Characterization Composition of Soluble Microbial Products in an Aerobic Granular Sludge System

Abstract

Using flocculent activated sludge as seed sludge to cultivate aerobic granular sludge in a SBR, the main objective of this study was focused on the accumulation, relative molecular mass distribution, and composition of soluble microbial products (SMP) in an aerobic granular sludge (AGS) system. SMP were predominant (71-85 mg·L-1) in the effluent of the AGS system. The formation of SMP was related to substrate utilization, biomass decay, and EPS hydrolysis. A relative molecular mass distribution analysis indicated that the majority of SMP, accounting for about 54.8%-71.7%, had Mr<3×103; whereas, the Mr>100×103 formed a small fraction, constituting only 9.3%-14.5%. Three-dimensional excitation emission matrix fluorescence spectra (3D-EEM) identified four peaks in SMP, belonging to aromatic protein-like, tryptophan protein-like, humic acid-like, and fulvic acid-like substances. Gas chromatography-mass spectrometry (GC-MS) analysis revealed that esters (39.0%), short chain alkanes (14.9%), alkenes (11.7%), and alcohols (7.6%) were the main compounds in SMP. Most notably, bis(2-ethylhexyl) phthalate, as one kind of ester, accounted for 32% of the identified SMP.