Technology
Figure 2: Ultrasonic reactor placement locations
waste is highly degradable, it is recommended that only the
thickened waste active sludge (TWAS) be treated. The TWAS
being treated should be in the range of 30,000 to 60,000
mg/L solids concentration. A thicker
solids content optimizes the effectiveness of the reactor because water in
sludge acts as a barrier from the ultrasound, minimizing the effectiveness
of the acoustic cavitation. Sludge with
minimal water content will cause rupturing of the microorganisms more
effectively. Figure 2 shows the optimal locations (as described above)
for placing the ultrasonic reactor in
a wastewater treatment process. The
ultrasonic reactor can be placed in
either of the two locations; however,
they can also be used in both.
organic molecules), is the rate-limiting step
and, therefore, should this stage be altered
or "boosted," the anaerobic digestion process is able to be improved. Ultrasonic
disintegration not only breaks the sludge
floc apart, but with the appropriate dose,
the microorganism cell walls are ruptured,
providing easy access to the intercellular
material (see Figure 3 on the next page).
The cell lysis created by the ultrasonic
reactor has been shown to change the
reaction kinetics of the anaerobic digested
sludge. The process allows for improved
volatile solids (VS) reduction, which in
turn correlates to an increased gas production. Because of the change in the reaction
kinetics, the hydraulic retention time (HRT)
is also altered, allowing for more capacity
in the digester tank. One study comparing
treated and nontreated sludge found that
the VS destruction with a four-day HRT on a treated sample
had the same VS destruction on a nontreated sample with
a 16-day HRT.
Ultrasonic Disintegration In
Anaerobic Digestion Applications
Providing pretreatment with the ultrasonic reactor prior to the anaerobic digestion
process provides several benefits, including 15 to 30 percent improved methane
gas production, increased volatile solids
destruction (resulting in reduced sludge
disposal costs and/or reduced tank sizes
and retention times), viscosity reduction,
foaming control, and even improved
dewatering.
There are four stages of the anaerobic digestion process, and it is wellknown that the first stage, hydrolysis
(complex organic matter to soluble
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