Real textile effluents treatment using coagulation/flocculation followed by electrochemical oxidation process and ecotoxicological assessment

Evaluating the effectiveness of coagulation-flocculation treatment on a wastewater from the moroccan leather tanning industry : An ecological approach

The removal of pollutants from tannery wastewaters, which is renowned for its substantial volumes, intricate composition, and considerable hazards to human health and the environment, is a prominent research area in the field of water treatment. The aim of this study is to employ a bio-coagulant derived from Parkinsonia aculeata seeds and a bio-flocculant derived from Hibiscus esculentus to minimise the concentration of pollutants in the combined wastewater originating from tanneries. In the course of the research, a thorough physicochemical analysis of the coagulating and flocculating agents, Parkinsonia aculeata (PA) and Hibiscus esculentus (HE), was performed using techniques such as XRD (X-ray diffraction), FTIR (Fourier-transform infrared spectroscopy), and SEM-EDS (scanning electron microscopy-energy dispersive X-ray spectroscopy). This analysis aimed to determine the composition and characteristics of these biomasses. Subsequently, a comprehensive overview was conducted to summarize the various factors that influence the treatment of tannery wastewater through coagulation/flocculation. This was accomplished by manipulating the target factors and observing their impact on the removal of specific physicochemical parameters such as chemical oxygen demand (COD), electrical conductivity (EC), total chromium (Cr) and Optical density (OD). The variables that were established include pH, dosage of coagulant and flocculant, as well as the speed and duration of agitation in both the fast and slow mixing stages. The experiments were carried out while taking into account the optimal parameters, leading to the near-complete removal of all analyzed pollutants. The optimal requirements for the Parkinsonia aculeata-Hibiscus esculentus Coagulation Flocculation System involve adjusting the pH to 8, choosing concentrations of approximately 1.25 g L-1 and 0.6 g L-1 for the coagulant and flocculant respectively, maintaining a fast speed of 170 rpm for 3 min while keeping the slow agitation at around 30 rpm for 20 min. The removal rates achieved after treating tannery wastewater using the PA-HE coagulant-flocculant combination demonstrate high efficacy, with values reaching approximately 100% for TSS, 98.71% for BOD5, 99.93% for COD, 98.88% for NH4+, 98.21% for NO3-, 90.32% for NO2-, 93.13% for SO42-, 95.44% for PO43-, 96.08% for OD and 60% for total chromium. These results indicate the successful removal of a wide range of pollutants from tannery wastewater through the PA-HE treatment method. In predicting the CF treatment approach, PCA has been employed to preprocess the input data and determine the key variables that impact the process. This can streamline the modeling process and enhance the precision of the predictions.

Molecular transformations of dissolved organic matter during UV/O3-assisted membrane filtration of UASB-treated real textile wastewater

A ceramic membrane reactor (CMR) integrated with in-situ UV/O₃ was assessed for post-treatment of the effluent out of an up-flow anaerobic sludge blanket (UASB) reactor treating real textile wastewater, focusing on the transformation of dissolved organic matter (DOM). Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) revealed the transformation of heteroatomic DOM containing S, N or both to simpler DOM containing mainly C, H, and O atoms. The decreased N contents in products (N/C = 0.0249) compared to precursors (N/C = 0.0311) and the higher O/C ratios in the N-containing products suggest the removal of R-NH₂ groups accompanying DOM oxidation. While, S-containing compounds in the products had lower O/C and H/C ratios, suggesting a reduced state and the transformation of R-SO₃ to R-S-R. H-abstraction and OH addition were identified as the primary oxidation mechanisms, thus enhancing the dominance of highly unsaturated and phenolic DOM in the effluent (70.3%) compared to the feed (56.6%). The double bond equivalent (DBE) was also increased by 26% in the effluent compared to the feed and by 33% in products compared to precursors. These findings help understand the DOM transformation in UV/O₃-assisted ceramic membrane reactors and call for comprehensive toxicity analyses of effluents from the advanced oxidation processes.

Environmental pollution, toxicity profile, and physico-chemical and biotechnological approaches for treatment of textile wastewater

Textile industries discharges a huge quantity of unused synthetic dyes in wastewater leading to increased environmental pollution and pose a great risk to human health. Thus, a significant improvement in effluent quality is required before it is discharged into the environment. Although, several physicochemical methods have been practiced for the efficient color and dyes removal from textile effluents, these approaches have some drawbacks of greater use of expensive chemicals, low sensitivity, formation of excess sludge which also have secondary disposal problem. Thus, there is still a need for energy efficient, affordable, effective, and environmentally friendly treatment technologies. Bioremediation has been considered as a promising an upcoming active field of research for the treatment of unwanted color and target compounds from the contaminated environment. In order to efficient treatment of textile effluent, the main objective of the present study was to isolate and characterize the indigenous microbial isolates from textile industry effluents and sludge samples and investigate their dye removal and decolorization ability along with the influence of various process parameters on effluents decolorization that draining into the open environment.

Water recovery from yarn fabric dyeing wastewater using electrochemical oxidation and membrane processes

This study intended to evaluate and compare the efficiency of electrochemical oxidation (EO), nanofiltration (NF), and reverse osmosis (RO) membranes processes in the treatment of yarn fabric dyeing wastewater (YFDW) in terms of chemical oxygen demand (COD) removal, color removal, salinity reduction, and conductivity removal. EO tests of the textile effluent were conducted under various current densities and solution pH conditions employing a graphite electrode. Membrane filtration experiments were conducted using two different NF membranes: NP010 and NP030 and two distinct RO membranes: BW30 and SW30 flat-sheet membranes. The experimental results showed that NF membrane process is not suitable for yarn fabric wastewater treatment showing low removal efficiencies for COD, color, and conductivity. However, both EO and RO membranes could reduce COD and color to high removal performances. EO results showed more than 99% of color removal and 80% of COD elimination at pH = 6 and current density of 50 mA/cm² after 180 min of reaction. Using RO membrane for yarn fabric wastewater treatment demonstrated relatively complete removal of color concentration and 98% of COD elimination. However, EO process showed less performance in conductivity removal efficiency compared to the RO membranes. EO treatment of YFDW decreased conductivity by 31.2%, whereas RO membrane process reduced conductivity to a greater extent and recorded 97.1% of removal elimination percentage. Therefore, the treated water by RO membrane could be recycled back to the process such as washing and dyeing, in that way offering economic profits by decreasing water consumption and wastewater treatment cost. PRACTITIONER POINTS: Electrochemical oxidation and membrane filtration processes were combined for the treatment of yarn fabric dyeing wastewater (YFDW). A 100% color removal of color and 98.5% COD elimination efficiencies were obtained for the electrochemical oxidation (EO) + RO combined process. EO treatment of YFDW decreased conductivity by 32.7%, whereas the RO membrane process reduced conductivity to a greater extent and recorded 97.7% of removal elimination percentage.

Variation and comparison of biotoxicity during typical biological treatment of dyeing wastewater

In present study, dyeing wastewater samples were collected from three typical dyeing wastewater treatment plants in Wujiang, Shengze and Shanghai, China. Physicochemical properties and biotoxicity indicators (luminescent bacteria acute toxicity and umu genotoxicity) were tested and the relationships among them were analyzed. The results revealed that two biotoxicity indicators varied significantly among different treatment units of three plants. After treatment by plant A, luminescent bacteria acute toxicity of dyeing wastewater reduced effectively, while umu genotoxicity increased significantly. Two biotoxicity indicators exhibited decrease and increase trends during the treatment processes of plant B and plant C, respectively. Correlation analysis indicated that there was little correlation among biotoxicity indicators and physicochemical properties, meanwhile two kinds of biotoxicity indicators were relatively independent. Therefore, it was recommended that comprehensive evaluation of dyeing wastewater toxicity needs the combination of various biotoxicity indicators, and the relationship among biotoxicity indicators and physicochemical properties of dyeing wastewater should be established individually. The results of this study would offer a general understanding and evaluation of biotoxicity during actual dyeing wastewater treatment processes and provide database for toxicity reduction and management of dyeing wastewater.

Physico-chemical processes

By summarizing 187 relevant research articles published in 2019, the review is focused on the research progress of physicochemical processes for wastewater treatment. This review divides into two sections, physical processes and chemical processes. The physical processes section includes three sub-sections, that is, adsorption, granular filtration, and dissolved air flotation, whereas the chemical processes section has five sub-sections, that is, coagulation/flocculation, advanced oxidation processes, electrochemical, capacitive deionization, and ion exchange. PRACTITIONER POINTS: Totally 187 research articles on wastewater treatment have been reviewed and discussed. The review has two major sections with eight sub-topics.

Carboxymethyl cellulose improved adsorption capacity of polypyrrole/CMC composite nanoparticles for removal of reactive dyes: Experimental optimization and DFT calculation

In this study, polypyrrole/carboxymethyl cellulose nanocomposite particles (PPy/CMC NPs) were synthesized and applied for removal of reactive red 56 (RR56)and reactive blue 160 (RB160) as highly toxic dyes. The amount of CMC was found significantly effective on the surface adsorption efficiency. Different optimization methods including the genetic programming, response surface methodology, and artificial neural network (ANN) were used to optimize the effect of different parameters including pH, adsorption time, initial dye concentration and adsorbent dose. The maximum adsorption of RR56 and RB160 were found under the following optimum conditions: pH of 4 and 5, adsorption time of 55 min and 52 min for RR56 and RB160, respectively, initial dye concentration of 100 mg/L and adsorbent dose of 0.09 g for both dyes. were obtained for RR56 and RB160, respectively. Also, the results indicated that ANN method could predict the experimental adsorption data with higher accuracy than other methods. The analysis of ANN results indicated that the adsorbent dose is the main factor in RR56 removal, followed by time, pH and initial concentration, respectively. However, initial concentration mostly determines the RB160 removal process. The isotherm data for both dyes followed the Langmuir isotherm model with a maximum adsorption capacity of 104.9 mg/g and 120.7 mg/g for RR56 and RB160, respectively. In addition, thermodynamic studies indicated the endothermic adsorption process for both studied dyes. Moreover, DFT calculations were carried out to obtain more insight into the interactions between the dyes and adsorbent. The results showed that the hydrogen bondings and Van der Waals interactions are dominant forces between the two studied dyes and PPy/CMC composite. Furthermore, the interaction energies calculated by DFT confirmed the experimental adsorption data, where PPy/CMC resulted in higher removal of both dyes compared to PPy. The developed nanocomposite showed considerable reusability up to 3 cylces of the batch adsorption process.

Electrochemical oxidation of indanthrene blue dye in a filter-press flow reactor and toxicity analyses with Raphidocelis subcapitata and Lactuca sativa

Alternative routes to degrade dyes are of crucial importance for the environment. Hence, we report the electrochemical removal of indanthrene blue by using a boron-doped diamond anode, focusing on the toxicity of the treated solutions. Different operational conditions were studied, such as current density (5, 10, and 20 mA cm-2) and electrolyte composition (Na2SO4, Na2CO3, and NaNO3). Besides, the pH was monitored throughout the experiment to consider its direct influence on the ecotoxicity effects. The highest electrochemical oxidation efficiency, measured as color removal, was seen in the 180 min condition of electrolysis in 0.033 M Na2SO4, applying 20 mA cm-2, resulting in a color removal of nearly 91% and 40.51 kWh m-3 of energy consumption. The toxicity towards Lactuca sativa depends solely on pH variations being indifferent to color removal. While the inhibition concentration (IC50) for Raphidocelis subcapitata increases 20% after treatment (in optimized conditions), suggesting that the byproducts are more toxic for this specific organism. Our data highlight the importance of analyzing the toxicity towards various organisms to understand the toxic effect of the treatment applied.