The utmost importance of water become a prime apprehension to the civilizations as the water is polluted day by day through industrial, agricultural and domestic activities. The addition of undesirable chemicals into the water deteriorates the quality as well as aesthetic appearance of the water. The presence of some chemicals also causes diseases acute or chronic also.
As per the report, global population will be 9.3 billion by 2050 and this population may be under great fresh water scarcity. Dyes are such chemicals which are inevitably discharged into the environment from the industries like, pulp and paper, ink, pharmaceuticals, plastics, textiles etc.
More than 100,000 dyes are commercially existing and 7X105 tonnes are produced annually.
Some dyes have mutagenic and carcinogenic effect also. Presence of little amount of dye (less than 1 ppm) demerits the aesthetic look of fresh water. Hence, removal and degradation of such dyes may have an attention to the concern. Several technologies are available for removal of dyes like biological treatment, coagulation, floatation, adsorption, oxidation, hyperfiltration, osmosis, reverse osmosis etc and these technologies are effectively used depending on the biological, physical, chemical, electrical and thermal properties of water.
In general, reverse osmosis, ion exchange, electro-dialysis, electrolysis as well as adsorption are highly appreciated due to its excellent efficiencies towards waste water treatment. But adsorption is one of the cost-effective technologies (5.0-200 US$200 per cubic meter of water) than other technologies (10-450 US$200 per cubic meter of water.
Adsorption process is widely acceptable due to its universal nature, inexpensiveness, removal efficiency as well as ease of operation.
Basically, adsorption is a simple process where substance (adsorbate) accumulates on the surface or interface of adsorbing phase (adsorbent). Activated carbon is an effective adsorbent for the removal of various pollutant from waste water. Despite of its efficiencies, it is inapt for industrial application due to its cost-prohibitive and difficulties in regeneration.
An immense emphasises has been given to evaluate the feasibility as well as suitability of natural, renewable, waste bio-mass and low cost materials (bamboo dust, peat, chitosan, lignite, fly ash, fungi, hark, hull, husk, sugar cane bagasse, tea leaves, animal shell and sago waste) as alternative adsorbents for decontamination of waste water.
Due to the rapid urbanization, man has led to generation of huge amount materials of little value that have no fruitful use which are considered as waste. The utilization of such materials as adsorbents may make them some importance. Egg Shell is one of such waste materials which is approximately 11% of the total egg weight. Most of the breaking shell of egg is traditionally useless and mostly applied in landfilling sans of any pre-treatment.
But the egg shell has high nutrient contents (calcium, magnesium and phosphorous), high amounts of minerals, amino acids. It has high porosity, antibacterial or anti-inflammatory characteristics. Hence, waste egg shell can be used as good adsorbents for removal of dyes from aqueous environment.
Literature state that egg shell can effectively remove metal ions, inorganic anions as well as complex molecules through adsorption process. But, in depth study of adsorption process is necessary to understand the process fruitfulness by understanding the non-linear isotherm models with respective error estimation.
Different types of error estimation provide the idea of fittings of experimental results with their actual/predicted value and comparison of different non-linear isotherm models suitably explain the dynamicity of the adsorption process. The variable parameters of adsorption process such as pH, dose, initial concentration, time of contact have significant role for removal of dyes.
These factors are investigated by ‘one factor at a time’ which are time taking and overlook the interactions among the factors. Design of experiment (DOE) is a necessary modelling technique which is helpful to understand the interaction effect of variables in the adsorption process. Response Surface methodology (RSM), Central Composite Design (CCD), Artificial Neural Modelling (ANN) successfully analyse the interaction between the factors. However, Taguchi’s orthogonal array design is a convenient, sophisticated and cost-effective approach for the analysis of optimal conditions for adsorption process.