| The algae blooms caused by eutrophication have made the challenge to the drinking water treatment in the countries. Aside from the problems resulted from the excessive reproduction of algae, extracellular organic matter(EOM) yielded by them also threaten human health and increase the operating cost of water treatment plant. Thus, it should be paid more attention to the EOM removal. Coagulation is widely applied in the drinking water treatment. And it is interesting to study the removal efficiency and mechanisms of EOM by coagulation. The characteristics of coagulant will significantly influence the coagulation efficiency. Polyaluminum chloride(PAC) is the most commonly used inorganic coagulant, but its industrial preparation method has the defects that should be improved. In this study, PAC was prepared by fresh aluminum hydroxide gels. Its aluminum species distribution, stability and coagulation efficiency were analyzed, and the preparation condition was optimized. The effects of fresh aluminum hydroxide gels on the characteristic of PAC were also taken into consideration. PAC2.0 was applied in the treatment of dissolved extracellular organic matter(d EOM) and bound extracellular organic matter(b EOM).Their removal rates, removal mechanisms and roles in the algae treatment by coagulation were investigated. Besides, the interaction between them and PAC was studied as well. To confirm the coagulation efficiencies of d EOM, the study was carried out on the natural water treatment.The main contents and conclusions are as follows:①An alternative preparation method of PAC was presented in this paper, using fresh aluminum hydroxide gels as the aluminum source. In the preparation processes, aluminum hydroxide solid powder firstly reacted with sodium hydroxide under 100 oC, and the sodium aluminate solution was prepared. Then, the certain amount of hydrochloric acid was added into the sodium aluminate solution according to the desired basicity values. At last, PAC was prepared after the dissolution of fresh aluminum hydroxide gels. The prepared PAC2.0 had the highest Alb and Al13 content and the best performance in the treatment. But the properties of PAC were worse after increasing the basicity value. The preparation time was largely reduced with the increase of temperature after adding acid. However, it was more cost-effective for preparing PAC under the ambient temperature, and it is a potential preparation methodthat can be applied in the industrial scale. Extending the preparation time over the optimal time range decreased the Alb content. The moderate acid concentration was recommended in the PAC preparation.②In the preparation, adding the moderate fresh aluminum hydroxide gels increased the Alb content of PAC. In the aging period, the added fresh aluminum hydroxide gels increased Alb content of PAC at the initial phase, but Alb content rapidly reduced with extending the time since fresh aluminum hydroxide gels accelerated the aluminum hydrolysis. And the excessive fresh aluminum hydroxide gels and the long initial aging time would aggravate the decrease of Alb content. The performance of PAC was slightly worse due to the presence of fresh aluminum hydroxide gels, but the performance deterioration and the high residual aluminum concentration resulted from overdosing PAC was mitigated.③The d EOM and b EOM collected from the different culture time had the different organic matter concentration, composition and structure. The concentration of d EOM and b EOM often increased with the increase of culture time. The amino and the conjugation system of benzene were detected from d EOM and b EOM respectively. The b EOM possessed the wide range of molecular weight distribution that was not changed with the culture time. Conversely, the content of high MW organic matter in d EOM decreased in the death phase. The tryptophan-like, aromatic-like and soluble microbial product-like organic substances were always found in the b EOM while the component of d EOM changed with the culture time and the humic-like, fulvic-like and soluble microbial product-like substances were obviously discovered in the death phase. ④Compared with the d EOM treatment, the removal rate of b EOM was better and the dosage of PAC was less. There was a positive correlation between the removal of b EOM/d EOM and hydrophobic organic compounds. The removal rate of low MW organic matter was higher than that of high MW organic matter. The tryptophan-like and aromatic-like organic substances in d EOM and b EOM had the acceptable removal efficiencies. The removal rates of soluble microbial product-like organic substances were always different when the d EOM and b EOM collected from the different culture time. It represented that the functional groups, O-H, N-H, C-N and C-O, could complex with Al(III) well except C=N and P-H. ⑤The b EOM improved the coagulation performance of PAC in the algae treatment while the d EOM might react with Al(III) to form the complex, which impeded the coagulation. And after the treatment of algae-polluted water by coagulation, the d EOMwas the main residual EOM in the supernatant. Charge neutralization was not the main coagulation mechanisms in the treatment of algae, d EOM and b EOM. The small amount of d EOM was removed through the adsorption of Al13 and Al(OH)3(am). The generation of insoluble complex of Al(III)-b EOM, the bridge of Al13 and the adsorption/entrapment of Al(OH)3(am) and flocs contributed to the b EOM removal.⑥The turbidity was easily removed by PAC compared with dEOM in the natural water treatment. Although aromatic-like organic substances in the d EOM were partly removed after coagulation, the tryptophan-like and fulvic-like organic substances were still detected in the natural water. The d EOM removal in the natural water was related to the co-flocculation with algae and colloid particles. The removal rate of d EOM was increased via enhanced coagulation, adjusting p H of natural water and using compound coagulant of PAC-PDMDAAC. |
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