Identification of the production and biotransformational changes of soluble microbial products (SMP) in wastewater treatment processes: A short review

While the definition of soluble microbial products (SMP) remains somewhat contentious, they have been widely accepted to be the pool of organic compounds which are released by cells into their surroundings (liquid or otherwise) due to substrate metabolism and biomass decay. SMPs are also potential precursors of disinfection by-products, and are known to be important in membrane fouling. With recent developments in analytical methodologies, many of the low molecular weight (MW) compounds can now be identified, although they are often incorrectly identified as recalcitrant compounds present in the influent. The old hypothesis of “microbial infallibility” suggested that all organic compounds produced by bacteria will eventually be degraded by microorganisms. However, there are some limitations to this hypothesis due to; the time available for degradation, the rate of activity of the microorganisms themselves, synergistic effects, as well as the degree of complexity of the chemical substance. Therefore, it is important to identify and characterise the SMPs involved in these processes, which can then in turn support the research and development of improving wastewater treatment efficiency and effectiveness, and eventually reduce environmental damage. In addition, it is still unclear what the evolutionary purpose of these compounds are. This paper reviews the work that has been done on the production and biotransformation of chemical compounds up to now and which were reported to be found in wastewater treatment systems.