## 5 Applications of Activated Carbon from Waste Tyres
### Wastewater Treatment  
For the purification of air and liquid, amorphous carbon material with a specific surface and specific porosity makes it an ideal medium for adsorption and is considered an inexpensive and technically viable method. It is well known that solid carbon adsorbents produced from waste tyres are useful for applications such as wastewater treatment. Due to the high surface area and high pore volume, AC derived from tyres is considered an excellent adsorbent in the water treatment process as it removes organic pollutants such as phenol and p-chlorophenol. Experimental results demonstrated that AC derived from waste tyres is promising, as the amount of uptake was comparable to conventional AC derived from coal, wood, and biowaste [27]. For instance, [PERSON] et al. studied the AC derived from the waste tyres, which were pyrolyzed in the presence of CO\({}_{2}\) and nitrogen at various temperatures. The obtained char was activated in situ by post-pyrolysis oxygenation. It was reported that nitrogen-pyrolyzed char exhibited good Cu and Pb removal capabilities than the CO\({}_{2}\)-pyrolyzed char [60]. However, for both types, activation with post-pyrolysis oxygenation improved the efficiency of metal removal at faster rates as compared to that of commercially available activated carbon. [PERSON] et al. investigated the cadmium adsorbed by AC developed from the waste tyres. The waste tyre was heated at 400 to 900 \({}^{\circ}\)C for 2 h in a nitrogen atmosphere and at 850 \({}^{\circ}\)C for 2 h in a steam environment [26]. Concentrated solutions of NaOH, HCl, H\({}_{2}\)SO\({}_{4}\), HNO\({}_{3}\), and H\({}_{2}\)O\({}_{2}\) were also used. Waste tyre pyrolyzed at 900 \({}^{\circ}\)C was made to react with ozone at 25 \({}^{\circ}\)C for 1 h and with air at 250 \({}^{\circ}\)C for 1 h and 24 h. Highly porous carbons are achieved when the waste tyre is treated in presence of steam. Thermal and thermo-chemical treatments are found to be more effective than chemical treatments to increase the adsorption of Cd\({}^{2+}\) in an aqueous medium. The adsorption process is strongly dependent on the pH of the Cd\({}^{2+}\) solution which is higher at pH 4.6 or 7.0 based on the nature of the adsorbent. Other examples of using waste tyre-derived activated carbons in wastewater treatment include the removal of chromium, lead, copper, dyes, and phenol [61; 62; 63]. For the removal of dyes, [PERSON] et al. studied the activated carbon derived from the treads of the waste tyre which contains a small amount of inorganic compound and a high amount of carbon content. The material was made to react with KOH and ZnCl\({}_{2}\) and pyrolysis was done at 500 \({}^{\circ}\)C and also at 700 \({}^{\circ}\)C [64]. The adsorption capacity was high for the carbon obtained from KOH at 700 \({}^{\circ}\)C. Carbon produced through KOH activation seems to be the best and showed the pore size distribution and adsorbs methylene blue and methylene orange dyes at neutral pH. Dyes such as Procion Turquoise H-A and Procion Red H-E3B were adsorbed effectively by the AC produced by waste tyres that was carbonized at a temperature between 450 \({}^{\circ}\)C (36 mg/g adsorbent) and 800 \({}^{\circ}\)C (30 mg/g adsorbent). The absorption of Procion Red was over 300 mg/g when the chars were further activated by steam, demonstrating a strong adsorption ability for species with significant molecular weight [65]. In comparison with other commercial AC, activation by steam also showed improved dye-Black 5 adsorption ability and slightly reduced phenol adsorption capacity [66]. The production of AC from waste tyres under different conditions and their applications in wastewater treatment are presented in Table 2. It can be observed from the table that most of the reviewed papers have used the chemical activation process. A wide range of chemicals such as potassium hydroxide (KOH), zinc chloride (ZnCl\({}_{2}\)), phosphoric acid (H\({}_{3}\)PO\({}_{4}\)), and hydrogen peroxide (H\({}_{2}\)O\({}_{2}\)) were used for the activation process.