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随着水产养殖业在全球范围内的快速发展,水产养殖尾水的产生量也日益增多[1]。由于水产饲料的高氮特征,导致养殖尾水呈高氮低碳的特点[2]。近年来,为改善水环境质量和促进水产养殖业的绿色发展,各地相继出台了严格的水产养殖尾水地方排放标准,倒逼养殖尾水的有效处理。现阶段,常用的养殖尾水处理技术包括人工湿地、生态沟渠、生态浮床和生物滤池等,尽管也取得了良好的处理效果,但均存在着占地面积大、处理效果不稳定等技术问题[3-4]。因此,寻求稳定、高效的养殖尾水处理技术迫在眉睫。
生物滞留系统(bioretention system,BS)是最佳的雨水管理设施之一,因其成本低且效果好,被广泛应用于城市雨水径流污染的治理[5]。目前,有关BS的应用研究主要集中于降雨径流处理,将其跨行业应用于养殖尾水的处理还鲜有尝试。由于降雨径流和养殖尾水在水质特点和排放规律方面具有一定的匹配性,如,两者水质均呈现出高氮低碳和水量为间歇排放的特点,这使得将BS技术应用于养殖尾水处理具备了可能性。BS的脱氮性能与其填料的组成和构造形式密切相关[6-9]。如正置的BS技术主要以强致密性的介质土层置于上层,而将较好透气性的砂质过滤层及碎石排水层置于底层,通过介质的过滤、吸附、微生物作用和植物吸收达到污染物去除的效果,但仍然存在脱氮效率不稳定等问题[9]。LI等[8]为解决上述问题,设计的倒置BS构造则是与正置相反,径流被上层砾石层存储并缓慢排出,滞留的水分阻碍了氧气的扩散,使得下层介质土层创造了更好的缺氧区,NO3−-N去除高于正置的28.6%~53.9%。近年来,国内外对于正置和倒置BS的脱氮效能已有研究,但用于养殖尾水处理的效能尚未可知,且缺乏足够的证据阐述其背后的作用机理。
胞外聚合物(extracellular polymeric substances,EPS)是以蛋白质为主要功能成分的微生物分泌物,其产生可视为微生物个体的粘合剂,是形成生物膜的核心[10]。EPS包含的氧化还原介质对BS的脱氮性能至关重要,如C型细胞色素和腐殖质等[11]。有研究表明,EPS储存的氧化还原介质在电子传输过程中可有效充当电子供体和电子受体(NO3−)之间的传递桥梁,这决定了电子穿梭的效率,最终影响反硝化脱氮性能[12]。此外,EPS浓度也是影响微生物反硝化的重要因素,如WANG等[13]研究发现EPS的额外添加提高了系统1.66倍的电子传递活性(ETSA),从而提高了19%~34%的反硝化效率。基于此,解析EPS和电子传递活性对于探究BS的脱氮机制意义重大。
为此,本研究设计并构建了正置和倒置2组生物滞留系统,在不同进水条件下探究了其处理水产养殖尾水的运行规律,并通过EPS及电子传递活性分析揭示了BS的构建方式对脱氮效能的影响,旨在为应用生物滞留技术处理养殖尾水提供参考。
生物滞留系统处理水产养殖尾水的效能和机制
Efficiency and mechanism of bioretention systems for aquaculture wastewater treatment
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摘要: 为探究生物滞留系统(bioretention system,BS)对水产养殖尾水的处理效能,设计并构建倒置(inverted bioretention system,IBS)和正置(control bioretention system,CBS)2组生物滞留系统,在不同进水条件下比较了2种BS构建方式的运行效能,通过胞外聚合物(EPS)、三维荧光光谱和电子传递活性(ETSA)等方法阐述了不同构建方式下BS的脱氮机制。结果表明:在不同进水条件下IBS的处理效能优于CBS,当运行间隔周期为1 d时,IBS的TN和NO3−-N去除率分别达到71.79%~82.00%和68.70%~85.84%,平均去除率比CBS分别高出10.65%和15.89%。CBS和IBS的TN和NO3−-N去除率随进水负荷的增加呈先升高后稳定的趋势,TP波动最小,去除率均稳定在97.04%~99.22%。构建方式对EPS的组分无明显影响,但对EPS含量和ETSA影响显著。IBS的构建方式可促进微生物分泌更多的EPS,其中EPS的多糖(PS)和蛋白质(PN)含量分别比CBS高出66.89 ug·g−1和603.24 ug·g−1,并且IBS的酪氨酸、色氨酸和微生物代谢产物明显高于CBS;此外,与CBS的ETSA为(0.47±0.07) ug·(g·min)−1,相比IBS提高了0.35 ug·(g·min)−1。以上研究结果为应用生物滞留系统技术处理养殖尾水提供参考。Abstract: In order to explore the treatment efficiency of aquaculture wastewater by bioretention system(BS), two groups of the inverted bioretention system(IBS) and control bioretention system(CBS) were designed and constructed, and their efficiency was compared under different influent conditions. The denitrification mechanism of BS under different construction methods was analyzed through extracellular polymer(EPS), three-dimensional fluorescence spectroscopy and electron transport activity(ETSA). The results showed that the treatment efficiency of IBS was better than that of CBS under different influent conditions. When running interval period was 1d, the TN and NO3-N removal rates of IBS reached 71.79%~82.00% and 68.70%~85.84%, respectively, and the average removal rates were 10.65% and 15.89% higher than those of CBS, respectively. The TN and NO3-N removal rates of CBS and IBS increased first and then stabilized with the increase of influent load, while TP fluctuated slightly, and the removal rate was stable at 97.04%~99.22%. The construction method had no significant effect on the composition of EPS, but had a significant effect on EPS content and ETSA. The construction of IBS could promote more EPS secretion by the microbial, of which the polysaccharide(PS) and protein(PN) contents in EPS were 66.89 ug·g−1 and 603.24 ug·g−1 higher than CBS, respectively, and the tyrosine, tryptophan and microbial metabolites of IBS were significantly higher than CBS. In addition, IBS improved by 0.35 ug·(g·min)−1 compared to CBS's ETSA of (0.47±0.07) ug·(g·min)−1. The results provide a theoretical reference for the application of bioretention system technology to treat aquaculture wastewater.
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表 1 进水质量浓度
Table 1. Influent mass concentration
mg·L−1 类型 TN NO3−-N NH4+-N NO2−-N COD TP 池塘水(低) 7.72~8.78 5.99~6.11 1.37~1.74 0.12~0.33 92~99 1.93~2.35 循环水(中) 19.10~20.48 10.48~13.55 2.54~3.80 0.28~0.43 204~236 2.62~5.13 循环水(高) 27.13~30.15 18.65~21.46 2.32~4.67 0.34~0.9 248~308 6.03~7.8 -
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