Biosorption of Organic Dyes: Research Opportunities and Challenges - Green Chemistry for Dyes Removal from Wastewater - page 299

mixing tank equipment. Other advantages are, simplicity, well-established
experimental methods, controlled conditions and easily interpretable
results [4,9,13]. For dynamic systems (continuous operation), the most
common configuration is the packed column, but others, such as fluidized
bed and moving bed are possible. This method has a number of process
engineering advantages including high efficiency operations and relatively
easy scaling up from a laboratory scale procedure. The stages in the sepa-
ration protocol can also be automated and a high degrees of purification
can be attained in a single-step process. A large volume of DCEFs can be
continuously treated using a defined quantity of biosorbent in the column
[12,21]. This chapter is mainly focused on the batch system, since this
operation is more extensively studied in the literature and its investigation
is fundamental.
8.2 Biosorbents
Many alternative biological materials are capable of removing pollutants
(SODs for example) from aqueous solutions by biosorption. These biologi-
cal materials are known as “biosorbents” [6,12,15-19]. According to the
literature, the main biosorbents can be classified as follows: agricultural
wastes, algae biomass, bacterial biomass, chitosan and fungal biomass
[2,4,6,9,12]. In this section, these classes are discussed in detail.
8.2.1 AgriculturalWastes
Agricultural wastes are lignocellulosic materials that consist of three main
structural components, which are lignin, cellulose and hemicelluloses.
These organic compounds are useful for binding SODs through different
mechanisms [22,23]. Agricultural wastes are low-cost, renewable and avail-
able in large amounts. Furthermore, they are usually used without or with
a minimum of processing (washing, drying, grinding) and thus reduce
production costs by using a cheap raw material and eliminating energy
costs associated with thermal treatment [3,24-30]. Some examples of these
biosorbents are sawdust, bark, roots, hulls, leaves, stalks, bagasse, peels,
seeds and others [23-35]. Table 8.1 summarizes the biosorption capacities
of some important agricultural wastes.
Alencar et al. [23] studied the application of Mangifera indica (mango)
seeds as biosorbent for removal of Victazol Orange-3R (VO-3R) dye from
aqueous solutions. They obtained the best results (51.2 mg g -1 ) at a pH