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随着我国城镇化水平的不断提高,污水处理设施建设高速发展。有机污染物综合指标(COD、TN等)已无法准确反映水质污染的严重性。许多新兴有机微污染物(如酚类、苯系物等),虽然在环境中残留水平很低,对综合水质指标BOD、COD和TOC等的贡献极小,但其环境危害却很大[1-5]。为了进一步削减污水中痕量有机污染物的排放通量,目前已经有许多污水深度处理技术方面的研究,主要包括膜分离技术、高级氧化技术、电化学氧化技术和吸附技术等[6]。膜技术在再生水处理中应用广泛,但因膜污染严重,制约了其规模化应用[7]。氧化技术存在产生有毒副产物、催化剂的高度选择性以及难分离回收、处理成本高等问题[8-9],导致目前实际应用并不多。活性炭是一种多孔性物质,且易于自动控制,对水量、水质、水温变化适应性强[10-11]。因此,活性炭吸附法是一种具有广阔应用前景的污水深度处理技术。
污泥基生物炭(sludge-derived carbons,SC)是一种以城市污泥为原料制备的高含碳物质,具有高的孔隙率、发达的空隙结构和大的比表面积、丰富的表面活性结合位点,是一种新型廉价高效的吸附剂[12],对重金属、染料中间体、抗生素及内分泌干扰物具有较强的吸附性能[13]。有研究表明,污泥热解条件(温度、终温停留时间、升温速率)是影响污泥炭的微观形貌和表面化学性质的重要因素,不同的表面理化性质对有机物吸附能力各有不同。为了使污泥炭具有一定的应用性能,众多学者深入研究了污泥炭热解条件对污泥炭性质影响,分析了吸附过程的作用机制。YUN等[14]发现,在高温下,热解污泥会得到更大的比表面,同时炭基材料的芳香化程度更高。SEREDYCH等[15]研究指出,热解温度与终温停留时间和升温速率相比,是影响污泥微观形貌更为重要的因素。DING等[16]指出,在400 ℃条件下制备的污泥炭的微孔比例并不高,但其表面化学特性可提高其对抗生素的吸附能力。
本研究基于前人研究的基础,旨在通过分析热解温度对污泥炭基材料表面理化性质、微观形貌的调控,探究污泥炭表面理化性质对污水厂深度处理过程中有机物的吸附效能的影响,深入分析污泥炭表面的理化性质与吸附有机物种类的匹配机制,为污泥炭用于污水深度处理过程中有机物的吸附提供参考。
热解温度对污泥碳基材料表面性质及吸附性能的影响
Effect of pyrolysis temperature on the surface properties and adsorption performance of sludge biochar
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摘要: 以市政污泥为原料,在300、400、500、600、700和800 ℃无氧气氛下,热解制备了污泥基生物炭。采用BET、SEM、XPS、FT-IR对不同热解温度下污泥炭进行了表征分析;研究了不同热解温度下污泥炭对污水中有机物的吸附效果和动力学;探究了热解温度对污泥炭微观调控下吸附实际水体中有机物的匹配机质。结果表明,随热解温度的升高,C—H、C—C结合比例降低,C=C、C—O=C比例升高,芳香化程度增加,且比表面积、孔容及表面粗超度均有所增加,1~2 nm微孔比例增多,介孔向微孔发展趋势逐渐明显。800 ℃热解温度条件下制备的污泥炭对二沉池出水中有机物的吸附效果优于其他温度下制备的污泥炭。吸附温度为298.15 K时,最大吸附容量为282.5 mg·g−1,且符合准二级吸附动力学。高温下制备的污泥炭对水体中腐殖酸和富里酸具有较强的吸附效能。这主要是由于表面丰富的含氧官能团、芳香键与腐殖酸和富里酸发生了氢键、化学键缔合作用和π-π共轭作用,同时污泥碳表面发达的孔隙结构和较大的比表面积也提供了更多的活性结合位点,促进了污染物的吸附。Abstract: Biochar was derived from municipal sewage sludge at five different temperatures (400, 500, 600, 700 and 800 ℃) in an anaerobic environment, which was characterized by using BET, SEM, XPS and FT-IR. The adsorption effect and kinetics of organic matter in sewage on sludge biochar at different pyrolysis temperatures were studied. The matching mechanism of organic matter adsorption in actual water on micro-controlled biochar by pyrolysis temperature was also discussed. The results showed that with the increase of the pyrolysis temperature, the ratios of C—H, C—C decreased, while the ratios of C=C, C—O=C increased, the aromatization degree, specific surface area, pore volume, surface roughness and micro-pore ratio of 1~2 nm increased, the transformation trend from meso-pores to micro-pores was gradually obvious. The adsorption capability of organics in the effluent of secondary tank on sludge biochar prepared at pyrolysis temperature of 800 ℃ was better than that prepared at other temperatures.The corresponding maximum adsorption capacity was 282.5 mg·g−1 at adsorption temperature of 298.15 K, and the adsorption kinetics conformed to the quasi-second-order adsorption kinetics equation model. Biochar had strong adsorption efficiency towards humic acid and fulvic acid in water. The main reason was the hydrogen bonds, chemical bond association and π-π conjugation functions occurred between the abundant oxygen-containing functional groups, aromatic bonds on the surface of sludge biochar and humic acid or fulvic acid. Meanwhile, the developed pore structure and large specific surface area of sludge biochar provided lots of active binding sites and promoted the adsorption of pollutants.
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Key words:
- sludge biochar /
- pyrolysis temperature /
- adsorption /
- organic matter
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表 1 C1s XPS拟合得到的表面官能团相对含量(峰面积的百分比)
Table 1. Relative contents of functional groups in C1s XPS fitting (percent of total peak area)
% 样品名称 C—C C—OH/C—OR C—N O—C=O SC 21.11 18.76 10.15 5.94 SC400 18.22 22.34 5.76 2.26 SC500 22.02 16.15 5.2 2.81 SC600 19.75 17.38 4.3 2.45 SC700 21.37 15.48 5.63 2.4 SC800 27.84 19.24 3.52 2.05 表 2 不同热解温度下污泥炭及污泥的比表面积、孔容
Table 2. BET surface areas and porosity of sludge and biochar prepared at different pyrolysis temperatures
样品名称 比表面积/(m2·g−1) 孔容/(m3·g−1) SC 11.64 0.06 SC400 51.13 0.14 SC500 73.09 0.161 SC600 87.89 0.153 SC700 86.6 0.155 SC800 110.7 0.169 表 3 不同热解温度下污泥炭吸附后的有机物荧光强度
Table 3. Fluorescence intensity of organic matter adsorbed by biochar preparedat different pyrolysis temperatures
样品名称 腐殖酸荧光强度 富里酸荧光强度 SC 2 004 4 609 SC400 853.3 2 697 SC500 518.7 1 699 SC600 306.6 196.1 SC700 134.8 163.2 SC800 164.6 177.9 表 4 动力学拟合结果
Table 4. Kinetics fitting results
样品名称 Qe,exp/(mg·g−1) 准一级吸附模型 准二级吸附模型 颗粒内扩散模型 Qe,cal/(mg·g−1) k1 R2 Qe,cal/(mg·g−1) k2 R2 k3 C R2 SC800 282.5 171.79 0.011 8 0.910 1 302.11 0.000 12 0.998 9 10.304 94.41 0.781 8 -
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