Enhanced cadmium removal by growing Bacillus cereus RC-1 immobilized on different magnetic biochars through simultaneous adsorption and bioaccumulation

Abstract

Biosorption of cadmium by growing bacteria immobilized on the three magnetic biochars derived from rice straw (MRSB-pellet), sewage sludge (MSSB-pellet), and chicken manure (MCMB-pellet) was investigated, respectively. Total biosorption capacity of the pellets was tested under varying range of pH, culture time, and initial Cd 2+ concentration. The maximum biosorption capacity of 93.02 mg/g was obtained with MRSB-pellet, followed by MSSB-pellet (68.02 mg/g) and MCMB-pellet (63.95 mg/g). The biosorption by these immobilized bacterial pellets was more effective than free bacteria, this enhancement could be the result of simultaneous adsorption and bioaccumulation, mainly resulting from magnetic biochar carrier and active bacteria, respectively. The biosorption process by immobilized pellets was primarily driven by ion-exchange and complexation, which jointly contributed of 73.56% (MRSBpellet) to 78.62% (MSSB-pellet) the total adsorption, while the mechanisms of chemical precipitation and physical adsorption could averagely contribute 6.91% (MSSB-pellet) and 11.24% (MRSB-pellet), respectively. Intracellular accumulation was comparably tiny among these mechanisms accounting for 4.30-5.92% of total biosorption, in turn, it would maintain intracellular Cd 2+ concentration below a toxic threshold to promote cell growth. These suggested that magnetic biochar immobilized bacteria, particularly MRSB-pellet could be used as an effective biosorbent to remove the Cd 2+ from the growth medium. This study further deepened our understanding of biosorption process by microorganism immobilized onto magnetic biochar for the metals removal.

Application of BCXZM Composite for Arsenic Removal: EPS Production, Biotransformation and Immobilization of Bacillus XZM on Corn Cobs Biochar

“…A very intense band shift appeared at 1621.34 and 1497.63 cm −1 , which might be attributed to the aromatic/-NO 2 group. These peaks have also been observed for the adsorption of As(III) in the SBB process [ 19 , 42 , 43 ]; here, recognition of the arsenic redox activity of the bacteria is important. The bacterial As transformation converts it into different forms.…”

“…The EPS acted as a key material for the attachment of the As(V), thus assisting the bacteria to grow at high concentrations of arsenic [ 24 , 33 , 41 ], and ultimately promoted arsenic adsorption in the SBB process. The fluctuations in the surface properties have proven to be one of the major factors affecting the adsorption of arsenic [ 19 , 21 , 38 ].…”

“…Desorption of arsenic at alkaline pH might be attributed to the de-protonation of the –OH group at high pH, which might have resulted in a negative charge on the surface of BCXZM. As a result of this, there were dominant repulsive forces between arsenic oxyanions and negatively charged BCXZM surface leading to the desorption of arsenic [ 7 , 19 , 31 ]. Therefore, once the maximum adsorption capacity of the BCXZM composite is reached, the biochar can be reused after desorption as supporting material to grow biofilm, and newly prepared BCXZM can be used for arsenic bioremediation.…”

“…The key is to use biomass in a form that can be easily regenerated for reuse, which should be deliberated in the application of simultaneous biosorption and bioaccumulation (SBB) for the elimination of toxic metals from natural water or wastewater. Recently, immobilization bacteria have been reported on neem leaves/MnFe 2 O 4 composite [ 18 ], rice straw [ 19 ] and sawdust/MnFe 2 O 4 composites [ 20 ] for the bio-removal of arsenic, in both batch and fixed-bed reactors. However, there are some issues related to the utilization of these materials that should be addressed for the application of these materials, e.g., sawdust is biodegradable and once bacteria have grown, it is biodegraded and cannot be recycled.…”

“…Secondly, the bacteria used in this process have a major role in the arsenic removal. Undoubtedly, the process as a synergistic effect of bacteria and biosorbent is found to be more effective than a simple biosorption process; however, the individual role of bacteria in terms of arsenic redox transformations and metabolisation is not studied very clearly [ 19 , 24 ]. Moreover, the maximum adsorption capacity of a biosorbent-bacteria composite at specific operation conditions remains undetermined [ 25 ].…”