You are hereA Review Biotechnological removal of color and dye from waste water

A Review Biotechnological removal of color and dye from waste water


[C] Use white rot fungi to decolourise dyes
White rot fungus can decolourize a number of dyes, particularly crystal violet dye which is often used to dye jeans [32]. This rot fungus requires a growth substrate and a fixed surface for efficient colour reduction.

[D] Biodegradation of Leather
Acid dye by Bacillus subtilis

The Bacillus subtilis was used to decolorize the Acidblue113. The bacterial culture exhibited 90% decolorization ability within 50 h. Maximum rate of decolorization was observed (90%) when starch & peptone was supplemented in the medium. Decolorization of Acidblue113 was monitored by TLC, which indicated that dye decolorization was due to its degradation into unidentified intermediates. The optimum dye decolorizing activity of the culture was observed at pH 7.0 and incubation temperature of 370C. Maximum, dye-decolorizing efficiency was observed at 200 mg/l concentration of Acidblue113. A plate assay was performed for the detection of decolorizing ability of bacteria. Clearing zone (decolorization) was formed surrounding the bacterial culture. Decolorization was confirmed by UV-VIS spectrophotometer. The initial dye solution showed high peak at the wavelength of 560nm. The decolorized dye showed disappearance of peak, which indicated that the decolorization is due to dye degradation. The dye decolorization was further confirmed by COD & BOD Analysis.

[IV] Nanocatalyst for dye removal from waste water
Factories across the world are dumping thousands of tonnes of untreated dyes into rivers and waterways every year. The majority of these dyes are toxic to the environment and may lead to mutations and cancers in animals. Particularly in textile industries where considerable amounts of water and chemicals are used during the dyeing process the wastewater contains about 20% of dye as well as organic matter, salts and other substances. Also since synthetic dyes are used to resist bleaching by UV-light and chemicals to improve the quality of the textiles, they are also persistent in the environment and some dyes can be biologically modified into carcinogenic compounds. For example azo dyes, a commonly used dye to color fabrics can cause cancer if released into the environment with wastewater.

Removal of color from dye wastewater
The release of untreated wastewater has high color, high chemical oxygen demand, low biodegradabilityand high variability, it poses a threat to the animal and human health, environment and the most serious problems are ground water and surface water pollution. Further, the discharge of colored effluents into water bodies affects the sunlight penetration which in turn decreases both the photosynthetic activity and dissolved oxygen levels. The removal of dyes from wastewater is one of the major environmental challenges.

Removal techniques
Wastewater containing dye is conventionally filtered using activated carbon. However, the carbon can only be used once and is then commonly disposed of in landfill sites. Biotechnological treatment methods called dye remediation can be used for the treatment of dyes using biological and physico-chemical techniques. Different techniques are adopted to treat dye wastewater including adsorption, catalytic oxidation, chemical oxidation, photocatalysis, electrochemical process, biodegradation and catalytic wet oxidation by adding catalysts and oxidants to improve the oxidation rate.

Catalytic wet oxidation
Catalytic wet oxidation process is usually carried out at high temperature and pressure, which restrict its wide application. More and more efforts have been focused on developing new processes to improve the efficiency of CWO, such as the preparation of new type heterogeneous catalysts with high catalytic activity. CeO2 or CeO2-based oxides materials by virtue of their large surface area exhibit greater catalytic activity in CWO.

Recovery
It is very hard to recover pure CeO2 or CeO2-based oxides powders from water when they are used in aqueous systems. Coating the particles onto other materials is the promising method to resolve this problem. Supports of silica and γ-Al2O3 have been used to prepare the CeO2-based catalysts, but, the supports, synthesized by chemical reactions have inherent defects such high cost, time consuming reaction and low surface area.

Natural nanostructural material
Attapulgite (ATP) is a crystalline hydrated magnesium aluminum silicate with reactive –OH groups on its surface with a structure of zeolite-like channels. Due to its regular structure and large specific surface area, ATP has been used as absorbent, catalyst and catalyst support. Zhao et al. prepared copper modified palygorskite/TiO2 photocatalyst by hydrolysis method, which exhibited much higher activity than that of the pure titanium dioxides in the degradation of methylene blue. In addition, it was reported that the redox couple (Ce3+/Ce4+) in contact with metal particles promoted the catalytic activity in ceria-based materials. It is effective way to enhance the catalytic reaction rate that modified the palygorskite clay with copper ions since addition of rare metal ions to CeO2-based catalytic systems.

Color Removal from Textile and other Industrial Wastewater using Ozone
Ozone has been used for successfully for removal of color from textile wastewater streams in plants around the world as well as in other industrial wastewater processes.  In wastewater treatment, ozone is often used in conjunction with biological treatment systems such as activated sludge.  Organic dyes are mostly refractory due to their large molecular size and they can be poorly removed by adsorption on activated sludge.  In some cases ozone has been used before the biological process, but mainly after biological treatment.  If the wastewater is hardly biodegradable or toxic to activated sludge pretreatment is an option. 

Ozone can be used prior to a biological process[33] since it has a tendency to convert organic molecules into smaller more biodegradable species.  This can enhance the efficiency of the biological process.  In addition, ozone treatment of wastewater increases the oxygen content of the water (unconverted oxygen and ozone that decomposes back to oxygen that was mixed with the water) which results in improvement in aerobic processes.  While this benefit is well known in the literature it is difficult to practically apply since the amount of improvement is difficult to predict and pilot studies involving ozone and biological processes are difficult to carry out.  In textile wastewater processes, a 20-30% improvement in the action of the biological system has been observed.

Ozone is effective in removing the color from all dyes used in textile processing. The amount of ozone can vary depending on a number of factors: how much color was removed in the biological process, the type of dye used, where ozone is applied in the process, etc.  Knowing the proper amount of ozone required to meet the color removal objective for the receiving water body is critical to the economics of the ozone system.  In general it is not easy to predict the amount of ozone required, so in virtually all cases where specific previous experience is not available, pilot testing is employed.

Tosik [34] has shown that about 1 mg ozone/mg dye is required to achieve 95% color removal, although this ratio varies by dye type.  The ratio increases to about 1.5 for 100% removal.  Reaction times were on the order of 10 minutes.  In the textile industry a typical dosage might be 15 mg/l post biological treatment, but the levels could easily reach 25 mg/l.  It is important to note that the ozone dose only needs to make the dye compound uncolored and not necessarily completely mineralize the material.
The equipment operates in a temperature range of 40-95 degrees F.  

Treatment of reactive dyes and textile finishing wastewater using Fenton's oxidation for reuse
Fenton's oxidation (FO) was used to decolourise and degrade some reactive dyes (Remazol Black 5, Remazol Red, Remazol Blue, Remazol Yellow) and raw textile finishing industry effluents (S1, S2, S3) containing mainly reactive dyes. The operational conditions for pH varied between 2.5 and 4.0 while temperature ranged from 30°C to 50°C. The concentrations of FeSO4 and H2O2 varied to a wide range (200–600 mg/l of FeSO4, 300–1000 mg/l of H2O2) depending on the type of the dyes and their mixture and textile additives used in the process. FO is highly effective for colour removal (>99%) for reactive dyes and (87–94%) for textile finishing wastewater. It can be applied as a pretreatment and the remaining total dissolved solids (TDS) can be removed by an additional advanced process, e.g. membrane process.

Removal of Vat Dyes from Textile Wastewater Using Biosludge
The textile industry is an industry of interest .Textile wastewaters contain a high concentration of both organic matter and colourants (dyes). Due to its properties, vat dye  ( Vat Black 25, Vat Green 1, Vat Black 8, Vat Yellow 1, Vat Green 13 ,Vat Brown 1 is mainly used in the textile industry. At present, chemical treatment methods such as oxidation, ion exchange, precipitation, coagulation and adsorption are commonly used to remove colourants from textile wastewater, but the chemical and operating costs are high and solid wastes are produced (chemical-sludge waste). Conventional biological treatment processes such as activatedsludge system oxidation ponds and aerated lagoons are also used in the textile industry. Organic matter (BOD5) is easily removed by biological treatment processes, but the colourants remain in the wastewater. Over the last 20 years, research has concentrated on using microorganisms for the removal of colour from textile industrial wastewater. Biological colour removal ability was found in both aerobic and anaerobic microorganisms. The colourant removal mechanisms are due to adsorption or degradation, or both adsorption and degradation. Both living and dead microorganisms could adsorb colourants, such as azo, diazo and reactive dyes. Also both gram-negative and gram-positive biosludge bacteria showed an ability to remove colourants. However, all the researchers above used pure microorganisms to remove colour from the textile industrial wastewater. The colour removal efficiency of living biosludge(mixed microorganisms)  was tested in a sequencing batch reactor (SBR) system under various  hydraulic retention time (HRT) conditions.

Biosludge from a wastewater treatment plant was able to adsorb colourants, particularly vat dyes, from textile wastewater.Biosludge was collected from the recycle storage tank of a wastewater treatment plant. The biosludge was treated by washing with a 0.1 M acetate buffer (pH 6) and  used as the resting biosludge. The biosludge was autoclaved at 121ºC for 15 min and  was used as autoclaved biosludge.

Autoclaved and resting biosludge showed different adsorption abilities with different types of vat dyes. The adsorption ability of the biosludge increased with an increase in sludge age (solid retention time; SRT). Autoclaved biosludge showed the highest adsorption ability under acidic conditions (pH 3) while the resting biosludge showed the highest adsorption ability under neutral or weak alkaline conditions. The maximum colourant (Vat Black 25) adsorption capacities of autoclaved and resting biosludge with a sludge age of 24 days were 85.54 ± 0.5 and 37.59 ± 0.6 mg/g biosludge, respectively. Using a sequencing batch reactor (SBR) system, the biosludge was able to remove both organic matter and colourants from both textile and synthetic textile wastewaters. The removal efficiencies of the system increased with an increase in SRT of thesystem. The removal efficiency of the system with textilewastewater was lower than with synthetic textile wastewater.The advantages of SBR systemareas follows: Simple and cost effective; Ability to combine aerobic and anoxic phases in a single reactor; High degree of process flexibility in terms of sequence and cycle time; Near ideal quiescent settling conditions; More resistant to fluctuating influent loading.

Colourant Adsorption Test
The adsorption capacities of both the resting sludge and autoclaved biosludge were determined by the Jar Test System [35] using the STIWW containing various types of vat dyes. The colourant adsorption yields of both living and dead biosludge were analyzed by using Freundlich’s adsorption isotherm equation [35].

Chemical Analysis
The BOD5 (mg/L), COD (mg/L), mixed-liquor suspended solids (MLSS) (mg/L), suspended solids (SS) (mg/L), pH and dissolved oxygen (DO) of the influents and effluents were determined by using Standard Methods for the Examination of Water and Wastewater [36]. The colour intensity (Abs 608 nm) (units) (Abs 608 nm) (units) of the wastewater was determined in optical density as the absorbance at the wavelength at which absorption was maximum after dilution with 0.1 M phosphate buffer (pH 7).

Color removal
Decolorization was monitored by UV–Vis spectroscopic analysis. Decolorization of dye was followed by monitoring, changes in its absorption spectrum (λ610 nm for sulfur black) and comparing the results, to those of the respective controls. The pellet was discarded after centrifugation and clear solution was analyzed using the AGILENT UV visible recording spectrophotometer.

% Decolorization = Initial conc. of dye – Final conc. of dye/Initial conc. of dye X 100.

Removal of Direct Dyes from Aqueous Solution Using Various Adsorbents
Removal of direct dyes [direct yellow 50 (DY50), direct red 80 (DR80) and direct blue 71(DB71)] from an aqueous solution by different adsorbents such as activated carbon, raw kaolinite and montmorillonite was investigated. The adsorption isotherm data were fitted to the Langmuir isotherm. Parameters of the Langmuir isotherm have been determined using the adsorption data.

Treatment of textile dyeing and printing  waste water by SEMICONDUCTOR PHOTOCATALYSIS
Dyes are extensively used in the textile industry. The colour which dues impart to water bodies is very undesirable to the water user for aesthetic reasons. The textile dyeing and printing industry have been recognized as one of the most polluting industries in India, which contribute towards the pollution of the water environment. The textile dyeing and printing industries effluent contain high COD and colour it was observed that, the pollution potential of the printing industries are negligible as compare to that of textile dyeing. Pollution of water resources is thus high, as their location is mostly on the banks of small river [37]. Thus their high demand of finding a potential advanced  treatment process, which could be an economic and effective process treating coloured wastewater completely. Semiconductor photocatalysis is an attractive treatment for industrial wastewater. Semiconductor photocatalysis can be defined as the reaction in which the decomposition of organic substances in an aqueous solution by means of semiconductor like TiO2 or ZnO in presence of light. Semiconductor photocatalysis is an aqueous process where the water is integral part of the reaction residence time may vary from 100 to 150 minute, and the Chemical Oxygen Demand (COD) removal may typically about 50-60 % insoluble organic matter is converted to soluble organic compound which are turn in oxidizing and eventually converted to CO2 and water, without emission of NO2, SO2, HCl, furans, fly ash etc. Semiconductors are used to degrade the organic pollutant in water to less harmful materials. The removal of colour from wastewater is often more important than the removal of other organic colourless chemicals . Decolourization of effluent from textile dyeing and printing industry was regarded important, because of aesthetic and environmental concerns .The TiO2 and ZnO have photocatalytic properties to be promissing substrate for photodegradation of water pollution and show appropriate activity in the range of solar radiation.The overall benefits of the decolourization of textile industrial wastewater may include very interesting subject saving huge amount of water because textile dyeing industries are regarded as chemical intensive and water intensive. This type of industry has more pollutants and consumes a huge amount of water.

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