Design and optimization of a semi‐industrial cavitation device for a pretreatment of an anaerobic digestion treatment of excess sludge and pig slurry

Abstract

The use of hydrodynamic cavitation (HC) as a wastewater treatment and anaerobic digestion pretreatment is a well-known process. However, most of the experiments have been done at laboratory scale and using a low concentration of total solids in the sludge treated. In this study, the waste-activated sludge has been mixed with pig slurry with the aim of treating two wastes rich in nutrients and organic matter. The HC has been studied not only at laboratory scale but also at industrial scale (up to 500 L), using a novel rotating device consisting of a rotor with multiple teeth that rotate inside a grooved stator. The effectiveness of the process has been calculated using the disintegration degree (DD) and analyzing the volatile fatty acids, while the energy efficiency has been determined with specific energy of the sludge solubilization (SE SCOD) and the specific energy. Results show that both the SE SCOD and the specific energy decrease when the cavitation process is scaled from laboratory scale to industrial scale. Specifically, SE SCOD decreases from 2.71 × 10 2 to 0.16 × 10 2 kJ/g SCOD and specific energy decreases from 3.58 × 10 4 to 2.85 × 10 3 kJ/kg TS while DD values show reasonable values up to 17%. © 2020 Water Environment Federation • Practitioner points • A new industrial hydrodynamic cavitation device has been developed to treat industrial wastewater without chemical additives • A volume up to 500 L has been treated at industrial scale experiments. • Sludge with 7% of total solids content was satisfactorily disintegrated. • The process scale-up lead to an energy efficiency enhancement.

Investigation into cavitational intensity and COD reduction performance of the pinned disc reactor with various rotor-stator arrangements

“…Several different cavitator designs have been successfully employed for advanced oxidation of dissolved organic compounds (a review provided in [1] , [6] , [7] ) and disinfection (a review provided in [2] , [8] ) of WW. These include orifice plates [9] , [10] , venturi tubes [10] , [11] , vortex cavitation [12] , and rotating devices [13] , [14] , [15] , [16] , [17] , [18] , [19] , [20] , [21] , [22] , [23] , [24] that will be hereinafter referred to as rotational generators of hydrodynamic cavitation (RGHC).…”

“…This, on the other hand, comes at the expense of a greater complexity of internal geometry and cavitation mechanism as opposed to fixed-geometry cavitators. Several different RGHC designs have been developed in the recent years, including dimpled rotors [14] , [15] , [18] , [19] , [21] , [23] vaned rotor–stator devices [20] , serrated discs [16] , [17] , [25] , [26] , [27] , and pinned discs [22] . Dimpled rotors have been proven effective in sludge solubilization [3] , [15] , destruction of cyanobacteria [18] and in esterification of vegetable oil [23] but are limited by relatively low liquid throughputs and somewhat modest COD removal performance.…”

“…Unlike the RGHC designs discussed above, serrated disc (SD) and pinned disc (PD) variants of rotary cavitating devices are easily scalable, allowing for high wastewater and sludge processing capacity [17] , [22] . The performance of SD RGHC has so far been studied on both lab-scale [25] , [26] , [28] , [29] and pilot-scale [16] , [17] , [27] , [30] with promising results regarding sludge solubilization, fibrillation of conifer fibers, wastewater disinfection and degradation of various dissolved organic compounds (i.e. pharmaceuticals, bisphenols).…”

Multiparametric experimental analysis of the pin disc rotational cavitation generator

“…These were selected systematically and can be divided into three groups depending on the type of feature. First, the cylindrical rotor pins were varied by number of pins (8,12 1. RGHC device types sorted by the utilized cavitation generation mechanisms.…”

“…1 -B). A device in which cavitation is generated in a radial gap between the rotor and stator is studied by Villaroig [12] (Fig. 1 -C) and Cerecedoa [13] (Fig.…”