**2.2 Activated carbon**

The activated carbon, a low-cost and high-quality material, can be utilized for adsorption purpose in various applications. Generally, the activated carbon is prepared by burning lignite, coal, wood, etc., in pyrolysis over 600–900°C. Nowadays, a lot of emphasis has been given to lignocellulosic biomass, readily available in agriculture sector as waste, for generation of the activated carbon [22]. The activated carbon generated from agro-based waste has its own advantage due to its low cost and ubiquitous availability [23]. During the last few decades, there was growing research interest on the utilization of alternative origin of waste materials from industry and agriculture for activated carbon production [24–27]. A sizable numbers of reports have been published on generation of activated carbon from agro waste such as palm shell [28, 29], coconut shell [30, 31], corn cob [32], olive stones [33] and walnut shell [34], coir pith [35], rice bran [36], chickpea husks [37], oil palm shell [38], etc. Ioannidou et al. [23] have used the agricultural residues such as soya stalks, corn cobs, rapeseed stalks, and olive kernels as precursors for the generation of activated carbon. The pyrolysis were done in two stages: (a) the pyrolysis had been carried out over 800°C for about 1 h under nitrogen atmosphere (15 ml/min) along with heating rate at 27°C/min for the sake of producing char, (b) the physical activation of char was then carried out over 800°C for about ½ h under the flow of steam (40 g/min) at pressure of ½ bar. The obtained activated charcoals were subjected to study of removal of Bromopropylate, common pesticides in fruits crop, from water. Tay et al. [39] have isolated activate carbon on pyrolysis of soybean oil cake by chemical activation with potassium hydroxide and potassium carbonate at different temperatures of 600 and 800°C. Potassium carbonate was found to be more effectual as compared with potassium hydroxide under similar conditions.

The maximum surface area of activated carbon obtained with potassium carbonate at 800°C is found to be 1352.86 m2 /g, which is in accordance with the range of commercial activated carbons. Anne A. Nunes et al. [40] derived activated charcoal from defective coffee press cake by heating it under nitrogen atmosphere at 600/800°C for elimination of methylene blue from water up to 99% removal. The maximum adsorption capacity obtained for the coffee cake activated carbon/methylene blue system was observed to be 14.9 mg/g. The equilibrium data fitted favorable into Freundlich model as compared with others. Rice is one of the widely grown crops in the world, generating a large volume of waste. That has to deal with proper management due to short duration in between two crops. During last few decades, people have reported on generation of activated carbon from rice straw [41]. The utmost value of carbofuran adsorption capacity was observed to be 26.52 mg/g. Chang et al. [42] had studied elimination of bisphenol-A from water by using activated carbon obtained by with the help of chemical (potassium hydroxide) treatment of rice husk. At pH 2.5, the maximum adsorption capacity of bisphenol-A was found to be 181.191 mg/g. The experimental values perfectly fitted the Langmuir model for equilibrium data. It was found to be more inclination toward pseudo second order as compared with that pseudo first order. Isoda et al. [43] reported the generation of activated carbon from rice husk with more surface area, of about 1500 m2 /g and high mesopore volume of about 1.22 cm3 /g using chemical (zinc chloride) treatment over an activation temperature of 600°C without carbonization and using sodium hydroxide as chemical activating agent, with carbonization. Köseoğlu et al. [44] had studied the generation of activated carbon from orange peels using potassium carbonate and zinc chloride as chemical reagents for the purpose. The surface area of the activated carbon was observed to be 9–1352 m2 /g for potassium carbonate and that for zinc chloride 804–1215 m2 /g. Potassium carbonate was observed to have much potential as compared with zinc chloride as a chemical activating reagent in light of high surface area, development of porosity, and surface analysis of the activated carbon. Mahamad et al. [45] had studied the generation of activated carbon from solid pine apple waste mass such as leaves, stem, and crown using zinc chloride as chemical reagent at 500°C for 1 h. It can be deduced that the activated carbon obtained by a 1:1 ratio has the better removal of dye capacity, which can be attributed to its high surface area (914.67 m2 /g) and dye adsorption capacity (288.34 m2 /g). The Langmuir adsorption isotherm model is perfectly suited to the obtained adsorption equilibrium data with *R*<sup>2</sup> of 0.969. The maximum uptake of methylene blue with obtained activated carbon was observed to be 288.34 m2 /g. Baysal et al. [46] had prepared activated carbon from sunflower piths using NaOH and KOH as chemical reagents. The activated carbon prepared has high surface area of about 2690 and 2090 m2 /g. Activated carbon obtained from mahogany fruit shell successfully used for about 99.7% uptake of lead ion from wastewater [47] . Xue et al. [48] have used Angelica keiskei as a source for generation of activated carbon, which could be utilized as efficient adsorbent of organic dyes from wastewater. As shown in **Table 1**, activated carbon made up of various agro wastes with different temperatures of activations used as adsorbent for the removal of different impurities from wastewater. Furthermore, the maximum capacities of removal are complying well with the disposal standard of wastewater.

#### **2.3 Nanocellulose from agro waste**

The nanocrystalline cellulose can be generally isolated from different subsequent chemical process: starting with bleaching and alkali treatment succeeded by acid

*Perspective Chapter: Environmental-Friendly Agro Waste Management DOI: http://dx.doi.org/10.5772/intechopen.107505*


#### **Table 1.**

*Activated carbon generated from various agro wastes.*

hydrolysis of the natural fibers. The nanocellulose isolated from various sources of agro waste is becoming an attractive research avenue for its multifaceted utilization [49]. Nowadays, a lot attention has been given to generation of nanocellulose from various ago wastes such as olive tree pruning [50], pine cones [51], pineapple leaf [52], rice husk [53], sisal fiber [54], sorghum stalk [55], sunflower stalks [56], etc. Ferreira et al. had successfully isolated cellulose nanocrystals from sugarcane bagasse, on hydrolysis by sulfuric acid, which had very good hydrophilic properties with a high crystallinity. Adipic acid was used for surface modification of nanocrystal for suppressing the crystal dimension by elimination of amorphous region [57]. Johar et al. reported on the isolation of nanocellulose fibers from rice husk. They adopted alkali (NaOH) and bleaching (NaCl2O) treatment followed by acid (H2SO4). They observed a remarkable enhancement in crystallinity of the obtained nanocellulose [53]. Lu and Hsieh et al. had extracted an unblended form of nanocellulose from rice straw with about yield of 36%. The acid hydrolysis for about ½ h resulted in nanocellulose of size of 270 nm length and 5.95 nm diameter, whereas acid hydrolysis for 45 min resulted in nanocellulose of size of 117 nm length and 5.06 nm diameter [58]. do Nascimento et al. had successfully extracted cellulose nanocrystals from coconut fiber [59]. de Carvalho Mendes et al. isolated crystalline nanocellulose from various agro wastes such as garlic skin, palm oil, sesame, and rice husks [60] . Walnut shell (*Juglans regia* L.) was utilized as the raw material for the production of purified cellulose [61]. The lignin and hemicellulose present in walnut shell had been perfectly eliminated by sodium hydroxide treatment and followed by bleaching with equal amounts of 1.7 wt.% sodium chlorite

and acetate buffer solution, which leads to the enhancement of cellulose content up to 89%. Sijabat et al. had isolated nanocellulose from waste media of Kepok bananas (*Musa paradisiaca* L.) applying Gluconacetobacter xylinusbacteria in the fermentation procedure in utilization for membrane applications in water filter [62].
