چكيده به لاتين
Large quantities of wastewater containing azo dyes are produced globally due to high demand in various industries such as printing, textiles, pharmaceuticals, and food. A significant amount of these dyes is wasted through the dyeing process and then discharged along with wastewater. Untreated wastewater containing azo dyes and pigments has detrimental effects on the environment and aquatic life.
In this regard, several physical-chemical methods such as adsorption, ozonation, coagulation-flocculation, and advanced oxidation processes have been used to remove azo dyes. However, the high volume of sludge production, the formation of toxic by-products, and the high costs associated with the operation of physical-chemical methods are their drawbacks.
Biological degradation of dyes is considered a cost-effective and environmentally friendly option that decomposes contaminants to a significant extent and transforms them into simpler products. However, the use of activated sludge processes in conventional bioreactors, in addition to being time-consuming, leads to the production of toxic by-products in biological treatment methods.
In this study, the focus was on using a polyurethane sponge medium with a hydrogel coating composed of polyvinyl alcohol, sodium alginate, and activated carbon for the anaerobic-aerobic staged bioreactor for the biological degradation of Congo red azo dyes. The dominant bacterium Lysinibacillus capsici PB300(T) was selected after isolation from dye-contaminated soil and inoculation in liquid culture medium for DNA extraction, PCR, and sequencing. In the designed bioreactor, the isolated microbial consortium from dye-contaminated soil was used, and the effects of various parameters on the system were evaluated.
In batch studies for dye removal, with an initial COD concentration of 940 mg/L in the influent wastewater, a retention time of 24 hours, a dye concentration of 50 mg/L, a 60% fill fraction, and daily wastewater recirculation were assessed as optimal parameters. The dye and COD removal efficiencies under optimal conditions were 97% and 63%, respectively. Additionally, first-order and second-order kinetics were used to model the removal of dyes and COD under optimal conditions. The second-order kinetics exhibited better correlation with the obtained results, with kinetic coefficients of n, m, and K equal to 0.9968, 0.9029, and 8.2 (L2 /gVSS.gCOD.h) for dye removal and 1.2395, 9.5931, and 0.041 (L2 /gVSS.gCOD.h) for COD removal. Furthermore, the FTIR analysis results before and after the treatment process indicated the successful degradation of Congo red dye in the designed bioreactor system.
