Circular solutions for :

Starting status: three full scale one-stage digesters

2018 initiatives (€10M investment)

  1. Two-stage digestion system
  2. Thermal pressure hydrolysis (TPH) between the two stages
  3. System for struvite precipitation
  4. System for ammonium sulfate production

First stage

  • Substrates: sewage sludge and grease separator contents

Second stage

  • Additional substrate: primary sludge
  • Reuse of TPH heat for temperin


  • Cell lysis
  • Higher availability of dissolved carbon compounds
  • Higher methane yield in second digestion stage
  • Increase in dissolved phosphate and ammonium concentration

Within the project, the optimal mix of struvite and ammonium sulfate will be determined via ‘Communities of Prac ce’ to engage with local farmers.

Relevant Data

Population Equivalent
32 .000
of Agriculture
30 Ha

Demo site:

Braunschweig WWTP

Relevant sectors

Key innovations & actions

  • Follow-up a full scale nutrient and energy recovery from sewage sludge combining thermal hydrolysis and two-stage digestion together with ammonia stripping and struvite precipitation from the WWTP. Investigation of quality and quantity of recyclates produced
  • Effcient energy (biogas and heat) management for hydrolysis and digestion including seasonal demand
  • Set up and optimise a new nutrient recycling scheme. Requirement definition of a targeted product (grain size, moisture, chemical composition, quality variance over the year, optimal mix of struvite and ammonia sulfate) in order to increase acceptance

Lead partners