Natural dyes have been used from ancient times for multiple purposes, most importantly in the field of textile dying. The increasing demand and excessive costs of natural dye extraction engendered the discovery of synthetic dyes from petrochemical compounds. Nowadays, they are dominating the textile market, with nearly 8 × 105 tons produced per year due to their wide range of color pigments and consistent coloration. Textile industries consume huge amounts of water in the dyeing processes, making it hard to treat the enormous quantities of this hazardous wastewater. Thus, they have harmful impacts when discharged in non-treated or partially treated forms in the environment (air, soil, plants and water), causing several human diseases. In the present work we focused on synthetic dyes. We started by studying their classification which depended on the nature of the manufactured fiber (cellulose, protein and synthetic fiber dyes). Then, we mentioned the characteristics of synthetic dyes, however, we focused more on their negative impacts on the ecosystem (soil, plants, water and air) and on humans. Lastly, we discussed the applied physical, chemical and biological strategies solely or in combination for textile dye wastewater treatments. Additionally, we described the newly established nanotechnology which achieves complete discharge decontamination.

https://www.mdpi.com/2076-3417/11/14/6255/pdf

Diversity of Synthetic Dyes from Textile Industries, Discharge Impacts and Treatment Methods

This study aims to investigate treatment efficiency and evaluate the energy efficacy of integrated electrocoagulation system combined with ozonation, Fenton, and photo-Fenton processes for successful textile dye-bath effluents' treatment. In this regard, the characterization of physicochemical parameters such as pH, turbidity, salinity, total dissolved solids (TDS), total suspended solids (TSS), electrical conductivity (EC), and chemical oxygen demand (COD) was analyzed to estimate removal efficiency of each treatment process. Moreover, the electrical energy consumption of all aforementioned processes was measured individually to work out cost-effectiveness. Fenton process appeared to be ineffective for reducing COD and other parameters. While the overall performance of ECS alone showed far better results, COD and color removal efficiencies were 57.4%, and 40%, respectively. However, the application of ECS/O3 resulted in complete decolorization and almost 99.7% COD removal under optimized operating conditions including ozone flow 300 mg/h, pH 7.1, Temperature 25 °C. ECS/photo-Fenton process resulted in COD, and color removal of 95.6%, and 97%, respectively. Electrical Energy per Order of ECS was found 1.58 kWh/m3 for minimum removal of dyes and COD. ECS/Ozonation is responsible for 100% decolorization but at a very high cost. ECS/photo-Fenton process proved to be the second-best option in terms of treatment and energy consumption. Hence, an integrated treatment system of ECS with AOPs appeared to be the most feasible and eco-friendly. That could lead to the treated wastewater for reuse and recycling purposes within the industry. 

Comparison of ozonation, Fenton, and photo-Fenton processes for the treatment of textile dye-bath effluents integrated with electrocoagulation

The garment sector takes up a large portion of aquifers and emits massive amounts of poisonous azo dye (AD) effluents, resulting in an unavoidable state of severe contamination that poses a serious risk to humans. Physicochemical techniques for treatment of textile effluents are expensive, consume more energy, and are inefficient in terms of ecology. The innovation of eco-sustainable and inexpensive method is currently the subject of discussion around the globe. As a result, the application of biodegradation for ADs will be environmentally beneficial and is likely to be a profitable alternative to physicochemical methods. The aim of this article was to discuss the classification, source, and impact of AD. It also covered biodegradation methods such as biodegradation by bacteria, fungi, algae, and enzyme treatment. Finally, the recent advancements in AD removal in biodegradation were also addressed. 

Sustainable approach on the biodegradation of azo dyes: A short review

http://www.cell.com/article/S2405844022009203/pdf

Use of bacterial isolates in the treatment of textile dye wastewater: A review

Degradation of dyes by UV/Persulfate and comparison with other UV-based advanced oxidation processes: Kinetics and role of radicals.

\n The threat of dye contamination has achieved an unsurpassed abnormal state lately due to their massive consumption in several enterprises including textile, leather, cosmetic, plastic, and paper industries. This review focuses on the integrations of various advanced oxidation processes (AOPs), such as Fenton, photocatalysis, and ozonation, with biodegradation for the treatment of textile azo dyes. Such integrations have been explored lately by researchers to bring down the processing cost and improve the degree of mineralization of the treated dyeing wastewater. The review refers to the basic mechanisms, the influence of various process parameters, outcomes of recent works, and future research directions. All the three AOPs, independently, demonstrated substantial color reduction of 54–100%. The ozonation process, stand-alone, showed the most efficient decolorization (of 88–100%) consistently in all reviewed research works. In contrast, all three AOPs independently offered varied and inadequate COD reduction in the range of 16–80%. The AOPs, after getting integrated with biodegradation, yielded an additional reduction (of 11–70%) in the COD-levels and (of 16–80%) in the TOC-levels. Further, the integration of AOPs with biodegradation has potential to significantly reduce the treatment costs. The review suggests further research efforts in the direction of sequencing chemical and biological routes such that their synergistic utilization yield complete detoxification of the textile azo dyes economically at large-scale.

A comprehensive review on the integration of advanced oxidation processes with biodegradation for the treatment of textile wastewater containing azo dyes

The textile industry, at various stages of fabric dyeing, generates huge volumes of wastewaters which eventually overload the aquatic bodies with wide range of dyes as persistent pollutants. In the present study, a recirculating fixed-bed bioreactor (RFBB) was operated in anaerobic and, anaerobic-aerobic environments to treat the simulated textile wastewater containing Congo red dye. The performance of the RFBB was evaluated in terms of color, COD and TOC removal at varied organic loading rates in the range of 1.37–2.23 kg COD/m3.d (equivalent to 200–800 ppm inlet dye concentrations). Although the anaerobic treatment was found to remove the color efficiently, the COD and TOC were not removed completely even after its integration with an aerobic step; hence the toxicity of the finally treated dyeing water remained a concern. The main objective of this study was to determine and compare the acute and chronic toxicities of treated dyeing water using phytotoxicity and bacterial toxicity (based on luminescent P. luminescens). While Vigna radiata seeds exhibited only 23.33% germination in the polluted water, the germination increased to ~ 87% and 90% in the anaerobically and anaerobically-aerobically treated dyeing water respectively. On the contrary, the acute bioluminescence inhibitions for anaerobically and anaerobically-aerobically treated dyeing water were found to be 40.11% and 4.51% respectively. It was observed that the treated-water samples could be well-distinguished, in terms of their toxicity levels, using bioluminescence assays even when the same samples were non-differentiable in the phytotoxicity assays.

Comparative toxicity assessment using plant and luminescent bacterial assays after anaerobic treatments of dyeing wastewater in a recirculating fixed bed bioreactor

A rigorous knowledge of the bacterial growth kinetics is essential for the scaling-up and optimization of biodegradation process conditions in a bioreactor. Although a great deal of literature is available on the modeling of bacterial growth kinetics considering the inhibition at high substrate-loading, the inhibition caused by toxic metabolic byproducts was not accounted in the bacterial growth kinetics. This work primarily aimed at developing a parametric bacterial growth model to account for metabolite inhibition, indicated by a decelerating log-phase growth, which was rarely discussed in the previous studies. An efficient azo-dye degrading bacterium (Bacillus subtilis MN372379) was isolated from the sludge-waste nearby a carpet-dyeing unit. The isolated bacterial strain was used to decolorize the simulated wastewater containing Congo red dye. This study proposed a computational approach to calculate specific bacterial growth rate time-averaged over the entire sigmoidal log phase (including the decelerating phase) for incorporating the effect of metabolite-inhibition, in contrast to the conventional studies where only the initial part (accelerating) of log phase was considered. The nature of metabolite inhibition was also determined and found to be non-competitive. Next, the computed time-averaged specific bacterial growth rate was incorporated into three substrate inhibition models to account for both, the metabolite and substrate inhibitions, and subsequently their kinetic parameters were also determined. Finally, the initial dye concentration and inoculum size were optimized to yield maximum dye utilization rate. This study paves the way for predicting bacterial growth kinetic with improved accuracy to enable a better optimization of bioreactors at the industrial scale.

A Computational Approach to Incorporate Metabolite Inhibition in the Growth Kinetics of Indigenous Bacterial Strain Bacillus subtilis MN372379 in the Treatment of Wastewater Containing Congo Red Dye.

Wastewater treatment is an important concern as far as water-based industries are concerned. A large volume of polluting effluents containing significant residual chemicals are frequently generated from these workhouses and their auxiliaries. These harmful effluents discharged poses risk to so many water bodies and human health too. Ozone, being a powerful oxidant, reacts quickly with most of the organic compounds and have been effectively utilized with different bioreactor systems for complete mineralization and detoxification of wastewater effluents generated from hospitals, municipal, tanneries, and textile processing. However, the disposal of some harmful metabolites and recalcitrant organic chemicals is still the area where further studies are needed to focus upon. The presented chapter provides fundamentals of the ozonation process, the latest development in the hybrid bioreactor systems like membrane bioreactor, sequential batch reactor, activated sludge process and upflow anaerobic sludge bed for complex wastewater treatment. The presented work also focuses on the strategies for the selection of an optimal combination of biodegradation and ozone-based processes depending on the target contaminants.

Anuj Chaturvedi

Papers

A comprehensive review on the integration of advanced oxidation processes with biodegradation for the treatment of textile wastewater containing azo dyes

Comparative toxicity assessment using plant and luminescent bacterial assays after anaerobic treatments of dyeing wastewater in a recirculating fixed bed bioreactor

A Computational Approach to Incorporate Metabolite Inhibition in the Growth Kinetics of Indigenous Bacterial Strain Bacillus subtilis MN372379 in the Treatment of Wastewater Containing Congo Red Dye.

Hybrid bioreactor in combination with ozone-based technologies for industrial wastewater treatment

Investigation of External Mass Transfer during Biodegradation of Congo Red Dye in a Recirculating Packed Bed Bioreactor