StR Process – Sludge to Resource 

Advanced Processing of Sludge by German Technology

Future-oriented sewage sludge treatment process as a combination of

biological and thermal process steps

Maximum power generation by means of biogas power generation with balanced thermal energy balance

Much higher current efficiency compared to conventional incinerators

Complete ashing of sewage sludge 

Recovery of valuable substances phosphorus and nitrogen as fertilizer bases







The complete solution for sewage sludge disposal

Our expertise lies not only in providing users with high standards in accordance with German standards, but also in providing users with step-by-step solutions. Our tiered program is forward-looking to give users the opportunity to improve existing sludge treatment processes with a sufficient financial and environmental, environmentally friendly, low-carbon and healthy cycle.

We have been collecting experience with Chinese projects for 12 years. Therefore, it is time to apply our strong expertise in sludge treatment in China as well. For this we deliver:

– Advanced solution - Full StR ©

– Step-by-step solution - Partial StR ©


The process is composed of 6 essential treatment steps.

It is like every chain – every step is in the same way deciding about the good result of the holistic  process.


The process produces from the total of primary and biological excess sludge Electricity and fertilizer – nothing else.

The separated centrate from sludge dewatering goes back to the waste water treatment line over a simplified deammonification system in order to avoid ammonia backcharge.


Equalized heating balance.

Heating only with own produced waste heat. 

The share of cogeneration is intentional low because we transfer a maximum share of recovered energy towards electrical power in this way (about 40% of the energy content of the biogas although the drying process reaches more than 90% DS for the entire residue

Either the waste air from drying and also the flue gas from incineration is purified with efficient purification stages.

All emission standards for effluent, wasted air and flue gas are kept strictly.

Sludge Treatment Policy in China

National 13th Five-Year Plan



“Thirteen five” national urban sewage treatment and recycling facilities construction planning“ in the sludge treatment and disposal of technical requirements:

Adhere to the principle of harmless treatment and disposal, combined with the level of economic and social development in various places, and adopt mature and reliable sludge treatment and disposal technology according to local conditions. Encourage the use of energy and resource technology to recycle energy and resources in the sludge as much as possible, and encourage the sludge that has been stabilized and harmless to be made into organic carbon soil that meets relevant standards for afforestation in wasteland. Seedling raising, landscaping, etc.






Existing WWTP (2017): 3900

Sewege treatment capacity: 180,000,000 m3/d

Sludge produced: 40,000,000 t

Sludge production in 2020: 60,000,000 t

Current disposal methods in China:

Sludge Treatment Policy in Germany

Germany also deals with sludge treatment – over 30 years of discussion and controversy. In 2005, the sludge disposal approach was discontinued in the form of a law and a new sewage sludge law was introduced in August 2017. The new law stipulates that after a defined transition period (12 or 15 years) all sewage treatment plants with more than 50,000 population equivalents (approx. 10,000 m3/d) must carry out phosphorus return from sludge or sludge ash, whereby the use of sludge is prohibited. Dry sludge incineration in combination with previous anaerobic digestion will become the main path of sludge disposal in Germany.

There are also other supporting policies and laws, such as EEG since April 2000 to promote the use of renewable energy.

Total sewage sludge: approx. 2 millions tTR / a

StR© - Characteristics

  • Proven technology from Germany with 38 references in Europe

  • Auto-thermal operation (no demand of natural gas co-firing in continuous operation)

  • Small footprint

  • Low operation cost

  • Special design for Chinese market

  • High rate of return

  • High resource recovery

  • 8000 operation hours guaranteed

  • Upgradable in steps compliant to more strict government rules in the coming years

  • Qualified emission of the whole process and single unit according to Chinese regulations

BHU has 40 years of experience in municipal sludge treatment, and the relevant incineration plant in Germany has been in good operation for more than 15 years. Until now, there is not any environmental problem occured. The emmission of the process fully fulfill the chinese standards, including „GB16297-1996“, „GB18485- 2014“ and „GB 14554-1993“.

The final production of the process contains rich Nitrate and Phosphorus, which is resource utilization of the municipal sludge.

StR© - Mode of Treatment

Centralized treatment


Sludge from different waste water treatment plants is delivered to the sludge treatment center and get treated there.

Individual treatment

Sludge from the waste water treatment plant is directly treated in its own sludge treatment plant.

StR© - Main features





  • Simple design

  • Heating up to 65°C only

  • Normal pressure reaction vessel, RT 2 hours

  • Moderate design of sodium hydroxide solution (NaOH)

  • Biogas production in the digester increased by 30%

  • ODS after digestion reduced by 30%

  • Necessary retention time in digester reduced by 25 %

  • Digester volume reduced by 20 %

  • Improved dewaterability of sludge

  • Complete mixing without sludge settling zones

  • Proper gas flow guide inside the reactor

  • Optimized reaction temperature of 37 °C

  • Complete mixing without sludge settling zones

  • Proper gas flow guide inside the reactor

  • Optimized reaction temperature of 37 °C

  • Well designed reaction tank

  • High dewatering efficiency by high speed

  • Small foot print

  • Efficient abrasion protection

  • Typical dewatering efficiency:

    • Raw municipal sludge: 28%

    • Digested sludge: 30%

    • Digested after disintegration: 32%


  • Heated with waste heat

  • Small foot print

  • Explosion proof

  • Compliant waste air treatment

  • High thermal efficiency

  • Remaining water content less than 10 %

  • After Drying:

    • Consistent granulation of residue

    • Dust content < 2%

    • Pneumatically conveyable

    • Easy to be stored

    • Hygienized according to USEPA Class A


  • Developed as decentralized incineration with a small firing capacity

  • High thermal efficiency

  • No deposit tendency of residues in the boiler

  • Good quality of ashes

  • Small foot print by small reactors

  • Extremely low pollutant values in the exhaust gas

  • Compliant flue gas treatment according to Chinese Standards
    (GB18485-2001, GB16297-1996, GB14554-93)

StR© - Future


At high shares of ODS in the sludge we can offer the following options:

– Use of ORC-Turbine in flue gas of incineration can produce additional electrical engergy.

– With gasification we can reach additional electrical energy production.


Phosphorus recovery: approx. 97% 

Ash contents

> 10% Phosphorus

Phosphorus recovery from WWTP can be considered according to relevant regulations in many developed countries, such as the USA and Germany.

Phosphorus is completely retained in the residue. Transfer into struvite is possible as an option.

Phosphorus is of increasing value!

StR© - References

Our StR process is well referenced:

Between the first digestion plants in 1995 and combination plants from disintegration, digestion and drying in 2015 as well as digestion, drying and syngas incineration in 2017, a total of 38 plants are built. Each part of the plant included in the StR concept is referenced multiple times, in many cases several parts of the StR process have been implemented.

Environment, Security, Quality.

ISO 9001, ISO 14001, OHSAS 18001.

BHU Umwelttechnik GmbH | Einsteinstraße 57 | 71229 Leonberg | Germany |

Company of the Almawatech Group, Babenhausen