Evaluating the impact of operational parameters on the formation of soluble microbial products (SMP) by activated sludge

Soluble microbial products (SMP) are the major component of the residual organic fraction in biological wastewater treatment effluent. The impact of process parameters on SMP production by specific groups of bacteria is currently unknown. In this work, SMP production by activated sludge at different substrate concentrations, dissolved oxygen (DO) levels and temperatures, was evaluated by experimental and modeling approaches. The results showed that among the three parameters, SMP production was most sensitive to substrate concentration. Total SMP production was increased 70.5% by a threefold increase in substrate concentration, with SMP produced from heterotrophs, ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) increasing by 61.2%, 580.0% and 410.0%, respectively. The effect of temperature on SMP was less pronounced. Decreasing the temperature from 20 °C to 10 °C decreased total SMP by 17.2%, with SMP production from heterotrophs decreasing by 20.0%, and from the AOB and NOB increasing by 180.0% and 140.0%. DO concentration had nearly no effect on total and heterotrophic SMP production, while it did have a significant positive effect on autotrophic SMP production. SMP production from AOB and NOB decreased by 24.3% and 47.8%, respectively following a decrease in DO concentration from 8.7 to 1.5 mg/L. However, the net effect of DO on total SMP production was negligible.

► SMP production most sensitive to substrate concentration, least sensitive to DO. ► Heterotrophs responsible for >90% SMP. ► Different effect of parameters on autotrophic and heterotrophic SMP.