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Ultrasound DISINTEGRATION

What is behind this?

RESOLVING CONNECTIONS WITH VIBRATIONS

Ultrasound disintegration for biogas plants and WWTPs

Disintegration means the breakdown of biogenic sludge into minute particles by external forces. The resulting increase in surface area causes an acceleration of the organic breakdown process, and thereby results in an increased biogas yield. In addition, the release of exo-enzymes from the external cell layer increases the enzyme activity in the digester.

THE PHYSICAL PRINCIPLE: CAVITATION

High energy impulses with cavitation implosion in the μm range

In ultrasonic disintegration, the electrical oscillations created by a generator are transformed by a converter (sonic transducer) into mechanical vibrations. These vibrations are transferred into the surrounding medium by means of a device known as a sonotrode. Following the rhythm of the ultrasonic frequency, they cause high alternating positive and negative pressure phases, depending on whether the oscillator is expanding or contracting at the time. During the negative pressure phase, microscopical cavities are formed in the liquid exposed to the ultrasonics; these then collapse in the subsequent positive pressure phase. This process is known as cavitation. From the implosion, which releases high pressures and temperatures, strong impact and shear forces occur in the area immediately around the cavities, and these cause the surrounding micro-organisms to disintegrate.

The core of the DesiUS is the ultrasonic technology from Weber Ultrasonics. The BioPush reactor developed specifically for the treatment of biogenic slurries fulfils the demanding requirements of the disintegration process, and in many aspects is significantly better suited than the usual rod transducers or sonotrode technology.

  • Temperatures of up to 5.000 °C
  • Pressures of up to 1.000 bar
  • High accleration – high shear forces

The Biopush reactor

What is so special?

Due to the cavitation effect on the surface of the transducer, it becomes more and more rough and causes dry matter content of the sludge to get stuck when passing the transducer. Especially fibre materials (e.g. hair) can cause significant problems.

Once material is stuck on the transducer, more and more material will add on and cause the transducer to become increasingly amortized, so that on the one hand side it is not performing any more and on the other hand side, when the transducer will not be able to dissipate its energy, it may overheat and get destroyed. In order to avoid this to happen, the reactor body in which the transducer is installed needs to be opened and cleaned frequently to avoid the issue mentioned before and to avoid clogging. Some applications even inject water occasionally, to avoid (or try to avoid) obstruction.

Design scheme of the BioPush reactor

The BioPush Technology

Through its high-performance surface transducer, the BioPush reactor generates a homogeneous cavitation field within the reactor. The reactor body is rectangular and hosts 6 ultrasound transducers on each side. The 24 ultrasound elements cause the entire body to “swing” with a frequency of around 22 kHz, which virtually quadruples the amplitude.

The effect of the sludge is at least as high as with the standard rod transducer technology but the entire reactor is 100 % maintenance free and has a durability of three years and more. Even problematic substrates such as highly thickened mixed sludges from waste water treatment plants or from agricultural fermentation plants are treated at maximum performance. In traditional ultrasonic reactors, there is usually direct contact between the sonotrode and the substrate, and this inevitably results in continual gradual wear of the sonotrodes. At the start, these plants often produce the same performance as the BioPush, but this rapidly falls off noticeably, because tressing builds up rapidly on the sonotrodes, which are inevitably damaged by cavitation, and this causes damping even to the extent of complete acoustic insulation.

Technical Characteristics of the BioPush Reactor:

  • Up to 25 % more biogas (proven many times over)
  • 2,000 W ultrasound performance per ultrasonic reactor
  • Treatment of substrates with up to 15 % solids content
  • Mechanical pretreatment optional
  • Easy adaption to dynamic flow rates
  • Optimum energy input thanks to homogeneous, contact-free sound field
  • Compact structure
  • Can be cascaded as desired
  • Plug & play

To prove the homogenity, a metal structure wrapped with aluminium foil is placed into the with water filled reactor. After 15 s of ultrasound treatment, the structure will be taken out and the aluminium foil shows a homogenous destructions pattern on all four sides.

A REVIEW

traditional technology: rod transducers

In traditional systems, damping of the cavitation performance increases with the solids concentration. Frequently, therefore, biomass is treated only if it is in the immediate proximity of the ultrasound source.

Lasting time of rod transducers in sludge applications is between six month and two years, depending on the properties of the sludge. Additionally already after a short period of time, rod transducers require extensive maintenance.

 
 
 

Transducer after approx. 9 month in operation in a WWTP
2. Transducer after approx. 9 month in operation in a WWTP

1. New unused rod transducer which is made of Titanium

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