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近年来,我国许多水体因富营养化引起蓝藻水华现象频发。除“三大湖”每年夏秋季都会暴发蓝藻水华外,很多中小型湖泊[1-2]、饮用水源水库[3-5]、观赏娱乐性湖泊[6-7]也相继发生了不同程度的藻类水华。而且由于我国存在水质性缺水问题,对水库供水的依赖逐年加剧,加之水库独特的自然环境特征与水文特征,使水库型水源地较天然河流更容易发生蓝藻水华[8]。此外,蓝藻具有能适应低光,易联合成群体[[9-10],且具有能调节细胞升浮的结构体——伪空胞[11]等特性。这些生理结构特点使蓝藻在水体中更易形成优势种。
饮用水源地发生突发性蓝藻水华时,可采取超声处理[12]、投加天然大分子有机物[13]、生物操纵[14]和生态调度[15]等物理、化学、生物或生态的方法进行应急处置,不同方法具有最佳应用条件和地域、时效等适用范围。饮用水源地具有环境敏感、影响供水安全等特点,选取蓝藻水华治理措施应满足快速、无二次污染风险等要求。综合采用天然无毒的黏土(或沉积物)和絮凝剂[16-17]是有效可行方法之一。此外,壳聚糖是从海洋虾蟹类提取的生物聚合物,絮凝效果好、无毒、易生物降解,被广泛应用于蓝藻水华治理[18-19]。聚合氯化铝(poly aluminum chloride, PAC)作为常见的无机高分子混凝剂,具有良好凝聚、絮凝效果[20-21]。
2019年5月,广西梧州市岑溪市赤水水库暴发蓝藻水华,危及饮用水安全。建立针对发生蓝藻水华的饮用水源应急处理处置方案,对于保障饮用水安全、维护社会稳定具有重要意义。本研究分析了赤水水库蓝藻水华暴发时水质理化指标和藻细胞密度垂向分布特征,研究了壳聚糖改性黏土、PAC强化混凝联用除藻效果以及最佳投量配比,以期为后续赤水水库等水源地水华应急处置提供技术储备,亦为类似饮用水源地水华应急处置提供参考。
湖库型饮用水源蓝藻水华应急处置模拟实验
Simulation study on emergency treatment of cyanobacterial bloom in drinking water reservoir
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摘要: 水源水体富营养化及造成的藻类水华是淡水生态系统面临的主要问题之一,严重威胁城市供水。以华南地区赤水水库为例,基于2019年5月暴发的蓝藻水华事件,开展了水库水质、蓝藻密度的监测分析及壳聚糖改性高岭土复合聚合氯化铝的应急除藻技术研究,确定了絮凝剂的最佳投加量并评估了除藻效果。结果表明: 水华暴发时取水口表层TN、TP浓度超过地表水III标准且水体主要限制性元素为磷,若集水区内磷的浓度继续增大,则水华暴发的频率继续增加;此次蓝藻水华的优势种为铜绿微囊藻,且垂向主要聚集在表层及水下5 m处,随水深的增加藻细胞密度逐渐降低,表层藻细胞密度高达6.87×108 cells·L−1;采用壳聚糖改性高岭土复合聚合氯化铝去除蓝藻效果较好,在改性黏土投加100 mg·L−1,聚合氯化铝投加10 mg·L−1时,1 h去除率约60%,且随着时间延长,去除率持续提高。改性黏土复合聚合氯化铝能在短期内使藻类沉降至水库底部,可应用于湖库型饮用水源蓝藻水华的应急处置。Abstract: One of the major problems in freshwater ecosystem that threaten urban water supply is eutrophication and algal blooms that caused by it. In this paper, cyanobacterial bloom happened in May 2019 in Chishui reservoir, a drinking water reservoir in south China, was taken as a typical case to study variation of water quality and cyanobacterial cell density, as well as the emergency treatment technology. During this cyanobacterial bloom case, an in-field experiment of emergency treatment by adding chitosan-modified-kaolin and polyaluminum chloride (PAC) was carried on to assess the treatment efficiency and the optimal dosage. Results showed that total nitrogen (TN) and total phosphorus (TP) concentrations in the surface layer exceeded level III of the national water quality standard, and eutrophication in the reservoir was controlled by phosphorus concentration. If the phosphorus concentration kept increasing, so as the frequency of cyanobacterial bloom. Microcystis aeruginosa was found to be the dominant species in this case, and the M. aeruginosa cells were mainly distributed within 5m below the water surface. The cell density in the surface was highest and reached 6.87×108 cells·L−1 and it decreased with increase in water depth. The efficiency of chlorophyll a removal by adding chitosan-modified-kaolin and PAC was satisfactory. The removal rate was up to 60% after adding 100 mg·L−1 chitosan-modified-kaolin and 10 mg·L−1 PAC in one hour, which increased with the extension of time afterwards. Algal cells can be precipitated into the bottom area of the reservoir in a short period of time by addition of chitosan-modified-kaolin and PAC. As such, this technology is suitable for emergency treatment of cyanobacterial bloom in drinking water reservoir.
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Key words:
- reservoir /
- cyanobacteria bloom /
- chitosan-modified-kaolin /
- poly aluminum chloride /
- emergency disposal
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表 1 正交实验因素与水平
Table 1. Factors and levels of the orthogonal test
mg·L−1 组别 因素取值 (A)改性黏土 (B)聚合氯化铝PAC 1 100 10 2 50 5 3 0 0 表 2 水华期取水口理化指标变化
Table 2. Physic-chemical parameters of water in the phases of the bloom
取样水层 pH DO/(mg·L−1) T/℃ 电导率/(μS·cm−1) SD/m TP/(mg·L−1) TN/(mg·L−1) NH3-N/(mg·L−1) CODMn/(mg·L−1) 表层 9.45 9.82 31.9 43.5 0.15 0.09 1.96 0.34 6.81 水深5 m 8.43 8.78 26.6 36.9 — 0.04 0.67 0.14 1.9 水深12 m 7.4 5.71 24.2 36.2 — 0.04 0.72 0.15 1.4 -
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