CHARACTERIZATION OF SOLUBLE MICROBIAL PRODUCTS FROM ANAEROBIC TREATMENT BY MOLECULAR-WEIGHT DISTRIBUTION AND NICKEL-CHELATING PROPERTIES

Nine anaerobic chemostats fed glucose as the sole carbon and energy so urce were used to investigate the characteristics of soluble microbial products (SMP). These reactors were maintained at solids retention ti mes (SRT) of 15, 25, and 40 days (3 reactors for each SRT) with organi c loading rates of 0.25 or 0.50 g COD/1-d. Results showed that the con centration of SMP increased with increasing SRT (steady-state SMP for 15-, 25-, and 40-d systems were 54, 126, and 291 mg GOD/1, respectivel y). Distribution of SMP among three molecular weight categories (MW<10 00 daltons, 1000<MW<10,000, and MW>10,000) was bimodal. The fraction o f SMP with MW>10,000 was found to increase with increasing SRT (34 mg/ l and 48% of total SMP for a 15-d SRT, 83 mg/l and 62% for a 25-d SRT, and 242 mg/l and 76% for a 40-d system). The stability constant (CK) between Ni and SMP was approximately 10(3.62), a value very similar to some naturally occurring organic acids. The total SMP-ligand concentr ation (C-T,C-L) ranged from 0.07 to 1.33 mM as Ni and increased with i ncreasing SRT. The complexation capacity ranged from 0.65 to 5.97 mu m ol of Ni/mg SMP, and was independent of SRT with an average of 2.49 mu mol of Ni/mg SMP.