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近年来,不少湖泊、水库水体都存在不同程度的富营养化现象。富营养化水体爆发“水华”现象带来的藻类大量繁殖使水质恶化,严重威胁着饮用水水质的安全和人类的健康[1]。铜绿微囊藻 (microcystis aeruginosa) 作为最常见的蓝藻之一,是我国富营养化水体中最具生长优势的藻种[2]。由于藻类具有密度小、电动电位低等特点,可以稳定存在于水中,去除藻类难度较大,严重影响了水处理的效率[3]。目前藻类去除方法主要包括物理法、化学法和生物法3类,混凝是最为常见的化学除藻方法之一。
原水水质是影响混凝效率的主要因素之一。原水中包含的天然有机物 (natural organic matter, NOM) 主要由2部分构成,一类是腐殖质包括腐殖酸、富里酸等,大约占水中溶解性有机物50 %以上,其中腐殖酸占腐殖质总量的50%~80%;另一类是非腐殖质,如蛋白质、糖类、木质素等,大概占有机质总量的20%~40%[4]。NOM的质量浓度和化学组成会影响混凝效率和混凝后絮体形态[5]。腐殖酸和蛋白质常被当作典型NOM物质来进行研究[6]。在含藻水体中,水中NOM会与藻类有机物抢夺混凝剂,从而影响混凝效果及絮体的形成。KIM等[7]和CHOW等[8]研究发现混凝工艺中,疏水性的有机物较亲水性有机物更易被去除。MATILAINEN等[9]研究发现铁盐或铝铁混合盐能去除95%的大分子有机物,而仅有10%的相对分子质量小于1 kDa的小分子有机物能被去除。雷青等[10]研究发现腐殖酸较富里酸更容易被混凝药剂去除,水中腐殖酸和富里酸质量浓度较大时会影响水中藻细胞的去除。刘艳静[11]探究了腐殖酸和牛血清蛋白对混凝效果和出水余铝的影响。苏航等[12]探究了水中有机物对混凝的影响及无机絮凝剂的使用。但目前较少有文献研究NOM存在时对藻类混凝效果的影响。
以含铜绿微囊藻的水体作为研究对象,以牛血清蛋白 (BSA) 和腐殖酸 (HA) 为NOM的代表物,通过改变BSA与HA的投加量来调节水中有机物质量浓度,探究了有机物种类和质量浓度对含藻水体混凝效果的影响,结合水体有机物去除和絮体形成特征进一步分析影响机理。并探究不同水质下较优混凝药剂投加量,以期为含不同有机物源水或源水有机物含量波动状况下混凝除藻工艺提供参考依据,优化混凝工况,保证出水水质。
不同有机物对含藻水体混凝效果和絮体特性的影响
Effects of different organic substances on the coagulation effect and floc properties of water containing algae
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摘要: 为了解不同有机物对含藻水体混凝过程的影响,以含铜绿微囊藻水体作为实验对象,考察牛血清蛋白(BSA)和腐殖酸(HA)2种有机物及其质量浓度对含藻水体浊度、藻类有机物的去除效果以及絮体形成、破碎、再絮凝的影响。结果表明,少量的BSA对混凝反应起促进作用,当BSA的投加量超过1 mg·L−1转为抑制作用,因为投加量升高时,BSA抢占混凝剂活性位点,抑制混凝反应。HA不利于混凝反应的进行,因为HA中的官能团优先与混凝剂结合,从而导致混凝效果变差。提高混凝药剂投加量可缓解有机物质量浓度增加对混凝效果的影响。当BSA投加量为5 mg·L−1,PACl投加量为0.06 mmol·L−1时,能达到出水浊度小于1 NTU,藻细胞去除率大于90 %的混凝效果,HA添加量为5 mg·L−1,PACl投加量为0.12 mmol·L−1时,也能达到相同的混凝效果。混凝更容易去除分子质量较大的BSA和HA,而对小分子亲水性有机物的去处效果较差,如藻类有机物或HA中小分子有机物。少量的BSA和HA增加了混凝絮体的生成速率和初始粒径。本研究结果可为天然水体混凝除藻工艺优化运行提供参考。Abstract: In order to understand the influence of different organic substances on the coagulation process of algal water, this study took the water containing Microcystis aeruginosa as the experimental object, and investigated the influence of two kinds of organic substances, bovine serum albumin (BSA) and humic acid (HA), and their mass concentrations on the turbidity of the algal water, the removal of algal organic matter, and the formation of flocs, fragmentation, and re-flocculation. The results showed that: 1) a small amount of BSA promoted the coagulation reaction, and when the dosage of BSA exceeded 1 mg·L−1, it turned into an inhibition, because when the dosage was elevated, the BSA seized the active sites of the coagulant and inhibited the coagulation reaction. 2) HA was detrimental to the coagulation reaction because the functional groups in HA preferentially bound with the coagulant, which led to the deterioration of coagulation effect. 3) Increasing the dosage of coagulant could alleviate the effects of organic matter mass concentration and floc formation. The dosage can alleviate the effect of increasing organic mass concentration on the coagulation effect. When the dosage of BSA was 5 mg·L−1 and the dosage of PACl was 0.06 mmol·L−1, the coagulation effect of effluent turbidity less than 1 NTU and algal cell removal rate more than 90% can be achieved, and the same coagulation effect can be achieved when the dosage of HA was 5 mg·L−1 and the dosage of PACl was 0.12 mmol·L−1. 4) Coagulation was more likely to remove molecular weights BSA and HA, while it was less effective in removing small hydrophilic organics, such as algae organics or small molecule organics in HA. 5) Small amounts of BSA and HA increased the generation rate and initial particle size of coagulated flocs. The results of this study can provide a reference for the optimal operation of coagulation and algal removal processes in natural waters.
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Key words:
- source water quality /
- organic matter /
- coagulation /
- microcystis aeruginosa /
- floc properties
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表 1 不同BSA的含量下絮体的特性
Table 1. Characteristics of flocs at different BSA contents
BSA投加量/(mg·L−1) 强度因子/% 恢复因子/% 破碎前分形维数 破碎后分形维数 再絮凝分形维数 0 47.94 55.09 1.86 2.29 2.19 1 62.69 62.96 2.03 2.30 2.24 3 52.38 47.98 2.15 2.34 2.28 5 56.16 51.01 2.24 2.35 2.31 表 2 不同HA的含量下絮体的特性
Table 2. Characteristics of flocs at different HA contents
HA投加量/( mg·L−1) 强度因子/% 恢复因子/% 破碎前分形维数 破碎后分形维数 再絮凝分形维数 0 47.94 62.96 1.86 2.29 2.19 1 50.10 73.75 2.13 2.31 2.25 3 35.40 53.68 2.23 2.36 2.31 5 44.72 30.29 2.15 2.40 2.42 -
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