Moisture distribution in sewage sludge based on soil-water characteristic curve
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摘要: 市政污泥的脱水特性与其水分分布特性密切相关,对市政污泥的水分分布特性开展研究具有重要的理论意义。目前测试污泥水分分布曲线采用热重-差热分析方法,该方法中试样量仅有50 mg,测试结果复现性较差。拟提出一种基于持水曲线的市政污泥水分分布测试方法,并构建了新测试方法的理论框架。随后采用渗析法联合相对湿度法测试了市政污泥的水分分布曲线,并与传统的热重差热试验结果进行对比分析。研究结果表明,基于持水曲线的污泥水分分布测试方法具有如下特点：试验量多；测试过程中试样结构状态变化小；测试的结合能范围更广泛。Abstract: The dewatering characteristic of sewage sludge is closely related to its moisture distribution. The researches on the moisture distribution characteristics in the sewage sludge are of important theoretical significance. Currently the measurement of moisture distribution curve of the sewage sludge mainly adopts the thermal gravimetry-differential thermal method, in which the amount of samples is only 50 mg, and the reproducibility of the tests is poor. A new method for measuring the moisture distribution in the sewage sludge based on the soil-water characteristic curve is proposed. Firstly based on the relationship between water potential and bond strength of moisture in the sewage sludge, the formula for bond strength of moisture and matric suction of the sewage sludge is derived. Accordingly the moisture distribution curve of the sewage sludge can be obtained by measuring its soil-water characteristic curve. The osmotic method and the relative humidity method are employed to obtain the moisture distribution curve of the sewage sludge. The results are compared with those based on the combined thermal gravimetry-differential thermal method. The proposed method for the moisture distribution in sewage sludge based on the soil-water characteristic curve has following features: the amount of samples is enough and representative, the change of structure of samples is small during measurement process, and the range of bond strength of measured moisture is wider.
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图 2 污泥水分结合能、吸力与含水率的关系
Figure 2. Relationship among water-solid bound strength, matrix pressure and residual moisture content
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图 5 渗析法不同吸力作用下污泥试样含水率变化曲线
Figure 5. Residual moisture content versus time under different suction pressures in osmotic method
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图 6 相对湿度法不同吸力作用下污泥试样含水率变化曲线
Figure 6. Residual moisture content versus time under different suction pressures in relative humidity method
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图 9 纯水恒速蒸发过程中DTG-DTA关系
Figure 9. Relationship between mass loss rate and voltage difference data in pure water tests
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图 10 热重差热分析得到的污泥水分结合能-含水率关系
Figure 10. Solid-water bound strength versus residual water content by combined thermal gravimetry analysis and differential thermal analysis
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图 11 不同测试方法（持水曲线方法、热重差热法）测得的污泥水分分布曲线
Figure 11. Continuous moisture distribution of sewage sludge by different methods
表 1 污泥试样的基本性质
Table 1 Basic properties of sewage sludge
含水率/% 有机质含量/% 密度/(g·cm-3) 相对质量密度 pH 粒径/μm Zeta电位/mV 860 40 1.05 1.8 8.2 0.6~677 -22.5 
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表 2 PEG20000溶液的浓度及其对应的吸力
Table 2 Concentrations of PEG 20000 solution and corresponding osmotic suction pressures
吸力/MPa 4.2 1 0.625 0.3162 0.1 0.033 浓度c 0.618 0.301 0.238 0.169 0.095 0.055
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表 3 相对湿度法中饱和盐溶液及控制吸力值
Table 3 Salt solutions and corresponding suction pressures in relative humidity method
饱和盐溶液 相对湿度/% 对应吸力/MPa MgCl2.6H2O 33.1 149.51 K2CO3 43.2 113.50 Mg(NO3)2.6H2O 55.0 82.00 NaCl 75.5 38.00 (NH4)2SO4 81.0 24.90 NaSO3.7H2O 90.9 12.90 K2SO4 97.6 3.29
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