Page 360 - Industrial Wastewater Treatment, Recycling and Reuse

332 Industrial Wastewater Treatment, Recycling, and Reuse

production of tea in India is approximately 857,000 tonnes, which is 27.4%
of the total world production (Wasewar et al., 2008). It is said that 100 kg of
green tea leaves produces 22 kg of dry mass on average and 18 kg tea goes
for marketing. The remaining 4 kg of dry tea material is therefore wasted
¸
(Cay et al., 2004). The amount of TW produced annually by the factories
after processing is believed to be thousands of tonnes in India alone.

8.2.2 Preparation and Activation of the Adsorbent
The standard procedure for preparation of raw untreated samples for utiliza-
tion as adsorbents involves washing, color removal, drying, powdering, and
sieving to the desired sizes. Color removal is required so that interference can
be avoided from water-soluble fractions of the sample under study. Surface
activation of the adsorbent surface is necessary because it increases the surface
area, porosity, and number of functional groups that are known to enhance
the adsorption process. The activation procedure can involve either physical
or chemical activation. The selection of the time and temperature of activa-
tion needs to be optimized by characterizing the surface properties, such
as surface area of the adsorbents obtained by treating the raw materials for
different intervals of time and temperature. For the studies reported here,

the activation temperature of 500 C was chosen as an optimum temperature

because the products obtained at a temperature higher or lower than 500 C
exhibited lower adsorption capacity, which is probably due to the collapse of
the surface functional groups. In addition, all adsorbents were sieved to a
particle size of 200–300 B.S.S. mesh size for use in adsorption studies.
Physical activation has two forms: (1) carbonization of the material in an
inert atmosphere and (2) activation of the char at high temperatures in the
presence of carbon dioxide or steam (Ahmad et al., 2007). In the activation
process, the density as well as the number of the pores can increase, and amor-
phous decomposition products such as tars are burned off. However, the yield
of the adsorbent is low in this method of activation, and thus the method is less
preferred. This method is not included in the present study.
Chemical activation is carried out by impregnation of chemical agents
followed by pyrolysis in an inert atmosphere at a high temperature. The pur-
pose of activation here is to enhance the adsorption efficiency besides car-
bonizing the raw precursor without the evolution of huge amounts of fumes
as in the case of physical methodology. Chemical activation is a preferred
method over physical activation due to comparatively lower temperatures
of 400–700 C. Also, the yield is higher since carbon burnoff is not required.