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市政脱水污泥是城镇污水处理厂的副产物,其中含有大量的有机污染物、病原体[1-2],如处置不当会对人体健康和环境安全产生威胁[3]。因此,市政脱水污泥被美国环保局定义为一种环境污染物[4]。2016年,我国污泥的产量约为3×107 t,日本为7.4×107 t,欧洲为9.8×106 t (干质量),美国为5.6×106~5.7×106 t (干质量)。预计至2020年,我国的污泥产量将达到6×107 t[5-6]。目前,大多数的污泥都用来填埋、焚烧、堆肥发酵以及土地利用,这些处理处置方式易造成资源浪费,也均有一定产生二次污染的风险[7]。因此,越来越多的研究关注于寻找污泥处理处置的新途径。
污泥中含有大量有机物,适合热解制备生物炭,而且热解能够有效杀灭病原体,达到减量化、无害化、稳定化、资源化的目的。由于污泥的成分复杂,因此,热解后的污泥基炭通常具有一定的官能团和孔洞结构,可用于吸附和催化降解污染物[8]。1971年,KONG等[9]就开始利用炭化淤渣制备污泥基炭。随后,污泥基活性炭的制备的得到了广泛关注。近年来,出现了以市政污泥做为原材料,利用物理活化、化学活化与高/低温热解技术为主体的污泥炭基功能材料的制备技术。这些制备炭材料的技术也正逐步成为污泥资源化利用的新方式[10]。任爱玲等[11]利用天津市东郊污水处理厂的污泥为原料,通过40%的ZnCl2溶液活化,制备得到的污泥基活性炭的比表面积为193~256 m2·g−1;碳材料对于制药废水中的COD去除率达到87%,对于溶液中色度的吸附率可以达到80%。刘庆等[12]将城市污泥负载上TiO2制备光催化剂用于Hg2+的去除,当水溶液中Hg2+的浓度为20 mg·L−1时,材料对溶液中Hg2+的去除率达88.5%。庞浩亮等[13]以焦化废水污泥作为原材料,通过浸渍的方法负载纳米TiO2,以ZnCl2作为活化剂制备污泥基光催化材料降解罗丹明B,去除率达98.16%。游洋洋等[14]利用生物法处理污水的剩余污泥与芬顿氧化法产生的含铁化学污泥为原材料,添加玉米芯为增碳剂,以ZnCl2为活化剂,制备臭氧催化剂降解罗丹明B,其降解效果高于80%。
Fe等金属元素可以促进芬顿反应,因此,很多研究利用污泥制备Fe负载型活性炭。传统的制备方法包括共沉淀或浸渍方法制备的Fe负载型活性炭:通过物理或化学活化的方式处理污泥先得到多孔前驱体,再通过含铁离子的溶液浸渍后进一步炭化[15-16]制得负载铁的活性炭。将污泥制备成吸附剂或者催化剂均有良好的应用价值。但是,无论是将污泥热解为吸附材料还是对污泥进行负载将其制备为催化剂,都需要对其进行活化。单独活化需要加入大量的化学药剂[17-18],以增加材料的孔隙率。例如,以KOH作为活化剂的浓度大约为3 mol·L−1,该方法费用高、工艺设备复杂,还存在未负载上的铁在炭表面结块的现象。本研究选用FeCl3·6H2O(Fe)[19]改性污泥基生物炭(C),提前将脱水污泥与铁盐混合,一步制备铁炭复合材料。以罗丹明B、对硝基苯酚为目标污染物进行实验,检验材料的光芬顿催化效果和稳定性,为污泥的资源化利用和难降解有机污染物的去除提供参考。
脱水污泥基铁炭复合材料用于光Fenton催化降解有机污染物
Dewatered sludge derived iron-carbon composite as a photo-Fenton catalyst for organic pollutant degradation
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摘要: 为实现市政脱水污泥资源化并达到简化制备工艺、节省试剂的目的,采用提前掺杂铁盐的方式一步热解制备铁炭复合催化材料。首先,固定温度为850 ℃,探究铁盐的最佳掺杂量;随后,固定铁盐掺杂比,对其制备温度进行优化。实验共制备了8种材料,选取其中4种代表性材料做XRD、FT-IR、SEM等表征,并选取催化效果最佳的材料探究其可循环性及其在不同pH下对罗丹明B和对硝基苯酚的去除效果。结果表明:铁盐与干污泥的质量比为1∶1、焙烧温度为750 ℃条件下制备材料的催化效果最佳;材料表面形成了具有一定孔隙和花型片状结构,而且存在多种含铁化合物;在pH=7的条件下,对罗丹明B、对硝基苯酚的降解率分别可达88.6%和97.5%。这表明,该材料具有良好的催化性能及宽广的pH适用范围。铁炭复合材料经5次循环使用后,罗丹明B的降解率仍然可达到93.7%,该材料具有较好的稳定性能。Abstract: In order to recycle municipal dehydrated sludge and achieve the purpose of simplifying the preparation process and saving reagents, iron-carbon composite catalytic materials were prepared by one-step pyrolysis with iron salt doping in advance. Firstly, the optimal doping amount of iron salt was explored at the fixed temperature of 850 ℃. Then, the preparation temperature was optimized at fixed iron salt doping ratio. Eight materials were prepared in the experiment, among which four representative materials were selected for XRD, FTIR, SEM and other characterization. The materials with the best catalytic effect were selected to explore their recyclability and the removal effects of RhB and p-nitrophenol at different pHs. The results showed that the composite with the best catalytic effect were prepared at the iron salt-sludge ratio of 1∶1 and the calcination temperature of 750 ℃, which had certain pores, flaky structure and various iron compounds. At neutral pH of 7, the degradation rates of RhB and p-nitrophenol were 88.6% and 97.5%, respectively. After five cycles, the degradation rate of RhB still reached 93.7%. This indicates that the material has a wide range of pH applications, good catalytic properties and good stability.
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Key words:
- dewatering sludge /
- iron modification /
- biochar /
- Fenton /
- photocatalytic /
- organic pollutant
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