Integrated biological and ozone treatment of printing textile wastewater

Textile effluents are among the most difficult industrial wastewaters to treat because of their compositional variability and of the presence of numerous different chemicals intentionally designed to resist degradation. Though biological technologies offer a cheaper and more environmental friendly alternative for the treatment of textile effluents, an additional step to remove recalcitrant compounds is still needed. Integrated biological and chemical treatment is a rather new approach that allows improving treatment performance and stability without increasing too much treatment costs. Ozone integration in a sequencing batch biofilter granular reactor was tested at laboratory scale for treating a printing wastewater characterized by high concentrations of surfactants and nitrogen. The process was optimized in terms of applied organic load and ozone dose. The results have shown that the process assures the possibility to comply with the limits for direct discharge for all investigated parameters by operating at an organic load value lower than 1.5 kgCOD/m3 d and with an ozone dose of 135 mg/l. A synergetic biological and chemical oxidation activity was observed with a ratio between ozone dose and COD removed lower than 0.75. Finally, the process was characterized by a sludge production as low as 0.17 kgTSS/kgCODremoved due to the high biomass concentration in the biological system used.