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

luis@ultrawaves.co.uk

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.