Ehsan Farno

Net positive energy wastewater treatment plant via thermal pre-treatment of sludge: A theoretical case study

ABSTRACT In a wastewater treatment process, energy is mainly used in sludge handling and heating, while energy is recovered by biogas production in anaerobic digestion process. Thermal pre-treatment of sludge can change the energy balance in a wastewater treatment process since it reduces the viscosity and yield stress of sludge and increases the biogas production. In this study, a calculation based on a hypothetical wastewater treatment plant is provided to show the possibility of creating a net positive energy wastewater treatment plant as a result of implementing thermal pre-treatment process before the anaerobic digester. The calculations showed a great energy saving in pumping and mixing of the sludge by thermal pre-treatment of sludge before anaerobic digestion process.

Comparison between classical Kelvin-Voigt and fractional derivative Kelvin-Voigt models in prediction of linear viscoelastic behaviour of waste activated sludge

Appropriate sewage sludge rheological models are essential for computational fluid dynamic simulation of wastewater treatment processes, in particular aerobic and anaerobic digestions. The liquid-like behaviour of sludge is well documented but the solid-like behaviour remains poorly described despite its importance for dead-zone formation. In this study, classical Kelvin-Voigt model, commonly used for sludge in literature, were compared with fractional derivative Kelvin-Voigt model regarding their predictive ability for describing the solid-like behaviour. Results showed that the fractional Kelvin-Voigt model best fitted the experimental data obtained from creep and frequency sweep tests. Whereas, classical Kelvin-Voigt could not fit the frequency sweep data as this model is not a function of angular velocity. Also, the Kelvin-Voigt model was unable to predict the creep data at low stresses.

Role of regression analysis and variation of rheological data in calculation of pressure drop for sludge pipelines

Sludge pumps in wastewater treatment plants are often oversized due to uncertainty in calculation of pressure drop. This issue costs millions of dollars for industry to purchase and operate the oversized pumps. Besides costs, higher electricity consumption is associated with extra CO2 emission which creates huge environmental impacts. Calculation of pressure drop via current pipe flow theory requires model estimation of flow curve data which depends on regression analysis and also varies with natural variation of rheological data. This study investigates impact of variation of rheological data and regression analysis on variation of pressure drop calculated via current pipe flow theories. Results compare the variation of calculated pressure drop between different models and regression methods and suggest on the suitability of each method.

Investigation on shear induced isothermal crystallization of poly (lactic acid) nanocomposite based on graphene

ABSTRACT In this study, the isothermal crystallization of poly (lactic acid) (PLA) and its graphene-based nanocomposites (containing 0.5, 1, 2, and 3 wt% of graphene nanoplatelets – GNp) was studied at 135°C under quiescent and different presheared conditions (0.1, 0.3, 0.5, 1.1, and 1.8 s for 60s). Induction time of crystallization was determined from the plot of storage modulus versus time in time sweep test. Results showed that increase in GNp content decreased the induction time significantly. The preshear flow did not significantly affect the induction time of PLA containing 0.5 wt% of GNp and neat PLA. However, an increase in the intensity of preshear for graphene-based nanocomposites containing 1, 2, and 3 wt% of GNp first decreased the induction time and then increased it. The induction time also decreased with increase in the duration of shear flow.