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制药废水具有高盐度、高色度、高化学需氧量(chemical oxygen demand,COD)等特点,属于难降解有机工业废水之一。经过生化处理后,仍存在溶解性有机物(dissolved organic matter,DOM)浓度较高、毒性较大等问题,难以达到排放标准和回用水要求[1]。生化处理后,废水中DOM由腐殖质类、多糖类、蛋白类、脂质类和小分子的氨基酸等组成[2],含有未完全降解的小分子有机物,以及长链烷烃、芳香烃等大分子质量有机物,废水多呈现淡黄色[3]。DOM排入水体后将对水环境造成不利影响,并产生一定的生态风险。因此,须对制药废水进行深度处理,以消减DOM物质排放量,降低生物毒性,减少水环境生态风险。
废水深度处理工艺主要包括高级氧化法(advanced oxidation processes,AOPs)、膜分离法、吸附法和生物法等[4-6]。AOPs由于其氧化能力强、清洁、无二次污染得到广泛应用。AOPs可在水中生成羟基自由基(HO·),HO·具有高氧化活性和无选择性特征,能够氧化大多数有机污染物,因此得到广泛关注[7]。传统臭氧化技术存在HO·产生效率差、臭氧利用率低、气液传质速率慢等问题,使得难降解有机物矿化效率有限,制约了其实际应用[8]。微气泡(microbubble,MB)通常是指直径小于50 μm的微小气泡,有研究表明,微气泡臭氧传质速率是普通气泡的1.3~1.5倍,且能够有效加速臭氧分解产生HO·,进而提高臭氧化能力[9]。同时,有研究[10-13]表明,微气泡表面存在电荷聚集效应,在液相收缩过程中表面电荷密度和ζ电位急剧升高,并在破裂时可产生HO·,产生类催化效应。在微气泡催化臭氧化中,臭氧微气泡类催化效应与催化剂催化效应协同,可显著提高HO·氧化能力,使得臭氧利用率和有机物矿化率显著提高[9, 14-15],并可提高废水的可生化性,降低其生物毒性[16]。LIU等[17]采用微气泡臭氧化技术处理阿特拉津废水,发现臭氧微气泡通过臭氧分解以及微气泡破裂可提高阿特拉津降解率。ZHANG等[18]以活性炭为催化剂催化微气泡臭氧化处理酸性大红3R废水,可将TOC去除率由传统气泡(coarse bubble,CB)的36.2%提升至91.2%。可见,微气泡臭氧化技术在废水深度处理领域具有良好的应用前景。
非均相催化臭氧化通过将臭氧转化为HO·来提高氧化能力和污染物去除效率[19-20]。选用活性金属离子制备具有水滑石结构的层状双羟基复合金属氢氧化物(layered double hydroxides,LDHs),往往具有优异的催化性能,但其应用于催化臭氧化的研究甚少。HASSANI等[21]采用镍基层状氢氧化物纳米材料催化臭氧化处理模拟染料废水,其对COD的去除率可由传统臭氧化的30%提高到72%。FU等[22]采用钴铁层状双氢氧化物催化臭氧化降解甲苯磺酸溶液,TOC的去除率可达85%。
本研究将微气泡与催化臭氧化技术相结合,采用镁铝层状双氢氧化物催化剂(Mg-Al-LDHs,MAL)催化微气泡臭氧化实际制药废水,考察了普通气泡臭氧化(CB/O3)、普通气泡催化臭氧化(MAL/CB/O3)、微气泡臭氧化(MB/O3)和微气泡催化臭氧化(MAL/MB/O3)体系处理实际制药废水的效能及有机物降解特征,分析了废水中亲水性酸(hydrophilic acid,HIA)、亲水性碱(hydrophilic base,HIB)、亲水性中性(hydrophilic neutral,HIN)、疏水性酸(hydrophobic acid,HOA)、疏水性碱(hydrophobic base,HOB)、疏水性中性(hydrophobic neutral,HON)DOM组分的变化,以期为制药废水深度处理提供参考。
微气泡催化臭氧化深度处理制药废水的效果及DOM组分特性的变化
Performance of advanced treatment of pharmaceutical wastewater by microbubble catalytic ozonation and component variation characteristics of dissolved organic matter
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摘要: 采用镁铝层状双氢氧化物(MAL)微气泡催化臭氧化(MAL/MB/O3)体系深度处理实际制药废水,考察了该体系对溶解性有机物(DOM)的深度去除性能及DOM组分的变化特性,并与普通气泡臭氧化(CB/O3)、普通气泡催化臭氧化(MAL/CB/O3)、微气泡臭氧化(MB/O3)工艺进行了比较。结果表明,MAL/MB/O3处理性能优于CB/O3、MAL/CB/O3和MB/O3,在臭氧投加总量与处理废水初始COD值之比为0.6、气流量0.5 L·min−1、催化剂投加量0.5 mg·L−1的条件下,整体COD去除率可达49.79%,COD去除量与臭氧消耗量的比值为0.83,废水的可生化性得到了一定改善,生物毒性显著下降。废水DOM中疏水性组分氧化去除率高于亲水性组分。臭氧直接氧化可去除疏水性组分,而亲水性组分去除主要依赖HO·氧化。MAL/MB/O3对DOM的去除效率最高,可达到52.51%,其中疏水性组分整体去除率56.67%,亲水性组分整体去除率46.93%。废水DOM在氧化处理中存在官能团向酸性基团转化、类腐殖质向类富里酸和类胡敏酸转化、其他组分向亲水性酸(HIA)组分转化的趋势。MAL/MB/O3强氧化能力对于DOM组分不饱和结构和荧光结构的破坏作用最为显著。以上研究结果可为制药废水深度处理提供参考。Abstract: The catalytic microbubble ozonation with magnesium-aluminum layered double hydroxides (MAL) as catalyst (MAL/MB/O3) was used to perform advanced treatment of actual pharmaceutical wastewater. In comparison with common bubble ozonation (CB/O3), catalytic common bubble ozonation (MAL/CB/O3) and microbubble ozonation (MB/O3), the performance of advanced treatment of pharmaceutical wastewater by microbubble catalytic ozonation and component variation characteristics of dissolved organic matter (DOM) were studied. The results showed that the overall treatment performance of MAL/MB/O3 was better than that of CB/O3, MAL/CB/O3 and MB/O3. When the ratio of total ozone dosage to total initial COD of treated wastewater was 0.6, gas flow was 0.5 L·min−1 and catalyst dosage was 0.5 mg·L−1, the total COD removal efficiency could reach 49.79%, and the ratio of COD removal to ozone consumption was 0.83 in MAL/MB/O3. The biodegradability of MAL/MB/O3 treated wastewater was improved and the biological toxicity decreased significantly. The oxidation removal efficiency of hydrophobic components in wastewater DOM was higher than that of hydrophilic components. The hydrophobic components could be removed by ozone direct oxidation, while the hydrophilic components removal mainly depended on HO· oxidation. MAL/MB/O3 had the highest DOM removal efficiency of 52.51%, including 56.67% removal of hydrophobic components and 46.93% removal of hydrophilic components. During the oxidation treatment of wastewater DOM, some conversion tendencies occurred, such as functional groups to acidic groups, humic-like substances to fulvic acids-like and humic acids-like, and other components to hydrophilic acid (HIA) components. The strong oxidation ability of MAL/MB/O3 had the most significant destructive effect on the unsaturated structure and fluorescent structure of DOM components. This study can provide a theoretical and technical reference for advanced treatment of pharmaceutical wastewater.
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