Treatment of textile effluent by radiation for dyeing and irrigation purpose

Abstract

This research demonstrated the scope of using high energy gamma radiation for textile wastewater treatment and studied the possibility of recycling the irradiated water for fabric processing and reusing in irrigation purposes. The treatment was carried out in Cobalt-60 gamma radiation source at different irradiation doses (3, 5, 8 and 12 kGy) with a dose rate of 13 kGy/h. The change of pH, decoloration percentage, reduction of total suspended solids (TSS), total dissolved solids (TDS), biological oxygen demand (BOD5) chemical oxygen demand (COD), variation of electrical conductivity (EC) and heavy metal content of irradiated wastewater were extensively investigated. It was observed that, colored wastewater become almost colorless due to the breakage of the chromophoric groups of the dye molecules by gamma irradiation. Smaller organic compounds (mainly acidic) were formed due to the fragmentation of large dye molecules that results the reduction of pH of the irradiated wastewater. Total suspended solids (TSS), COD and BOD5 were also decreased significantly because of the degradation of the organic solid particles. However, the change of TDS, EC and metal content were found less for treated wastewater after application of gamma irradiation. The irradiated wastewater was recycled to the pretreatment (chemical singeing, scouring and bleaching) and dyeing of cotton knit fabric with reactive dyes. The detailed experimental results demonstrated that, the irradiated water performed perfectly as an alternative to the fresh water in the pretreatment of cotton knit fabric samples. The chemical singeing, scouring and bleaching performance i.e. weight loss, visual appearance, absorbency and whiteness of fabric was found almost similar to the fabric treated with fresh water. The performance of the fabric dyed with treated wastewater was also compared with the fabric dyed with fresh water by analyzing the depth of shades of both types of dyed fabrics from the measurement of absorption spectrum (K/S value versus wavelength). The absorption curves of fabric dyed by irradiated wastewater at light, medium and deep shade of three different colors have shown close match to their corresponding fresh water dyed fabric. Variation of shade between the dyed fabrics, representing by ∆E values, were also found within the maximum acceptable limit as it ranges from 0.1 to 0.75. The color fastness of dyed fabric was also assessed with respect to perspiration, rubbing and washing. In case of color fastness, both types of fabrics have shown similar rating (4 to 5) which lies between ‘good’ to ‘excellent’. Furthermore, the absence of carcinogenic azo dyes and formaldehyde in the cotton fabric dyed with irradiated water signifies the nontoxicity of the fabric for human health. The irradiated wastewater was also used for irrigation of Malabar spinach plant and its growth was compared with controlled plant that uses normal underground water. Remarkable results have been noticed for the plant growth, leaves count and root length of plant irrigated with irradiated wastewater. This unusual enhancement of various growth factors of Malabar spinach indicated that, gamma radiation degrades the textile dyes and create nitrogeneous compounds that may supply the various nutrients to the plant and acts as a biofertilizer. The mineral content of the plant was also analyzed by using a Tandem accelerator and the results showed significant increase of minerals content for the plants irrigated with treated wastewater than the plants irrigated with fresh water.