Fabrication of calcite based biocomposites for catalytic removal of heavy metals from electroplating industrial effluent

Abstract

Treatment of wastewater for heavy metal removal is gaining much attention due to increase in pollution and insufficiency of water. Wastewater treatment processes is important in preventing heavy metal pollution of the receiving waters when discharged particularly from industrial effluents including electroplating industries. In this article, a novel actinobacterium Zhihengliuella sp. ISTPL4, along with different biomaterials synthesized were studied comprehensively for the removal of toxic heavy metals including Cr, Cd, Mn, Ni, Pb, Zn and Fe. Among these heavy metals, Cr(VI) being more lethal than other metal ions and present in a very high concentration of ⁓1000 mg/l in effluent of electroplating industry, pose serious health issues when enters the body. Cr(VI) reduction by the strain ISTPL4 when studied in the reactor, showed 20 % reduction of Cr(VI) to Cr(III) at an initial concentration of 1100 mg/L, along with >90 % removal of other heavy metals. The whole genome analysis of the strain showed the presence of heavy metals resistant genes and transporters, corroborating the above results. The bacterium’s adsorption capacity was then compared with synthesized biomaterials viz. only biochar, biochar with reductase enzyme, and calcined biochar with reductase enzyme. Synthesized biomaterials in the packed columns provided excellent adsorption capacity for all the heavy metals within 10–15​ min of run time and reusability potential of 5 cycles. Calcined biochar with reductase enzyme showed maximum adsorption of Cr. Langmuir isotherm and Lineweaver Burk plot best explained their adsorption mechanism and strong affinity towards heavy metals. FTIR and SEM-EDX analysis confirmed the involvement of carboxyl, hydroxyl, and amino groups in heavy metal ions’ biosorption. Furthermore, MTT assay in HepG2 showed greatest cell viability at the concentration where maximum reduction of Cr(VI) to Cr(III) occurred. We propose this current technology, which provides an excellent biosorbent in the form of calcined biocomposite with bacterial reductase enzyme for heavy metals reduction and remediation and also implementation of this technique would have great significance in wastewater treatment of metal contaminated sites.