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随着经济的快速发展,城乡一体化的速度不断加快,导致城镇河湖水体中无机和有机污染物的输入量前所未有[1]。然而,随着城市排水系统和污水处理设施的升级改造,地表水水质得到了一定改善,但微污染水体仍普遍存在。污染江河水源表现为氨氮、总磷、色度、有机物等指标超出饮用水源卫生标准[2],或导致湖泊、水库水体的富营养化,造成水质恶化。水体富营养化因其对生态环境和人类健康的负面影响而引起了关注,例如藻类和其他浮游生物的快速繁殖、水质恶化、鱼类和其他生物的死亡以及饮用水污染[3-4]。但水体的自净能力是有限的,水体的污染物总量超过某限度时将会造成水体污染,需要借助修复技术实现污染水体的净化。近年来,已开发各种水体修复技术如曝气[5]、引水[6]、化学絮凝[7]、化学杀藻剂添加[8],用于修复各种污染类型的水体。然而,物理化学方法虽然能在一定程度上缓解水体污染,但在实际应用中表现出局限性。例如,曝气和引水的成本很高,还需要较大工程量[9]。添加化学药剂对污染河流的处理效果明显,但化学试剂带来的二次污染也是不可避免的[10]。为了不造成河湖水体进一步恶化,并改善区域环境,迫切需要具有成本效益的技术。与传统工程技术相比,植物修复技术因其高效和生态友好的特性得到了广泛的研究[11-12]。
植物修复是指利用植物从环境中去除和积累污染物[13],包括利用植物来减轻、转移、稳定或降解土壤、沉积物和水中的污染物。根据近期对特定植物的研究,在污水处理设施末端过滤出的污染物,可通过植物进行净化和去除[14]。水生植物可以通过富集和自身生长的生物量累积作用,以及与微生物的协同修复,有效净化水体[15]。沉水植物植株整体生活在水中,各器官直接吸收养分[16];漂浮水生植物在光竞争中具有明显优势,通过迅速繁殖,其茎和根吸收营养[17]。此外,挺水植物根系发育良好,能有效吸收养分,同时为微生物提供良好的生长环境[18]。植物修复技术在水处理中研究包括水体中金属[19]、除草剂修复[20]等。不同的植物种类,如水葫芦 (Eichhornia crassipes) 、浮萍 (Lemna minor) 、水莴苣 (Pistia stratiotes) 、香根草 (Chrysopogon zizanioides) 和芦苇 (Phragmites australis) ,已用于污染河水的修复[21-22]。其中,水葫芦可以改善水质,减少总溶解性固体 (26%) 和磷酸盐 (33%) [23]。对比不同水生植物净化水质除机理方面,水葫芦、水莴苣、狐尾藻3种水生植物对氮和磷的去除主要依赖于植物吸附,水葫芦和水莴苣对氮的去除也与微生物硝化/反硝化密切相关[13]。以往研究多集中在水生植物对水体氮、磷的去除上,但关于不同挺水植物对水质净化效能及影响因素的研究相对较少[24],这在微污染水体植物修复中至关重要。
水生植物生长受温度等环境因素影响,不同物种生长及水质净化的最佳温度不同[2]。当水温高于或低于最适温度时,会影响水生植物对养分尤其是氮、磷的吸收能力,影响其生长和水净化能力[25]。然而,很少有关于水生植物在不同温度下从微污染水体中去除污染物的研究,并探讨挺水植物净水效能及环境因子影响机制[26]。本研究旨在评价不同挺水植物对污染物去除效果,确定不同挺水植物配置模式,探讨不同温度下挺水植物系统对污染物去除效率。本研究结果可为挺水植物水质净化和微污染水体生态修复提供理论基础。
Simulation study on water purification of emergent plant floating island
- Received Date: 09/10/2023
- Available Online: 26/01/2024
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Key words:
- slightly polluted water /
- emergent plant /
- water purification /
- low temperature
Abstract: According to the actual needs of environmental treatment and ecological protection of surface water ecosystem, phytoremediation technology, as an ecological remediation technology with low cost and wide application range, needs to be systematically discussed for water purification function of aquatic plant types and allocation modes. In this paper, aiming at the water purification problem of constructed wetland in micro-polluted water, five emergent plants, Typha orientalis, Iris tectorum, Canna indica, Lythrum salicaria, Sagittaria trifolia, and their different configuration modes were used to study the water purification function. On the basis of screening the dominant plants for water purification, the pollutant removal efficiency at different temperatures was discussed. The results revealed that the removal rate of ammonia nitrogen (NH4+-N) by aquatic plants in 30 days was more than 95%. Canna and Lythrum groups had the highest removal rates of of total nitrogen (TN) and total phosphorus (TP), and the removal rates of TN were 60.2% and 57.8%, and the removal rates of TP were 66.3% and 73.2%. Sagittaria arrowhead felled into the water body due to withering of plants, which led to the release of nitrogen and phosphorus into the water body, with the release rates of 18.7% and 43.0%, respectively. Root decay, denitrification and total phosphorus release appeared in Iris group. In the combined plant experiment, the combination of Iris, Canna and Lythrum showed better purification effect on polluted water than the combination of Typha, Canna and Lythrum, which was suitable for wetland and other ecological restoration measures to control micro-polluted water. The study on water purification efficiency of Canna, a dominant plant for water purification, at different environmental temperatures showed that the average TN and COD removal rate decreased significantly at low temperature (5~10 ℃). Moreover, the removal efficiency of COD, NH4+-N, TN and TP in micro-polluted water at 20~25 ℃ was significantly higher than that in low temperature environment. The diversity of bacterial community in rhizosphere fillers of composite floating island plants in normal temperature environment was higher than that in low temperature environment. Proteobacteria was the dominant bacterium in normal temperature environment, while Chloroflexi was the dominant bacterium in low temperature environment.