Process monitoring of anaerobic azo dye degradation by high-performance liquid chromatography–diode array detection continuously coupled to membrane filtration sampling modules

Process integrated microfiltration and ultrafiltration based membrane sampling modules were compared by means of HPLC with diode array detection based monitoring of an anaerobic azo dye biodegradation process. The sampling matrix consisted of anaerobic sludge from a municipal wastewater treatment plant. The hydrolysed azo dye Reactive Black 5 (RB5-H) and three products (ionic and nonionic) released from reductive cleavage under anaerobic conditions were continuously monitored by simultaneously separation by ion-pair chromatography. Microfiltration membrane-based sampling showed no retention for any compound observed. Sampling by ultrafiltration significantly retained the observed ionic compounds between 58 and 83% whereas a nonionic compound was not retained. On-line monitoring of an oxygen-sensitive compound was possible whereas off-line detection failed. Robust long time monitoring could be performed for up to 1 week without cleaning the membrane.