Physical Treatment
Physical treatment is used for the de-colouration of wastewater and reduction of azo
dyes by coagulation, flocculation, etc. But these processes have low de-colouration
efficiency and large production of sludge, because textile wastewater contains large
amount of highly reactive dyes. The attractive physical process is adsorption which
is utilized for the de-colouration of wastewater with high efficiency. Its efficiency
depends on the adsorption and regeneration capability of adsorbent. The common
and useful adsorbent is activated carbon, but it is costly and it has regeneration
problems for decolouration (Navin et al. 2018).
Chemical Treatment
The chemical treatment of wastewater in textile industry can be categorized into two
processes viz. advanced oxidation and chemical oxidation. The toxic materials and
their by-products are degraded by using these processes. In advanced oxidation
process, hydroxyl radicals are generated that vigorously react with dyes, because
they are strong oxidizing agents as compared to hydrogen peroxide, potassium
permanganate, etc. In chemical oxidation, ozone and hydrogen peroxide are used
as oxidizing agents, because these compounds generate strong non-selective
hydroxyl radicals. These hydroxyl radicals have high oxidation potential to break
conjugated double bonds of dye chromophores and functional groups that reduces
colour of effluents. The rate of degradation in chemical oxidation is lower than
advanced oxidation process, because in the former, few number of hydroxyl radicals
are produced.
The other chemical process is ozonation where ozone is used as the oxidizing
agent for treatment of wastewater. But, in this process, some toxic by-products are
generated.
Another type of degradation of dyes is the combination of ultra-violet light and
hydrogen peroxide which again generates high concentrations of hydroxyl radicals.
This process is advantageous, since there is no sludge formation and at the same time
odour is reduced. The factors affecting the rate of oxidation are the intensity of ultraviolet radiation, the pH of wastewater, structure and composition of dyes (Navin
et al. 2018).
Biological Treatment
The biological method is utilized for the removal of dissolved organic matter in the
textile wastewater. The removal efficiency of this method depends on the ratio of
organic or dye load to microorganism load, enzyme activity, flexibility of the
selected microbes, temperature of wastewater and dissolved oxygen concentration.
This process is classified as aerobic, anaerobic and a combination of both, depending
8 Treatment of Petroleum Hydrocarbon Pollutants in Water
269
Physical treatment is used for the de-colouration of wastewater and reduction of azo
dyes by coagulation, flocculation, etc. But these processes have low de-colouration
efficiency and large production of sludge, because textile wastewater contains large
amount of highly reactive dyes. The attractive physical process is adsorption which
is utilized for the de-colouration of wastewater with high efficiency. Its efficiency
depends on the adsorption and regeneration capability of adsorbent. The common
and useful adsorbent is activated carbon, but it is costly and it has regeneration
problems for decolouration (Navin et al. 2018).
Chemical Treatment
The chemical treatment of wastewater in textile industry can be categorized into two
processes viz. advanced oxidation and chemical oxidation. The toxic materials and
their by-products are degraded by using these processes. In advanced oxidation
process, hydroxyl radicals are generated that vigorously react with dyes, because
they are strong oxidizing agents as compared to hydrogen peroxide, potassium
permanganate, etc. In chemical oxidation, ozone and hydrogen peroxide are used
as oxidizing agents, because these compounds generate strong non-selective
hydroxyl radicals. These hydroxyl radicals have high oxidation potential to break
conjugated double bonds of dye chromophores and functional groups that reduces
colour of effluents. The rate of degradation in chemical oxidation is lower than
advanced oxidation process, because in the former, few number of hydroxyl radicals
are produced.
The other chemical process is ozonation where ozone is used as the oxidizing
agent for treatment of wastewater. But, in this process, some toxic by-products are
generated.
Another type of degradation of dyes is the combination of ultra-violet light and
hydrogen peroxide which again generates high concentrations of hydroxyl radicals.
This process is advantageous, since there is no sludge formation and at the same time
odour is reduced. The factors affecting the rate of oxidation are the intensity of ultraviolet radiation, the pH of wastewater, structure and composition of dyes (Navin
et al. 2018).
Biological Treatment
The biological method is utilized for the removal of dissolved organic matter in the
textile wastewater. The removal efficiency of this method depends on the ratio of
organic or dye load to microorganism load, enzyme activity, flexibility of the
selected microbes, temperature of wastewater and dissolved oxygen concentration.
This process is classified as aerobic, anaerobic and a combination of both, depending
8 Treatment of Petroleum Hydrocarbon Pollutants in Water
269