The Application Of Sodium Alginate Compound With Polyaluminium Chlorid On Treating TiO₂ Nanoparticles In Water

With the rapid development of nanotechnology, people began to pay close attention to its harm to environment. Nano particles (NPs) will enter the water through the discharge, leakage and then it will be most likely to bind natural organic matter (NOM) to form "NPs-NOM" combined pollutant, which would enhance the toxicity of both. Aiming at the limitation of traditional coagulants which can not effectively remove the "NPs-NOM" combined pollutant, this study chosen the most widely used nano TiO2 as the research object to discuss the effect of PAC-SA compound on coagulation performance,floc formation process and floe characteristics in different organic fractions of coagulant water (humic acid, simulated water samples, secondary effluent water sample and the Xiaoqing River water sample) under different conditions.; In order to study the effects of PAC-SA on the subsequent membrane fouling, we selected HA-TiO2 simulation water to conduct the ultrafiltration(UF) experiment; At the same time, through the analysis of three dimensional fluorescence characteristics of organic matter to discusses the effect of TiO2 nano on the removal of organic matter in water. The main research contents and results are as follows:(1) In HA-TiO2 simulation water, PAC-SA composite coagulant can remove nano TiO2 effectively, the removal efficiency was obtained over 90%, the optimum dosage is PAC=6mg/L, SA=0.4mg/L. The DOC removal efficiency was increased by 10% in low dosage due to the adsorption bridging action of SA. And the formation of PAC-SA can make floc size bigger, growth rate faster, and better performance after the restoration, so that subsequent membrane fouling is reduced about 25%. Coagulation process can reduce the fluorescence intensity of humic acid samples, especially fulvic acid-like, soluble microbial by-product-like and humic acid-like; Compared with single dosing PAC, SA will make the fluorescence intensity of the coagulation effluent increase. Solution pHs have certain impact on coagulation performance, floe characteristics and membrane fouling, when pH> 6, the removal rate of HA-TiO2 increased by about 10%, floe size increased by 400 nm, membrane resistance reduction of about 30%. In addition, there were little effect on floe characteristics and membrane fouling under different B values conditions; Better performance, larger floes and less membrane fouling were shown in B=2.0.(2) In TiO2-secondary effluent water sample, the effect of two coagulant on water treatment was not very well, the highest was only 23%, but the T1O2 removal efficiency is obtained over 90%the optimum dosage was PAC=8mg/L,SA=0.4mg/L. In the selected dosage range of PAC, the removal rate of DOC increased by 9%and the removal rate of T1O2 increased by 10%compared with dosing PAC. Coagulation process can reduce the fluorescence intensity of secondary effluent water sample, the addition of SA can increase the fluorescence intensity of water samples, but the PAC-SA compound coagulant has a better effect on the removal of the soluble microbial by-product-like.The effect of pH on coagulation performance and floe characteristics was evidently, when pH> 6, the removal rate of combined pollutant increased by about 7%, floe size increased by 350 nm.(3) In TiO2-Xiaoqing River sample, the coagulation result of DOC was similar to TKVsecondary effluent water sample, namely, the removal efficiency of DOC for PAC-SA was higher in the selected dosage range, the removal rate of DOC increased by 7%and the removal rate of I1O2 increased by 10%, the optimum dosage was PAC=8mg/L, SA=0.4mg/L. Coagulation process decreased the fluorescence intensity of DOM in Xiaoqing River, however, the fluorescence intensity would be increased when SA was added, this result was consistent with the results of other two water samples. The effect of pH on coagulation performance and floe characteristics was evidently; In the selected range of pH, the PAC-SA can make the removal rate of combined pollutant in water sample increased by about 6%; In addition, the strength factor (SJ) and recovery factor (RJ) under pH=7 and pH=9 can be increased due to the addition of S A.(4) For the three kinds of water samples, the effect of TiO2 concentration on DOC was different under different pH, and the effects were adverse in most cases; the concentration of DOC was lowest at pH=5 and highest at pH=9, however, there was little impact on fluorescence intensity under different pH; DOC concentration was not associated with fluorescence intensity.