Adsorption and biodegradation of commercial dyes using chemically-modified empty fruit bunch biochar assisted by bacteria

The aim of this study was to investigate the adsorption capacity of activated empty fruit bunch biochar (EFBB) in removing commercial dyes (methylene blue and direct red 80) assisted by dye degrading bacteria. Empty fruit bunch (EFB) is one of the wastes that has been produced from oil palm industry and it can be utilised by converting them into biochar and use them as potential adsorbent of contaminants. Raw biochar usually possesses lower adsorption capacity. Therefore, activation of EFBB was required to increase its surface area, porosity and surface functional groups and consequently enhancing their adsorption capacity. In this study, EFBBs were modified chemically by treating them with sulphuric acid (H2SO4), potassium hydroxide (KOH) and by iron impregnation (FeCl3). The acid coated biochar was known as A-EFBB, alkali coated biochar as B-EFBB and Iron coated biochar as Fe-EFBB. These adsorbents were used to remove cationic dye, methylene blue (MB) and anionic dye, direct red 80 (DR 80) at various initial concentration and their adsorption capacity was compared. The Langmuir model fitted the isotherm data better than the Freundlich’s model which indicated that adsorption was homogeneous and monolayer. Results for MB showed higher adsorption capacity in the order of A-EFBB (125 mg/g) > BEFBB (76.336 mg/g) > Fe-EFBB (10.130 mg/g) > EFBB (6.139 mg/g). While for Direct Red 80 results showed higher adsorption capacity in the order of B-EFBB (78.125 mg/g) > A-EFBB (40.160 mg/g) > Fe-EFBB (4.708 mg/g) > EFBB (1.150 mg/g). Apart from adsorption, biological treatments which are cost-effective and environmentally friendly techniques, have been also widely used for many years, but there are only a limited number of microorganisms that can degrade contaminants at high concentrations. Hence to make use of both adsorption and biological treatment techniques, a hybrid treatment which combined the two treatment processes was introduced in the removal of high concentration of dyes from wastewater. Pollutants can be removed efficiently and completely using this new strategy. Therefore, biodegradation was tested on MB which is being widely used in dye industry at various initial concentrations and mixed bacterial culture was able to remove MB (100 mg/L) efficiently at 94.6% in 24 hours. The dominant bacterial orders present in the mixed culture were identified as Sphingomonadales followed by Pseudomonadales, Betaproteobacteriales, Micrococcales, Clostridiales, Bacillales and others. The highest decolourisation percentage was observed at 100 mg/L (94.60%), but the values were lower at higher concentrations. At the highest MB dye concentration (400 mg/L), the decolourisation percentage was the lowest (56.30%). The highly efficient combined treatment was able to remove MB at 99.2% within 24 hours. In nutshell, the highest percentage of MB dye decolourization was observed to be 76.5% by A-EFBB, 94.6% by mixed culture bacteria, and 99.2% by the mixed culture bacteria immobilized on A-EFBB at 100 ppm in 24 hours. The combined treatment has thus been proved to be an efficient way to remove dyes from wastewater compared to the individual adsorption and biodegradation process.

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