RESUMEN
The hydrodynamic disintegration process depends, among others, on operational parameters like rotational speed or introduced energy. The study presents an interdisciplinary approach to the hydrodynamic disintegration parameters impact assessment on the internal processes and disintegration effects on the example of sewage sludge treatment. Three rotational speeds were considered, including fluid properties change at selected disintegration stages. Disintegration effects were measured in the bench tests. Soluble chemical oxygen demand (SCOD) and volatile fatty acids (VFA) were measured before and after disintegration process. The assessment of the effects of disintegration employed the disintegration degree and the assessment of the course of methane production employed biochemical methane potential (BMP) tests. Fluid properties change during the disintegration stages does not cause a significant change in the flow structure. Due to the mathematical modelling results, at 1500 rpm no cavitation phenomenon was observed. Although, the bench tests results indicates, for the rotational speed 1500 rpm, organic compounds released to the liquid were characterised by higher susceptibility to biological decomposition than those released for 2500 and 3000 rpm (as suggested by the low SCOD/VFA values for 1500 rpm). Obtained results have confirmed, that the main phenomenon responsible for the disintegration effect is mechanical shredding not cavitation.
Asunto(s)
Análisis de la Demanda Biológica de Oxígeno , Hidrodinámica , Modelos Teóricos , Aguas del Alcantarillado , Eliminación de Residuos Líquidos , Eliminación de Residuos Líquidos/métodos , Ácidos Grasos Volátiles/metabolismo , MetanoRESUMEN
Until recently, sewage sludge produced in wastewater treatment processes was considered problematic waste. It currently constitutes a valuable substrate for raw materials and energy recovery. One of the methods of intensifying resource recovery from sludge is its pretreatment by means of disintegration methods. This study presents the CFD modelling and experimentally investigates the use of a hydrodynamic cavitation rotor operated with various rotational speeds (1500, 2500, and 300 rpm) for the recovery of organic compounds, nutrients, and energy. Rheological properties of raw sludge, a non-Newtonian fluid, were determined and used in the modelling calculations. Cavitation zones were observed for 2500 rpm and 3000 rpm, although a stronger cavitation effect occurred for a rotational speed of 3000 rpm. A rotational speed of 1500 rpm was too low to generate a pressure drop below 1705 Pa, and no cavitation was recorded. An increase in rotational speed from 1500 rpm to 3000 rpm for each analysed energy density caused an increase in SCOD and nitrogen concentration. Moreover, it was determined that at low energy densities (<105 kJ/L), mechanical tearing was the dominant factor responsible for carbon recovery, and at its higher values (≥105 kJ/L), the cavitation phenomenon became increasingly important. Rotation speed also had a significant effect on methane yield (YCH4). An increase in YCH4 by 6.2% was recorded only for disintegrated sludge at a rotational speed of 1500 rpm in reference to untreated sludge. Disintegration conducted at higher rotational speeds led to a decrease in YCH4 (-0.7% for 2500 rpm and -7.9% for 3000 rpm).