The Development Of New Sodium Alginate Composite Coagulant And The Control Study For Membrane Pollution

Coagulation/flocculation is a widely used process for particle in water and wastewater treatment. And the removal of colloids and dissolved organic matter by coagulation and flocculation is a widely employed treatment process. In order to ensure the safely of drinking, realize water reuse and improve the coagulation-ultrafiltration efficiency. In this study, active blue K-GL (active blue14), disperse yellow RGFL (disperse yellow23) and humic acid (HA) were selected as organic matters, and a series of conventional coagulants composite sodium alginate (SA) were used to treat the test waters containing organics. In the above conditions, the effect pH on the efficiency of coagulation was investigated and the floc size, strength and reversibility were obtained by on-line monitor of coagulation using PDA2000and Mastersizer2000. In the coagulation optimized conditions, three test waters respectively treated in in coagulation-ultrafiltration process and preliminary studied the new sodium alginate composite coagulant effect on membrane flux and membrane fouling. The main conclusions are as follows:(1) A series of conventional coagulants composite SA were used to treat the printing and dyeing test wastewater, different coagulants acomposite sodium alginate had different decoloring effects and the treatment effect of aluminum salt was better than physico-chemical process. Compared to PAC, PAC/SA had a better effect in in a wide range of dosing quantity (the mass ratio of SA composite PAC from1:10to1:5). When the dose of PAC and SA respectively was lOmg/L and lmg/L, the decolorization rate reached a maximum in treating active blue K-GL. For disperse yellow RGFL, the better ratio of SA composite Al2(SO4)3was from2:13. The optimal dose of Al2(SO4)3and SA was6.5mg/L and1mg/L. In the acidic conditions, charge neutralization was the main mechanism, but decoloring effect is not apparent; In the acidic conditions, electricity and neutralizing action is the main coagu-flocculation mechanism, but decoloring effect is not apparent; In a neutral and alkaline conditions, adsorption and sweep and bridge is main mechanism. SA could enhance the adsorption of bridge role, which improve the rate of decoloring.(2) In printing and dyeing teat water, compared to the conventional coagulant, More compact and larger flocs can be obtained by the new sodium alginate composite coagulant, the growth rate of flocs was much faster, strength and recovery ability of flocs were evidently improved. The effect of pH on floc was evidently, floc size changed obviously as pH increased. Smaller flocs were formed at acid ragion, while strength and recovery ability of flocs was better at alkaline ragion. The optimal pH is6.(3) Compared to PAC, PAC/SA had a better effect in turbidity removal in a wide range of dosing quantity, the mass ratio of SA composite PAC ranges from1:20to3:10. The effect in UV254removal was not obviously. The optimal dosing quantity of PAC and SA respectively was6mg/L and0.3mg/L. The effect of pH on coagulation effect was evidently, When pH=6, the effect is the best.(4) In HA test water, compared to PAC, More compact and larger flocs can be obtained by the new sodium alginate composite PAC coagulant, the growth rate of flocs was much faster strength and recovery ability of floes were evidently improved. Due to the effect bridging of sodium alginate, the flocs obtained by t sodium alginate composite PAC was more flocculant close-grained and the strength and recovery ability of flocs were evidently improved when flocs was broken by shear force.(5) In three kinds of test water, the new sodium alginate composite coagulant can increase membrane flux and reduce the effect of membrane fouling in the subsequent ultrafiltration technology process. When dealing with active blue K-GL simulation water, PAC and PAC/SA relative membrane flux were0.511and0.582, flux improve rate is7.1%; When dealing with dispere RGFL simulation water, Al2(SO4)3and Al2(SO4)3/SA relative membrane flux were0.525and0.568, flux improve rate is4.3%%; When dealing with HA simulation water, Al2(SO4)3and Al2(SO4)3/SA relative membrane flux were0.414and0.464, flux improve rate is5.0%%.The aboving results indicate that the new sodium alginate composite coagulant had significant effect in terms of enhancing coagulation efficiency and coagulation behavior, controling the ultrafiltration membrane pollution. The primary coagulation mechanism was confirmed. Further, this thesis lays fundamental basis for the developing of new sodium alginate composite coagulant and provides guidences for the practical application of it.