MMBR system has been suggested as a promising system to resolve harvesting problems induced from low settling efficiency of microalgae. And recently, a lot of research on reducing fouling at the MMBR system has investigated focused on EPS in many cases. EPS of microalgae mainly consists of polysaccharides and protein components, and is produced through photosynthesis and nitrogen-carbon metabolic pathways. Especially, P-EPS is one of major compounds which occur membrane fouling phenomenon, as its hydrophobic protein components cause floc formation and cake layer accumulation. And it is already known that almost every microalgae can metabolize P-EPS or Chl-a when nitrogen sources as a substrate is insufficient or exhausted situation. With the above backgrounds, uptake rates of P-EPS or Chl-a by Scenedesmus quadricauda according to the type of carbon source and nitrogen concentration were evaluated in order to verify correlation between carbon source vs P-EPS production, and indeed Scenedesmus quadricauda uses P-EPS or Chl-a when the amounts of nitrogen sourc es in the feed is not satisfied. As a result, it was shown that P-EPS and Chl-a production were increased proportional to nitrogen concentration under organic carbon condition. And especially, the amo unts of P-EPS and Chl-a in the cell were diminished with the nitrogen source becomes insufficient or exhausted. Because P-EPS accelerates fouling at the MMBR system, P-EPS degradation by Scenedesmus quadricauda in order to get nitrogen source may contribute to reducing fouling. About a affects of N-consumed Chl-a to the MMBR fouling, more survey is needed. On the contrary, considering the purpose of MMBR system of this study, i.e. harvesting useful high value microalgae efficiently feeding adequate industrial process wastewater, it seems like difficult to maintain satisfied metabolic activity and to harvest with high yield rate using nitrogen-poor MMBR feed.

In general, trans-membrane pressure (TMP), flux, filtration resistance are used as indicators to evaluate the degree of fouling in MBR. However, they have limitations in determining the level of EPS generation, which is known as an important factor of fouling. Therefore, a new evaluation method is required to monitor the amount of EPS generation. In this study, the applicability of capillary suction time (CST), which is used to measure the dewaterability of sludge, was evaluated as an indirect fouling evaluation index. Statistical analysis was performed to evaluate the effect of EPS on CST, and to determine whether EPS has high similarity with representative fouling evaluation indicators and CST, and quantitatively compared them. As a result, the correlation coefficient between CST and bEPS was 0.7988, which was higher than the correlation coefficient between filtration resistance and bEPS. Since bEPS is a major factor inducing fouling by affecting the formation of the cake layer, it was evaluated that CST, which has a high correlation with bEPS, is suitable to represent EPS. In addition, it was evaluated that the correlation coefficient between filtration resistance and CST was high as 0.7187, which could be used as a fouling evaluation index.