Environmental Engineering Reference
In-Depth Information
such waste-based adsorbents and the relevant challenges will be addressed
in addition to their comparative dye uptake capacities.
5.2
Agro-Based Waste Materials as Dye Adsorbents
Agricultural waste materials are abundantly available, renewable, inex-
pensive and nontoxic [34]. All these specifications account for the high
popularity of these waste substances, primarily as pollution sources, to be
widely used as a carbonaceous source for the production of inexpensive,
high-value activated carbon [23,27]. The economic value of these lingocel-
lulosic materials coupled with their high potential in the economically-
viable sequestration of pollutants renders them particularly attractive to be
used in eco-friendly wastewater treatment.
Although the basic components of agricultural waste materials are cel-
lulose, hemicelluloses and lignin [23], the appropriate choice of these mate-
rials and proper activation techniques is a critical factor affecting their
ultimate performance. Herein, an exhaustive literature review on the sub-
ject of the application of various waste agro-based materials for the produc-
tion of activated carbons with different surface areas, nanopore structures
and functional groups has been summarized. Also, it has been endeavored
to examine the influence of the original precursor type and the modifica-
tion parameters on the dye adsorption properties of the resulting activated
carbon.
5.2.1 Rice Husk
Rice husk is the outermost protective coating of a rice kernel which com-
prises significant amounts of silica and carbon [35]. During the rice har-
vesting season, the rice is milled and the husk is separated from the grain
in a so-called husking stage. Annually, over 500 million tons of paddy is
produced globally over 20 wt% of which is assumed to be husk [36]. This
amount is steadily increasing due to the cultivation growth as well as an
increase in the production yield per unit area.
Due to the large quantities of rice husk produced in developing coun-
tries, rice husk used to be either dumped into the landfill or open-burnt
in order to decrease the space required to landfill this voluminous waste.
However, with the swift progress in technology and increasing public envi-
ronmental awareness, this problematic waste has turned out to be a popular
focus of research for energy recovery [37], fuel production [38], electrodes
in batteries and capacitors [39], catalyst [40], hydrogen storage [41] and
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