Planning of a thermal sewage sludge recycling plant with upstream sludge digestion in Bergen on the island of Rügen

Commissioning on the 14th of June 2017:

On the 14th of June 2017 our customer, the Zweckverband Wasserversorgung und Abwasserbehandlung Rügen (ZWAR) on the island of Ruegen, was celebrating its 25th anniversary together with the commissioning of the new sewage sludge recycling plant.

After the newly erected digester and the associated combined heat and power plant had already been working properly for a long time, the start-up burner of the sewage sludge incineration plant was ignited at this date to begin the drying process for the refractory in the furnace. After completion of this warm-up phase, the sludge can then be thermally utilized.

In the presence of federal and provincial politicians, the festivities were commemorated by the mayors of the island communities as members of the association ZWAR.

Axel Roediger, Managing Director, presented in his speech both the long-standing successes of the ZWAR for the construction of an ecological water supply and disposal as well as the independence of the association, which is documented with the construction of the new sewage sludge recycling plant.

Dr. Born - Dr. Ermel GmbH - Engineers -, being the owners engineer to ZWAR organized guided tours through the plant for the guests and the visitors of the subsequent open day for the public.


Groundbreaking on 27th of November 2015:

On the 27th of November 2015 the groundbreaking ceremony for the construction of the thermal sewage sludge recycling plant took place on the island of Rügen.

In July 2015, construction measures began with the construction of the excavation pit and the construction measures for the digestion tower. In November 2015 the construction work for the machine building started and from April 2016 on the installation of the technical installations. The sludge digestion is planned to start in September 2016 and the thermal sludge recovery in May 2017.

Our customer (the ZWAR Rügen) sets the course for future-oriented sewage sludge treatment.
With the commissioning of Dr. Born - Dr. Ermel GmbH for the planning of a thermal sewage sludge recycling plant with upstream sludge digestion, the ZWAR is taking the first step towards a safe and future-oriented sewage sludge treatment. The sewage treatment plant is constructed in Bergen and will treat  all sewage sludge from the islands of Rügen and Hiddensee.

The digester has a volume of 3,000 m³ and is planned as a cylindrical concrete tank. The sludge is recirculated by means of a central long shaft agitator.

For the required heating of the sewage sludge, the vessel is equipped with heat exchangers inside. The cylindrical design with a long shaft agitator and heat exchanger tubes inside is an optimal construction according to economic aspects. The resulting heat from the cogeneration plant is used for digester and building heating.

In the second treatment step, the sewage sludge is dewatered to approx. 27% by means of dewatering centrifuges. The dewatered sludge enters the screw dryer via a solids pump and is cooled to a TS content of approx. 44%, so that autothermal combustion is possible. The dryer has a water vaporization capacity of 550 kg H2O / h and uses the waste heat from the subsequent sludge combustion. After sludge drying, the thermal utilization is concluded in the form of a two-stage fluidized bed furnace. The two-stage design allows for a larger control range for combustion and achieves lower NOx and CO emissions compared to conventional combustion due to optimized airflow.

The design of the furnace was examined in advance by a CFD simulation. It has been shown that the stepped combustion results in a faster reaction of the oxidation products in the combustion chamber compared to the conventional fluidised bed furnace.
A downstream thermal oil boiler couples the heat and supplies the drying as well as the heating system with sufficient energy.
Electricity generation was deliberately omitted since the electrical energy from the CHPW could completely supply the site.

Quasi-dry flue gas cleaning, consisting of an electrostatic precipitator, spray cooler and fabric filter, is used to clean the flue gas from combustion. The purified exhaust air is then discharged via a chimney, observing the legal limits.

The vapors from the thermal drying are introduced into the fluidized bed combustion and are post-combusted. As a result, the thermal sewage sludge treatment can be operated almost without water.