There are almost 9000 types of dyes beingused in textile, tannery, paper and pulp, cosmetic, plastics,coffee pulping, pharmaceuticals, food processing, electroplating anddistilleries spew industries to color the products.
Among this textilesindustry is very much important and it stands first in the usage of dyes 1. Alarge portion of the colors utilized for shading in industries are taken out ineffluent streams, in this way creating a lot of waste water. Which in turn isvery harmful for the aquatic eco system as well as human beings 2. Thetextile dyeing and finishing industry has created a huge pollution problem asit is one of the most chemically intensive industries on earth, and the No. 1polluter of clean water (after agriculture).
More than 3600 individual textiledyes are being manufactured by the Industry today. The industry is using morethan 8000 chemicals in various processes of textile manufacture includingdyeing and printing 3.So under such circumstances the removal ofdyes for the treatment of wastewater is very much needful, in an economicalway. There are lot of different processes for this separation. However, all ofthese process is not economical and all the processes cannot handle a largeamount of dye wastewater. Theadvantages and disadvantages of some methods of dye removal from wastewatersare given in Table 1.4 table 1.
Advantages anddisadvantages of the methods used for dye removal from industrial effluents (Robinson et al., 2001) Physical/chemical methods Advantages Disadvantages Fentons reagent Effective decolorisation Sludge generation Ozonation No change in effluent volume Short half-life (20 min) Photochemical No sludge generation Formation of byproducts NaOCl Initiate azo-bond cleavage Release of aromatic amines Cucurbituril Good sorption capacity for dyes High cost Electrochemical Non-hazardous end products High cost of electricity Activated carbon Highly effective for various dyes Very expensive Peat Good adsorbent Surface area is low Silica gel Effective for basic dyes Side reactions in effluent Membrane filtration Removes all dyes Concentrated sludge production Ion exchange No adsorbent loss Not effective for all dyes Adsorption is an economical process andthe separation efficiency of adsorption is quite higher. So in this processadsorption is being used for removal of dye.Here malachite green has been used. Firstof all, it is cheap and it is easily available in market.
Besides thismalachite green is widely used in aquaculture as a pesticide and in food,health, textile and other industries for one or the other purposes. Due to itstoxic nature It controls fungal attacks, protozoan infections and some otherdiseases caused by helminths on a wide variety of fish and other aquaticorganisms. Ithas been reported to cause carcinogenesis, mutagenesis, chromosomal fractures,teratogenicity and respiratory toxicity 5. So it is very harmful in nature. Soit is very needy to know an economic, safe and easy removal process of MG.Fly ash is being used here as adsorbate.Fly ash is generally waste material from coal plants. Fly ash cannot be disposedanywhere due to its toxic action towards soil, ground and surface water.
It isalso very cheap and easily available. So using fly ash as adsorbate is usefulhere. Hydro cyclone is being used here in thisprocess. It has several advantages rather than others. A further advantage of hydro cyclonesis their high operational reliability as they are simple in constructionwithout any moving parts.
In addition, in case of changing operationalconditions, for example with unsteady volume flow, a good separation efficiencycan be achieved 6.A small modification has been done in thishydro cyclone. The modification is the spiral ribs attached in the cylindricalsection of the hydro cyclone. This modification will enhance the swirling ofthe feed and increase the centrifugal force, which in turn enhance theefficiency.