| Anaerobic batch-fed enrichment reactors and chemostats fed glucose or acetate were used to investigate the production and characteristics of soluble microbial products (SMP). Solids retention times of 15, 25, and 40 days were used with organic loading rates of 0.25 and 0.50 g COD/L-day. Results showed that as SRT increased, production of SMP increased. Systems fed glucose produced more SMP than those fed acetate. The fraction of influent COD converted to SMP ranged from 0.2 to 1.0% for acetate systems and from 0.6 to 2.5% for glucose systems. The fraction of effluent COD comprised of SMP in chemostats fed glucose ranged from 81 to 97% and increased with increasing SRT.; The distribution of SMP among three MW categories (MW {dollar}<{dollar} 1000, 1000 {dollar}<{dollar} MW {dollar}<{dollar} 10,000, and MW {dollar}>{dollar} 10,000) was bimodal with the lowest SMP levels falling in the 1000 {dollar}<{dollar} MW {dollar}<{dollar} 10,000 category. The fraction of SMP with MW {dollar}>{dollar} 10,000 increased with increasing SRT. The stability constant for SMP with Ni was approximately 10{dollar}sp{lcub}3.62{rcub}{dollar}, the total SMP-ligand concentration ranged from 0.07-1.33 mM Ni, and the complexation capacity ranged from 0.65 to 5.97 {dollar}mu{dollar}mole Ni/mg SMP. In general, the total SMP-ligand concentration increased with increasing SRT.; Chemostats fed glucose were dosed with 50, 150, or 250 mg Ni/L to investigate the role SMP plays in reducing metal toxicity. SMP quantity and character remained essentially constant in response to the 50 mg Ni/L dose. For the higher Ni doses, significantly higher levels of SMP were produced. The MW distribution of SMP shifted from predominantly high-MW ({dollar}>{dollar}10,000) to low-MW (MW {dollar}<{dollar} 1000). A significant proportion of the soluble nickel was found to be associated with SMP of MW {dollar}>{dollar} 1000 in the systems with 40-day SRT. There was no significant change in the Ni-chelating properties of SMP. However, SMP did have a significant impact on process performance in that it accounted for at least 8 to 43% of the soluble Ni in the reactors. |
