Study On Membrane Fouling Of Novel Nonwoven Bioreactor

In view of problem that membrane module in MBR is easy to block, in order to reduce project cost, save membrane clean and replacement cost, this experiment used nonwoven fabric combining operation mode of overflow which can minimize the transmembrane pressure, to study the effluent quality and fouling characteristics of nonwoven bioreactor under filamentous bulking and after sludge properties changed by dosing diatomite and kaolin+aluminum sulfate in it. Feasibilities of applying diatomite and kaolin combining aluminum salt to reduce membrane fouling in nonwoven bioreactor were explored and proved.The main results are as follows:During bulking sludge state and normal sludge state, average COD removal rates of nonwoven bioreactor were90.1%,91.4%respectively, average NH4+-N removal rates were91.9%,97.0%respectively, average effluent turbidities were1.33NTU,0.99NTU respectively. Average diameter and median diameter of bulking sludge floe were both larger than those of normal sludge floe. Average membrane flux decay rates during normal state and bulking state were4.87L·m-2·h-2,3.29L·m-2·h-2respectively. Fouling resistance accounted for9.88%of total resistance during normal state and consisted mainly of irreversible fouling resistance. During bulking state, fouling resistance accounted for7.67%of total resistance and consisted mainly of reversible fouling resistance, membrane fouling was slighter. SMP gross in mixed liquid was related to fouling resistance and its P/C was associated with reversible fouling proportion. The relation between loosely bound EPS in mixed liquid sludge and membrane fouling was similar to SMP. Sludge with more EPS could accumulate on membrane more easily, and the EPS that accumulated on membrane was mainly protein. EPS gross in mixed liquid sludge, EPS in membrane surface sludge and their P/C all had positive correlations to reversible fouling.By conducting jar tests, lg/L and0.2g/L were determined as the two concentrations which applied to diatomite dosing experiment. After dosing diatomite, supernatant and effluent COD both rised a little, average COD removal rates of blank group,1g/L group,0.2g/L group were90.73%,85.67%,85.25%respectively, average NH/-N removal rates were96.86%,94.40%,94.59%respectively, average effluent turbidities were0.81NTU,2.03NTU,1.71NTU respectively, diatomite revealed a noticeable inhibition of organics degradation ability of microbes. Particle size of diatomite was significantly smaller than the sludge particle, dosing diatomite had little effect on average diameter and median diameter of sludge floe. Average membrane flux decay rates of blank group, Ig/L group,0.2g/L group were3.63L·m-2·h-2、6.08L·m-2·h-2、3.45L·m-2·h-2respectively. Fouling resistance of blank group accounted for10.69%of total resistance, fouling resistance of1g/L group accounted for16.71%and consisted mainly of irreversible fouling resistance, fouling resistance of0.2g/L group accounted for9.59%and consisted mainly of reversible fouling resistance, dosing diatomite with low concentration reduced membrane fouling. Dosing low concentration of diatomite increased content of SMP and changed its P/C, but had little effect on SMP content and its P/C when added high concentration. After dosing high concentration of diatomite, LB-EPS contents and their P/C in mixed liquid sludge and membrane surface sludge were both increased significantly; after dosing low concentration, LB-EPS contents varied little and P/C of LB-EPS in mixed liquid sludge increased significantly. Dosing diatomite significantly reduced TB-EPS contents in both mixed liquid sludge and membrane surface sludge, the more dosing concentration, the lower TB-EPS content. TB-EPS contents in both mixed liquid sludge and membrane surface sludge had positive correlations to reversible fouling, the change of its P/C had no obvious law.By conducting jar tests,0.2g/L kaolin+0.1g/L aluminum sulfate were determined as the dosing concentration which applied to nonwoven bioreactor operation. Average COD removal rates of blank group(group A), aluminum sulfate control group(group B), experimental group(group C) were89.37%,87.90%,89.16%respectively, average NH/-N removal rates were97.36%,97.15%,97.99%respectively, average effluent turbidities were0.64NTU,0.56NTU,0.54NTU respectively. Dosing aluminum sulfate increased the size of sludge particle slightly, but sludge floe had not sufficient stability. After dosing kaolin+aluminum sulfate, because of the sludge floe stability enhanced so that difficult to deflocculate, particle size of sludge floe significantly increased. Average membrane flux decay rates of group A, group B, group C were3.83L·m-2·h-2,3.65L·m-2·h-2,2.94L·m-2·h-2respectively. Fouling resistance of group A accounted for10.95%of total resistance, fouling resistance of group B accounted for10.23%and consisted mainly of reversible fouling resistance, fouling resistance of group C accounted for7.30%and reversible fouling slightly more than irreversible fouling, membrane fouling had a notable decrease. After dosing kaolin+aluminum sulfate, both protein and polysaccharide content in SMP decreased significantly, LB-EPS content in mixed liquid sludge increased significantly, but LB-EPS content in membrane surface sludge decreased; meanwhile, P/C of LB-EPS in both mixed liquid sludge and membrane surface sludge increased significantly. Dosing aluminum sulfate decreased TB-EPS contents in both two sludges, dosing kaolin+aluminum sulfate decreased TB-EPS further; meanwhile, dosing kaolin and aluminum sulfate decreased the P/C of TB-EPS apparently. TB-EPS contents in mixed liquid sludge had a positive correlation to irreversible fouling as well.