Dye Removal Techniques

Environmental contamination resulted from the emission of effluents of dyeing industries is a global problem, therefore different methods of effluents treatment have been used in an attempt to minimize the problems resulted from this contamination. Coagulation, foam flotation, precipitation, ozonation, ion exchange, filtration, solvent extraction, electrolysis, chemical oxidation, membrane separation technology, liquid-liquid extraction and adsorption on activated carbon have been used for the removal of dye contaminants from wastewater [32, 52]. The technologies can be divided into three broad categories: physical, chemical and biological [53]. The advantages and disadvantages for dyes and colour removal of industrial wastewater applied over the time into different industrial units are summarized in Table 3.

Agricultural Solid Wastes in Aqueous Phase Dye Adsorption: A Review

175

Table 3. Advantages and disadvantages of dyes removal techniques updated and

modified from [2]

Separation

Techniques

Advantages

Limitations

Physical-Chemical processes

Precipitation,

Coagulation-

flocculation

Short detention time and low capital costs. Relatively good removal efficiencies.

Sometimes expensive, Agglomerates separation and treatment. Specific to operating condition.

Electrokinetic

coagulation

Economically feasible

High sludge production.

Solid-Liquid physical adsorption such as:

Activated carbon

Economically attractive. Good removal efficiency of wide variety of dyes.

Very expensive; cost intensive regeneration process

Peat

Effective adsorbent due to cellular structure. No activation required.

Surface area is lower than activated carbon.

Industrial solid wastes such as ash, red mud etc

Economically attractive. Good removal efficiency.

Slow kinetics. Specific surface area for adsorption are lower than activated carbon.

Raw wood chips/ Wood sawdust

Other agricultural solid wastes such as pine cone, pine leaves, eucalyptus bark etc.

Effective adsorbent due to cellular structure. Economically attractive. Good adsorption capacity for acid dyes.

Sustainable cost-effective good adsorbents. Moderate to high removal efficiency

Slow kinetics and activation may be required

Sometime slow kinetics and activation may be required

Silica gels Ion Exchange

Effective for basic dyes

Effective with ionic compounds removal and easy regeneration

Side reactions prevent commercial application Specific and effective for dyes removal and softening of water

Biological separation processes

Aerobic process

Partial or complete decolonization for all classes of dyes.

Not cost-effective

Anaerobic

process

Resistant to wide variety of complex coloured compounds.

Bio gas produced is used for stream generation.

Longer acclimatization Phase, odour

Microbial

processes

Good removal efficiency for low volumes and concentrations. Very effective for specific colour removal.

Culture maintenance is cost intensive. Cannot cope up with large volumes of wastewater.

Table 3. (Continued)

Separation

Techniques

Advantages

Limitations

Advanced separation processes

Electrochemical

oxidation

No additional chemicals required and the end products are non-dangerous/hazardous.

High cost

Other advanced oxidation process

Complete mineralization ensured. Growing number of commercial applications. Effective pretreatment methodology in integrated systems and enhances biodegradability.

Cost intensive process

Fenton process

High efficiency for colour removal

Generation of sludge and expensive

Membrane

filtration

Removes all dye types; recovery and reuse of chemicals and water.

High running cost. Concentrated sludge production. Dissolved solids are not separated in this process.

Photo catalysis

Process carried out at ambient conditions. Inputs are no toxic and inexpensive. Complete mineralization with shorter detention times.

No sludge production

Effective for small amount of coloured compounds. Expensive process.

Photochemical

process

Irradiation

Effective oxidation at lab scale

Formation of by-products

Requires a lot of dissolved oxygen (O2).

Sonication

Simplicity in use. Very effective in integrated systems.

Relatively new method and awaiting full scale application.

Redox mediators

Easily available and enhances the process by increasing. electron transfer efficiency

Concentration of redox mediator may give antagonistic effect. Also depends on biological activity of the system.

Engineered wetland systems

Cost effective technology and can be operated with huge volumes of wastewater

High initial installation cost. Requires expertise and managing during monsoon becomes difficult.

 
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