Cadmium Biosorption by Non-Living Biomass of Locally Isolated Rhodopseudomonas sp. Strain SBL

Rhodopseudomonas sp. strain SBL is a purple non-sulfur bacterium (PNSB) originating from the Proteobacteria phylum and was locally isolated from the Kim Kim River in Pasir Gudang, Johor, Malaysia. PNSBs are widely used in the bioremediation of heavy metal removal through biosorption due to their membrane surface characteristics. Biosorption is a sustainable biotechnological method for minimizing waste using natural or modified forms. The non-living biomass of Rhodopseudomonas sp. strain SBL has been shown to remove cadmium from aqueous solutions via biosorption effectively. In this study, the biosorption capacity of cadmium by Rhodopseudomonas sp. strain SBL was investigated using the one factor at a time (OFAT) method, examining various environmental factors such as biomass dosage, pH of the cadmium solution, incubation temperature, and contact time with cadmium. It was quantitatively analyzed using an atomic absorption spectrophotometer (AAS). This was followed by kinetics and morphological characterization of the cadmium biosorption by Rhodopseudomonas sp. strain SBL. The surface morphological changes and the functional groups involved were analyzed before and after biosorption using Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-Ray (EDX), and Fourier Transform Infrared Spectroscopy (FTIR). Rhodopseudomonas sp. strain SBL removed the largest amount of cadmium with 0.5 mg/mL of non-living Rhodopseudomonas sp. strain SBL biomass at a pH of 5 in the cadmium solution, an incubation temperature of 30°C, and a contact time of 30 minutes. The biosorption kinetics of cadmium follow a pseudo-second order model. Observations via FESEM showed morphological changes on Rhodopseudomonas sp. strain SBL’s cell surface, and FTIR analysis indicated that hydroxyl (O-H), alkenes (C=C), and alkyl (C-F) groups were the main functional groups involved in the biosorption by Rhodopseudomonas sp. strain SBL. Our results highlight the potential of using the non-living biomass of the purple non-sulfur bacterium, Rhodopseudomonas sp. strain SBL, as a biosorbent for cadmium in solution.