Ultrasound pre-treatment of waste activated sludge

Abstract

Waste activated sludge (WAS) is more difficult to digest than primary sludge due to rate limiting cell hydrolysis. High-power ultrasound can effectively disintegrate the bacterial cells and thus enhance the subsequent digestion. This research examines the effectiveness of ultrasound pretreatment on WAS disintegration at different specific energy inputs, ultrasonic densities and total solids (TS) contents. The results show that the cut diameter (d50) for WAS with 2% TS content declined nearly 6.5-fold at an ultrasonic density of 0.67 W/ml. For higher TS contents of 4 and 6%, higher densities of 1.03 and 0.86 W/ml, respectively, were needed to achieve the same degree of particle size reduction. The efficacy of ultrasonic disintegration measured as soluble chemical oxygen demand (SCOD) release was primarily governed by ultrasonic density (W/ml); whereas ultrasonic density did not show a significant effect on protein release at all TS levels. SCOD release of about 320 mg SCOD/g TS was obtained at a TS content of 2% and specific energy input of 5 kWs/gTS. The SCOD release, however, decreased to 160 and 90 mgSCOD/gTS at 4 and 6% TS contents, respectively. The highest protein release of 73 mg/gTS was obtained at a TS content of 2% and specific energy input of 10 kWs/gTS. The sludge disintegration efficiency declined significantly at higher TS content. Thus, there is a limiting TS concentration that could be effectively disintegrated by ultrasound, and this is governed by the capability of an ultrasonic unit in producing cavitation. The degree of disintegration also depends on types of ultrasonic unit used.

Effect of pre-treatments on hydrolysis and methane production potentials of by-products from meat-processing industry

“…This is comparable or higher than the 40 and 89% increase in CODsol when sonicating (20 kHz) raw sewage sludge [32] and waste activated sludge [21,24]. The studied physical (ultrasound and thermal) pre-treatments showed good potential for pre-treating meat-processing industry by-products rapidly, and they have already been reported as the most potential pretreatments for sewage sludge [43].…”

“…in sewage and waste activated sludge [20][21][22][23][24][25], municipal wastewaters [26] and industrial wastewaters [27,28]. Ultrasound pre-treatment evokes cavitation by bubble formation in the liquid phase [20].…”

Ozonation-Based Decolorization of Food Dyes for Recovery of Fruit Leather Wastes

“…17,18 Ozone-based decolorization has been studied combined with other techniques such as ultrasonic irradiation, 19 UV catalysis, 20 or membrane filtration. 21 Oxidative radicals can be generated from ultrasonic irradiation of oxygen and water, 22 and this technique can be applied together with ozonation. 19 The use of ozone-based oxidative treatment started from the early 1900s and has been widely used in the food industry.…”

“…19 The use of ozone-based oxidative treatment started from the early 1900s and has been widely used in the food industry. 23 Ozone-based oxidation was proven to be selective and effective enough for colorant degradation. 18 Combination with other AOP techniques is expected to result in a higher oxidative potential 20,24,25 and lower selectivity in a complex system.…”

Ultrasound ionization of biomolecules

“…Ultrasound has been broadly used in medical imaging for disease diagnosis27–29 and other industrial applications 30, 31. Many of these applications involve the process of cavitation, a phenomenon in which bubbles form in a region where the pressure of the liquid falls below its vapor pressure.…”