Managing Dyeing Effluents by Upcycling Expended Bacterial Biomass Remains from PHB Production: A Zero-Waste-Inspired Eco-Efficient Biorefinery Approach

The synthesis of polyhydroxybutyrate (PHB) biopolymer results in a considerable quantity of residual bacterial biomass (RBB) following PHB extraction. The RBB, regarded as zero-value waste, can be tuned and modified into activated carbon through pyrolysis utilizing potassium hydroxide. This study intends to develop a bacterial biomass activated carbon (BBAC) adsorbent derived from RBB for the removal of methylene blue (MB) dye from wastewater. The batch adsorption approach yielded a maximum removal efficacy of 99.67% at an adsorbent dosage of 0.2 g/L, a contact period of 60 min, a concentration of 40 mg/L, a pH of 8, and a temperature of 298 K. A maximum equilibrium adsorption of 32.14 mg/g was attained at pH 8. The adsorption characteristics of the adsorbate on BBAC were optimally represented by the Langmuir model [correlation coefficient (R2) = 0.989] and the pseudo-second-order kinetic model. The adsorption process appears to be exothermic, as exhibited by the thermodynamic characteristics. Furthermore, the adsorption process is readily reversible, allowing the adsorbate to be reused even after the fifth cycle. Moreover, density functional theory (DFT) simulations indicated that the adsorption of MB onto the BBAC adsorbent is advantageous. The carboxyl group demonstrated the most significant impact on the adsorption process among the examined oxygen functional groups, displaying the greatest negative adsorption energy of –68.756 kJ/mol. The BBAC originating from RBB possesses considerable potential for efficiently eliminating MB dye pollutants from wastewater.