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Sewage sludge drying

Current situation

The major disadvantage of the sewage sludge drying processes currently available on the market is the high energy consumption. This can only be reduced by compensatory measures such as waste heat utilization, mechanical treatment or the use of solar energy.

With its newly developed sewage sludge drying in the low-temperature range, PH2 now provides a very cost-effective disruptive process that allows the sewage sludge to be dried in an energy- and time-efficient way. Any existing waste heat can thus be used for other processes.

PH2 plant for sewage sludge drying

Up to 80% energy and cost savings compared to processes previously available on the market

Input: Sewage sludge with DM from 0.5 to 30 %
Output: Sewage sludge powder with DM of 85 %

Example calculation:
1 t sewage sludge (at TS 20) yields 220 kg sewage sludge powder

Several demonstration plants under construction and soon ready for operation
Place of use of the demonstration plants: Sewage treatment plants in the vicinity of PH2


Reduction of current disposal costs by 30 to 70%

High energy efficiency: 80% savings compared to previous processes by using low temperature

Reduction of the amount of sewage sludge by 70 to 99.5% by drying. This significantly reduces storage and transport costs.

Amortization of the plant at 2 to 4 years

Better conveyability and dosing due to fine-grained sewage sludge powder

Inhibition of microbiological processes

Hygienic safety

Increase of the calorific value

Sewage sludge drying with low temperature -
the future-oriented technology

The sewage sludge drying is in operation on a laboratory scale and produces a sewage sludge powder with a dry content of 70% – 85% from sewage sludge, which has been pre-treated in a decanter to a dry content of 20 % – 30 %.

With an extension of the drying the contained phosphorus in the sewage sludge can be separated.

The demonstration plant for sewage sludge drying will be ready for trial operation in autumn 2023.

The demonstrator is to be installed and operated at one of the sewage treatment plants in the surrounding area of PH2. The installation site is currently being clarified with the sewage treatment plants.

Your questions about SEWAGE SLUDGE DRYING

Is the energy extracted from the sewage sludge “green”?

The energy obtained from sewage sludge is green because it is generated in a material cycle. In our process a new raw material is extracted from the sewage sludge. During recycling in the plants of PH2 Technology GmbH, green hydrogen or green methanol is produced or even green methane in a downstream process.

Doesn´t the recycling of sewage sludge produce CO2?

As with biogas plants no additional CO2 is produced. The recycling is CO2 neutral, but it is not a CO2 sink. CO2 is therefore not removed from the environment or stored. For this the CO2 released during recycling would have to be stored. CO2 is an important substance in our environment. Without CO2 no plants would grow. Only the use of fossil energy by humans let CO2 become a greenhouse gas. Two goals must be achieved in the future. The fossil raw materials must be replaced by substances from a circular economy and the CO2 released by humans in recent centuries must be stored again in nature.

Is sewage sludge a renewable energy?

Sewage sludge itself is a waste product that currently has to be disposed with considerable energy expenditure. The plants of PH2 Technology GmbH are designed in such a way that sewage sludge recycling can be performed in an energy-neutral way and new raw materials can be obtained from the sewage sludge. The raw materials obtained from sewage sludge,such as green hydrogen are renewable energies.

Which investigations are prescribed for the recycling of sewage sludge from small sewage treatment plants?

After drying no additional investigations are prescribed. The drying plant reduces the water content of the sewage sludge by 70 – 98%. If the phosphorus content in wet sewage sludge is higher than 2% of the dry residue, phosphorus must be separated. If the sewage sludge is treated in our plant for recycling no investigations are required. The remaining ash must be disposed. Depending on the proportion of sand this is 1.5 – 30 % of the dry matter. The raw materials obtained from recycling are subject to quality control, which is integrated in the measurement technology of the plants.

Why can’t the sewage sludge be co-incinerated in another plant?

The co-incineration of sewage sludge is still permitted for a limited period of time. Co-combustion makes phosphorus recovery more difficult and causes additional energy expenditure in phosphorus recovery due to the higher amount of residual ash compared to mono-combustion. The ash from co-combustion contains other substances that make phosphorus recovery more complex.

What are the benefits of sewage sludge drying and what happens to the contaminated evaporated water?

Sewage sludge drying reduces the weight and volume of sewage sludge by 70 – 98%. This saves transport costs when the drying is realized directly at the sewage treatment plant. The sewage sludge becomes a fuel through drying. Another possible process step would be the carbonization of the sewage sludge. This would increase the calorific value of the sewage sludge. Investigations on the carbonization of sewage sludge are currently conducted at PH2 Technology GmbH. The evaporated water is cleaned in the plant and can be fed into the wastewater.

Why is sewage sludge dried?

Sewage sludge is dried to reduce weight and volume. Dried sewage sludge can be incinerated without additional fuel. In the case of wet sewage sludge the use of an additional fuel is required. In the process of PH2 Technology GmbH green hydrogen or green methanol is obtained from the dried sewage sludge in an additional plant.

How does sewage sludge combustion work?

In the simplest case sewage sludge is dried and combusted. In a mono-conbustion the heat from incineration is used to dry the wet sewage sludge. However it would be more advantageous to dry the sewage sludge with the drying plant of PH2 Technology GmbH and to recycle it in the plant for the raw materials. As a result green hydrogen or green methanol can also be produced with the sewage sludge.