Combining submerged membrane technology with anaerobic and ...

Protein (mg·L -1 )Materials and methodsReagent D: Mixture of reagents A, B, C in ratio of 100:1:1. Reagent D has to be donefreshly.Reagent E: Solution of Folin-Ciocalteu-reagent (1:2 in deionised water)Determination procedureA sample of 1.5 mL is rapidly mixed with 2.1 mL of reagent D and left for 10 minutesat room temperature. Then 0.3 mL of reagent E are added rapidly and mixed. After 45minutes, the absorbance at 750 nm is measured with a spectrophotometer Cecil CE 7200.A blank with reagents must be also measured as a reference. The quantification is donewith 6-8 points calibration curve in the range of 0-250 mg·L -1 , using protein standardbovine serum albumin (BSA) (figure 2.8).6005004003002001000y = 368.2x 2 + 193.7x + 4.539R² = 0.9970.0 0.2 0.4 0.6 0.8 1.0absorbance (750 nm)Figure 2.8. Calibration curve for carbohydrate concentration determination.2.4.4.3. Biopolymer clusters (BPC)A pool of biopolymer clusters (BPC) ranging from 2.5 to 60 µm in size was identifiedin the liquid phase of the MBR sludge and in the cake sludge on the membrane surface.According to the CLSM examination, BPC are free and independent organic solutes thatare different from biomass flocs and EPS and much larger than SMP (Sun et al., 2008).Concentration of total dissolved organic carbon (tDOC) was measured with a Shimadzuanalyser (TOC-5000). The difference in tDOC concentration between the sludge mixtureafter filtration through a 0.45 µm nitrocellulose membrane filter (HA, Millipore) and thepermeate was assigned to the colloidal fraction of BPC in the liquid phase of the sludgemixture suspension.81