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水资源短缺是一个全球性环境问题,影响着数亿人的正常生产生活. 再生水因其可靠、经济等优点,成为城市非常规水源而被广泛应用. 数据显示,在美国加利福尼亚州,较早就有约25%再生水作为各类湖泊生态用水的补充;在日本大阪,大约50%的再生水被用于城市景观水景. 随着“海绵城市”建设的全国推进,以污水处理厂尾水或再生水为补给水源的城市湿地公园近年来在国内也大量涌现,在生态生境、城市景观、游憩活动等多种生态经济服务中发挥着重要的作用. 数据显示中国约有50%再生水用于补充城市水体,约13.2%城市水景受再生水补充[1]. 但是,由于再生水中COD、总氮和总磷等污染物通常较高(高于《地表水环境质量标准GB3838-2002》中限值),使受再生水补给的水体面临富营养化污染问题.
为减轻再生水带来的污染,需要采取水污染控制技术来削减或控制污染. 其中,底泥疏浚可以消除内源性污染,但工程量较大,经济成本较高[2]. 絮凝剂等化学药剂的投加,可以去除氮磷等营养物,但易导致二次污染[3]. 水生植物修复方法不但能够通过植物和微生物代谢作用转化去除水中污染物,还有助于重新构建的水生生态系统平衡,促进氮、磷等物质的长期循环,具有成本低、环境友好、兼具景观效果等特点,因而受到广泛应用[4]. 虽然水生植物对氮、磷和有机物等具有良好的去除能力,但是修复效果往往受到许多外界条件的影响和限制[5]. 例如,水生植物生长的最佳水温为15—28 ℃,过高的水温不利于水生植物向水体复氧,从而使夏季表现出较差的修复效果[6]. 另外,pH值、光照条件和种植密度等都会影响水生植物修复性能. 现阶段,大多数对植物修复效能的研究均在实验室模拟装置内进行,很难对实际场景中的植物修复措施进行复现. 而再生水的水质特征是其有机污染物多为难降解有机物,氮磷浓度偏高,碳源不足. 对于以再生水作为补给水源的水体,对实际应用中的效果以及季节变化等影响并不了解. 水生植物能否在城市水体应用中起到良好的恢复水质的效果仍然不太清楚.
圆明园是一个著名的遗址公园,由于北京所面临的缺水问题,该园自2007年以来一直以再生水作为唯一的补水水源,年补水量约900万m3[7]. 为净化水质,园区持续多年采取了水生植物修复措施. 本研究选择圆明园作为对象,研究了再生水进入园区后,水体中COD、TP和TN等污染物的时空分布与变化,结合水体理化性质和水生植物生长状况,分析了水生植物对水体的修复效果与机制,以期为再生水的实际应用提供理论支撑.
水生植物修复改善再生水补给水体水质效能的研究
Effect of aquatic plants on water quality restoration in the urban water bodies recharged by reclaimed water
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摘要: 再生水已成为缺水地区的重要非常规水源. 但是,再生水中的营养性污染物质往往高于地表水水质要求,易导致受纳水体出现富营养化污染. 本文选取了一个仅以再生水为水源补充的城市水体进行研究. 根据水生植物生长状况,划分为修复程度不同的区域,使用普通克里金插值法获取了再生水流入后的总氮(TN)、总磷(TP)、化学需氧量(COD)等污染物的空间分布与变化,分析了水生植物修复的效能与机制. 结果显示,水生植物能够在再生水流入下游之前削减57.9%的TN,且在春、夏季修复效果更加突出. 植物修复区域最高削减了78.3%的TP,挺水植物区对TP的修复效果较为稳定. 但受高温影响,沉水植物区对TP的削减率从最高的63.4%下降到了夏季的6.61%. 由于沉积物的持续释放,植物修复对COD的去除效率比对TN和TP低,仅在沉水植物区表现了相对较好的修复效果.Abstract: Reclaimed water (RW) has become an important unconventional water source in water-scarce areas. However, the nutrient pollutants in RW are higher than the limits in the standard of surface water quality, which lead to the eutrophication pollution in the waterbody recharged by RW. In this study, an urban waterbody using RW as the sole water source was selected as a case. The waters were divided into areas with different phytoremediation degrees according to the growth status of aquatic plants. The spatial and temporal variations of pollutants including total nitrogen (TN), total phosphorus (TP) and chemical oxygen demand (COD) after the inflow of RW were obtained by using the common Kriging interpolation method. The efficiency and mechanism of phytoremediation were analyzed. The results showed that the replenishment of RW was a crucial reason for TN and TP pollution. Aquatic plants reduced 57.9% of TN at the highest level before the RW flows downstream, and the remediation effect was more prominent in spring and summer. The highest reduction rate of TP in phytoremediation area was 78.3%. The reduction rate of TP in the area with submerged plant decreased from the highest 63.4% to 6.61% in summer due to the high temperature, while that of emergent plant on TP was relatively stable. Due to the continuous release of sediment, the removal efficiency of COD was lower than those of TN and TP, and the remediation effect was relatively outstanding only in submerged plant areas.
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表 1 主要植物修复区域各季节总磷去除效率
Table 1. Removal efficiency of total phosphorus by season in major phytoremediation areas
修复区域
Phytoremediation area主要植物类型
Main type of aquatic plants总磷去除效率 /%
Removal efficiency of total phosphorus春
Spring夏
Summer秋
Autumn冬
Winter14—15号点 挺水植物 78.3 34.4 72.4 70.9 18—21号点 沉水植物 43.4 6.6 57.2 52.4 28—30号点 挺水植物 63.4 34.6 45.8 65.8 -
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