Successful commissioning of the sewage sludge drying plant in Backnang

The dewatered sludge is fed by the pelletising system at the so-called head piece 1. The dried sewage sludge exits the drying plant directly below.
The dewatered sludge is fed by the pelletising system at the so-called head piece 1. The dried sewage sludge exits the drying plant directly below.

About 6000 t of sludge per year from Backnang and the municipalities of cooperation partners were dried in the past with a stationary drying plant on the central sewage treatment plant Neuschöntal. In December 2012, the contract with MSE Mobile Schlammentwässerungs GmbH expires and cannot be renewed due to contractual reasons and the technical state of the plant. It was in 2008 / 2009 when the Abfallwirtschaftsgesellschaft (AWG) of the Rems-Murr-district thought about to add a fermentation stage to the composting plant Backnang-Neuschöntal for the treatment of biowaste. It became clear very soon that it was technically feasible and also economical to use the exhaust heat from the biowaste fermentation system to dry sewage sludge. The idea was born to make use of the direct neighbourhood of both plants and utilise the heat which is generated in the block heat and power plant of the fermentation system to dry sludge.

Short ways are characteristic for the Backnang drying plant: The dewatered sludge is delivered to the entrance of the hall where the dryer and exhaust air treatment plant are installed. The dried sewage sludge is stored in a nearby silo.
Short ways are characteristic for the Backnang drying plant: The dewatered sludge is delivered to the entrance of the hall where the dryer and exhaust air treatment plant are installed. The dried sewage sludge is stored in a nearby silo.

The first calculations showed that 12,000 tons of sewage sludge would be needed and have to be provided reliably to dry the sewage sludge. Cooperation with several municipalities was therefore required: Althütte, Aspach, Backnang, Burgstetten, Großerlach, Murrhardt, Oppenweiler, Remshalden, Schwaikheim, Spiegelberg, Sulzbach an der Murr and Weissacher Tal Association finally founded the Städtische Klärschlammverwertung Backnang GmbH. The advantages of such a sewage sludge treatment association are obvious:

  • Secures the utilisation of the generated sewage sludge in the long run
  • Provides independence from fossil energy sources and their costs (previous annual consumption of fuel oil: approximately 850,000 l)
  • Utilisation costs below market price
  • Profits remain in the hands of the municipalities.

HUBER won the tender for the supply and installation of a belt dryer with an investment volume of € 3.7 million in 2010. The HUBER Belt Dryer BT 18 is designed to dry 16,000 t sewage sludge per year from initially 27% to 90% dry residue. Presently, about 10,000 t of sewage sludge are treated on this site. The HUBER solution secures regional sewage sludge utilisation for the long term and even allows Städtische Klärschlammverwertung Backnang GmbH to take in additional cooperation partners. The energy required for sludge drying is available for free. They use the exhaust heat from the Rems-Murr District’s bio-fermentation plant. This heat energy, in total 8.5 million kWh, would otherwise be released into the atmosphere and remain unused. The operators of the bio-fermentation plant receive 3 cent per kWh in return. Furthermore, the dry granulate is stored in a silo and weekly delivered to a coal-fired power plant in Heilbronn for electricity generation. The thermal value of the dried sludge is similar to that of brown coal!

The HUBER sludge drying plant in Backnang represents the core of this project which is a showcase in terms of energy efficiency and environmental sustainability. Due to intelligent process engineering plant operators also benefit from a significantly reduced amount of exhaust air and low specific electric energy consumption. They will be happy to hear that, in the future, they could profit from another development: recovery of phosphorus from dried sludge. We are doing research on different processes solutions in this field and hope to soon offer our customers an efficient method which allows them to even more increase the economic potential of their sewage sludge drying plant.