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焦化废水产生于高温焦炭生产、气体净化和副产品回收过程,其化学成分复杂,含有大量的酚类物质、氰化物、硫化物、杂环化合物和多环芳烃等[1]. 因此,为了控制和减少其对环境的不利影响,通常采用物化预处理、生物处理、深度处理和回用处理相结合的组合工艺处理焦化废水[2]. 在处理过程中会产生大量污泥,而废水中的一部分难降解有机物会被污泥吸附[3]. 因此,焦化废水处理过程中产生的污泥如果不经妥善处置,会对环境造成危害. 污泥通过高温热解转化为高附加值的污泥炭是解决污泥处理处置问题的一个有发展前景的途径. 通过热解不仅能去除污泥中的有害污染物,杀灭污泥中的病原体,还能回收资源和能源. 污泥经过高温作用不仅形成了导电石墨碳,还形成了具有氧化还原活性的含氧官能团以及过渡金属及其氧化物等[4]. 污泥炭能够作为电子供体、受体和媒介,充当电子转移介质进一步提高催化性能,催化活化过硫酸盐、过氧化氢(H2O2)和臭氧等氧化剂生成硫酸根自由基(SO4-·)、羟基自由基(·OH)、超氧自由基(·O2-)和单线态氧非自由基(1O2)等[5 − 6].
在以过氧化氢(H2O2)为氧化剂的高级氧化体系中,研究者发现污泥炭的金属、杂原子掺杂的碳结构以及官能团可以作为电子转移的介质,使H2O2分解产生·OH,降解水体中的有机污染物[7]. 催化湿式过氧化物氧化 (CWPO) 工艺可以在温和的反应条件下高效降解废水中的难降解污染物[8]. 近年来,关于市政污泥热解炭化制备催化剂并用于CWPO体系中降解有机污染物的研究逐渐增多[6, 9]. 然而,工业废水处理过程中产生的污泥制备生物炭催化剂的研究相对较少. 焦化废水中含有的多种成分使焦化污泥中的元素种类更丰富,可能有利于其制备的污泥炭性质的改善[3]. 氯离子是高盐工业废水中的主要阴离子,能影响CWPO反应中生成的自由基种类,降低催化剂的活性,从而影响有机物的降解. 在制革和染料制造废水中,经常可以检测到高浓度的NaCl(>50 g·L−1),但是其对有机物降解过程的影响还未有很好的解释[10]. 因此,研究Cl-对有机物降解的影响对处理实际废水具有重要意义.
本研究以焦化废水处理厂再生水处理段排放的污泥为原料制备生物炭催化剂,采用硝酸低温改性方法,提高其催化性能,以间甲酚为模型污染物,研究在催化湿式过氧化氢反应体系中污泥炭催化剂对氯介质下间甲酚降解的催化活性和稳定性,并分析间甲酚的降解过程,考察氯离子对间甲酚降解的影响.
焦化污泥基生物炭在氯介质下催化降解间甲酚的性能
Catalytic degradation of m-cresol by coking sludge based biochar in chloride medium
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摘要: 以焦化污泥制备生物炭,并在硝酸溶液中低温条件下进行改性,研究其在氯介质下对间甲酚降解的效率与机理. 焦化污泥(CSS)具有较大的比表面积和丰富的官能团,其吸附作用较强,对间甲酚的吸附去除率为27.1%. 而通过炭化和改性的焦化污泥炭的比表面积显著降低,官能团数量减少,吸附作用极弱. 在催化降解过程中,改性焦化污泥炭(CSSC-N)对间甲酚和总有机碳(TOC)的去除率分别为98.1%和80.1%,远高于未改性的焦化污泥炭(CSSC-0),主要归因于CSSC-N中具有多种含铁物质,有利于铁循环,且表面铁含量高达60.10%,能提供丰富的催化活性组分. Cl-对间甲酚和TOC的去除率有抑制作用,随着Cl-浓度的升高,去除率降低. 当废水中的NaCl为5%wt时,在催化重复实验中间甲酚的去除率均高于70%. CSSC-N具有一定的抗氯性能,在氯介质下具有较高的催化活性和稳定性. 三维荧光光谱分析和中间产物鉴定结果表明Cl-的存在影响了间甲酚的降解过程,生成了难降解的氯代副产物.
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关键词:
- 催化湿式过氧化氢氧化 /
- 焦化污泥 /
- 生物炭 /
- 间甲酚 /
- 氯介质.
Abstract: A biochar was prepared from coking sludge and modified with nitric acid at low temperature. Afterwards, the degradation efficiency and mechanism of m-cresol in chloride medium was studied. Coking sludge (CSS) had a large specific surface area and was rich in functional groups, so its adsorption effect was strong. The adsorption removal rate of m-cresol with CSS was 27.1%. However, the adsorption effect of the coking sludge carbon through carbonization and modification was very weak, because the specific surface area and the number of functional groups were significantly reduced. In the catalytic degradation process, the removal rates of m-cresol and Total organic carbon (TOC) with the modified coking sludge carbon (CSSC-N) were 98.1% and 80.1%, respectively, which were much higher than those with the unmodified coking sludge carbon (CSSC-0). That was mainly because there were a variety of iron-containing substances in CSSC-N which was conducive to iron circulation, and the surface iron content was as high as 60.10%, providing catalytic active components. The removal rate of m-cresol and TOC was inhibited by Cl-, which was deceased with an increase of Cl- concentration. When the concentration of NaCl in wastewater was 5% wt, the removal rates of m-cresol during the catalytic repeat experiment were all above 70%. Therefore, CSSC-N with the chorine-resistant property had a high catalytic activity and stability in chlorine medium. Based on the results of three-dimensional fluorescence spectrometry analysis and intermediate products identification, the presence of Cl- affected the degradation process of m-cresol and chlorine-containing intermediates were produced.-
Key words:
- catalytic wet peroxide oxidation /
- coking sludge /
- biochar /
- m-cresol /
- chloride medium.
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表 1 焦化污泥炭样品的基本理化性质
Table 1. Physicochemical properties of the coking sludge carbon samples
样品
SamplesC/% wt H/%wt O/%wt N/%wt S/%wt Fe/%wt Al/%wt Ca/%wt SBET/(m2·g−1) Vp/(cm3·g−1) CSS 13.27 2.54 19.21 1.72 6.57 28.32 0.91 12.16 86.024 0.154 CSSC-0 21.43 1.27 16.71 1.02 0.61 32.96 1.47 13.25 0.0807 0.00293 CSSC-N 17.69 0.65 26.57 0.98 4.82 30.14 0.33 2.36 9.665 0.0228 表 2 氯介质下间甲酚催化降解中间产物
Table 2. Intermediates generated during the catalytic degradation of m-cresol in chlorine medium
产物
Product分子式
Molecular
formula分子结构
Molecular structure检测值
Measurement
value (m/z)理论值
Theoretical
value (m/z)离子类型
Ionic
typesP1 C7H5ClO3 170.9853 170.9584 [M-H]- P2 C7H4Cl2O3 205.9463 205.9465 [M-H]- P3 C7H8O2 183.06616 183.06628 [M+CH3COOH-H]- P4 C7H6O2 243.06613 243.06628 [2M-H]- P5 C7H10O2 185.08181 185.08193 [M+CH3COOH-H]- P6 C7H12O2 255.15986 255.16018 [2M-H]- P7 C6H10O 157.08685 157.08701 [M+CH3COOH-H]- P8 C6H12O 199.17017 199.17036 [2M-H]- P9 C5H10O 171.13892 171.13904 [2M-H]- P10 C5H6O3 227.05587 227.05610 [2M-H]- P11 C5H8O3 231.08721 231.08740 [2M-H]- P12 C4H8O 71.05016 71.05023 [M-H]- P13 C3H4O3 87.00875 87.00876 [M-H]- P14 C2H4O3 121.01457 121.01424 [M+CH3COOH-H]- P15 CH2O2 91.00382 91.00368 [M+CH3COOH-H]- -
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