Experimental Study On The Screening And The Effeciency Evaluation Of An Innovative Membrane Fouling Inhibitor

The problem of membrane fouling is one of the major factors that restrict the application of MBR. In my study, sorbents are added to the mixed liquor in the membrane bioreactor in order to change the chemical and physical characteristics and enhance the membrane filterability of the mixed liquor then meet the aim to control membrane fouling.Batch experiments were carried out to make studies on the effects on the production of EPS, particle size distribution (PSD) and the specific filtration resistance of the mixed liquor by adding two types of sorbents respectively such as kieselguhr clay and powder active carbon (PAC). Microscopical observations of the mixed liquor were operated and the mechanism of the improvement of membrane filterability was studied further. The optimal dose of each sorbent is calculated with the concern of the controlling efficiency both on EPS and PSD in our study circumstance. The effect on membrane filtration in optimal dose and the cost of the sorbents were compared and quantitively analyzed to determine the most suitable sorbent which will compose the membrane fouling inhibitor. In the coutinuous experiments, the effect on membrane fouling control of the sorbent was validated and the assistance of the addition of coagulant was examined. The major conclusions are as follows:In the batch experiments, with the addition of kieselguhr clay , the total amount of EPS and its components(protein and polysaccharide) in the active sludge decreased, the number of smaller floc of sludge(<4μm) declined and larger ones(>15μm) increased, the optimal dose of the kieselguhr clay was 1g/L; when it comes to the addition of PAC, the effect can be determined only after a certain period of cultivation, in most cases, this time confine should be 0-30 days, the effect on the PSD was obvious, the quantity of smaller floc (<10μm) decrease obviously, and the larger ones(>15μm) increase slightly, the optimal dose of thePAC was 0.5g/L.Based on the result of batch experiments and mathematics model on membrane fouling, the quantitive reduction of fouling resistance per unit dose of kieselguhr clay was calculated out as 6.11×10^-11m^-1/gl^-1and that value of PAC was 11.21×10^-11m^-1/gl^-1. Compared with their cost, the controlling efficiency on membrane fouling per unit expense was 7.63×10^-8 m^-1·l/yuan and that value of PAC was 1.87×10^-8 m^-1·l/yuan, hence, kieselguhr clay was selected as the major component of the membrane fouling inhibitor.In the continuous experiments, it was proved that the efficiency of kieselguhr clay in dose of 1g/L was better than dose of 0.5g/L, and the addition of coagulant can enhance the controlling efficiency on membrane fouling. With the addition of Al₂(SO₄)₃ in dose of 50mg/L and kieselguhr clay in dose of 1g/L, in the first 30 minutes, the flux decline to 82.96% of initial flux, which was 45.3% higher than that of blank reactor (the one without any addition of fouling inhibitor), and the decline slope was much slower; it was at the 300th minute that the flux became steady, which was later than the blank one; steady flux was 13.68% higher than that of e blank reactor, which was higher than the 10.21% of the reactor with only addition of kieselguhr clay. Hence the component of the inhibitor was 1g/L of kieselguhr clay and 50mg/L of Al₂(SO₄)₃.