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随着经济的迅速发展,我国城市化进程加快,为保障供水,水库已逐渐成为众多城市的主要水源地。由于水库水一般浊度较低、停留时间较长易导致藻类繁殖,故会产生由藻类代谢产物引起的异味等问题,从而降低饮用水的品质[1],引发公众对饮水安全的担忧[2]。在我国,2-甲基异莰醇(2-MIB)引起的土霉味是饮用水嗅味问题的主要原因之一[3]。由于2-MIB嗅味阈值极低(4~10 ng·L−1)[4],且混凝、沉淀及过滤等常规处理工艺对其去除效果有限,往往需要投加粉末活性炭等深度处理工艺对其加以去除,这不仅会增加制水成本,而且会增加给水厂的运行管理难度。已有研究[5]表明,水库水源中的2-MIB主要由底栖丝状蓝藻生长代谢产生,包括颤藻、席藻等。近年来,日本[6]、美国[7]、中国湖北[8]等许多国家和地区都暴发了浮游型丝状蓝藻伪鱼腥藻产生2-MIB引起的土霉味问题。不同于常规的底栖产嗅藻,伪鱼腥藻细胞内具有伪空胞结构[9-11],能在一定程度上调节其在水体中的垂向位置,以获取适宜的光能与充分的营养盐,进而增加自身的竞争优势[12]。目前,关于伪鱼腥藻的研究相对较少[13-14],尤其是关于伪鱼腥藻和致嗅物质的昼夜与垂向分布规律及其驱动因素的研究鲜有报道。
本研究选取华东地区某水源水库为研究对象,该水库平均水深为4.3 m,最大水深为6.5 m,水力停留时间为2 ~ 3 d左右。该水库以东太湖为水源,后经太浦河流入水库。该水库近年来出现季节性嗅味问题,通过在库区及太浦河长期对比原位监测,解析了嗅味产生来源,识别了潜在产嗅藻种;同时在嗅味高峰期间,开展了连续72 h的监测,分析了潜在产嗅藻的昼夜及垂向分布特征,并探讨了伪鱼腥藻与理化指标间的关系,以期为解决水源水库中典型嗅味问题提供参考。
某水源水库嗅味来源及潜在产嗅藻分布特征解析
Odor source and distribution characteristics of odor-producing algae in drinking water reservoir
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摘要: 华东地区某水源水库近年来出现季节性嗅味问题。为解析嗅味产生来源及其成因,于2018年4月至2019年12月对该水库上游以及库内水体进行长期监测。监测结果表明,2-甲基异莰醇(2-MIB)是主要的土霉味致嗅物质,伪鱼腥藻是该水库潜在产嗅藻种,且其主要为外源输入。相关性分析结果表明,伪鱼腥藻的生长与水温及水下光照(透明度、浊度)等有关。为进一步解析水下光照因素驱动下伪鱼腥藻在水库水体中的分布特征,在水库高嗅期间开展了72 h连续监测,重点分析了伪鱼腥藻昼夜与垂向分布特征。结果表明,在08:00,伪鱼腥藻往表层迁移,在10:00—14:00,表层密度达到最高值,白天在水体中呈现明显的垂向迁移特征,而夜晚在水体中各层的分布无明显变化,这进一步说明水下光照对伪鱼腥藻生长的重要性。以上结果进一步提升了对实际水体中伪鱼腥藻分布规律的认识,可为水源地中伪鱼腥藻导致的嗅味问题提供借鉴。Abstract: Taste & odor problems have been occasionally observed in a drinking water reservoir in East China. In order to analyze the source and cause of ordor fromation, specific investigation of this reservoir as well as the upstream has been performed from April, 2018 to December, 2019. The result indicates 2-methylisoborneol is the major musty odorant, while Pseudanabaena, mainly comes from the upstream, is the potential 2-MIB producer. The correlation analysis suggests water temperature, underwater light availability (water transparency, water turbidity) are the major drivers responsible for the growth of Pseudanabaena. A 72 hour-field study was performed in the reservoir during the odor period in July of 2018, aiming to identify the diurnal variation and vertical distribution of Pseudanabaena. The result shows the cells tend to move upwards to surface water from 08:00, reach the highest cell density in this layer during 10:00 and 14:00. Significant vertical migration of Pseudanabaena cells was observed along with solar irradiance changes in the daytime, while insignificant distribution variaitions in each layer of reservoir water occurs in night, further indicating the importance of light underwater for the growth of Pseudanabaena. The result enhanced the understanding of the distribution pattern of Pseudanabaena and provided a reference for the odor problem caused by Pseudanabaena in water reservoir.
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Key words:
- Pseudanabaena /
- 2-methylisoborneol /
- diurnal variation /
- vertical distribution /
- drinking water
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表 1 伪鱼腥藻与常规水质指标的相关性分析
Table 1. Correlation analysis of Pseudanabaena and regular water quality indicators
水质参数 Pearson相关系数 P 水温 0.115 4 0.065 2 电导率 0.306 4 0.000 0 溶解性总固体 0.306 7 0.000 0 盐度 0.306 3 0.000 0 溶解氧 0.166 6 0.007 6 pH 0.321 7 0.000 0 氧化还原电位 −0.251 0 0.000 0 浊度 −0.137 4 0.028 0 叶绿素a 0.311 3 0.000 0 氨氮 0.052 5 0.537 3 亚硝酸盐氮 −0.144 2 0.415 8 硝酸盐氮 0.041 5 0.626 5 透明度 0.289 2 0.000 1 采样点 0.110 2 0.069 7 总氮 0.307 5 0.458 7 总磷 0.221 0 0.598 8 耗氧量 −0.130 0 0.443 1 -
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