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Vergara L1, Swain D1, Melia J1, Neis U2,3 & Nickel K2
1Ultrawaves Reactors UK. 2Ultrawaves GmbH, Germany & 3Technical University of Hamburg - Harburg, Germany
Introduction
Sludge produced in wastewater treatment
plants (WWTP) reaches 1% of the volume
treated whilst the processes for sludge
handling represent up to 60% of O&M costs.
Moreover, the each time stricter EU Directive
requirements regarding Biological Nutrient
Removal (BNR) present a challenge whenever
many of the facilities generate a weak sewage
that can not provide adequate carbon to drive
an efficient BNR which leads to external carbon
sources, meaning significant costs and new
collateral (environmental) problems to be faced.
Ultrawaves ultrasound (US) technology
represents a well proven solution for both
issues. Disintegrated sludge is easy to
biodegrade and provides with an
autochthonous carbon source which leads to
excess sludge reduction and BNR respectively.
Metrics
Sludge cell disruption is determined by the
soluble Chemical Oxygen Demand COD (CODs).
The activities of hydrolytic enzymes related to
the hydrolysis of the particulate COD (CODp) is
also affected by sonication.
Both effects (CODs release & CODp hydrolysis)
and the right US dose to be applied, play an
important role in excess sludge reduction and
denitrification step modelling.
References
Bünde WWTP is one of the full-scale
installations where Ultrawaves performs on
ASP + BNR. The site has a capacity of 54,000
PE and includes an alternating nitrification &
denitrification process where 500 kg/d of
methanol had to be dosed to reach the required
nitrogen level in the final effluent.
The first Ultrawaves US technology effect
implies an excess sludge (WAS) reduction.
The second main effect consists on the supply
with an autochthonous carbon source to
support an efficient denitrification process,
meaning an important concept: a waste (cost)
has been transformed into a resource (saving).
Other positive results of sonication are the
complete elimination of associated problems
with bulking and foaming and an improvement
in the sludge cake dewaterability.
Objective
This work aims to close the loop concerning US
effect on Activated Sludge Process (ASP) which
also includes BNR.
The acquired know-how (R&D, pilot plants and
full-scale installations) allows the ASP + BNR
modelling.
The Ultrawaves technology
In aqueous media and certain frequencies and
intensities, US waves produces cavitation
bubbles. When these bubbles collapse, they
cause mechanical shear forces capable of
destroying all type of biomass.
Extensive R&D and Hi-Tech standards have led
Ultrawaves to the development of an US reactor
which optimises biomass disintegration.
Summary
• Yh can be reduced from 0.67 up to 0.43 mg
CODsynthesized/mg CODremoved.
• Released CODs supports 1st kinetic
denitrification (meaning between 10 to 20%
of the nitrates removed by US).
• Sludge hydrolysis rate (increased by ≈ 200%
through sonication) supports the 2nd kinetic
denitrification meaning the removal of the
remaining nitrates (between 80 to 90%).
• US dose to be applied rounds 4 kWh/m3.
• The amount of sludge to sonicate depends
on several variables (required carbon
source, Stress Factor (SF), etc.).
Contact details
Luis Vergara
00 44 (0) 151 424 4621
Application
The application consists on the thickened
waste activated sludge (TWAS) sonication and
its recycling back into the AS + BNR process.
TWAS sonication solubilises sludge biomass
and produces more biodegradable compounds.
Moreover, sludge growth yield (Yh) and
denitrification rates are enhanced.
The Ultrawaves US technology has a very small footprint (1.45 m x 0.25 m) and is
very easily integrated in municipal and industrial WWTP.
Process modelling of excess sludge reduction
and biological nutrient removal through ultrasonic
disintegration of the biomass
Ultrawaves US technology
R&D and installations
ASP + BNR modelling
Disintegration of sludge biomass in WWTP. The first effect is floc deagglomeration
and further sonication opens the biomass cells and releases enzymes.
US effect on TWAS
leads to cell lysis
and cryptic growth
process, where part
of the new substrate
is mineralised as by-
product of
respiration. In
addition, sonicated
sludge is an
autochthonous
carbon source to
support
denitrification
Ultrawaves US technology may be installed in different applications within WWTPs
and red circle shows the right place to optimise excess sludge reduction & BNR.
Sludge reduction & BNR
Before US
After US
By sonication of sewage sludge, biological cells are disrupted and more dissolved
organic material (colloidal and soluble fractions) is made bioavailable.
Dehydrogenase activity (DHA) is directly responsible for driving the e- transfer
chain reaction in respiring cells and assess the biomass metabolic activity.
One 5 kW US unit was installed to sonicate a TWAS flow of 1 m3/h (aprox. 30% of
the TWAS). Sonicated flow had a TS content between 4 to 5% (TS = Total Solids).
Excess sludge reduction is assessed in terms of the specific WAS production
(WAS generated per COD at the inlet) with and without sonication.
Nitrogen level in the final effluent is reached without an external carbon source to
be added (methanol dosing was stoped) and using just sonicated sludge.