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在我国的经济发展过程中,煤炭使用不可或缺,地位不可替代[1],但在使用时会造成大气污染,为了预防或减少煤燃料对环境和人体健康带来的危害,洗煤、洁净煤技术应运而生,煤的气化技术[2]为其中之一,但煤炭在气化过程中会产生大量的煤气化废水(coal gasification wastewater,CGW),该废水的主要特点是可生化性差,酚类物质含量高、毒性强、有机物浓度高、色度深,属于难处理工业废水[2-3]。
煤气化废水通常采用生物组合工艺(如厌氧、缺氧和好氧)处理[4]。但在生物处理厌氧段的废水存在可生化性差、处理效率低和出水毒性大等问题,导致后续处理工艺运行不稳和出水污染物浓度高。为了提高厌氧段的可生化性,提高污染物的去除效率,降低出水毒性(如降低酚类污染物含量),寻求高效且低成本的预处理方法势在必行。吸附法因其成本低、处理效果好、处理工艺简单、可实现废物资源化等优势,在工业废水的预处理中得到较多的研究,吸附法的使用吸附剂的选择尤为重要,直接影响吸附效果和使用成本。钠基膨润土(Na-Bentonite,Na-BBT)与粉煤灰(pulveized fuel ash,PFA)具有天然无害、价格低廉、来源丰富等优点,是一种潜在的廉价吸附剂[5-7],具有广阔的应用前景,被常用于工业废水处理[8-11]。罗秋艳等[12]使用Na-BBT吸附模拟酚类废水中的2,4,6-三氯苯酚,以物理吸附为主,吸附容量达到16.90 mg·g−1;BATABYAL[13]等用PFA吸附模拟废水中2,4-二甲基苯酚,结果表明,吸附过程符合准一级动力学模型。KHANSAA[14]用Na-BBT吸附处理橄榄油废水中的总酚类化合物,最大平衡吸附量为81.323 mg·g−1;赵伟高等[15]用PFA吸附处理焦化废水,以物理吸附为主,挥发酚的最大平衡吸附量为 39.5 mg·g−1。Na-BBT和PFA对酚类物质的吸附等温线均符合Langmuir模型[12-14]。目前,使用Na-BBT和PFA作为吸附材料对含酚废水吸附应用有一些研究,但在煤气化废水预处理领域还没有相关应用,尤其是对于复杂的、实际的煤气化废水中种类繁多的酚类化合物吸附去除效果研究较少,没有对其酚类物质的吸附去除机理进行深入研究。
鉴于此,本研究以实际煤气化废水厌氧段进水为研究对象,以Na-BBT和PFA作为吸附剂,对比分析了2种吸附剂对煤气化废水中主要的特征污染物(酚类物质)的吸附效果,探讨了煤气化废水的可生化性和毒性改变原因,并揭示了其吸附机理,以期为后续相关研究提供参考。
钠基膨润土、粉煤灰吸附预处理煤气化废水效果及机理
Adsorption effect and mechanism of sodium bentonite and pulveized fuel ash on pretreatment of coal gasification wastewater
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摘要: 煤气化废水具有可生化性差,酚类物质含量高、毒性强的特点,导致生物处理效果不理想。以煤气化废水厌氧段进水为研究对象,分别以钠基膨润土(Na-BBT)与粉煤灰(PFA)作为吸附剂,探究其对煤气化废水中主要特征污染物的去除效果和吸附机理。结果表明:Na-BBT、PFA对煤气化废水中的化学需氧量(COD)、氨氮(NH3-N)与总酚(total phenols,Tph)有一定的去除效果,其可生化性得到提升,经过Na-BBT和PFA处理后,BOD5/COD由0.29分别提高至0.37和0.32;废水中的NH3-N由221.3 mg·L−1分别降至128.6 mg·L−1和180.8 mg·L−1,总酚由554.8 mg·L−1分别降至360.6 mg·L−1和386.7 mg·L−1。气相色谱质谱(GC-MS)分析结果表明,去除的主要物质为苯酚、4-甲基苯酚、邻苯二酚、(R)-(+)-3-甲基环戊酮和对羟基苯乙酮等毒性物质,废水毒性得到降低,毒性单元(toxic unit,TU)值由 22.3 分别降至 15.2和18.4。通过吸附等温和吸附动力学分析可知,Na-BBT和PFA对煤气化废水的吸附符合 Langmuir模型和准一级动力学模型;三维荧光光谱、孔径比表面积(BET)、扫描电镜(SEM)、红外光谱(FT-IR)、X 射线衍射(XRD)、X射线荧光光谱(XRF)和X射线电子能谱(XPS)等分析结果表明,Na-BBT和PFA对煤气化废水中污染物的吸附去除过程和机理主要受物理扩散控制,为表面和孔道的物理吸附,同时也存在离子交换吸附。以上结果表明Na-BBT和PFA作为吸附剂,可以有效提高煤气化废水的可生化性,降低毒性,将其用于煤气化废水的预处理,具有潜在和广泛的应用前景。Abstract: Coal gasification wastewater is characterized by poor biodegradability, high phenolic content and strong toxicity, which leads to its unsatisfactory biological treatment effect. In this study, the anaerobic section influent of coal gasification wastewater was taken as the research object, the removal effect and adsorption mechanism on the main characteristic pollutants were absorbed by Na-bentonite (Na-BBT) and pulveized fuel ash (PFA). The result showed that Na-BBT and PFA could remove COD, NH3-N and The total phenol (Tph) from coal gasification wastewater to a certain extent, and the biodegradability of wastewater could be improved because BOD5/COD increased from 0.29 to 0.37 and 0.32, respectively, NH3-N in wastewater decreased from 221.3 mg·L−1 to 128.6 mg·L−1 and 180.8 mg·L−1, and Tph decreased from 554.8 mg·L−1 to 360.6 mg·L−1 and 386.7 mg·L−1, respectively. Gas chromatography mass spectrometry (GC-MS) results indicated that the main toxic substances such as phenol, 4-methylphenol, catechol, (R)-(+)-3-methylcyclopentanone and p-hydroxyacetophenone were removed, and the toxicity of coal gasification wastewater was reduced because the toxic unit TU value decreased from 22.3 to 15.2 and 18.4, respectively. When Na-BBT and PFA removed the pollutants from coal gasification wastewater, the adsorption process was consistent with Langmuir model and quasi-first-order kinetic model through analysis of adsorption isotherms and adsorption kinetics. It was found that the adsorption process and mechanism of Na-BBT and PFA removed pollutants from coal gasification wastewater were mainly controlled by physical diffusion due to their surfaces and pores, also including ion exchange adsorption based on the analysis of three-dimensional fluorescence spectrum, pore specific surface area (BET), scanning electron microscope (SEM), infrared spectroscopy (FT-IR), X-ray diffraction (XRD) , X-ray fluorescence spectrum (XRF) and X-ray electron spectroscopy (XPS). The results showed that Na-BBT and PFA, as adsorbents, could effectively improve the biodegradability and reduce the toxicity of coal gasification wastewater, which had potential, extensive, and practical application prospects for the pre-treatment of coal gasification wastewater.
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Key words:
- Na-bentonite /
- pulveized fuel ash /
- coal gasification wastewater /
- adsorption /
- mechanism
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表 1 荧光区域积分和占比
Table 1. Integration and proportion of fluorescence region
样品 区域积分/(×105) 区域占比/% I II III IV V I II III IV V 原水 1.75 0.44 0.25 2.10 0.48 55.4 22.3 5.2 13.6 3.4 Na-BBT 0.99 0.25 0.51 1.15 0.42 48.2 19.4 16.5 11.4 4.5 PFA 1.30 0.30 0.19 1.46 0.40 56.8 21.3 5.6 13.0 3.9 表 2 吸附等温线模型拟合参数
Table 2. Fitting parameters of adsorption isotherm model
吸附剂 Langmuir Freundlich D-R qmax/(mg·g−1) KL/(L·mg−1) R2 KF/( mg·L−1) 1/n R2 β qm/(mg·g−1) Na-BBT 257.48 0.039 8 0.979 9 17.19 2.78 0.851 3 1 678.2 10.46 PFA 137.46 0.002 9 0.909 2 14.74 3.698 0.762 3 3 019.9 7.78 -
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