Biodecolorization of cationic dyes by biochar derived from agricultural wastes as low cost adsorbents

Abstract

A wide range of industries use different dyes to colour their products and thus release substantial amounts of coloured wastewater, which is of both toxicological and aesthetical concern. The discharge of coloured wastewater from these industrial units are enormously high in day to day operations. This discharged coloured wastewater contains huge quantity of dye wastes which are mostly carcinogenic as well as non-biodegradable in nature. Since these dyes are non-degradable, their concentration must be reduced to acceptable levels before being released into the environment. Basic dyes are mostly used for colouring acrylic fiber that are generally more toxic than other classes of dyes and these are the brightest class of water-soluble dyes used by the industries. Presence of these types of dyes in water leads to various impacts on human health and environment, therefore, it s a challenge to devise an effective and feasible wastewater remediation technique. Since most of the commonly used remediation techniques are lack in the advantages of being economic and environment friendly, which necessitates the need to develop an alternate and efficient process for the treatment of dye bearing wastewaters. Biochar, a carbon-rich product synthesized through thermochemical conversion of biomass in an oxygen-limited environment. Biochar seems to be appropriate sorbent for remediation of basic dyes. However, the previous works on the effectiveness and practicability of biosorbent based on biochar for the remediation of basic dyes are very limited. Thus, the thesis focusses on the potential of different biochars, synthesized from locally available agricultural wastes (Coconut Shell, Groundnut Shell and Rice Husk), towards sorption of three basic dyes (Basic Blue 41; Basic Red 09; Basic Violet 03). In order to apply in real conditions, a comprehensive understanding of the sorption mechanism is essentially required. The batch experiments were focussed on to optimize the biochar dosage, solution pH, temperature and initial concentration of dyes for effective dye removal. The results showed that biochar dosage strongly influenced the dye uptake potential of biochar. The results also showed that pH played a vital role and maximum sorption observed at pH 8. The impact of temperature on the basic dye sorption on to different biochar was examined by varying temperature from 30 50°C resulting an ideal temperature of 35and#730;C shows favourable condition towards BB41 and BRO9 sorption and 40and#730;C for BV03 sorption process. The scanning electron microscopy results indicated that surface of agricultural wastes-derived biochar was rough with various pore sizes compared to raw agricultural wastes. After sorption of dye molecules, the surface of all biochar samples was found to be relatively smooth. Fourier transform infrared spectrophotometer analyses were conducted on biochars and dye-bounded biochars where the observed multiple spectral peaks of biochar reveals the presence of different binding sites. newline