Quantitative structure-biodegradability relationships （QSBRs） were established to develop predictive models and mechanistic explanations for acid dyestuffs as well as biological activities. With a total of four descriptors, molecular weight （MW）, energies of the highest occupied molecular orbital （EHOMO）, the lowest unoccupied molecular orbital （ELUMO）, and the excited state （EES）, calculated using quantum chemical semi-empirical methodology, a series of models were analyzed between the dye biodegradability and each descriptor. Results showed that EHOMO and Mw were the dominant parameters controlling the biodegradability of acid dyes. A statistically robust QSBR model was developed for all studied dyes, with the combined application of EHOMO and Mw. The calculated biodegradations fitted well with the experimental data monitored in a facultative-aerobic process, indicative of the reliable prediction and mechanistic character of the developed model.
The transformation of an anthraquinone dye blue 324 in a facultative-aerobic(F-A) system was investigated.Kinetic parameter study showed that higher Vmax coupled with more recalcitrant chemical oxygen demand(COD) were found in the facultative biofilm reactor(FBR) than in the aerobic reactor(AR).Results of the product analyses indicated that most of dye molecular could be facultatively broken down into simple intermediates,which would be further degraded under subsequent aerobic condition.The main metabolites in each reactor were detected by infrared(FT-IR) and high performance liquid chromatography and mass spectrometry(HPLC-MS).Comparison of the toxicities among the dye and its metabolites was conducted,surprisingly,the colorless intermediates from FBR possessed less inhibitory than original dye and the median effective luminescence concentration(EC50) in 15 min for aerobic effluent could not be detected,showing that hardly toxic products existed in the aerobic process effluent.
