Phenol being toxic in nature needs to be removed from wastewater before its discharge. This research therefore aims for removal of phenol from its aqueous solution through adsorption process. Four bio-adsorbents such as guava tree bark, rice husk, neem leaves, activated carbon from coconut coir and four industrial waste adsorbents such as rice husk ash, red mud, clarified sludge from basic oxygen furnace, activated alumina have been used in this research work. The surface characterization of the adsorbents were carried out by SEM, XRD, FTIR and BET analyzers. The phenol removal percentage by the adsorbents were investigated through batch experiments with the variation of initial phenol concentration (5-500 mg/L), initial pH (2-12), adsorbent dose (0.10-20 gm/L), temperature (25-50°C) and contact time (30-600 min). The maximum removal percentage was obtained as high as 97.50%. The experimental results were used for kinetic study which showed that the pseudo-second order was best fitted for all adsorbents except red mud and the adsorption mechanism was supportive of film diffusion, intra-particle diffusion and chemisorption for all adsorbents. The isotherm analysis suggested that Freundlich isotherm model was best supportive for guava tree bark, rice husk, neem leaves, activated carbon, red mud and activated alumina, whereas Langmuir and D-R isotherm was best supportive for rice husk ash and clarified sludge respectively.
The thermodynamics study successfully revealed the spontaneity, randomness and endothermic / exothermic nature of the adsorption process for each adsorbent. The adsorption experiments were also performed with the real industrial wastewater collected from a coke oven plant. The innovative ANN modelling using two popular algorithms viz., Levenberg-Marquardt and Scaled Conjugate Gradient was also studied which established that the experimental and predictive data were within the allowable range. The scale-up designs and the safe disposal of used adsorbents were studied for examination of their commercial applications. The regeneration of the adsorbents were studied using distilled water and ethanol solution separately to find out their regeneration efficiency. The research however concludes that all the adsorbents are effective for phenol removal and therefore can be considered for circular economy.