Effect of Thermal Hydrolysis
on Rheological Behavior
of Municipal Sludge
- Publication date
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Abstract
Properly
understanding of sludge rheological properties is important
for designing of pumping and translating. Effect of thermal hydrolysis
on rheological properties of municipal sludge was studied using a
rheometer (DHR-2) with concentric cylinder geometry. Test results
indicated both raw and thermal treated sludge displayed non-Newtonian
rheological behavior with shear thinning, exhibiting thixotropic properties
and viscoelasticity. The Herschel–Bulkley model could represent
their flow behavior more accurately than other models. However, for
the raw sludge, as solid content reached 120 g/L, fluidity disappeared,
and all the rheological models could not describe it accurately. After
thermal hydrolysis, the consistency index (<i>k</i>) decreased
significantly, while the flow index (<i>n</i>) increased,
suggesting that thermal treated sludge was much closer to the Newtonian
fluid compared to the raw sludge. Both raw and treated sludge exhibited
strong dependence on solid content and temperature. Correlations between
solid content, temperature, and viscosity were expressed by an exponential
equation and an Arrhenius type equation, respectively. Analysis of
thixotropic properties illustrated that evolution of viscosity over
time could be expressed by a first-order (solid content lower than
100 g/L) and a second-order thixotropic kinetic equation (solid content
higher than 100 g/L), respectively, for raw sludge. For treated sludge,
it could be simulated by a first-order thixotropic kinetic equation.
Furthermore, the dynamic test indicated viscoelasticity of treated
sludge decreased remarkably. For treated sludge, as the solid content
was larger than 120 g/L, viscoelastic parameters were linearly correlated
with logarithm frequency