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随着我国城镇生活污水处理量的日益增加,污泥处理处置问题越来越受到社会的关注。截至2019年底,我国污泥产生量已超过6 000×104 t(以含水率80%计),预计2025年将突破9 000×104 t[1]。作为污水处理过程的副产物,剩余活性污泥含水率较高,组成复杂,呈类凝胶结构,存在脱水困难的问题[2]。为改善污泥脱水性能,需要投加药剂对其进行调理,而调理药剂的费用占污水处理厂运行费用的比例可达20%[3-4],显著影响了污水处理厂的运行。因此,实时反馈污泥脱水性能、精确控制调理药剂的投加具有一定的现实意义。
污泥的流变学测量常用于间接确定污泥调理的最佳投药量,国内外多位学者通过监测污泥流变学参数(粘度、初始峰值、剪切模量、总扭矩)反馈污泥脱水性能、预测污泥调理过程中的聚丙烯酰胺(PAM)投加量[5-8]。WANG等[9]通过Floccky和Haake RV20流变仪研究了阳离子聚丙烯酰胺(CPAM)调理对消化污泥流变特性的影响,发现2种流变图中初始峰值和面积的最大值所对应的CPAM投加量与优化出的CPAM最佳投药量接近。OLIVEIRA等[10]采用流变学参数监测了污泥脱水性能的变化,发现污泥的剪切粘度可以反馈污泥脱水性能。然而,在污泥调理过程中,在线测量流变参数尚未实现,流变模型的选择亦较为主观,高度依赖于实验条件(剪切速率、污泥种类等),另外,流变仪结构精密、价格昂贵,限制了其在污泥调理中的应用[11]。因此,仍需进一步研究能够实时反馈污泥脱水性的相关技术。
电化学阻抗谱(electro chemical impedance spectroscopy, EIS)是一种通过对电场微扰动的监测来在较大频率范围内测量系统阻抗(交流电势与电流信号的比值)的方法[12],具有检测精确且无损的优点,被广泛应用于生物、电池、半导体材料等领域[13-15]。DIEUDE等[16]研究了污泥流变和电化学特性之间的联系,发现在温度变化的条件下,污泥的粘度和电化学阻抗模量Z之间呈线性关系,并且电化学参数有望实现现场在线测量。SEFALEN等[17-18]研究了污泥的含固率和温度2种因素分别对污泥流变和电学特征的影响。结果表明,污泥的表观粘度随着污泥含固率的升高、温度的降低而升高,其导电性则随着污泥含固率的升高、温度的升高而升高。虽然已有的研究对污泥流变学特征与电化学特征之间的联系进行了分析,但均未涉及到污泥混凝调理的过程,且污泥的电化学阻抗特征能否用来指示脱水性能尚未可知[19]。
本研究选取FeCl3作为调理药剂,对北京3座具有不同处理工艺的污水处理厂的剩余活性污泥进行混凝调理,考察FeCl3投加量对剩余活性污泥脱水性能、理化性质和电化学阻抗谱的影响,探讨剩余活性污泥脱水性能参数与电化学阻抗谱参数之间的关联关系,判断电化学阻抗谱参数指示污泥脱水性能的可行性。
活性污泥脱水性能与电化学阻抗谱参数的关联特性
Study on the correlation between dewatering performance of activated sludge and electrochemical impedance spectroscopy parameters
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摘要: 为探究FeCl3混凝调理过程中活性污泥脱水性能与电化学阻抗谱参数的关联关系,选取北京3座污水处理厂的剩余活性污泥,研究不同调理投药量下活性污泥的毛细吸水时间(CST)、比阻(SRF)、抽滤含水率、Zeta电位、电导率以及电化学阻抗等指标的变化,通过Pearson相关性分析讨论污泥脱水性能与阻抗谱参数(ds/fc)的相关性,并探讨ds/fc预测污泥脱水性能的可行性。实验结果表明,FeCl3调理活性污泥的较适投加量为100 mg·g-1;超过100 mg·g-1时,活性污泥CST、SRF、抽滤含水率基本不再下降,Zeta电位却缓慢升高;电化学阻抗Z则随着投加量的增加而持续下降,且Nyquist图中高频区半圆面积减小,这表明电子更易转移、污泥更易导电。相关性分析表明,活性污泥的脱水性能均与ds/fc呈显著正相关(r > 0.639,p < 0.01);3种活性污泥CST、SRF、抽滤含水率分别与ds/fc的线性回归结果显示它们之间呈线性关系,且线性方程斜率为正值(R2 > 0.921,p < 0.01)。上述研究结果表明,活性污泥的ds/fc参数可以作为指示脱水性能的潜在指标。本研究结果可为污泥减量化技术提供参考。Abstract: In order to explore the correlation between the dewatering performance and electrochemical impedance spectroscopy parameters of activated sludge (AS) conducted by FeCl3 coagulation, the AS samples were taken from three sewage treatment plants in Beijing. The variations of capillary suction time (CST), specific resistance to filtration (SRF), moisture content after vacuum filtration, zeta potential, conductivity and electrochemical impedance spectroscopy with FeCl3 doses were investigated. Pearson coefficient was used to explore the correlation between sludge dewatering performance and impedance spectrum parameter (ds/fc), and the feasibility of impedance spectrum parameter ds/fc predicting the sludge dewatering performance was also discussed. The results showed that the appropriate dosage of FeCl3 was determined as 100 mg·g-1. Beyond this dosage, CST, SRF, moisture content after vacuum filtration of activated sludge basically did not decrease, and the rising rate of zeta potential slowed down. However, with the increase of dosage, the electrochemical impedance Z decreased, the semicircle area in the high frequency region in Nyquist plot decreased, which indicated that more easy charge transferred and higher conductivity could occur. Significant positive correlations occurred between AS dewatering performance and ds/fc with the corresponding indicators of r>0.639 and p < 0.01. Moreover, the linear regression equations with positive slopes (R2 > 0.921, p < 0.01) could be determined between the dewatering performance parameters, such as CST, SRF and moisture content after vacuum filtration, and the ds/fc values of three types of AS, respectively. This implied that the parameter ds/fc can be taken as the potential index to indicate the dewatering performance of AS. Therefore, this study provides a support for sludge reduction technology.
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表 1 剩余活性污泥样品的基本特性
Table 1. Basic characteristics of the sewage activated sludge sample
实验编号 供试工艺 处理规模/(m3·d−1) 含水率 pH CST/s TSS/(g·L−1) 电导率/(mS·cm−1) S1 A/O 1.0×106 98.78%±0.01% 7.35±0.02 75.2±0.2 12.1±0.1 1.21±0.01 S2 A2/O 6.0×105 97.40%±0.01% 5.91±0.02 80.3±0.3 25.6±0.2 1.74±0.02 S3 氧化沟 2.0×104 97.43%±0.03% 7.26±0.02 63.5±3.5 25.7±0.5 1.13±0.01 表 2 活性污泥脱水性能指标与ds/fc的K-S检验
Table 2. K-S test of activated sludge dewatering performance index to ds/fc
变量 样本量 平均值 K-S检验 Z值 P值 ds/fc 20 2.924 6 0.113 0.200 CST 20 51.685 0 0.109 0.200 SRF 20 0.894 0 0.191 0.055 抽滤含水率 20 84.930 0 0.150 0.200 表 3 活性污泥脱水性能指标与ds/fc的Pearson分析结果
Table 3. Pearson analysis of activated sludge dewatering performance index to ds/fc
变量 样本量 ds/fc Pearson相关系数 p CST 20 0.724** 0 SRF 20 0.930** 0 抽滤含水率 20 0.639** 0.002 注:**,在0.01水平(双侧)上显著相关。 -
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