环境水质学国家重点实验室知识库

        流域内水体外源输入得到有效控制后，内源会成为主要的污染输入源，威胁上覆水环境质量。白洋淀作为我国“华北之肾”，沉积物污染，尤其是氨氮 NH 4N 含量高 是现阶段面临的重要问题之一。 亟需在充分认识白洋淀沉积物 NH 4N 污染特征的基础上 开展 高 NH 4 N 沉积物原位 修复 工作，进而提升流域水环境质量 。 目前，针对沉积物 NH 4 N 污染的原位修复材料和技术并不成熟，生物炭作为一种绿色环保的沉积物修复材料具有较好应用前景。 故 本文以 探究生物炭原位覆盖技术对高 NH 4 N 沉积物的修复效果及其关键机理 ”为科学问题 以“问题导向 技术研发 效果验证 机理探索” 为 研究主线 开展相关研究并得到以下主要研究成果：
        （1) 白洋淀 沉积物 中 NH 4 N 含量 偏高 沉积物 NH 4 N 平均 释放通量 高达 8.71 mg·m 2 ·d 1 NH 4 N 内源释放 风险 较 高 。 白洋淀水体中 NH 4 N 和总氮TN 平均 浓度分别为 0.36 mg · L 1 和 2.22 mg·L 1 在 空间分布 上，水体中氮素浓度从 北到南 逐渐增加。 在 沉积物中 NH 4 N 和 T N 的含量范围分别为 48 235mg · kg 1 和 445 3499 mg · kg 1 平均值分别为 108 mg · kg 1 和 1809 mg · kg 1 90 区域 处于或高于 沉积物 TN 的中度污染等级（ 美国环境保护局（ EPA 制定 沉积物孔隙水中， NH 4 N 浓度 范围在 0.33 16.75 mg·L 1 之间 且沉积物 NH 4 N 潜在 释放通量 范围是 5.35 48.76 mg·m 2 ·d 1 。
        （2) 热解 温度 500 、 热解 持续时间 3 小时 、热解 气氛 3% 氧气 是 吸附 NH 4N 毛竹 生物炭 的 最优 制备条件 。 综合考虑 NH 4 N 吸附效果、 产率 、 耗能等多 因素， 筛选“ 毛竹为原材料， 3% 氧气 气氛下 500 热解 3 小时” 为 NH 4 N 污染控制 的 生物炭 制备 最优条件 。该条件制备的生物炭 对 NH 4 N 的 最大吸附容量 可达 13.79 mg·g 1 生物炭 含有 的 C H 、 COO 、 O=C=O 、 CH 2 、 OH 等官能团能够 通过阳离子交换作用提高 其 对 NH 4 N 的吸附效率 。
        （3) 生物炭 原位覆盖 对沉积物 NH 4 N 释放 的 抑制效果 明显 ，能够削减 沉积物 NH 4 N 释放通量 。 实验 室沉积柱 培养 发现，沉积物 覆盖 2 cm 生物炭 30 天后， 2 组平行实验上覆水中 NH 4 N 浓度分别 从 0.90 mg·L 1 降至 0.05 mg·L 1 ，从3.51 mg·L 1 降至 0.11 mg·L 1 沉积物 NH 4 N 释放 通量 明显 减小 分别从 8.28 mg·m−2·d−1降至 1.75 mg·m−2·d−1，从38.19 mg·m−2·d−1降至-0.49 mg·m−2·d−1。野外现场实验 发现 在 2 cm 生物炭覆盖 沉积物 30 天后， 沉积物 NH 4 N 释放 通量从 6.79 m g·m 2 ·d 1 降至 0.11 m g·m 2 ·d 1 生物炭 表现 出 对沉积物 NH 4 N 内源释放良好 的 抑制效果。
        （4) 物理阻隔 与 化学 吸附 影响界面 理化性质 和 再补给 过程”是 生物炭 覆盖抑制 沉积物 NH 4 N 释放 的 主要 机理 。 生物炭 覆盖 在沉积物表层 形成物理阻隔层， 对沉积物 NH 4 N 释放 具有 明显的 阻隔效应。 运 用薄膜扩散梯度技术（ DGT和薄膜扩散平衡技术（ DET 发现， 生物炭 可 以 从孔隙水中吸附 NH 4 N 改变沉积物 水界面 NH 4 N 浓度 梯度，对 NH 4 N 的内源释放 有较好 的抑制效果 生物炭改变了沉积物 pH 、 LOI 值 、 孔隙率 、 C/N 等理化性质，可 直接或间接 抑制沉积物中 NH 4 N 释放。 在野外围隔实验中， 生物炭覆盖 围隔中 覆盖层 孔隙水中R 值 C DGT NH 4 N C D E T NH 4 N ）为 0.3 表明该层孔隙水的 NH 4 N 再补给 能力较弱。
        （5) 生物炭 覆盖能够改变 参与 NH 4 N 循环的微生物群落结构 与 相关功能基因 的丰度 。 对 生物炭覆盖后 微生物 群落 结 构与功能基因 进行 分析 生物炭的引入能够提高沉积物中 Proteobacteria 、 Planctomycetes 、 Nitrospirae 等几 类 与氮循环相关 的 微生物相对丰度；提高 Nitrospira 、 Thiobacillus 、 Comamonadaceae 、Desulfobulbus 、 Hydrogenophaga 等几种 与 NH 4 N 转化 相关的微生物相对丰度。在 生物炭 覆盖 层中 amoA 、 amoB 、 nrfA 、 nirK 、 nirS 、 ureC 和 hzsB 基因 的丰度有很大 幅度 的提升。其中 amoB 、 nirS 和 ureC 基因的拷贝数与 16s 基因 的拷贝数比值 明显 升高 表明 生物炭不仅 能够提高 与 氮循环相关的微生物量，还能 提高amoB 、 nirS 和 ureC 基因的表相对丰度。
 

         After external inputs of water in the basin is effectively controlled, the endogenous pollution will become the main source of pollution input, threatening the quality of the overlying water environment. In Baiyangdian Lake BYDL )), as “kidney of North China” s ediment pollutio n, especially ammonia nitrogen NH 4 N pollution, wa s one of the important problems at this stage. Thus , it wa s urgent to fully understand the characteristics of NH 4 N pollution in BYDL sediments and to develop in situ control technology for the ecological re mediation of NH 4 N contaminated sediments thereby improving the water environment quality of the basin. At present, in situ re mediation materials and technologies for NH 4 N pollut ed sediment are not mature, and biochar has a good application prospect as a green environmentally friendly sediment remediation material. This paper t ook Investigate the effect of biochar in situ c apping technology on high NH 4 N sediments and its key mechanism as the scientific problem and "problem oriented , technology research and development , effectiveness verification , mechanism exploration" as the main line The main research results were as follows:
        (1) The NH 4 N content in the sediments of BYDL was high . The mean NH 4N release fluxes were 8.71 mg·m 2 ·d 1 t he risk of endogenous release of NH 4 N was high In the water of BYDL , t he mean concentrations of NH 4 N and total nitrogen( in the water samples were 0.36 and 2.22 mg·L 1 , respectively. The N concentrations in water gradually increased from the north to south of BYDL. In the sediments of BYDL , NH 4 N and TN were 48 235 mg · kg 1 and 445 3499 mg · kg 1 ,respectively. S ediment s at 90% of area s w ere in or above th e moderately contaminated class defined in US Environmental Protection Agency EPA) T N pollution standards.In the porewater of BYDL, concentrations of NH 4 N were from 0.33 to 16.75 mg·L 1 NH 4 N fluxes were 5.35 48.76 mg· m 2 ·d 1
        (2)The optimal conditions for the preparation of Phyllostachys pubescens BC were pyrolysis temperature 500 ℃℃, pyrolysis duration 3 hours and pyrolysis atmosphere 3% oxygen. Considering the multiple factors such as NH 4 N adsorption effect, yield and energy consumption, it was confirmed that Phyllostachys pubescens was the raw material and pyrolysis at 500 °C for 3 hours u nder 3% oxygen atmosphere was the optimal condition for the preparation. The BC ha d a maximum adsorp tion capacity of 13.79 mg·g 1 for NH 4 N. The prepared BC material contain ed a small amount of functional groups such as C H, COO --, O=C=O, CH 2 and OH, and could enhance the adsorption efficien cy of NH 4 N by cation exchange .
        (3) I n situ BC capping has good inhibitory effect of on the release of NH 4 N from sediments. It significantly reduce d the release flux of NH 4 N from sediments. The laboratory culture of sediment s proved that after 30 days of 2 cm BC capping , the concentration of NH 4 N in the two groups decreased from 0.90 mg·L 1 to 0.05 mg·L 1and from 3.51 mg·L 1 . 0.11 mg·L 1 respectively. At the same time, the release flux of NH 4 N in sediments decreased significantly from 8.28 to 1.75 mg·m 2 ·d 1 , from 38.19 to 0.49 mg·m 2 ·d 1 respectiv ely . Field experiments showed that after 30 days of 2 cm BC capping , the release flux of NH 4 N from sediment decreased from 6.79 to 0.11 mg·m 2 ·d 1 , and BC showed it had a good inhibitory effect on sediment NH 4 N endogenous release .
        (4)T he main mechanisms which BC inhibits the release of NH 4 N from sediments were e xplore d They were physical barriers , chemisorption affecting the physical properties of sediments and affecting the re supply effect. Through the BC capping , a physical barrier layer formed on the surface of the sediment, which had a significant barrier effect on the release of NH 4 N from sediment s . Using thin film diffusion gradient technique DGT and thin film diffusion balance technology DET )),it was found that the BC capping c ould adsorb NH 4 N from pore water, br oke the concentration gradient of NH 4 N at SWI and had a good inhibitory effect on the release of NH 4 N ; the BC capping layer change d the pH, LOI value, porosity, C/N and other physical and chemical properties of sed iments , which c ould indirectly or directly inhibit the release of NH 4 N from the sediment. In the field mesocosm experiment, the Rvalue C DGT NH 4 N /C DET NH 4 N in the pore water of the BC capping layer wa s 0.3,which wa s significantly smaller than other mesocosm s, indicating that The resupply capacity of the NH 4 N in the pore water of this layer wa s weak.

        (5) BC capping c ould change the microbial community structure related to the nitrogen cycle and the abundance of related functional genes involved in the NH 4 N cycle Microbial community structure and functional gene analysis after BC capping The introduction of BC c ould increase the r elative abundance of several microbial p hylum related to nitroge n cycle , Proteobacteria Planctomycetes and Nitrospirae ; increase the r elative abundance of microbial species associated with NH 4 N removal , Nitrospira , Thiobacillus , Comamonadaceae , Desulfobulbus ,Hydrogenophaga . T he abundances of amoA, amoB, nrfA, nirK, nirS, ureC and hzsB in the BC layer were greatly increased. The ratio of the copy number of the amoB, nirS and ureC genes to that of 16s increase d. It indicate d that BC not only increase d the microbial biomass assoc iated with nitrogen cycle, but also enhance d the r elative abundance of amoB, nirS and ureC genes.