Behavior of microbial communities developed in the presence/reduced level of soluble microbial products.

Soluble microbial products (SMP) are organics produced by microorganisms as they degrade substrates. The available literature does not reveal how SMP affect and regulate microbial activities. In this study, we monitored variations in pH, dissolved oxygen concentration, soluble biological and chemical oxygen demands (sBOD5 and sCOD) as a measure of microbial activity in synthetic wastewater. Aerobic degradation tests were carried out under the following conditions: aeration, 1,500 cm3 /min; initial sBOD5, 515+/-5 mg/l; initial sCOD, 859+/-6 mg/l; initial biomass concentration (defined as mixed liquor suspended solids), 1,200+/-25 mg/l; sludge retention time, 24 h; and temperature, 20+/-1 degrees C. The study involved non-acclimated biomass (R0 flora), biomass developed in the presence of SMP (R1 flora), and biomass developed in reduced level of SMP (R2 flora). We also determined which of these flora produced more refractory SMP. The results showed that R2 flora utilized the synthetic feed more quickly, and produced less refractory organic matter than R0 and R1 flora. The production of more refractory organics by R0 and R1 flora shows that not all the biomass was active. R1 flora degraded the substrates irregularly, suggesting that some microbes were dependent on the metabolic products of those that could utilize the feed components. These results show that production of SMP also depends on the prior substrates and on the ability of the flora to respond to changes in substrate composition.