Activated rice husk-based adsorbents for chlorophenol removal and their bioregeneration

Studies on the development of alternative adsorbent using rice husk have been extensively reported. However, relatively little has been reported on the comparative adsorptive removal of phenolic compounds using rice husk activated with different methods as well as their bioregeneration potential and reusability. This study aimed to investigate the adsorption capacities of rice husk activated with nitric acid (ARH), ethylenediamine (MRH), and potassium hydroxide (KRH), respectively, for 4-chlorophenol (4-CP) and 2,4-chlorophenol (2,4-DCP) in comparison to powdered activated carbon (PAC) and the bioregeneration efficiencies and reusability of chlorophenol-loaded activated rice husks. For both cases using 4-CP and 2,4-DCP as adsorbates, the adsorption capacities were found in the order of KRH>PAC>ARH>MRH. Despite the much lower abiotic desorption efficiencies, the bioregeneration efficiencies were found comparable for all the adsorbents (>80% for the first cycle except for 2,4-DCP-loaded KRH). The total capacity losses for all the bioregenerated adsorbents were observed to increase with increasing number of cycles of use. In terms of the efficacy, KRH showed the highest accumulated amount of 4-CP and 2,4-DCP removed followed by PAC, ARH, and MRH. Amongst the adsorbents, KRH was found to be the most efficient adsorbent to remove 4-CP and 2,4-DCP, respectively, based on the accumulated amount of adsorbate after successive bioregeneration.