| Based on the previous researches on Al13species, coagulation behavior and efficiency of Al13were investigated in this study. Meanwhile, the floc characteristics formed by Al13, including floc size, strength, re-growth ability and fractal dimension, were systemically studied. Additionally, on the basis of previous studies on ultrafiltration technology, Al13was applied in coagulation/ultrafiltration hybrid process, and its effects on water quality and membrane fouling were evaluated. The main research and conclusions are as follows:1. Simulated dye wastewater, humic acid (HA) solution and the Yellow River water were coagulated by Al13species. The decolorization efficiency as well as turbidity, UV254and DOC removal efficiencies were measured to evaluate the coagulation behaviors of Al13. The results showed that:at low dose, pre-hydrolyzed Al13with high positive charge could keep stable after addition into the coagulation system and contribute to effective charge neutralization and thus higher efficiencies compared with A12(SO4)3and PACl. At high doses, besides charge neutralization, bridging and sweep mechanisms caused by Al13aggregates and amorphous precipitates also played important roles in Al13coagulations and the coagulation efficiencies of Al13were similar with those of other Al-based coagulants, Al2(SO4)3and PACl. Al13presented more stable coagulation behaviors and efficiencies than Al2(SO4)3and PACl when pH of water sample varied. Al13could better remove the small hydrophilic natural organic matters than PACl in the Yellow River water treatment.2. Using light transmittance pulse testing technology and laser light scattering technology to monitor the dynamic flocs during coagulation. Floc properties were assessed by measuring floc d50and determining the strength factor, recovery factor of flocs. The results showed that:compared with other Al-based coagulants, Al13could react immediately after addition into the coagulation systems and the flocs grew fast. Additionally, the flocs formed by Al13had stable properties when exposed to various pHs. For simulated dye wastewater, Al13contributed to smaller and denser flocs with better settling than PACl at the same dose. Flocs formed by Al13had better recovery abilities than those formed by PACl due to the better charge neutralization of Al13. For HA samples, Al13contributed to larger flocs than PACl at lower doses; while PACl flocs were larger at higher doses. The sequence of floc size in the Yellow River water treatment by Al-based coagulants was as follows: Al2(SO4)3>PACl>Al13. Flocs formed by Al13were stronger and had better recovery abilities than those formed by other aluminum coagulants in both HA and the Yellow River water treatments.3. Floc fractal structures formed by various Al-based coagulants in HA water and the Yellow River water treatments were measured using small-angle laser light scattering (SALLS). The results showed that:at acidic ambience, aggregates formed by Al-based coagulants were compacter and denser than those formed at alkaline pH. Al13contributed to flocs with larger fractal dimension (Df) than PACl under the same coagulation conditions. The Df of flocs increased continuously during the whole coagulation process. Breakage of flocs could improve floc fractal structure at acidic pH while this effect was not so evident at alkaline pH. Compared with PACl coagulation, the increase of floc Df caused by floc breakage was more evident in Al13coagulation.4. HA solution was coagulated with two dosing methods:1-shot dosing and2-times dosing methods. The coagulation efficiencies and mechanisms by these two dosing methods were evaluated through the measurements of UV254and zeta potentials. The experimental results showed that:at the same total dose with1-shot dosing,2-times dosing could increase the removal efficiency of HA. The additional Al13dosed at the end of breakage phases displayed charge neutralization, adsorption, bridging and sweep mechanisms, which could apparently improve the recovery abilities of broken flocs. The additional Al13dose near the isoelectric point contributed to the flocs with best recovery abilities and highest HA removal efficiency. Proper additional dose of Al13could improve the floc fractal structure. Compared with Al13, PACl had less positive charge and thus the charger neutralization of additional PACl was weaker and the main coagulation mechanisms of additional PACl were adsorption, bridging and co-sedimentation, which had negative effect on floc fractal structures. For both Al13and PACl, the2-times dosing could alleviate the damage of high shear on flocs.5. Al13was applied in the coagulation/ultrafiltration hybrid processes to treat HA solution, and its effects on HA removal and membrane fouling were evaluated by measuring UV254removal and flux declines, respectively. The results indicated that:HA removal efficiency treated by coagulation (sedimentation)-ultrafiltration and coagulation-ultrafiltration hybrid processes with PACl and Al13were similar. Al13contributed to higher HA removal efficiency at low doses. In coagulation (sedimentation)/ultrafiltration process, feed water pre-coagulatd by Al13caused smaller total resistance and thus less flux decline than that coagulated by PACl; while in coagulation/ultrafiltration process, the feed water treated by Al13caused larger adsorption and cake layer resistances when compared with those coagulated by Al2(SO4)3and PACl, and thus Al13coagulation effluent caused the least ultrafiltration flux. The flux changed least when pre-generated flocs by Al13were exposed to higher shears; while the flux of Al2(SO4)3effluents fluctuated most with the increased shears during coagulation unit. The membrane flux decreased with the increasing of breaking shear. Long breaking time could lead to larger cake layer resistance and smaller membrane flux. The flux caused by Al2(SO4)3effluents decreased most evidently by the prelonged breaking time during coagulation; while that caused by Al13was almost unaffected by the breaking time.6. PACl-Si and Al13-Si were applied in the coagulation/ultrafiltration process, and their effects on ultrafiltration were compared with those by PACl and Al13. The results proved that:compared with PACl and Al13, PACl-Si and Al13-Si contributed to flocs with larger sizes and strength but weaker recovery abilities and fractal dimensions. As a consequence, the feed water pre-coagulated by PACl-Si and Al13-Si could decrease the adsorption and cake layer resistances and thus higher membrane fluxes. Additionally, the addition of pSi reduced the differences bewteen floc properties generated by Al13and PAC1in terms of floc sizes, strength, recovery abilities and fractal structures. The gap between fluxes caused by PACl-Si and Al13-Si coagulation effluents was rather limited.
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