Azo dyes decolorization under high alkalinity and salinity conditions by Halomonas sp. in batch and packed bed reactor

Bioremediation of azo dye: A review on strategies, toxicity assessment, mechanisms, bottlenecks and prospects

The synthetic azo dyes are widely used in the textile industries for their excellent dyeing properties. They may be classified into many classes based on their structure and application, including direct, reactive, dispersive, acidic, basic, and others. The continuous discharge of wastewater from a large number of textile industries without prior treatment poses detrimental effects on the environment and human health. Azo dyes and their degradation products are extremely poisonous for their carcinogenic, teratogenic and mutagenic nature. Moreover, exposure to synthetic azo dyes can cause genetic changes, skin inflammation, hypersensitivity responses, and skin irritations in persons, which may ultimately result in other profound issues including the deterioration of water quality. This review discusses these dyes in details along with their detrimental effects on aquatic and terrestrial flora and fauna including human beings. Azo dyes degrade the water bodies by increasing biochemical and chemical oxygen demand. Therefore, dye-containing wastewater should be effectively treated using eco-friendly and cost-effective technologies to avoid negative impact on the environment. This article extensively reviews on physical, chemical and biological treatment with their benefits and challenges. Biological-based treatment with higher hydraulic retention time (HRT) is economical, consumes less energy, produces less sludge and environmentally friendly. Whereas the physical and chemical methods with less hydraulic retention time is costly, produces large sludge, requires high dissolved oxygen and ecologically inefficient. Since, biological treatment is more advantageous over physical and chemical methods, researchers are concentrating on bioremediation for eliminating harmful azo dye pollutants from nature. This article provides a thorough analysis of the state-of-the-art biological treatment technologies with their developments and effectiveness in the removal of azo dyes. The mechanism by which genes encoding azoreductase enzymes (azoG, and azoK) enable the natural degradation of azo dyes by bacteria and convert them into less harmful compounds is also extensively examined. Therefore, this review also focuses on the use of genetically modified microorganisms and nano-technological approaches for bioremediation of azo dyes.

Biological treatment of methyl orange dye and textile wastewater using halo-alkaliphilic bacteria under highly alkaline conditions

As the textile wastewater is highly saline and has high pH it is important to employ extremophilic microbes to survive in harsh conditions and provide effective bioremediation of textile dyes. This study aims to find a sustainable solution for dye removal by investigating the potential of an indigenously isolated bacterium, Nesterenkonia lacusekhoensis EMLA3 (halo-alkaliphilic) for treatment of an azo dye, methyl orange (MO) and textile effluent. MO dye decolorization studies were conducted using mineral salt media (MSM) by varying incubation time (0-120 h), initial dye concentration (50-350 mg/L), pH (7.0-12.0), inoculum dose (3-10%), agitation (stationary, 100 rpm and 200 rpm), and temperature (20-55 °C). Dye removal by the bacterium for 50 mg/L of dye was > 97.0% within 72 h of incubation at pH 11.0 in stationary condition. Bacterium had excellent reusability i.e. > 97% dye removal for up to 5 cycles. Moreover, bacterium has the potential for co-removal of chromium (VI) (3.5-28 mg/L), and also almost complete dye removal in presence of high amount of NaCl. Liquid chromatography-mass spectrometry showed degradation as the mechanism of dye removal. Application of the bacterium to MO dye spiked real textile wastewater showed excellent dye removal. Phyto-toxicity assessment conducted on Vigna radiata and Triticum aestivum seeds, showed 100% germination of biotreated textile wastewater indicating its reuse potential.

Microbial alchemists: unveiling the hidden potentials of halophilic organisms for soil restoration

Salinity, resulting from various contaminants, is a major concern to global crop cultivation. Soil salinity results in increased osmotic stress, oxidative stress, specific ion toxicity, nutrient deficiency in plants, groundwater contamination, and negative impacts on biogeochemical cycles. Leaching, the prevailing remediation method, is expensive, energy-intensive, demands more fresh water, and also causes nutrient loss which leads to infertile cropland and eutrophication of water bodies. Moreover, in soils co-contaminated with persistent organic pollutants, heavy metals, and textile dyes, leaching techniques may not be effective. It promotes the adoption of microbial remediation as an effective and eco-friendly method. Common microbes such as Pseudomonas, Trichoderma, and Bacillus often struggle to survive in high-saline conditions due to osmotic stress, ion imbalance, and protein denaturation. Halophiles, capable of withstanding high-saline conditions, exhibit a remarkable ability to utilize a broad spectrum of organic pollutants as carbon sources and restore the polluted environment. Furthermore, halophiles can enhance plant growth under stress conditions and produce vital bio-enzymes. Halophilic microorganisms can contribute to increasing soil microbial diversity, pollutant degradation, stabilizing soil structure, participating in nutrient dynamics, bio-geochemical cycles, enhancing soil fertility, and crop growth. This review provides an in-depth analysis of pollutant degradation, salt-tolerating mechanisms, and plant-soil-microbe interaction and offers a holistic perspective on their potential for soil restoration.

Biotreatment of azo dye containing textile industry effluent by a developed bacterial consortium immobilised on brick pieces in an indigenously designed packed bed biofilm reactor

This study highlights the development of a lab-scale, indigenously designed; Packed-Bed Biofilm Reactor (PBBR) packed with brick pieces. The developed biofilm in the reactor was used for the decolourisation and biodegradation of the textile industry effluent. The PBBR was continuously operated for 264 days, during which 301 cycles of batch and continuous treatment were operated. In batch mode under optimised conditions, more than 99% dye decolourisation and ≥ 92% COD reduction were achieved in 6 h of contact time upon supplementation of effluent with 0.25 g L^-1 glucose, 0.25 g L^-1 urea, and 0.1 g L^-1 phosphates. A decolourisation rate of 133.94 ADMI units h^-1 was achieved in the process. PBBR, when operated in continuous mode, showed ≥ 95% and ≥ 92% reduction in ADMI and COD values. Subsequent aeration and passage through the charcoal reactor assisted in achieving a ≥ 96% reduction in COD and ADMI values. An overall increase of 81% in dye-laden effluent decolourisation rate, from 62 to 262 mg L^-1 h^-1, was observed upon increasing the flow rate from 18 to 210 mL h^-1. Dye biodegradation was determined by UV-Vis and FTIR spectroscopy and toxicity study. SEM analysis showed the morphology of the attached-growth biofilm.

Biotechnological impacts of Halomonas: a promising cell factory for industrially relevant biomolecules

Extremophiles are the most fascinating life forms for their special adaptations and ability to offer unique extremozymes or bioactive molecules. Halophiles, the natural inhabitants of hypersaline environments, are one among them. Halomonas are the common genus of halophilic bacteria. To support growth in unusual environments, Halomonas produces various hydrolytic enzymes, compatible solutes, biopolymers like extracellular polysaccharides (EPS) and polyhydroxy alkaloates (PHA), antibiotics, biosurfactants, pigments, etc. Many of such molecules are being produced in large-scale bioreactors for commercial use. However, the prospect of the remaining bioactive molecules with industrial relevance is far from their application. Furthermore, the genetic engineering of the respective gene clusters could open up a new path to bio-prospect these molecules by overproducing their products through heterologous expression. The present survey on Halomonas highlights their ecological diversity, application potential of the their various industrially relevant biomolecules and impact of these biomolecules on respective fields.

Microbial decolorization of Reactive Black 5 dye by Bacillus albus DD1 isolated from textile water effluent: kinetic, thermodynamics & decolorization mechanism

Reactive Black 5 is one of the most widely used dye in textile and other industries. It is one of the significantly toxic azo dye which poses a serious threat to the environment when discharged into water bodies. A bacterial strain having potential to decolourise and degrade RB5 was isolated from textile effluent, and further identified and characterized. On the basis of morphological, biochemical, and 16s rRNA sequence analysis, the isolate was identified as Bacillus albus DD1. It showed 98% removal of RB5 from aqueous medium within 38 h under optimum parameters, pH 7, temperature 40 °C, in the presence of 1% yeast extract as a co-substrate, and 25% inoculum size at the initial dye concentration of 50 mg/l. Kinetic study revealed the decolorization reaction is a first order non- spontaneous reaction. The rate constant and reaction rate for RB5 decolourization in presence of the isolate was 0.0523 s-1 and 2.6 × 10-3 mol/m3 sec, respectively. Values for ΔH and ΔS of the decolourization reaction, determined by thermodynamic analysis, were estimated to be +20.80 kJ/mol and ΔS = -0.1 kJ/mol K, respectively. LC-MS analysis revealed that decolorization was due to degradation of RB5 by cleavage of azo-bond by the bacterium, with the formation of s 3,6,8-trihyroxynapthalene and phthalic acid as degradation products. Therefore, the bacterium Bacillus albus DD1 has potential for application in biological treatment of dye contaminated industrial waste water.

Development and characterization of a halo-thermophilic bacterial consortium for decolorization of azo dye

Textile wastewater is characterized by high salinity and high temperature, and azo dye decolorization by mixed cultures under extreme salinity and thermophilic environments has received little attention. High salinity and temperature inhibit the biodecolorization efficiency in textile wastewater. In the present study, a halo-thermophilic bacterial consortium (HT1) that can decolorize azo dye at 10% salinity and 50 °C was enriched. Bacillus was the dominant genus, and this genus may play a key role in the decolorization process. HT1 can decolorize metanil yellow G (MYG) at a wide range of pH values (6-8), temperatures (40-60 °C), dye concentrations (100-200 mg/L) and salinities (1-15%). Laccase, manganese peroxidase, lignin peroxidase and azoreductase are involved in the decolorization process of MYG. In addition, the decolorization pathway of MYG was proposed based on GC-MS and FTIR results. The toxicity of MYG decreased after decolorization by HT1. A metagenomic sequencing approach was applied to identify the functional genes involved in degradation. Overall, this halo-thermophilic bacterial consortium could be a promising candidate for the treatment of textile wastewater under elevated temperature and salinity conditions.

Enhanced azo dye biodegradation at high salinity by a halophilic bacterial consortium

The aim of this work was to study the bioaugmentation of hydrolysis acidification (HA) by a halophilic bacterial consortium. A bacterial consortium was enriched at 5% salinity, and it decolorized metanil yellow G (MYG) at salinities of 1%-15% and dye concentrations of 100-400 mg/L under static conditions. A HA system was constructed to assess the effectiveness of bioaugmentation by the halophilic bacterial consortium. The HA system showed obviously better performance for decolorization and COD_Mn removal and presented higher the 5-day biological oxygen demand (BOD₅)/COD_Mn (B/C) ratio after bioaugmentation. MiSeq sequencing results indicated that the bacterial communities remarkably shifted and that the bacterial diversity was increased after bioaugmentation. Marinobacterium invaded the native microbe community and became the dominant bacterial genus in the bioaugmented HA, and it played a key role in azo dye decolorization. Therefore, bioaugmentation with a halophilic bacterial consortium improved the HA system for decolorization of azo compounds.

Recent Achievements in Dyes Removal Focused on Advanced Oxidation Processes Integrated with Biological Methods

In the last 3 years alone, over 10,000 publications have appeared on the topic of dye removal, including over 300 reviews. Thus, the topic is very relevant, although there are few articles on the practical applications on an industrial scale of the results obtained in research laboratories. Therefore, in this review, we focus on advanced oxidation methods integrated with biological methods, widely recognized as highly efficient treatments for recalcitrant wastewater, that have the best chance of industrial application. It is extremely important to know all the phenomena and mechanisms that occur during the process of removing dyestuffs and the products of their degradation from wastewater to prevent their penetration into drinking water sources. Therefore, particular attention is paid to understanding the mechanisms of both chemical and biological degradation of dyes, and the kinetics of these processes, which are important from a design point of view, as well as the performance and implementation of these operations on a larger scale.