Waste Activated Sludge Disintegration in an Ultrasonic Batch Reactor

Abstract

The production of excess sludge is one of the most serious challenges in biological wastewater treatment. In the present work, disintegration is added as a new additional unit operation in a wastewater treatment plant, and the main objective is to reduce the amount of excess sludge. The use of high power ultrasound can effectively disintegrate the bacterial cells, and thereby, enhance the subsequent biodegradation during digestion. In the study, attempts are made to determine the disintegration capacity of waste activated sludge that has different total solids (TS) concentrations with low ultrasound frequency (20 kHz) and a fixed amplitude value (50%). The results show that in terms of soluble chemical oxygen demand (SCOD) release, sludge disintegration was primarily governed by ultrasonic density (W mL -1 ), whereas specific energy input appears to be more critical for protein release. A SCOD release of about 329 mg SCOD gTS -1 was obtained at a TS content of 2% and specific energy input of 5 kWs gTS -1 . The SCOD release decreased to 248.5 and 124.2 mgSCOD gTS -1 at TS contents of 4 and 6%, respectively. The highest protein release of 80.7 mg gTS -1 was obtained at a TS content of 2% and a specific energy input of 10 kWs g -1 . The sludge disintegration efficiency declined significantly at higher TS content.

Modelling of the ultrasonic disintegration of activated sludge

“…These observations are in high contrast to the claims formulated by Feng et al (2009), who postulated that the ammonia nitrogen concentration of the supernatant rapidly increased with increasing energy input as a direct consequence of the ultrasonic sludge disintegration. The results are, however, confirmed by Khanal et al (2006), Bougrier et al (2005) and Akin (2008), who claim that the ammonium release is a secondary phenomenon due to biological hydrolysis of the released organic nitrogen. The rate of hydrolysis is dependent on the electron donor available, or rather the oxygen concentration in the activated sludge.…”

Effects and modelling of ultrasonic waste‐activated sludge disintegration

“…However, increase in the TS content from 0.5% to 2.0% resulted in a significant decrease in the DD COD because of the reduction of ultrasonic energy per unit amount of solid matters in the sludge. Similar to our study, Akin () and Huan et al . () reported that the higher the concentration of the sludge, the harder it is to disintegrate.…”

“…; Zhang et al . ; Akin ). However, the modelling of ultrasonic sludge disintegration had been scarcely studied so far.…”

Synergistic effects of sono-alkaline pretreatment on anaerobic biodegradability of waste activated sludge

“…This rapid disintegration achieved in the first 2.5 min was likely resulted from the rapid cavitational effect arising from the collapse of powerful transient bubbles generated in fractions of microseconds close to microbial cells [21]. In addition, sonication at higher densities in shorter periods was determined as a more effective alternative for US sludge pretreatment [22,23]. Therefore, these outcomes suggested that US pretreatment could be performed in periods shorter than 2.5 min to reduce both capital and operating costs of the pretreatment process.…”