Studies on biosorption of textile dye from environment using a selected microbial biomass

Abstract

The presence of textile dyes in aquatic environment is of great environmental concern. Rapid industrialization has led to increased disposal of textile dyes in the environment. A large quantity of dyes approx 5 to 10% of annual global production (ca 107kg) is discharged as effluent mainly by paint and textile industries. Dyes prevent the penetration of sunlight into the stream and reduce photosynthetic activity. The reactive tri-azine dyes such as Reactive Blue 4, are heavily used in textile industries for coloring different cloth materials and their metabolites (e.g. aromatic amines) can be highly toxic and potentially carcinogenic, mutagenic and allergenic on exposed organisms. The dye components are hardly degradable by physicochemical or biological methods. Most of the tri-azine dyes are also resistant to chemical, photochemical and biological degradation. Biomass of some natural microbial species, including bacteria, fungi and algae, is capable of removing the different textile dyes by biosorption, biodegradation or mineralization. Rapid industrialization and increase in human population has led to many fold increase in the release of toxic chemicals including textile dyes in the environment. Traditional treatment technologies for the removal of harmful textile dyes from wastewater are either inadequate or costly besides generating huge quantity of toxic sludge. In this regard, technically and economically viable pre-treatment procedures using biomaterials are gaining importance in recent years. In view of the environmental, ecological and societal health issues, it is considered necessary to develop suitable cost effective methods for the removal of textile dyes from wastewater. The use of microorganisms as biosorbents is an attractive alternative to the existing methods for toxicity reduction and removal of dyes from industrial effluents because of their good performance and low cost. On review of literature, a stark revelation of lack of research in fungal adsorbents compared to other microorganisms is seen. Unfortunately, the use of native biomass (such as bacteria, yeast, fungi and algae) in freely suspended state is limited owing to their inherent disadvantages such as small particle size, possible clogging and low mechanical strength of the biomass. In addition, a density similar to that of the suspending medium may complicate biomass/effluent separation. Immobilized biomass overcomes some of these problems and offers greater potential applications. Benefits being better control of particle size, easy separation of biomass and effluent, capability of regeneration, high biomass loadings and minimal clogging under continuous flow. The efficacy of any biosorbent depends on the micro-environment of the targeted toxicant and also on the availability of the material. Thus there is always a need for search of new biosorbents. Further an intimate understanding of the adsorption mechanism is also a prerequisite for improving the efficiency of the process. Although there are few reports of dye biosorption by bacterial extracellular polymeric material, but research in this area is lacking in the field of dye removal with fungal biomass. The present study deals with the adsorptive removal of Reactive Blue 4 by dry as well as immobilized and pre-treated cells of a Rhizopus oryzae (MTCC 262). The model dye used asadsorbate was Reactive Blue 4, which is an anthraquinone based chloro-triazine dye very important in dyeing of cellulosic fabrics. Physicochemical parameters that influence the adsorption process have been included in this investigation. Equilibrium adsorption isotherm and kinetics of adsorption data will be analyzed in the light of different models.

The investigation will focus on the elucidation of the mechanism of interaction between adsorbate and adsorbent employing Fourier transform infrared spectroscopy, Scanning electron microscopic study. The relative role of the functional groups in the overall binding process will also be investigated by applying some physical pre-treatment procedure. Removal of Reactive Blue 4 by the biosorbent immobilized in a suitable matrix is also included in the present investigation. Adsorption experiments will also be carried out in a continuous packed bed reactor using both dry and immobilized biomass. In order to assess the reusability of the selected biosorbent desorption studies are planned using various desorbing agents in four consecutive cycles.