ROLE OF AQUATIC PLANTS AND INDIGENOUS MICROBES IN IMPROVING PHYTOREMEDIATION EFFICIENCY OF INDUSTRIAL SLUDGE

Abstract

The aim of the present research was to assess the metal phytoextraction potential of some selected plant species (Hemarthria compressa L., Lemna minor L. and Typha angustifolia L.) growing on industrial sludge along with resistant microbial strains (Aspergillus terreus, Aspergillus niger, Bacillus sp. and Acinetobacter sp.) either alone or in combinations. Based upon the result of preliminary experiments, the sludge concentrations selected for the actual greenhouse and field experiments were 30 and 60% along with control (0%). Keeping in view the metal resistance efficiency of microbes, the experiment comprised of seven treatments i.e., C (control without microbes), F1 (Aspergillus terreus), F2 (A. niger), F1+F2 (A. terreus + A. niger), B1 (Bacillus sp.), B2 (Acinetobacter sp.), B1+B2 (Bacillus sp. + Acinetobacter sp.), respectively. Six independent experiments (4 green-house and 2 field) were launched simultaneously. Physicochemical analysis of initial sludge samples revealed that tannery and paper sludge had a high pollution load due to higher values of pH, conductivity, total dissolved solids (TDS), sodium chloride (NaCl), biochemical oxygen demand (BOD), chemical oxygen demand (COD) and metals like Cr, Cd, Zn, Cu and Pb. After 90 days of plant growth in sludge, the growth was significantly decreased with increase in the concentration of sludge. On the other hand, in sludge concentrations along with microbial inoculum, plants showed the maximum shoot length, roots, leaves and fresh/dry weight in F1+F2 and F+B treatment as compared to all other tested treatments. Physicochemical parameters also showed a substantial decrease except TDS that showed an increasing trend. Minimum values of all were observed in combined microbial treatment as compared to control and other treatments. The chlorophyll content of leaves in all selected plants decreased with increasing the concentration of industrial sludge. Plants growing in different concentration of sludge, supplemented with combined fungal treatments in pot experiments and F+B treatments in field experiments, showed higher chlorophyll contents than the plants growing in other treatments. Results revealed that all the tested plants species showed a higher accumulation of essential (Ca, K, Na and iii Mg) and heavy (Cd Cr, Cd, Zn, Cu and Pb) metals at 60% concentration of sludge as compared 0 and 30% after 90 days of plant growth. The metal uptake was higher in their shoots as compared to roots in case of all the plant species, in both paper and tannery sludge. Further, the uptake of metals was significantly higher in F1+F2, B1+B2 and F+B treatment as compared to rest of the treatments i.e. F1, F2, B1, B2, F, B alone and control treatment. The metal extraction efficiency of the experimental plants was observed to be in the order of T. angustifolia > H. compressa > L. minor. The translocation factor and enrichment coefficient indicated that a higher amount of heavy metals was absorbed by the plants than was present in the sludge. The least bioaccumulation was observed for Na in all the cases. Typha angustifolia proved to be a better metal accumulator than all other hydrophytes. Biochemical analysis of T. angustifolia and H. compressa showed that in 60% TS with combine fungal and bacterial inoculum, superoxide dismutase (SOD) and catalase (CAT) activity was high i.e. in the order of 60% TS> 30% TS> 0% TS. The results from this work in the light of contemporary literature indicates that a probable genetic modification at cellular level resulted in an acquisition of metal tolerance that was also evident in enhanced biochemical activity of antioxidant enzymes, uptake of high metal contents and ultimately better plant growth in all the treatments as compared to control. The results of these experiments emphasize that efficient pollution hyperaccumulators can be used for commercial and large-scale cleaning and bioremediation of tannery sludge. The plants can then be harvested easily and incinerated. Constructed wetlands offer the treatment benefits of natural wetlands in a more controlled environment, if developed along the industrial units. The treatment processes within such a system will be self- sustainable, requiring little input of energy, chemicals and operator maintenance