Effects of thermal hydrolysis temperature on physical characteristics of municipal sludge

Abstract

Effects of thermal hydrolysis temperature on the physical properties of municipal sludge was further studied by a series of experiments. There was a decrease in bound water content with an increase in hydrolysis temperature, while there was an increase in pH at temperatures below 120 °C, and a decrease at temperatures exceeding 120 °C. An analysis of settleability, centrifugation and vacuum filtration of the treated sludge indicated that the threshold temperature was 120 °C, which was the same as the temperature for the bound water content and particle size. In addition, raw sludge with a solids content of 100 g/L, exhibited significant non-Newtonian fluid characteristics. At thermal hydrolysis temperatures exceeding 120 °C, non-Newtonian fluid characteristics including liquid and solid characteristics were significantly weakened. The consistency index (k) decreased from 5.90 Pa·s to 0.068 Pa·s, while the flow index (n) increased from 0.31 to 0.74, suggesting that thermal hydrolysis sludge was much closer to Newtonian fluids compared to raw sludge. Modification of bound water content, particle size and viscosity with hydrolysis temperature, revealed the nature of improved dewaterability by thermal hydrolysis. The fractal dimension of the sludge floc increased from 2.74 to 2.90, meaning that the floc became more compact after thermal hydrolysis.

Mixing Due to Natural Convection in a Hydrothermal Reactor: A CFD Study

“…For this reason, we employed a modified version of the model with a user-defined-function (UDF), with the following form η ( T ) = k ( T ) γ̇ n ( T ) − 1 μ ( T ) μ 20 ° C where η is the non-Newtonian viscosity, k ( T ) and n ( T ) are the parameters of the power-law model, specified as functions of temperature, γ̇ is the shear rate, μ( T ) is the viscosity of water as a function of temperature (as per the equation reported in Table ), and μ 20 °C is the viscosity of water at 20 °C. The values of k ( T ) and n ( T ) are interpolated among the values reported in Table 2 of the work of Feng et al for the convenience of readers, these values are reported in the Supporting Information, together with a plot that depicts the viscosity trend.…”

“…In the work by Feng et al, 50 the authors study the behavior of a sludge with 100 g/L of solids (a typical value for sludges) after thermal treatment, for temperatures up to 200 °C. The treatment largely reduces the viscosity and changes the fluid's behavior to Newtonian when performed at least at 120 °C.…”

Energy and exergy optimization of food waste pretreatment and incineration

“…By TH pretreatment, the internal structure and cell walls of FW are destroyed. And bound water inside the FW gradually converts to free water, resulting in a remarkable improvement of FW dewaterability, and the moisture contained can be easily reduced (Feng et al 2015;Song et al 2014).…”

Reducing Sludge Viscosity and Improving Dewaterability through a Thermochemical Hydrolysis Process

“…Excessively high viscosity requires higher energy input for mixing (Russ et al 2015). Thermal hydrolysis pretreatment significantly decreases sludge viscosity (Feng et al 2015, Bougrier et al 2008 and enables better mixing in anaerobic digester for high solids digestion (Baudez et al 2011).…”