Influence of extraction methods on proteins and carbohydrates analysis from MBR activated sludge flocs in view of improving EPS determination

Abstract

One of the main operational problems in membrane bioreactors (MBRs) is membrane fouling. It can be stated that extracellular polymeric substances (EPSs) analysis is of paramount importance for membrane fouling prediction and subsequently to enhance the performance of the MBR process. In this way, the standardization of EPS separation and their analytical procedures is a non-solved problem that plays an important role in order to be able of comparing data of pilot and full-scale bioreactors. Prior to unveil this fact, it is necessary to assure the accuracy of the analyzed data. In this paper, the Standard Addition Method (SAM) is applied with the aim of studying eventual interferences by other mixed liquor substances or by reagents used in the extraction procedures on the analytical methods for determining proteins and carbohydrates and as a consequence, to improve the data accuracy and reliability. For that, several extraction protocols were applied and compared in order to obtain the EPS from the activated sludge. Moreover, DNA was measured and viability tests were carried out to evaluate cell lysis extent. BCA and Lowry methods were used to quantify proteins, meanwhile Dubois and Anthrone were applied for carbohydrates. Results showed that Triton X-100 achieved the highest extraction values in terms of proteins (81.64 ± 12.9 mg BSA/g VSS) and carbohydrates (10.3 ± 1.4 mg Glucose/g VSS) concentrations linked to lower DNA values (4.9 ± 0.8 mg DNA/g VSS). In addition, epifluorescence microscope images showed the high extent of the extraction achieved. For this protocol, BCA and Dubois analytical methods were chosen since SAM found out interferences with Anthrone and Lowry, and consequently, they were recommended for data comparison in MBR plants, and for fouling prediction.