Chelating properties and molecular weight distribution of soluble microbial products from an aerobic membrane bioreactor

摘要

This paper presents a detailed study on soluble microbial products (SMPs) in an aerobic membrane bioreactor (MBR) treating synthetic wastewater simulating municipal waste-water. The concentration of SMP in the reactor conformed to a cyclical pattern of accumulation and reduction in relation to SRT. The molecular weight (MW) distribution of accumulated SMP was determined to vary from < 1kD to > 100 kD. Copper chelating properties of various SMP fractions in the MBR were compared before and after copper addition to the feed. The conditional stability constant (Log~C K), complexation capacity (C_C), and SMP-ligand concentration (C_L) were evaluated to determine the impact of copper on the chelating properties. The results indicated that accumulated SMP in the aerobic MBRs without copper addition are moderate chelators with Log~C K values of 7.6-8.3 mol~(-1) for the moderate ligands and 6.3-6.8mol~(-1) for the relatively weaker ligands. SMPs with MW of 1-10 kD were found to have the highest complexation capacity among all SMP fractions. The complexation capacity of accumulated SMP after feeding copper was 0.11 μmol/mg of SMP, almost half of its value prior to feeding copper. The reduction of C_C after feeding copper was a result of an increase in large molecular weight SMP ( > 100kD).