Diversification Of Extracellular Polymeric Substances (EPS) From Activated Sludge In Membrane Bioreactor (MBR) And Its Influence To Bioreactor Operation

A membrane bioreactor (MBR) combines the activated sludge process with a membrane separation process. Membrane Bioreactor is a comparably new type of biological reactor that has attracted great attention in recent years. The advantages offered by MBR over conventional activated sludge process (ASP) include a small footprint, reduced sludge production and so on. However, membrane fouling and high cost are main factors that prevent MBR from applied further. In this dissertation, submerged membrane bioreactor was used to treat municipal wastewater. Through collecting the operation data from startup from May 2006 to October 2007, the extraction of extracellular polymeric substances (EPS), diversification of EPS and its influence to bioreactor operation were studied.First, the optimum conditions and effectiveness of extraction of EPS from activated sludge in membrane bioreactor were studied under seven conditions, such as thermal, acid, alkaline methods. After giving overall considerations to the accuracy, simplicity, attraction efficacy and the damage to the sludge cell, it was concluded that both thermal treatment and EDTA bi-sodium treatment were effective according to the extraction of extracellular polymeric substances (EPS) from activated sludge in membrane bioreactor (MBR).Second, sampling data was spatial interpolated by Krieger interpolation method, and software Surfer 8.0 was applied to display the results straightly. Experimental results showed that: in level, the gross EPS was higher at both sides but lower in the centre lengthwise. The diversification trend of carbohydrates and protein, which were the main components, was the same. Nevertheless, the gross EPS was higher in the centre, decreased to both sides but increased when slightly far from the membrane module widthwise. In vertical, the gross EPS decreased with the increase of depth.Third, based on experimental data, the relationships of the diversification of EPS with aeration intensity, organic loading and sludge retention time (SRT) as well as their influences on sludge settleability were studied. Moreover, the accumulation of soluble EPS in MBR had adverse effect on sludge MLVSS/MLSS value and dehydrogenase activity, and the microbial metabolism activity was then restrained. The microbial metabolism products were main pollutants of mixture supernatant and effluent. Finally, through operation data, the influences of aeration intensity, sludge concentration and organic loading on microfiltration membrane fouling were explained in terms of membrane biological fouling. Accordingly, the range of optimum operation modes was obtained to lessen membrane biological fouling.