Sonication of Biosolids

Biosolids as for example sewage sludge or biomass from renewable primary products, bring a definitely higher output if processed with ultrasonic tech. The effect is an intensification of the digestion process without the need to add chemical agents.

The sonication of biosolids is a process whose basics were analyzed at the University of Hamburg-Harburg (TU). After an intense research period, SONOTRONIC put this process into practice, presenting an innovative technology for biomass disintegration and for disinfection of different liquids.

The function of this technology can be explained as follows: Sonication treatment destroys parts of the cells of the biomass liquefying them. This liquefied material is definitely better decomposable by micro-organisms for example in the digesters of a biogas plant. This means that the digesting process runs off much better, increasing the biogas output by up to 50 % and a corresponding reduction of residual substrate as waste. Further positive effects are: an important reduction of digesting-tower volume and an increased dehydration rate of the biomass.

One big advantage of ultrasounds in this field is also the possibility to increase production of environmental-friendly energy and to reduce the volume of waste materials (applies for waste water treatment plants) which must be disposed. The ultrasonic treatment turns out to be an economically and ecologically extremely reasonable process for urban and industrial waste water treatment plant operators as also for biogas plant operators.

The ultrasonic effect is very helpful for the treatment of biosolids because it generates a periodic compression and depression of the sonicated substance. If the ultrasonic intensity is high, the medium in the substance will be torn apart during the depression phase. This generates microscopic bubbles inside the liquid, which are filled with vapour or gas.

In the following compression phase these bubbles implode under extreme conditions in micro scale (cavitation). This generates pressures of over 500 bar and enormous shear forces at temperatures of up to 5,200 Kelvin. These processes tear up the walls of organic cells, bacteria, fungi etc.

Ultrasonic and cavitation principles

Ultrasonic and cavitation principles

In the lower frequency range (20 kHz to 100 kHz) big cavitation bubbles are generated which excite extremely high shear forces and strong effects.In the middle frequency range (100 kHz to 1 MHz) the bubbles are smaller but the cavitation is more effective, generating radical sono-chemical reactions in the water. Sonicating such a liquid with a frequency of over 1 MHz, the liquid begins to flow on molecular level.

The SONOTRONIC system works with the frequency of 20 kHz which gives the best reactions and effects in the biomass.

Change of the biomass structure through sonication

Change of the biomass structure through sonication

SONOTRONIC succeeded to turn this technology into practice together with academics of the University of Hamburg-Harburg (TU) by developing a product until maturity phase: the High-Output Ultrasonic Reactor. Biosolids in urban and industrial waste water treatment plants as also in biogas plants can be effectively processed with systems of one or more ultrasonic reactors.

Function diagram of the High-Output Ultrasonic Reactor

Function diagram of the High-Output Ultrasonic Reactor

  1. Feed pipe
    The bio mass is brought from the clarification plant to the system by a pump (waste water treatment plant).
    The bio mass is brought from the digesting tower to the system by a pump in bypass (biogas plant).
  2. Ultrasonic transmitter
    Generation of a cavitation field inside the biomass by several ultrasonic transmitters with 20 kHz.
  3. Cavitation field
    Cracking of organic cells, bacteria and fungi inside the biomass through high shear forces.
    Release of cell ingredients.
  4. Flow
    Cascade flow of the biomass through the ultrasonic reactor with the effect that every single flake is sonicated and led through the cavitation field.
    Upward gas and air exhaust.
  5. Downpipe
    Discharging of the sonicated biomass into the digesting tower
    (waste water treatment plant).
    Backflow of the sonicated biomass in the fermenter (biogas plant).
  6. Drain pipe
    To drain the reactor with water.

 

Principle of the sonication