1. The NextGen solution implemented at the Braunschweig WWTP includes a two-stage digestion system with thermal pressure hydrolysis (TPH) between stages, and systems for struvite and ammonium sulfate production. 2. Testing showed the TPH led to a 25% increase in methane production and improved dewatering, while struvite and ammonium sulfate recovery removed phosphorus and nitrogen. 3. Further optimization is planned to increase struvite particle size and phosphorus recovery rate, and to optimize ammonium sulfate production and heat management across the new systems.

1. 1
#1. Braunschweig
Germany
Circular solutions for
Energy
Materials
WWTP(actual load: 350,000PE)
Lead partner:
Relevant sectors
Horticulture
Water
treatment
Relevant data
Energy
Other partner:

2. 2
1. Objectives of the NextGen solutions
Starting status of sludge treatment at the WWTP:
three full-scale one-stage digesters
NextGen solution implemented in the sludge treatment:
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
Benefits of thermal pressure hydrolysis:
- Higher methane yield in second digestion stage
- Improved dewatering process of digested sludge
- Increase in dissolved phosphate and ammonium concentration

3. 3
Technology Evidence Base (TEB).
Braunschweig
Positioning of demo case within the CE
1. Objectives of the NextGen solutions

4. 4 4
T= 53 °C T= 53 °C
2. New NextGen solutions: Two-stage digestion system and TPH

5. 5 5
2. New NextGen solutions: struvite production
Struvite

6. 6
2. New NextGen solution: Ammonium sulphate production
6
NH3
stripping
unit
(NH4)2SO
4
storage
tank
(NH4)2SO4

7. 7
3. Results and key performance indicators (KPIs)
Up to 25% increase in methane production rate during TPH operation
0 200 400 600
Time [d]
0
100
200
300
400
500
Methane
production
rate
[m³/h] F1 (53 °C) + F2 (38 °C) + F3 (38 °C)
Stop
TPH
Start
TPH

8. 8
0 200 400 600
Time [d]
0
1
2
3
4
5
Organic
loading
rate
[kg
DM/(m³*d)] Estimated OLR via flow rates and average DM contents
3. Results and key performance indicators (KPIs)
Organic loading rate ranges mainly between 1 and 3 kg DM/(m³*d)
 Increase in methane production rate due to TPH
Stop
TPH
Start
TPH

9. 9
0 0.5 1 1.5 2 2.5 3 3.5
Time [d]
0
200
400
600
PO
4
-P
[mg/L]
0
25
50
75
100
Recovery
rate
[%]
Influent
Effluent
Recovery rate
90
51
Expected recovery rate:
Full-scale nutrient recovery
GOAL: Phosphorus recovery
T= 53 °C T= 53 °C
Struvite
 Recovery rate is still too low: crystal size is too small
3. Results and key performance indicators (KPIs)

10. 10
Full-scale nutrient recovery
GOAL:Nitrogen recovery
T= 53 °C T= 53 °C
 Recovery rate is higher than required
 Optimization in order to save energy and chemicals
0 2 4 40 42 44 46 48 50 52
Time [d]
0
500
1000
1500
NH
4
-N
[mg/L]
0
25
50
75
100
Recovery
rate
[%]
Influent
Effluent
Recovery rate
Expected range
(NH4)2SO4
3. Results and key performance indicators (KPIs)

11. 11
4. Lessons learned so far
• Thermal pressure hydrolysis:
• High-maintenance product
• Constant high gas quality for steam generator -> avoiding higher fluctuations of
system pressure (< 20 – 30 mbar)
• Struvite precipitation
• Very low concentration of suspended solids in process water needed
(TSS < 600 mg/L)
• Long commissioning time for increasing particle size > 3 mm
• Ammonium sulfate production
• Well-established + fail-safe technique
• Very high recovery rates possible: up to 98%
• System control
• Interaction of single technical units complex -> to be considered in system design

12. 12
5. Outlook
Struvite production:
Optimization of production process aiming at the increase in grain size and a
high P recovery rate via changes in hydrozyclone geometry, different MgCl2
dosages, varying HRT
Ammonium sulfate solution production:
Optimization of production process aiming at a high N recovery rate and low
energy and chemicals consumption ( varying temperature & NaOH
addition)
Heat management:
Analysis of internal heat management for TPH & two stage digestion system

13. 13
Thank you!
xtGen - Community of Practice
13
anna.serra@eurecat.org
sandra.cases@eurecat.org