Biodegradation of azo and anthraquinone dyes in continuous systems

The purpose is to develop a complete microbiological model system for the treatment of wastewater from textile mills in developing countries. Artificial wastewater was treated by microorganisms growing on wood shavings from Norway spruce during unsterile conditions. The microorganisms were inoculated from forest residues. Mixtures of the azo dyes Reactive Black 5 and Reactive Red 2 were degraded in batch as well as continuous experiments. Reactive Red 2 mixed with the anthraquinone dye Reactive Blue 4 was also treated in the continuous system. The system consisted of three reservoirs - the first two with an anaerobic environment and the third with an aerobic. The dye concentrations were 200 mg l⁻¹ of each dye in the continuous system and the retention time was approximately 4 days and 20 h per reservoir. Samples from the process were analysed with spectrophotometer and LC/MS to monitor the degradation process. 86-90% of the colour was removed after a treatment of 4 days and 23 h in the continuous process. Two metabolites were found in the outlets of reactors one and two, but they were degraded to below the detection limit in the aerobic reactor.