Efficient removal of dyes using carboxymethyl cellulose/alginate/polyvinyl alcohol/rice husk composite: Adsorption/desorption, kinetics and recycling studies.

Rapid industrialization is polluting the water resources and is becoming a serious environmental issue. In present study, the adsorption-desorption behavior of Direct Orange-26 (DO-26), Direct Red-31 (DR-31), Direct Blue-67 (DB-67) and Ever direct Orange-3GL (EDO-3) dyes on to native, modified rice husk (MRH), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC) and alginate (ALG) immobilized biomasses were investigated under different experimental conditions. For adsorbent modification, physical and chemical treatments were performed. The results showed that HCl pre-treatment considerably increased the sorption capacity of dyes versus native biomass. The sorption data were optimized using pseudo 1st order, intra-particle diffusion, pseudo 2nd order and Elovich models. The results revealed that the two-step rate equation was followed for the desorption kinetics of dyes. The involvement of -OH (hydroxyl), -COOH (carboxylic) and -NH2 (amino) groups in the adsorption of dyes onto biomasses was shown by FTIR analysis. Studies exhibited that among adsorbents employed, the MRH has the excellent potential for the dyes degradation from textile effluents.

By-product identification and phytotoxicity of biodegraded Direct Yellow 4 dye.

Citrus limon peroxidase mediated decolourization of Direct Yellow 4 (DY4) was investigated. The process variables (pH, temperature, incubation time, enzyme dose, H2O2 amount, dye concentration, co-metal ions and surfactants) were optimized for maximum degradation of dye. Maximum dye decolourization of 89.47% was achieved at pH 5.0, temperature 50 °C, enzyme dose 24 U/mL, H2O2 concentration 0.25 mM and DY4 concentration 18.75 mg/L and incubation time 10 min. The co-metal ions and surfactants did not affect the dye decolourization significantly. Response surface analysis revealed that predicted values were in agreement with experimentally determined responses. The degradation products were identified by UPLC/MS analysis and degradation pathway was proposed. Besides, phytotoxicity assay revealed a considerable detoxification in response of biodegradation of DY4 dye. C. limon showed promising efficiency for DY4 degradation and could possibly be used for the remediation of textile effluents.