Intermittent aeration strategy for azo dye biodegradation: A suitable alternative to conventional biological treatments?

Most solutions for biological treatment of azo dyes are based on conventional anaerobic-aerobic processes, but transition to full scale demands technology simplification and cost reductions. We suggest a new approach, in which aeration is intermittently supplied for simultaneous removal of color and toxic metabolites in a single compartment. Effects of aeration strategy and glucose concentration on decolorization and organic matter removal were assessed using factorial design (32) and response surface analysis. Bioreactors were inoculated with microorganisms previously acclimated to Direct Black 22 (DB22), which was the azo compound used in this study. Assays performed with synthetic textile wastewater showed that long-term decolorization was not impaired at a moderate level of aeration (4 hourly-cycles per day). Aerated batches presented lower color removal velocities, but these negative impacts were offset by increasing initial glucose concentration. Higher degrees of mineralization of the azo compound and higher organic matter removals were achieved in intermittently aerated experiments, which led to lower toxicity to Daphnia magna. Biomolecular analysis revealed that the microbial community structure was strongly associated with operational efficiency parameters. These findings suggest intermittent aeration can be implemented to accomplish enhanced azo dye biodegradation.

Chironomus sancticaroli (Diptera, Chironomidae) as a Sensitive Test Species: Can We Rely on Its Use After Repeated Generations, Under Laboratory Conditions?

In ecotoxicological assays, previously selected and standardized organism tests are exposed to an environmental sample. Some species of the Chironomus genus have been extensively used in ecotoxicological assays. Among these, Chironomus tentans is usually utilized in the USA and Chironomus sancticaroli in Brazil. We conducted ecotoxicological bioassays to compare a population of C. sancticaroli, kept for 6 years under laboratory conditions, with a sylvatic population of the same species, collected in the field. The aim was to test the hypothesis that populations of C. sancticaroli, maintained in the laboratory for long periods, could have a different response to stressors/substances. We analyzed the responses of C. sancticaroli for potassium chloride, zinc chloride, potassium dichromate, linear alkylbenzene sulphonate (LAS) and caffeine. The results showed no significant differences between the two populations in the analyses and seems to indicate the possible use of C. sancticaroli from populations kept in the laboratory for long periods.