Characterization of soluble microbial products (SMP) in effluents from anaerobic reactors

The residual COD from anaerobic treatment processes is usually too high to comply with legislative discharge levels. It has been shown that in well operated systems the majority of the effluent COD originates from soluble microbial products (SMP) produced by the system itself, hence the characteristics of these compounds become important when assessing post-treatment systems to remove the residual COD. The molecular weight (MW) distribution and the identification of SMP in the effluents from three different anaerobic reactors will be presented. It has been found that the bulk of SMP lies in the low MW range, though compounds with MW as high as 300 kDa were also present in all anaerobic effluents. Preliminary results on the identification of such compounds using GC/MS surprisingly revealed the presence of long chain alkenes (C12-C24) and alkanes (C12-C16), as well as some aromatic compounds. These compounds that likely come from cell lysis and endogenous decay may not be easily biodegradable, hence their presence in the effluent is likely to cause the residual COD.