BIOLOGICAL REMOVAL OF ZINC FROM INDUSTRIAL EFFLUENT

Abstract

With the development of civilization and industrialization during last few decades, the level of heavy metal ions in natural water resource has increased substantially. Zinc is one such type of heavy metals, presenting in the list of hazardous chemicals, produces various ranges of zinc toxicity to the environment when it is discharged from various industrial effluents with higher concentration. In the present work, the heavy metal zinc in its divalent form along with copper and iron has been considered since these are usually found associated with zinc in various types of industrial effluents. The limit of zinc in wastewater laid down by various environment protection agencies such as US EPA (United States Environment Protection Agency), World Health Organization (WHO) and Central Pollution Control Board (CPCB) is 5 mg 1-1. Various 'conventional metal ion remediation technologies have been extensively practised in past. Most of these technologies are not cost effective, eco friendly, has technical shortcomings and also produces secondary pollutants. According to the literature review, bioremediation can be a viable possibility for the zinc removal, since it is not only cost effective, also does not produce any secondary pollutants. Hence, the present investigation aimed at the bioremoval of zinc along with copper and iron from synthetic simulated wastewater and real industrial wastewater. In the present work, both the batch and continuous column studies have, been performed. The bioremoval of Zn (II), Cu (II) and total Fe (II, III) was performed by biosorption on the surface of various biomasses and on isolated dead cells of Zinc sequestering bacterium VMSDCM accession no. HQ108109. Four types of metal ion combinations namely pure zinc, Zn (II)- Cu (II), Zn (II)- total Fe (II, III) and Zn (II)- Cu (II) — total Fe (II, III) have been studied in the present work. Nine different bioadsorbents namely Cedrus deodara sawdust, Eucalyptus leaf powder, Eucalyptus bark sawdust, Pine apple peel powder, Mango bark sawdust, Jack fruit peel powder, Egg shell with egg shell membrane, Orange peel and dead cells of Zinc sequestering bacterium VMSDCM accession no. HQ 108109 have been used in the present work. The physico-chemical characterization of adsorbents revealed the fact that these bio-adsorbents have high content of carbon. The surface characterization of adsorbents, performed by Scanning electron microcopy (SEM) and Fourier transformation infrared analysis (FTIR), revealed the fact that the. surfaces of adsorbents are quite heterogeneous, non-crystalline, rough and highly enriched with negatively charged functional groups such as amine, amide, carboxyl, carbonyl and hydroxyl stretching. The sorption of Zn (II), Cu-(II) and total Fe (II, III) ion was performed on all the adsorbents. The adsorption of these metal ions was performed in various combinations. The individual metal ion system was studied and subsequently various physical process parameters such as pH, temperature, initial concentration of Zn (II), Cu (II) and total Fe (II, III), agitation rate, particle size, and contact time were optimized. Through the physical parameter optimization, two out of nine adsorbents namely Cedrus deodara sawdust and dead cells of Zinc sequestering bacterium VMSDCM accession no. HQ108109 were found highly efficient to remove Zn (II), Cu (II) and total Fe (II, III) in various combinations in liquid phase. The maximum removal of zinc obtained in pure zinc, Zn (II) - Cu (II), Zn (II)- total Fe (II, III) and 'Zn (II)- Cu (II)- total Fe (II, III) were 89.19%, 69.12%, 74.31% and 69.11%, respectively in case of Cedrus deodara sawdust. The removals of total Fe (II, III) and Cu (II) ion obtained in Zn (II) - total Fe (II, III), Zn (II) - Cu (II) and Zn (II)- Cu (II)- total Fe (II, III) in metal ion systems were 37.19%, 71.11%, 32.14% and 65.5%, respectively. In case of dead cells of Zinc sequestering bacterium VMSDCM accession no. HQ108109, the maximum removals of Zn (II) ion obtained in pure zinc, Zn (II) - Cu (II), Zn (II)- total Fe (II, III) and Zn (II)- Cu (II)- total Fe (II, III) was 100%, 86.66%, 88.19% and 74.61%, respectively. The removal of total Fe (II, III) and Cu (II) ion in case of dead cells of Zinc sequestering bacterium VMSDCM accession no HQ108109 was 81.1%, 88.19%, 73.34% and 81.23% respectively. The initial concentrations of metal ions were taken as 150 mg 1-I. Various isotherm models, kinetic, mechanistic and thermodynamic modeling have been performed on both the biomasses. Results showed that the Freundlich, Temkin, pseudo second order and Bangham models were found suitable to interpret the sorption of Zn (II) ion on the surface of Cedrus deodara sawdust. Additionally, the sorption of Zn (II) ion on the surface of Cedrus deodara sawdust seemed to be endothermic and spontaneous in nature. However, in case of sorption of Zn (II) ion on dead cells of Zinc sequestering bacterium VMSDCM accession. no. HQ108109, a modified isotherm model has been proposed. The model constant was calculated through code written in C++ language. The modified and proposed isotherm model was validated between 298 K to 308 K. Kinetic, mechanistic and thermodynamic modeling of sorption of Zn (II) ion indicated that the binding of Zn (II) ion on surface of dead cells of Zinc sequestering bacterium VMSDCM accession no. HQ108109 followed pseudo second order and intra particle model. Thermodynamic analysis proved that the biosorption of Zn (II) ion on dead cells of Zinc sequestering bacterium VMSDCM accession no. HQ108109 was spontaneous and endothermic in nature. Cedrus deodara sawdust and dead cells of Zinc sequestering bacterium VMSDCM accession no. HQ 1.08109 were used to treat synthetic simulated wastewater and real industrial wastewater. The industries considered in present work for the purpose of treatment of synthetic simulated waste and real wastewater were copper smelting plant, zinc-plating industry and zinc-producing unit situated SIDCUL, HARD WAR, UTTRAKHAND. The order of removal of metal ions in liquid phase was Cu (II) > Zn (II) > total Fe (II, III). The present work also embodies surface, biochemical and phylogenetic characterization of Zinc sequestering bacterium VMSDCM accession no. HQ108109. The 16s rRNA sequencing of Zinc sequestering bacterium VMSDCM accession no. HQ 108109 was performed and the sequences were submitted to National Center Biotechnology Information (NCBI, US) under the accession no. HQ108109. The phylogenetic and biochemical characterization of Zinc sequestering bacterium VMSDCM accession no. HQ108109 revealed the fact that the bacterium seemed to cluster up with arsenite oxidizing bacteria when plotted in a maximum likelihood tree. The isolated microbial strain was grown in various environments of zinc, copper and iron. The growth curve of the bacterium was made in absence of metal ions (standard curve) and in presence of metal ions in various combinations. The growth curve of the bacterium in ternary metal ion system revealed the fact that 167.52 g 1-1 of total iron and 190.62 g 1-1 of copper with 457.66 g 1-1 of Zn (II) ion was found as optimum concentration for growth of Zinc sequestering bacterium VMSDCM accession no. HQ 108109. The microbial strain of cell was immobilized on the bed of Cedrus deodara sawdust. The immobilization of microbial cell was carried out in column reactor and simultaneous biosorption and bioaccumulation of metal ion was performed. The real wastewater, treated in lab scale column reactor was pumped into the column at various flow rates ranging between 109 ml h-1 to 318 ml h-1. The break through curve of metal ions was obtained at various flow rates and time interval. The flow rate of 109 ml/h offered the maximum removal of metal ions from industrial effluent. Present investigation reveals that the treatment, i.e., simultaneous biosorption and bioaccumulation (SBB) gives the best result for the removal of Zn (II), Cu (II), Fe (II, III) from industrial wastewater. We believe that this can be applied in practice for the successful removal of ternary metal ion complex.