A review of soluble microbial products (SMP) in wastewater treatment systems

A review concerning the characterisation, production, modelling, significance and implications of soluble microbial products (SMP) in wastewater treatment is presented. The precise definition of SMP is open to debate, but is currently regarded as "the pool of organic compounds that are released into solution from substrate metabolism (usually with biomass growth) and biomass decay", although for anaerobic systems volatile fatty acids are not included as SMP. Some of the SMP have been identified as humic and fulvic acids, polysaccharides, proteins, nucleic acids, organic acids, amino acids, antibiotics; steroids, exocellular enzymes, siderophores, structural components of cells and products of energy metabolism. Crucially, SMP have been found to comprise the majority of soluble organic material in the effluents from biological treatment processes and their presence is, therefore, of particular interest in terms of achieving discharge consent levels for BOD and GOD. SMP also exhibit several characteristics, such as toxicity and metal chelating properties, which effect the performance of the treatment system, and their presence has also been shown to adversely affect the kinetic activity and the flocculating and settling properties of sludge. This review outlines some important discoveries with regard to the MW distribution, biodegradability;and treatability of SMP and also the effect of process parameters on their production. It also summarises the attempts at incorporating SMP formation into the modelling of wastewater treatment. However, it concludes that the knowledge regarding SMP is far from complete and that much work is still required to fully understand their contribution to the treatment process; some of these future research areas are then outlined. (C) 1999 Elsevier Science Ltd. All rights reserved.