Chemical Engineering, School of Engineering, RMIT University, 3001, Melbourne, Australia.
Department of Chemical & Material Engineering, The University of Auckland, Auckland, New Zealand.
Water Res. 2019 Jun 1;156:445-455. doi: 10.1016/j.watres.2019.03.039. Epub 2019 Mar 23.
Rheological properties are important in the design and operation of sludge-handling process. Despite this, the rheology of sludge in thermal hydrolysis processes (TH) is not well described. In-situ measurements were performed to characterize the flow behaviour of various concentrations (7-13 wt%) of waste activated sludge (WAS) at TH conditions. Equations were presented for predicting in-situ rheological parameters (high-shear viscosity, η, consistency index, k, and yield stress, σ) under various treatment conditions, which are useful for design of process units. The equations enable convenient estimation of in-situ properties based on ambient rheological measurements. Results suggested that the proportion of sludge solubilization and its rate were unaffected by varying sludge concentration. Thermally treated sludge still exhibited gel-like, viscoelastic characteristics similar to untreated sludge; however, the storage (G') and loss (G") moduli decreased with higher treatment temperatures. Frequency and creep responses were described by a fractional derivatives Kelvin-Voigt (FKV) model, which showed increasing viscous characteristics of treated sludge. These equations can be utilised in CFD models. Results obtained from oscillatory measurements can also approximate steady-shear behaviour by comparing dynamic viscosity, η'(ω), and steady-shear viscosity, η(γ̇), whose values were very similar. This enables convenient estimation of steady-shear behaviour of sludge from oscillatory measurements, which is found to be a non-destructive technique for measuring flow behaviour of highly concentrated sludge. Yield stress can also be predicted from the product of modified Cox-Merz shift factors and storage modulus (G'). Practical engineering implications of the rheological observations were discussed.
流变性质在污泥处理过程的设计和运行中很重要。尽管如此，热水解工艺（TH）中污泥的流变性并没有得到很好的描述。进行了原位测量，以表征各种浓度（7-13wt%）的废活性污泥（WAS）在 TH 条件下的流动行为。提出了用于预测各种处理条件下原位流变参数（高剪切粘度η、稠度指数 k 和屈服应力σ）的方程，这些方程对于工艺单元的设计很有用。这些方程可以根据环境流变测量方便地估算原位特性。结果表明，污泥的溶解比例及其速率不受污泥浓度变化的影响。经过热处理的污泥仍然表现出与未经处理的污泥相似的凝胶状、粘弹性特征；然而，储存（G'）和损耗（G"）模量随处理温度的升高而降低。频率和蠕变响应由分数导数凯夫林-伏格特（FKV）模型描述，该模型显示出处理过的污泥的粘性特征增加。这些方程可用于 CFD 模型。通过比较动态粘度 η'（ω）和稳态剪切粘度 η（γ̇），还可以通过振荡测量来近似稳态剪切行为，其值非常相似。这使得可以从振荡测量方便地估算污泥的稳态剪切行为，这被发现是测量高浓度污泥流动行为的一种非破坏性技术。屈服应力也可以通过修正的 Cox-Merz 移位因子和储存模量（G'）的乘积来预测。讨论了流变学观察的实际工程意义。
