Journal of Ecology and Rural Environment ›› 2018, Vol. 34 ›› Issue (4): 380-384.doi: 10.11934/j.issn.1673-4831.2018.04.012

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Effects of Double Frequency Ultrasound Improving Dehydration Property of Waste Activated Sludge in Pretreatment

XU Hui-min1, QIN Wei-hua1, LI Zhong-lin1, GU Qi1, DAI Xiao-hu2   

  1. 1. Nanjing Institute of Environmental Sciences, Ministry of Environmental Protection, Nanjing 210042, China;
    2. National Engineering Research Center for Urban Pollution Control/College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China
  • Received:2017-08-21 Online:2018-04-25 Published:2018-04-17

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Abstract:

The use of ultrasound to pretreat waste activated sludge (WAS) is one of the cleanest means, but its practical application is restrained by its high energy consumption. Double frequency as a new parameter is expected to improve dehydration property of WAS and consequently reduce energy consumption. To explore effect of the use of double frequency ultrasound in pretreatment of WAS on its dehydration property, a sequencing batch experiment on use of ultrasound was designed to have three treatments in terms of frequency, i. e. 17, 33 kHz and 17+33 kHz, and carried out under the specific energy of 0-12 000 kJ·kg-1 per unit of total solids (TS). Changes in filterability and centrifugal dehydration property of WAS were monitored by measuring specific resistance of filtration (SRF) and moisture content of dehydrated WAS cake. Results show that double-frequency ultrasound was far too superior to single-frequency one in improving dehydration property of the WAS, when the ultrasounds were low in energy. When treated with ultrasound of 17, 33 kHz, and 17+33 kHz, separately, SRF of WAS was reduced by 44.67%, 57.30%, and 80.41%, respectively. The maximum effect of reducing moisture content in WAS cake by 20.62% was observed in the treatment of double frequency, 17+33 kHz and specific energy of 1 000 kJ·kg-1. With increasing specific energy, mean particle size of WAS declined steadily, but degradation degree of WAS increased steadily, which indicates that extracelluar polymers and organic matter in cells of WAS were changing steadily from solid phase to liquid phase. The higher energy utilization efficiency of double frequency enables it to achieve better dehydration effect with lower energy supply than single frequency, which may serve as a scientific support to extrapolate the pretreatment technique of double frequency ultrasound in practical application.

Key words: waste activated sludge, ultrasound, double frequency, SRF, particle size

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