The increasing restriction of the agricultural use of sewage sludge is associated with mounting
pressure on municipalities and sewage treatment providers. Moreover, the high power needs drive
up the expenses of wastewater treatment plants. Thus, more and more sewage treatment plants
decide to employ energy-saving sludge stabilisation in an anaerobic reactor and utilisation of the
digestion gas for the generation of energy.
The administrative partnership Burgebrach in Bavaria, Germany, is one of the municipal organisations that
have decided to consistently reduce the sludge volume and make use of the sewage gas. Accordingly,
the technical operator SüdWasser GmbH has commissioned the biogas plant manufacturer WELTEC
BIOPOWER as the general contractor for the setup of an anaerobic digestion unit and the utilisation of
the sewage gas for the generation of energy in the combined heat and power (CHP) plant for the existing
wastewater treatment plant, which serves a population equivalent of 13,000. In addition to the aerobic
treatment stage, the organic material will be subjected to anaerobic treatment starting from April.
To ensure optimum treatment of the daily influx of 16 m³ of raw sludge with a dry matter content of
4 to 4.5 percent, a specially designed V4A stainless-steel digester has been installed. In it, a diagonally
installed long-axis agitator will mix the sludge in order to gently carefully promote the microbiological
transformation to methane. With its capacity of 420m³ and a flexible gas storage roof with a storage
volume of up to 68m³, the bioreactor is large enough to run the CHP plant with its electrical output of
28kW and thermal output of 58kW without any interruptions. The generated power will be used directly
at the facilities, and the heat will be employed both for speeding up the digestion process and for use
at the sewage treatment plant site.
Apart from the energy generation and the sludge stabilisation, the minimisation of odour emission
was another decisive factor in favour of the WELTEC anaerobic stage. Through the systematic anaerobic
sludge stabilisation, unpleasant odours will henceforth be largely prevented. Prior to the upgrade, this
problem occurred constantly in Burgebrach.
Arne Nath, Head of the Wastewater department of the operator SüdWasser GmbH, explains:
In the sewage treatment plant in Burgebrach, we used to stabilise the sludge without using the digestion
gas. Through the installation of the digestion unit, we have established a sustainable, climate-friendly
energy concept and can reduce the amount of sludge. In total, the COD load in the wastewater will be
reduced by about a third.
However, the plant upgrade also delivers financial advantages: The said benefits and
the bonus under the German Combined Heat and Power Act (KWKG) will result in a yearly cost advantage
in the medium five-digit range.
Jens Flerlage of WELTEC BIOPOWER, summarises the system‘s benefits:
Our customers appreciate our anaerobic sludge digestion for its economic and ecological sustainability.
It produces energy, cuts disposal costs and generates municipal income. Moreover, the plant capacity
can be expanded without any major need for additional space. These positive aspects make this smart alliance of wastewater
treatment and energy generation basically viable for all sewage treatment plants for population sizes
of 8,000 to 50,000.
The procedural approach of WELTEC BIOPOWER and the modular stainless-steel tanks have already
resulted in a significant improvement of existing wastewater systems in various countries. Besides the
said benefits, the high process stability and low maintenance and operating costs help to combine the
energy reform with the highly important value creation through renewable energies.