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热处理技术常用于去除石油烃 (total petroleum hydrocarbons, TPH)、多环芳烃 (polycyclic aromatic hydrocarbons, PAHs)[1]、多氯联苯(polychlorinated biphenyls, PCBs)[2]、氯苯(chlorobenzene, CBz)[3]等土壤有机污染物。热处理技术类型的选择与污染物性质及其沸点密切相关,不同类型技术有不同的特征和适用场合(见图1)。热处理温度的高低会影响污染物的去除机制:低温热处理时,污染物主要以气相脱附(物理挥发)的形式去除;高温热处理时,污染物则以缩合转化(炭化)、氧化(燃烧)等热反应形式转移[4]。土壤热处理技术快速、高效、彻底、可控,但是有学者担忧会改变土壤结构和性质[5],破坏有机质[6]和微生物菌群[7],从而可能影响再利用特性。关于热处理中有机污染物的化学转化,特别是炭化行为,文献报道并不多见。本文将探讨、分析热处理过程中的炭化行为、炭化机理及其对土壤再利用特性的影响,以期为土壤热处理技术的科学研究与工程实践提供参考。
有机污染土壤热处理过程中的炭化行为及其影响
Charring behaviors and their influence of organic contaminated soil during thermal treatment
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摘要: 热处理技术在国内外均占有较高的市场份额,已成为有机污染场地的主要修复技术。尽管对热处理技术本身的研究和关注较多,包括工艺、参数、能源、效果、成本、应用等方面,但关于有机污染物热处理化学转化中炭化行为研究的报道并不多见。炭化行为可能会改善土壤再利用特性,对热处理工艺参数也可能有一定影响。指出了传统焦化行业中4种炭化反应类型及其机理过程,梳理了石油烃和芳烃化合物等污染土壤热处理过程中的炭化行为,总结了有机污染物炭化行为对土壤再利用特性的影响,并分析了生物质炭化产物对土壤肥力的促进机制。以此为基础,提出了有机污染土壤热处理炭化行为研究的几个重点关注方向。Abstract: Thermal treatment technologies occupy a high domestic/foreign market share, and have become the main remediation technology of organic contaminated sites. Though many studies and concerns are focused on the process, parameters, energy, effect, cost and application of thermal treatment, there are few literature reports on the charring behaviors in the thermochemical conversion of organic pollutants. The charring behaviors may improve reusability of soil and affect process parameters of thermal treatment. Four types of charring reactions and their mechanisms are shown in this paper, and the charring behaviors of petroleum hydrocarbons and aromatic compounds during thermal treatment are reviewed. The effects of organic pollutants charring on soil reusability is summarized, and the improvement of biochar to soil fertility is analysed. Based on the mentioned above, several important research topics of charring process during thermal treatment of organic contaminated soil are proposed.
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表 1 热处理过程中有机污染物的炭化反应过程相关研究情况
Table 1. Related research on charring reaction of organic pollutants during thermal treatment
序号 污染物 反应基质 污染物浓度/
(mg·kg−1)热处理
温度/℃热处理
时间/min反应气氛 载气流速/
(L·min−1)去除效率/
%炭化产物 文献 1 原油 模拟土壤 − 300~400 30~60 N2 − − char [16] 2 柴油 模拟土壤 6 271 100~350 5~120 N2 1.2 28~99 carbon [17] 3 TPH 实际土壤 16 000, 19 000 420 180 N2 1 >99.98, >98.47 char [18] 4 TPH 实际土壤 95 300 80~300 20 − − 40~99.52 char [19] 5 TPH 实际土壤 49 500 250~600 0.5, 30 N2 0.2 >67.3 char [20] 6 燃料油 模拟土壤 − 30~900 <80 CO2 0.5 − char [21] 7 杂环芳烃 − − 100~350 <120 Ar − − coke [22] 8 硫杂环芳烃 − − ≤600 <120 Ar − − coke [23] 9 蒽 − − 440~480 30~360 − − − mesophase [24] 10 菲 − − 540~560 60~300 − − − mesophase [24] 11 PAHs 河流沉
积物− 300 60 He − 95 char [25-26] 12 甲基萘 模拟土壤 40 000 200~400 10~120 N2 0.1~0.38 85.08 char [27] 注:−为文中无准确信息;“char”和“coke”表示“焦炭”,“carbon” 表示“碳”,“mesophase” 表示“液晶”。液晶指从液相到固相变化系统中间生成的中间相。 表 2 生物炭对土壤性能的改良效果
Table 2. Effects of biochar on improving soil properties
序号 生物炭原料 炭化方式 土壤类型 生物炭
含量实验类型 生物炭对土壤性能的影响 文献 1 柳树 热解炭化 壤土 2% 盆栽实验 C、N矿化分别减少了10%和75%,pH值升高了0.17个单位,总细菌、革兰氏阴性菌和放线杆菌分别增加了28%、27%和62% [39] 2 橡树和
山核桃树热解炭化 壤土 5~20 g·kg−1 土柱实验 C含量增加了17.6%~68.8%,总N含量增加了0.6%~6.9%,含水量增加了10%~15%,CEC增加了4%~30%,比表面积增加了约18%,pH增加了约1个单位 [44] 3 花生壳 热解炭化 砂质壤土 10~60 g·kg−1 盆栽实验 毛管持水量增加了1.2~1.69倍 [45] 4 牧草秸秆、茶树
枝条、果树枝
条、小麦秸秆热解炭化 山地黄壤 10~80 t·hm−2 田间实验 含水量提高1.05%~55.77%,pH 值提高0.03~1.68 个单位,微生物生物量碳含量提高10.24%~90.94% [46] 5 花生壳、松木屑 热解炭化 砂质壤土 22 t·hm−2 田间实验 CEC分别提高了15%、5% [47] 6 山核桃壳 热解炭化 砂质壤土 2% 土柱实验 Ca、K分别增加了58%和106%,C增加了11.8 g·kg−1 [48] 7 猪粪 热解炭化 沙姜黑土 0.5%~2% 盆栽实验 植物产量提高了26.50%~49.98%,氮素偏生产力提高 119.32%~162.81%,植物可溶性蛋白质和维C含量增加了33.11%~42.93%和15.16%~46.06%,硝酸盐含量降低了 17.80%~22.08% [49] 8 芒草 水热炭化 砂质壤土 100 t·hm−2 田间实验 吸附量增加了25%$ {\rm{N}}{{\rm{O}}^ -_3} $ [50] 9 芒草 热解炭化 砂质壤土 100 t·hm−2 田间实验 吸附量增加了58%,${\rm{NO}}_3^{-} $ 增加了40%${\rm{NH}}_4^{+} $ [50] 10 农业秸秆 热解炭化 棕壤 10~40 t·hm−2 室内大田实验 含水量提高了13.92%~74.14%,pH值降低了6.61%~23.97%,TOC提高了25.41%~70.92%,TN提高了25.51%~102.04%,TK提高了33.20%~108.26%,微生物总量提高了59.62%~132.69%,细菌提高了23.53%~41.43%,真菌降低了8.33%~37.12% [51] 11 烟杆 热解炭化 红壤土 40 t·hm−2 田间实验 微生物种类提高了26.4% [53] 12 辐射松 热解炭化 砂质壤土 10% 盆栽实验 微生物活性增加了15%,细菌群落丰度的时空变化>5% [54] 13 小麦秸秆 热解炭化 砂质壤土 20 t·hm−2 田间实验 16S rRNA基因拷贝数分别增加了28%,18S rRNA基因拷贝数分别减少了35% [55] 14 小麦秸秆 热解炭化 砂质壤土 40 t·hm−2 田间实验 16S rRNA基因拷贝数分别增加了64%,18S rRNA基因拷贝数分别减少了46%,嗜甲基和嗜氢菌科丰度下降了70%,厌氧菌科丰度增加了45% [55] 15 酵母 水热炭化 农田和森林土壤 30% 温室实验 真菌增加了16%,革兰氏阳性菌和革兰氏阴性菌
减少了7%~14%[56] 16 葡萄糖 水热炭化 农田和森林土壤 30% 温室实验 土壤革兰氏阴性菌和革兰氏阳性菌增加了2.1‰~4.7‰ [56] -
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