Proceedings

Sludge treatment in Germany – More than 50 years experience. Current discussions – future prospects

Dichtl, N., Dellbrügge, R.1 and M. Morcali, B., Technical University Braunschweig, Germany

(free)

In Germany, nowadays, more than 97% of inhabitants and industry are connected to modern wastewater and sludge treatment systems. Long-term experience exists in Germany especially with sludge digestion. These experiences will be presented and a special focus will be on technologies for sludge pre-treatment such as e.g. thermal hydrolysis or technical solutions to recycle the nutrients phosphorus and nitrogen (using e.g. struvite precipitation). Furthermore questions of energy consumption at wastewater treatment plants have a high significance. Thus the application range for anaerobic digestion actually is extended even to small wastewater treatment plants for e.g. 10,000 PE.

Keywords: Agricultural reuse, co-digestion, disintegration, nutrient recovery, sewage sludge treatment

Background: Legal regulations

In the context of closed substance cycle waste management, environmentally compatible disposal of waste and conservation of natural resources, avoidance and recovery of sewage sludge are to be preferred over disposal of sludge.  On EU level three directives provide the regulation on the treatment and reuse of sewage sludge:
 Directive 91/271/EC Urban Waste Water Treatment
 Directive 86/278/EC Protection of the environment, and of the soil in particular, when sewage sludge is used in agriculture
 Directive 99/31/EC Landfilling of waste

The European Sewage Sludge Directive (86/278/EC) aims for a safe reuse of sewage sludge in agriculture in order to prevent its harmful effects on the environment. Since 1997 sewage sludge has officially been identified as secondary raw material fertilizer for the reason of its positive characteristics and valuable compounds. Especially the important macronutrients nitrogen, phosphorus and potassium are available in the sludge.

In Germany, more than 30% of sewage sludge is reused for agricultural purposes (Durth, et al., 2003). When and how sewage sludge may be applied to agricultural land or landfill is regulated by the Technical Instructions on Waste from Human Settlements (TASi), Fertilizer Ordinance (DÜMV) and the Sewage Sludge Ordinance (AbKlärV), which regulates how to control the level of nutrient and pollutant concentrations in the sludge, how to monitor the soil and set limiting values for the land application of the sludge in Germany. Since July 2005 the landfill disposal of any waste with an organic content > 5% is prohibited by TASi. The following Table 1 lists current legal requirements for the reuse and disposal of sewage sludge.

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