moderate removals of total organic carbon - TOC - (30.5%), biological oxygen demand - BOD5 - (27.9%) and chemical oxygen demand - COD - (43.6%) were achieved; however, the operating costs are much smaller. The use of dissolved iron resulting from coagulation/flocculation (270 mg/L) as catalyst in the second stage - Fenton's oxidation - was shown to be an innovative and economically attractive strategy. Under optimal conditions overall removals of 51.6% for TOC, 45.7% for BOD5 and 69.2% for COD were achieved, and a biodegradable (BOD5:COD ratio = 0.54) and non-toxic effluent was obtained. In order to increase the efficiency of the process but using less hydrogen peroxide, the Fenton's oxidation was performed by gradually adding the oxidant. This procedure allowed to obtain the highest organic matter removal efficiency (as compared with the addition of all hydrogen peroxide at the beginning of the reaction). This way it was possible to minimize the reagent consumption and, consequently, reduce the treatment cost.

Degradation of polyvinyl alcohol in textile waste water by Microbacterium barkeri KCCM 10507 and Paenibacillus amylolyticus KCCM 10508

Microbacterium barkeri KCCM 10507 and Paenibacillus amylolyticus KCCM 10508 were isolated and identified for the degradation of polyvinyl alcohol (PVA) contained in textile waste water. Kinetic parameters such as growth rate and substrate utilization rate were determined using a pure culture of two isolated strains. The degradation rate by a mixed culture of two isolated strains was higher than that by single strain only. Also, the effect of polymerization degree on biodegradation was negligible, but initial PVA concentration was very sensitive to biodegradation. Forty-two per cent of PVA and 55% of chemical oxygen demand in textile waste water were removed by a mixed culture of two isolated strains after 5 days.

Effect of Fenton oxidation on biodegradability, biotoxicity and dissolved organic matter distribution of concentrated landfill leachate derived from a membrane process

The treatment of concentrated landfill leachate from membrane process is a troublesome issue due to high concentrations of biorecalcitrant pollutants. In this study, the effect of Fenton process on dissolved organic matter (DOM) distribution (i.e. humic acid (HA), fulvic acid (FA) and hydrophilic fraction (HyI)), chemical forms of toxic organic compounds and metals, and their biotoxicity were investigated. In the concentrated leachate, toluene, ethylbenzene and chlorobenzene predominated in the HyI fraction, while phthalate esters (PAEs) were mainly absorbed on the HA and FA fractions. PAEs were more readily removed from the HA and FA fractions than that from the HyI fraction in the Fenton process. The complexing abilities of DOM varied with types of metal in the concentrated leachate. The biotoxicities of the DOM fractions to luminescent bacteria (Photobacterium phosphoreum T3 mutation) were HA > FA > - HyI. The biotoxicities of the hydrophobic organic contaminants to luminescent bacteria were not obvious in the concentrated leachate due to their low concentrations. Metals might be the main contributor to the biotoxicity to luminous bacteria in the concentrated leachate. These results indicated that Fenton process could influence the pollutants distribution in DOM and their biotoxicities through the breakdown of HA and FA in the concentrated leachate.

Efficiency and chemical recycling capability of magnetite-rich clay towards Eriochrome Black T remediation in the fixed-bed system

The present study investigates a fixed-bed column by using magnetite-rich clay from Cameroon as an adsorbent for the removal of the Eriochrome Black T (EBT) from aqueous solution. The effect of various parameters such as bed depths and EBT concentrations was investigated. The Adams-Bohart, Thomas and Yoon-Nelson models were applied to adsorption under varying experimental conditions to predict the breakthrough curves and to evaluate the model parameters of the fixed-bed column that can be useful for the process design. The column regeneration studies were carried out for three different sorption-desorption cycles using HCl or NaOH solution at 1 M. The 1 M HCl solution was found to have the best bed regeneration capacity and the fixed-bed could be reused for several sorption-desorption cycles. The elution efficiency of EBT, 75 mg L(-1) was greater than 99.1% for all three cycles.

Nanofiltration and Fenton's process over iron shavings for surfactants removal

The presence of surfactants in wastewater composition tends to jeopardize the efficiency of the traditional aerobic treatment processes. In this regard, the application of Fenton's reaction and nanofiltration as single processes and integrated (nanofiltration followed by Fenton's process) was investigated on the abatement of a solution containing two surfactants usually found in effluents coming from detergent industry (dodecylbenzene--DDB and sodium lauryl ether sulphate--SLES). The potential of a solid waste (iron shavings) as catalyst in the Fenton's process was evaluated and the reaction system was optimized regarding the key operating parameters (iron and hydrogen peroxide concentration and pH). The highest chemical oxygen demand (COD) degradation (66%) was attained for pH 3, [H2O2] = 32 mM and 50 g/L of iron shavings. Besides, it was concluded that oxidation was due to hydroxyl radicals adsorbed on the metal surface even if bulk interaction between hydrogen peroxide and dissolved iron cannot be neglected. The main variables ruling nanofiltration were evaluated (pH, temperature and cross-flow rate). Eighty-four percent of COD rejection was determined at pH 7.5, cross-flow 14.4 cm3 s(-1), 20 degrees C and 15 bar of pressure drop. Finally, nanofiltration followed by Fenton's process under the best conditions was integrated; however, no significant improvement was attained with 85% of COD being globally removed.