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污泥产生于城市生活污水和工业生产废水的处理过程中,我国每年产生的湿污泥量约有7 400万t,并且呈现逐年增加的趋势[1]。未经处理的剩余污泥含水率超过90%,污泥中富含氮、磷等有机物和一定量的重金属等污染物质,并伴有恶臭气味,由于污泥成分极其复杂,处理不当或处理不及时将会造成土地污染、地下水污染和恶臭气体污染环境等情况[2]。
在城市用地日益紧张、环境相关法规日益严格、污泥产量日益增多的情况下,以往常用的污泥卫生填埋、海洋倾倒和土地利用技术[3]已难以大范围的应用。实现污泥的减量化、资源化和无害化是解决污泥带来的二次污染的有效手段。
作为污泥处理处置的前置工艺,污泥干化是成熟的污泥减量化技术,由于干化后污泥含水率降低、热值升高,无需外加辅助燃料即可维持自身燃烧,已经在国内外得到了广泛的使用[4-5]。然而,污泥干化过程仍然会产生废气形成二次污染,这些废气一般具有恶臭气味,其嗅阀值极低[6],干化废气直接外排可对4 km半径范围内的环境造成较大影响[7],所以采取相应的技术来治理干化废气是极为必要的。
含有大量的有机氮、有机硫化合物及蛋白质是污泥特有的性质,随着干化过程中污泥含水率的不断下降,含氮有机物会被热分解为氨气(NH.*?>=>3),含硫有机物会被热分解为硫化氢(H.*?>=>2S),此外还有大量挥发性有机物(VOCs)和易挥发含氮、含硫恶臭有机污染物释放出来[8],这些都是造成二次污染的物质。
利用水为介质的吸收法、以活性炭为主的吸附法和利用微生物的增殖代谢作用降解污染物的微生物法是当前污泥干化废气治理中主流的常规技术,这些技术虽然已经过长期的发展和完善,但由于其处理机理无法从根本上改变,所以各自都存在着自身的缺点。
在污泥生成量逐年升高、排放标准日益严格的情况下,常规技术的劣势也日渐显示出来。作为新兴处理技术的高级氧化技术,具有传统技术所不具备的处理迅速、降解能力强的优势而备受关注,其中光催化技术和低温等离子体技术已有应用于污泥干化废气处理的研究中,是极具应用前景的处理技术。
污泥干化废气特性及其治理技术研究进展
Study on the Characteristic and Treatment Technology of Sludge Drying Waste Gas
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摘要: 污泥干化是目前市政污泥主要处理方式,污泥干化过程会产生大量恶臭废气,严重污染大气环境,必须严格治理。文章总结分析了污泥干化废气的主要污染成分:粉尘、VOCs以及恶臭气体,如氨气、硫化氢、胺类有机物和有机硫化物气体等。并进一步分析了包括吸收法、吸附法、生物法、等离子体法和光催化法等,处理污泥干化废气的常用方法。在掌握污泥干化废气特征和处理方法优缺点的基础上,提出了未来污泥干化废气治理技术的发展方向。Abstract: At present, sludge drying is one of the main sludge treatment methods. There are a lot of waste odor gas produced in the drying process. Therefore, it is necessary to treat it very carefully. The major pollutants of the sludge drying waste gas are analyzed in this paper, including dust, volatile organic compounds (VOCs) and odor gas, such as NH.*?>=>3, H.*?>=>2S and other volatile nitrogen substances and sulfur substances. And the common treatment technologies for the sludge drying waste gas are also analyzed, including the absorbing method, the absorption method, the biological method, the plasma method and the photocatalytic method. Based on the characteristic of the waste gas and the strength and weakness of the treatment methods, the development direction of the sludge drying waste gas treatment technology in the future is proposed.
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Key words:
- Sludge Drying /
- Odor Gas /
- VOCs /
- Key Technology
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表 1 污泥干化废气释放特征表
mg·m−3 干化形式 无机恶臭气体 VOCs 参考文献 NH.*?>=>3 H.*?>=>2S SO.*?>=>2 苯系物 有机酸 有机硫化物 酮类 烯烃 醇类 醛类 酯类 醚类 卤代烃 热干化 检出 检出 467.97 15.94 10.20 1.53 1.39 5.79 2.92 2.97 1.49 1.49 5.79 [13] 热干化 NG NG NG 24.06 15.26 5.09 1.85 1.67 NG NG NG NG 10.08 [14] 热干化 4.43 ≈0.1 NG 1.48 NG <0.1 ≈0.1 ≈0.4 ≈0.1 NG <0.1 <0.1 <0.1 [8] 热干化 4.9 ≈0.2 ≈0.1 ≈0.7 NG ≈0.2 ≈0.5 ≈0.6 ≈0.1 NG ≈0.4 ≈1.3 ≈0.4 [15] 热干化 NG NG NG 27.83~40.13 9.10~17.66 5.89 2.14 NG 4.28 NG NG NG NG [16] 生物干化 229.45 1.39 NG ≈14.53 ≈0.16 ≈0.49 ≈0.13 ≈0.85 检出 检出 检出 检出 ≈0.15 [17] 太阳能干化 308.48 NG NG NG ≈7.0 NG NG NG NG NG NG NG NG [18] 注:NG表示未提及。 表 2 污泥干化废气关键技术对比表
技术分类 处理技术 技术原理与特征 投资与运行费用 优势 存在问题 常规 吸收法 利用酸液、碱液或水喷淋吸收废气中的污染物 低 系统阻力小,可处理大风量废气、适用范围广、维护成本低 流量大时处理效果变差,吸收液可能会成为危险废物,没有根本解决污染问题 常规 吸附法 污染物被吸附到活性炭、分子筛等吸附剂中 适中 设备占地小、吸附效率高、维护简单、适用条件广 气体含水量大时吸附效率差,吸附剂需要定期更换,吸附后成为危险废物,增加了处理成本 常规 生物法 利用微生物降解特定的污染物 较低 对低浓度废气处理效果特别好,运行费用低 只能处理特定成分的废气,反应器从启动到稳定运行过程非常缓慢,易堵塞,易产生剩余污泥和污水 新兴 低温等离
子体法高能电子、自由基把污染物彻底氧化为低毒性或无毒的物质 较高 可处理混合气体,不外加任何物质,适应性强、降解彻底 由于设备精密,一次性投资且维护成本较高 新兴 光催化法 利用光致空穴和光生电子引发的光催化反应降解污染物 较低 系统阻力小,污染物去除率高、不外加任何物质,运行成本低,适用条件广 光能利用效率低,颗粒物会阻挡光线降低处理效果,催化剂也会存在失活问题 -
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