Denmark’s largest wastewater treatment company uses BioSec®

Denmark’s largest wastewater treatment company uses BioSec®

After BIOFOS ran three independent field trials at their municipal wastewater plant in Avedøre, they chose to use BioSec® on an ongoing basis.

About Biofos

  • Denmark’s largest wastewater treatment company

  • Clean 104 million m3 wastewater/year

  • Serve 1.2 million people

  • Run three treatment plants in Denmark

  • Incinerate 24,000+ tons sludge dry solids per year

  • Generate electricity, biogas and district heating

Field trials lead to ongoing BioSec® use

The results of BIOFOS’ three independent field trials of BioSec® in 2017 and 2018 were convincing:

  • Cake dryness after mechanical dewatering increased by 1.5-1.6 %-points

  • Polymer consumption reduced by up to 15% (9.4 kg/t TS to 8.3 kg/t TS)

  • Reject water quality improved (lower TSS, COD)


So convincing, in fact, that BIOFOS has continuously been using BioSec® since April 2019. And nearly a year later, the Danish wastewater leader reported these results:

  • Up to 2 %-point improvement of cake dryness after dewatering

  • 15% reduction in polymer consumption 

  • Centrifuges running at lower speed (energy audit in progress)

"We have never seen such clean reject water before"

The plant treats mainly municipal wastewater

The setup at BIOFOS Avedøre is typical of most municipal wastewater facilities. BIOFOS Avedøre pre-thickens primary and secondary (excess activated) sludges in primary and secondary clarifiers. Then they treat and stabilize mixed primary and waste-activated sludge in four parallel anaerobic digesters.

Each egg-shaped digester operates as a one-stage reactor at mesophilic conditions with approximately 25 days hydraulic retention time (HRT). Then they pump digested sludge (800-1000 mper day) into four equalization holding tanks. These open basins use aeration for mixing with an HRT of 8-24 hours. 

Dewatering takes place in one of three centrifuge decanters, operated 24/7. The plant incinerates the biosolids generated on site.

Adding a small dose of BioSec® to the digested sludge can help increase cake dryness and save on polymers

A plug-and-play solution

In the trials, BIOFOS doses BioSec® into the sludge stream between the anaerobic digester and the post-digestion sludge holding tanks. They allowed 8-24 hours of enzyme reaction time with the digestate before dewatering.

"Implementation and dosing start-up was both quick and easy"

One dose of BioSec® was tested in all three trials (0.25 kg BioSec®P and 0.25 kg BioSec®C/t TS; total dosage 0.5 kg/t TS).

Ready to try it out?

Novozymes BioSec® is a liquid solution containing two different, proprietary enzymes – BioSec®P and BioSec®C. Novozymes has specifically developed these enzymes to condition anaerobically digested sludge and improve dewaterability. 

BioSec® is used to increase sludge cake dryness and decrease flocculant consumption during mechanical dewatering of digested sludge.

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Conditions during the field trials

BIOFOS evaluated the impact on dewatering of digested sludge by centrifuge based on:

  • Cake dryness after mechanical dewatering

  • Polymer consumption

  • Quality of reject water


They monitored the following operating parameters during both test and reference periods:

  • Digested sludge flow to centrifuges

  • Total solids flow to centrifuges

  • Ratio of primary and secondary sludge fed to digestion

  • Digestion performance


Centrifuge settings were constant throughout. BIOFOS also monitored parameters known to influence sludge dewatering performance and took them into consideration during data evaluation. These include load of primary and secondary sludges to anaerobic digestion, anaerobic digestion performance, sludge load and flow to the centrifuge. 

For complete details, graphs and tables of the test results, please contact us.

General questions

What is a microorganism? What is a microbe?

Microorganisms – also called microbes – are microscopic, living organisms that can reproduce if the proper environmental conditions are met. Microorganisms are the most abundant organisms on Earth. In fact, scientists estimate there are more than 5 nonillion (5 x1030) microorganisms on the planet. Microorganisms are the heart of any biological wastewater system.

What is the difference between microbes and enzymes?

The microbes in Novozymes biological solutions get the job done by producing enzymes. That’s why they’re often called “enzyme factories.” Enzymes are very specific catalysts in biochemical reactions that break down organics and grease. An enzyme’s activity depends on the molecular shape of the enzyme fitting to the shape of the compounds in the desired biochemical reaction. 

Enzymes are not alive, and they can’t reproduce themselves. In addition to producing enzymes, microbes ensure efficiency. As long as the microbes are alive, they can detect the organics present and produce exactly the enzymes needed to break down specific organics.

About sludge dewatering

How do the enzymes in BioSec® work?

The enzymes in BioSec® target and disrupt the colloids present in the digested sludge. The colloids are hydrophilic, and they saturate flocculants. By disrupting the colloids, enzymes make the floc more tightly aggregated. There is better water release from the sludge structure and better incorporation of the flocculant and particles. This results in an optimized mechanical dewatering process.

Can BioSec® increase the dewatering capability of challenging sludge to dewater? 

We can test the compatibility of a particular sludge to enzymatic conditioning. In most cases, you can expect benefits from disaggregating the sludge’s colloidal structures. 

Is the sludge cake different after dosing BioSec®? 

The stability of the cake is not altered after adding BioSec®. The only difference is less water content. 

What is the effect of overdosing BioSec®?

Overdosing would entail the loss of the desired performance by BioSec®. There would be no other effects on later steps in the process line.

Does your solution require a sludge holding tank? What if this is not present?

A minimum of 6 hours of enzymatic contact time is required. BioSec® can be applied via an existing post digester, buffer sludge tank or similar. These are found in many facilities for extra flexibility on sludge dewatering and handling.

Is an optimization or CAPEX required onsite to use your solution effectively?

No further optimization or process adjustments are needed to implement BioSec®

Could a side stream trial be performed to see if BioSec® has an impact?

Yes, assuming process requirements are met. However, BioSec®’s particularly small footprint and plug-and-play nature also make full-scale trial implementation convenient. 

Frequently asked questions

If you don’t find the answer to your question here, please contact our experts.