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城市尾水经过深度处理后可作为地表水体的重要补给来源[1]。然而部分沿海城市污水处理厂的尾水存在含盐量过高导致现有深度处理工艺无法达到理想的处理效果,进而影响尾水的再生回用,同时含盐尾水的排放也会对水生态环境产生巨大影响。故需要进一步寻求能够对城市污水处理厂含盐尾水进行深度脱盐处理的新技术。
目前高盐废水处理方法主要有间歇曝气膜生物反应器技术[1-2]、人工湿地法[3]、机械式蒸汽再压缩技术蒸发技术[4-5]、生物膜厌氧折流板反应器法[6]、膜生物反应器(membrane bio-reactor,MBR)污泥驯化法[7-8]等,但普遍存在操作技术难、成本高、进水浓度不宜过高等问题。电容去离子(capacitive deionization, CDI)技术作为一种新型污水处理技术,通过形成双电层吸附离子以去除污染物,其脱盐性能卓越、使用寿命长久、能源消耗极低、且不会对环境造成污染 [9-10]。
电极材料对于CDI技术十分关键。目前常用的电极材料有活性碳颗粒、活性炭纤维、碳气凝胶、碳纳米管、石墨烯、金属氧化物等,但具有成本高、环境要求高、容易产生性能限制等缺点[11-17]。生物炭电极材料以其低廉的成本、广泛的原料来源和丰富的活性官能团等优点,成为一种新型的环保材料,被广泛应用于污染治理领域,在处理废水方面显示出了广阔前景[18]。花生壳作为中国主要农业副产物之一,目前处理方式多为直接燃烧或丢弃,利用率较低[19]。以花生壳作为生物炭原材料,可使其资源化利用。然而,初期炭材料的孔隙结构相对较为狭窄,且其吸附能力受到一定限制,需要进一步改性以增加其孔体积、比表面积和官能团数量[20]。KOH改性可以增加炭材料中羟基、羧基等官能团的含量,提高炭材料孔隙结构,改变其吸附性能[21-22],其常见改性方法有浸渍法和熔融法[23]。其中,浸渍法因操作简便、绿色节能等优点受到广泛关注[24]。本研究选取花生壳粉末为原材料,通过炭化和KOH浸渍改性制备一种孔径结构和表面官能团更为丰富、电吸附性能更好的电极材料,构建和优化CDI系统,以青岛沿海某污水处理厂为例,将优化后的CDI装置和KOH改性炭电极用于对污水处理厂高盐尾水中Cl−的去除,使Cl−可达排放标准。
改性花生壳炭电极的电容去离子技术对高盐尾水中Cl−的去除性能
Cl− removal performance from high salt tailwater by capacitive deionization based on modified peanut shell carbon electrode and its application
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摘要: 以废弃花生壳为原料,探究了炭化条件和KOH改性对炭材料电吸附性能的影响。利用电容去离子(capacitive deionization, CDI)技术,探究KOH改性炭电极(KBPS)对于青岛污水处理厂高盐尾水中Cl−的去除效果。通过SEM、BET、FTIR、XRD、XPS、接触角手段对炭材料理化性质进行了表征。结果表明,随炭化温度增高,炭材料石墨化程度与有序度提升。KOH改性可改善炭材料的比表面积、石墨化程度和亲水性。电吸附实验结果表明,在1 000 ℃下炭化的KOH改性炭电极(KBPS1000)吸附量为11.097 mg·g−1,相比BPS1000提升了30%。在溶液流速为15 mL·min−1、工作电压为1.2 V时KBPS1000的电吸附性能最佳。经过9次吸附-脱附循环后,KBPS1000电极再生率为98.41%,电极再生性能稳定。配制Cl−浓度为2 000 mg·L−1的NaCl溶液,以5对电极板为一组循环,经22组循环后,Cl−浓度由2 000 mg·L−1降至454 mg·L−1,Cl−去除率可达77.3%。Abstract: In this study, the effects of carbonization conditions and KOH modification on the electroabsorption performance of carbon materials were investigated using waste peanut shells as raw materials. Capacitive deionization (CDI) was used to investigate the effect of KOH-modified carbon electrode (KBPS) on the removal of Cl− from the high-salt tailwater of Qingdao wastewater treatment plant. The physical and chemical properties of the carbon materials were characterized by SEM, BET, FTIR, XRD, XPS and contact angle. The result showed that the graphitization and orderliness of the carbon materials increased with the increase of carbonization temperature. The KOH modification improved the specific surface area, graphitization and hydrophilicity of the carbon material. The electrosorption experiments showed that the adsorption capacity of KOH modified carbon electrode KBPS1000 carbonized at 1000 ℃ was 11.097 mg·g−1, which was 30% over that of BPS1000. The best electrosorption performance was achieved at a solution flow rate of 15 mL·min−1 and an operating voltage of 1.2 V. After nine adsorption-desorption cycles, the regeneration rate of KBPS1000 electrode was 98.41%, and the electrode regeneration performance was stable. The NaCl solution with Cl− concentration of 2000 mg·L−1 was prepared, and a set of cycle was performed using 5 pairs of electrodes, the Cl− concentration could decrease from 2 000 mg·L−1 to 454 mg·g−1 after 22 sets of cycles, and the Cl− removal rate could reach 77.3%.
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表 1 BPS1000和KBPS1000中主要元素的质量分数
Table 1. Content of main elements in BPS1000 and KBPS1000
样品 C/% O/% P/% S/% BPS1000 73.4 24.9 1.5 0.3 KBPS1000 90.1 8.1 1.6 0.2 表 2 炭材料的比表面积、平均孔径及孔容
Table 2. Specific surface area, average pore size and pore volume of carbon materials
样品 比表面积/(m2·g−1) 平均孔径/nm 孔容/(cm3·g−1) BPS700 308.02 2.62 0.196 3 BPS800 84.77 6.28 0.121 4 BPS900 354.96 2.72 0.229 7 BPS1000 40.04 5.53 0.050 3 KBPS1000 85.73 7.57 0.151 8 -
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