BIOLOGICAL TREATMENT WITH SUSPENDED ANAEROBIC/AEROBIC BIOMASS OF A REAL TEXTILE WASTEWATER WITH AZO DYES

Abstract

Wastewater treatment from dyesof textile industry is a great environmental problem, to which a lot of attention has been given because many of this products used for dying in the textile industry are toxic. Such is de case of azo dyes, most of them are toxic and non-biodegradable and they are discharged to water bodies and channels with no change in there structure and remaining for long periods in the stream. As a pretreatment to this wastewater a coagulation – flocculation process was applied and then a sequenced anaerobic + aerobic + granular activated carbon (GAC), using the last step as a polish treatment. Global COD removal efficiency of 92% was achieved (21% for the anaerobic step, 79% for global anaerobic + aerobic step and 92% for the anaerobic + aerobic + GAC). Related to color removal this had 97% removal efficiency. For BOD5 a 74% removal was achieved for the anaerobic step, and a 89% for the anaerobic + aerobic step and 98% efficiency was achieved for the global process. For TOC the removal efficiency achieved for the anaerobic effluent was 53% and 78% for the anaerobic + aerobic stage and 98% for the global process (anaerobic + aerobic + GAC). Related to the toxicity test, this was measured by Vibrio fischerii, Daphnia magna and Selenastrun capricornutum bioassays. Toxicity results were different depending on the used bioassay. Using Vibrio fischerii the measured toxicity was high, after GAC filtration the toxicity was not detected. Using Daphnia magna the results reported moderate toxicity for the influent and anaerobic effluent. Toxicity was not detected after the aerobic treatment and also for the global sequenced treatment. For Selenastrum capricornutum moderate toxicity was reported for the influent and anaerobic effluent, not toxicity was detected for the anaerobic + aerobic effluent, and for the global sequenced process (anaerobic + aerobic + GAC) a moderate toxicity was reported.

Key Words: Azo dyes, biologic treatment, flocculation, toxicity.