12.3 Application of the Biosorption Processes

177

Zn²⁺ metal ions from industrial wastewater and fly ash possess greater biosorbent

potential in comparison to peanut husk charcoal and natural zeolite [12]. The

biosorbent potential of coconut tree sawdust (CTS), eggshell (ES), and sugarcane

bagasse (SB) was 3.89, 25.00, and 23.81 mg/g for CTS, 34.48, 90.90, and 35.71 mg/g

for ES, and 3.65, 21.28, and 40.00 mg/g for SB, for Cu²⁺, Pb²⁺, and Zn²⁺ metal ions,

respectively [15].

12.3.2

Removal of Organic Pollutants

Release of harmful organic pollutants such as phenolic compounds, polycyclic

aromatic hydrocarbons (PAHs), organic pesticides, and herbicides is increasing

day by day in the various ecosystems. These harmful compounds have a severe

toxic characteristic, and poor biodegradability can cause health and ecological

issues. For the eradication of these contaminants, several physical, chemical, and

biological techniques are presently being practised including chemical precipita-

tion, extraction, advanced oxidative processes, filtration, electrokinetics, membrane

bioreactor, etc. at industrial levels [12]. However, these techniques are expensive,

require high energy sources, and are not efficient in small amounts; hence, the

demand for inexpensive, harmless, agro-industrial wastes and byproducts has been

increasing [13]. In this context, biosorption is becoming a promising, cost-effective

technique to substitute the existing remedial methods of organic contaminants,

dyes, and organic compounds from wastewater [12]. Tannin-based biosorption has

a natural ability to absorb and accumulate dyes, surfactants, and pharmaceutical

moieties from polluted water. Tannin rigid foams also act as beneficial biosorbent to

accumulate long-chain anionic surfactants from water, such as poly-oxy-ethylene

sodium lauryl ether sulfate [13]. In addition to this, biosorption processes are also

employed for the enhancement of micronutrients, organic feedstuffs, and fertilizers,

which are beneficial to ecosystem organisms directly [14]. They are also helpful in

any 1^∘or 2^∘biological methods to aqueous clean-up ecosystems and other streams

such as domestic, municipal, industrial, and solid wastes [15].

Various plant wastes as biosorbents, i.e. wood chip, ryegrass root, orange peels,

bamboo leaves, and pine needles, were investigated through linear isotherms to

degrade PAHs and practised partition coefficient (Kd) to calculate their biosorption

capacity. It was found that Kd values of pine needles, which are 5306 ± 92.49 l/kg,

are maximum among all plant residues used [16]. Carbon extracted from sesame

stalks exhibited greater efficiency and considered as a good biosorbent for the

degradation of phenanthrene in aqueous solution [17]. Biosorbents obtained from

sugar cane bagasse, coconut shells, and rice husk remove PAHs such as naphtha-

lene, acenaphthylene, fluorene, and pyrene significantly. Of them, coconut shells

displayed higher PAHs uptake ability in comparison to sugar cane bagasse and rice

husk [16]. Raw and modified plant residues of bamboo wood, needles, and bark of

pine were reported to be better biosorbents for the efficient removal of PAHs from

wastewater [16]. Biosorption by raw plant residues occurred primarily by partition

method, whereas, in modified plant residues, biosorption took place by nonlinear

isotherms.