Phytoremediation technologies as an advanced tool for the removal of dyes from textile effluent

Prof. Sanjay P. GovindwarDepartment of Biochemistry, Shivaji University, Kolhapur, India, 416004

Abstract

The presence of color is the most obvious indicator of water pollution and it affects the water quality in a number of ways. The dyes and associated chemicals that are released in the form of wastewater are potentially carcinogenic, mutagenic and highly toxic in nature to all forms of life. Though there are a numerous physical, chemical and biological methods for dye decolorization and degradation, they fail when complete treatment of dyes is concerned along with other limitations such as cost, practical applicability and secondary pollution caused by sludge formation. Finding a solution which meets all the desired requirements and also solve the problem along with long term practical applicability is need of the hour.

Phytoremediation is one of such most promising approaches for the treatment of dye containing effluents. Use of common garden plants with fibrous and dense root system for treatment of dyes is a novel and aesthetically pleasing way which can also bring the polluted sites to productive use. Very common plants with a potential to degrade and remove dyes from wastewater as well as soil viz. Blumea malcolmii, Typhonium flagelliforme, Aster amellus, Glandullaria pulchella, Zinnia angustifolia, Portulaca grandiflora, Petunia grandiflora and Tagetes Patula have been reported for the degradation of dyes. All of these have economic importance as they are mostly ornamentals or are grown for harvesting flowers. The wild plants as well as the in vitro cultures were found to show dye removal from aqueous solutions and from the real textile effluents. The degradation of dyes is carried out by a specific set of enzymes viz. lignin peroxidase, veratryl alcohol oxidase, laccase, tyrosinase, DCIP reductase, azo reductase and riboflavin reductase. None of them is exclusive and some or all of them can act synergistically. The studies on purified plant, bacterial and fungal laccases and other enzymes have helped to understand the biochemistry of degradation of textile dyes. Plant root associated bacteria which were able to degrade the dyes were isolated and used for classical in vitro experiments which confirmed the differential metabolism of the dyes and the modes of action by individual cultures of plants, bacteria and the consortial systems. Plants with a difference in their enzymatic induction patterns were used to build plant-plant consortium for efficient removal of the textile dyes. The basic information obtained with earlier studies with wild plants, tissue cultures and in vitro consortial systems was used for the construction of different types of reactors. A horizontal subsurface flow phyto-tunnel and a vertical flow constructed wetland was designed and used for the treatment of real textile wastewater and different simulated dye mixture. The systems were augmented with the root colonizing bacteria and enhancement in the treatment efficacy of the phytoreactors was achieved. The treated samples were found to meet the standard values set by the regulatory agencies and legislations for the release in to the water bodies and soils.

Transgenic approach to improve the potential of the plant enzymes will enhance the capacity of phytoreactor that could be applied in wetlands for textile waste water cleanup.