This work presents results on the production and characterization (by both mass spectrometry and conventional chemical analyses) of Soluble Microbial Products (SMP) that accumulated in aerobic and anaerobic bench scale completely stirred tank reactors (CSTRs) fed with glucose or acetate under different hydraulic retention times (HRT) and temperatures. SMP accumulation varied from 2 to 68% of the influent COD in the aerobic reactor and from 9 to 27% in the anaerobic reactor and increased with the decrease in temperature and with the HRT reduction in the aerobic reactor. On the other hand, in the anaerobic reactor, the organic loading rate and the temperature had little impact on SMP production, implying that the SMP originated from different mechanisms in each system. For both reactors, a higher accumulation of SMPs was observed as the substrate was acetate when compared to glucose, and the chemical analysis showed that the majority of the SMP did not seem to be proteins or carbohydrates. Principal component analysis (PCA) of the mass spectra from positive and negative mode electron-spray ionization (LC-IT-TOF-MS) and results from matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF-MS) confirmed the chemical analyses and showed the absence of proteins in the effluents and the predominance of low molecular weight SMP. The PCA analysis also showed that the majority of the SMP from aerobic and anaerobic reactors did not seem to originate from soluble extracellular polymeric substances (EPS) or cell lysis products.
Biological wastewater treatment; Soluble microbial products; Residual COD; Volatile fatty acids; mass spectrometry
