WASTEWATER TREATMENT PLANTS

Theme: Bringing the Cold Back to Nature!
Sector: Energy, Textiles, Electrical Engineering, Media (ETEM)
Subjects: Wastewater, Energy, Water

1. Purpose

Systematic recovery of waste heat and ambient heat from water and air systems to relieve rivers and ecosystems while achieving energy savings, CO₂ reduction, and supporting a sustainable circular economy (phosphorus recovery, water re-hardening).

The objective is to present the content in line with the DGUV framework and to encourage political decision-makers and environmental organizations to actively advocate for implementation.

2. Scope

Applies to all municipal and industrial wastewater treatment plants and drinking water facilities in Germany and the EU, particularly those with digester gas production, wastewater heating, or high peak electricity demand.

3. Definitions

  • Heat Pump (HP): A device that utilizes ambient or wastewater heat for heating or cooling purposes.
  • Digester Gas: Methane-rich gas generated through anaerobic digestion in wastewater treatment plants.
  • Re-hardening: Increasing the carbonate hardness of softened water by adding calcium carbonate to stabilize water chemistry.
  • Phosphorus Recovery: Extraction of plant-available phosphate from wastewater streams.

4. Responsibilities

  • Municipal water utilities
  • Wastewater associations
  • Energy suppliers
  • Environmental authorities

Stakeholder involvement: Environmental organizations, political stakeholders (e.g., Green Party, local governments).

Technical responsibility: Wastewater treatment plant operators and drinking water facility management.

5. Description / Measures

Heat Pumps in Wastewater Treatment Plants

  • Use treated wastewater as a reliable heat source.
  • Operate heat pumps primarily during periods of surplus electricity to cool wastewater and reduce thermal stress on receiving waters.
  • Heat pump deployment can significantly reduce — and potentially eliminate — the need for gas, even during winter.
  • Integrate systems into district heating networks and municipal energy infrastructures.

Phosphorus Recovery

  • Implement lime-based processes to produce plant-available phosphates.
  • Link recovery processes with heat utilization strategies to enhance CO₂ reduction.

Re-hardening in Drinking Water Treatment

  • Utilize CaCO₃ reactor granules from rapid decarbonization in polishing ponds or aeration tanks.
  • Increase buffer capacity and support long-term water stability.

Municipal and Political Integration

  • Encourage municipalities, water associations, environmental organizations, and the German Environment Agency (UBA) to promote mandatory feasibility assessments.

Communication & Campaign

  • Guiding message: “Bringing the Cold Back to Nature!”
  • Support through flyers, short videos, and partnerships with schools and universities.

6. Applicable Documents

  • Technical datasheets for heat pumps, storage systems, and reactor granules
  • Measurement protocols, pilot studies, monitoring concepts
  • Legal requirements (Drinking Water Ordinance, Water Framework Directive, municipal regulations)

7. Documentation

  • Pilot trials in polishing ponds
  • Re-hardening dosing protocols
  • Temperature and water level records
  • Gas and energy consumption data

Phosphorus recovery: Chemical analyses and material flow documentation.

8. Control

  • Define responsible entities for technical management, monitoring, and municipal coordination.
  • Provide regular reports to associations, environmental organizations, and policymakers.
  • Continuously adapt measures based on monitoring results.

9. Attachments / Visualization

  • Flow diagrams of wastewater and heat streams
  • Pilot images from polishing ponds, heat pump installations, and reactor granules
  • Graphic representation of the cold recovery cycle

Core Statement for Brainstorming

Heat recovery is climate protection:
When wastewater and drinking water facilities store heat and return cold to nature, environmental protection begins exactly where energy was once lost.

Revision: 2Erstellt/Geändert:Geprüft:Freigegeben:Gültig ab:
Datum:05.02.202605.02.202605.02.202605.02.2026
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