Feasibility of the Somogyi-Nelson Method for Excluding the Residual Substrate When Quantifying the Soluble Extracellular Polymeric Substances Produced by Microalgae

This study investigates the correlation between soluble extracellular polymeric substances (sEPS) and fouling evoked according to mixotrophic metabolism in microalgae membrane bioreactor (MMBR). The Somogyi-Nelson (SN) method is used to the sEPS because, it can be applied also for low concentration levels (<200 mg/L) in the case of glucose solutions unlike the dinitrosalicylic acid method. The concentrations of sucrose, a nonreducing polysaccharide that can replace sEPS, and reducing sugar, which can serve as a substrate, are normally estimated via the total organic carbon (TOC) analysis. The sEPS content could be quantified by excluding the reducing sugar concentration through the SN method, which includes the residual reducing sugar injected as a substrate in the MMBR. The SN method could accurately measure the widest range at the 500-nm wavelength. To confirm the applicability of the proposed method for various types of reducing sugars, sucrose was then analyzed in mixtures with three reducing sugars, that is, glucose, fructose, and galactose. The resulting coefficient of the slope variation of the regression analysis, excluding the reducing sugar content via the SN method in the TOC of the mixed solution, was ≤15% and the determination coefficient was ≥0.99, indicating high accuracy and linearity. This confirmed that the SN method can be used to quantify sEPS in MMBR experiments by excluding the reducing sugars content, especially at low concentrations (<200 mg/L for glucose).