1. Content of VOC in process water from upgrading facilities for compressed biogas (CBG)
Sören Nilsson Påledal1, Katarina Stensen1 and Karine Arrhenius2
1 Tekniska verken i Linköping AB 2 SP, Borås

2. Tekniska verken i Linköping AB and Svensk Biogas
Tekniska verken i Linköping AB and Svensk Biogas
20 years experience of full scale biogas production
100 % renewable vehicle fuel produced using organic material
Local production of biogas at Tekniska verken
2016 ≈ 120 GWh
Co-digestion ≈ 100 GWh
WWTP ≈ 20 GWh
Operates its own filling stations for CBG (Svensk Biogas):
10 filling stations and 3 bus depots
>160 busses in three cities, 25 garbage trucks
>3 000 cars (public and private)

3. Tekniska verken R&D Biogas - experts on anaerobic digestion in full scale and labscale
Long experience of developing full-scale biogas production
Well-equipped laboratory
Patented reactors for continuous digestion investigations
BMP-tests
Water and sludge analysis
Perform both in-house research and external assignments

4. Background
Characterisation of contaminants in biogas before and after upgrading to vehicle gas (SGC report 246)
Odor from process water from biogas upgrading
Uncertainty about the content of VOC and how process water should be treated to minimize the impact on human health and the surrounding environment

5. The project The project was funded by Project leader: Tekniska verken
40 % Swedish Energy Agency
60 % Private Swedish biogas companies
Project leader: Tekniska verken
Sampling: participating plant owners
Analyses of VOC: SP

6. What we did in the project!
Literature review
Techniques for treatment
Environmental and health effects with respect to content of VOC in process water
Degradation of VOCs in anaerobic and aerobic environment
Characterization of VOC in process water from gas upgrading
Laboratory experiments for treatment of process water
Scientific article (Chemosphere) and Technical report (Energiforsk)

7. Literature review
A few studies about VOC in biogas, no studies about VOC in process water from biogas upgrading
Some VOC strongly connected to substrate used at the plant
Food waste
p-cymene and d-limonene
WWTP-sludge
alkanes, siloxanes

8. Literature review
Difficult to state general health and environmental effects without accurate site specific investigation
Treatment of water contaminated with VOC
Physical methods
Chemical methods
Biological methods

9. Material and methods
Characterization of process water with respect to content of volatile organic compounds, VOCs from gas upgrading facilities
Detailed instructions for sampling
Main substrate
Technique for upgrading
Agriculture main substrate
Amine
Water
Waste main substrate
Amine and water
Sewage sludge main substrate

10. Syntethic process water for inhibition and adsorption tests
Material and methods
Syntethic process water for inhibition and adsorption tests
VOC
Proportion
(w/w)
D-limonene
25 %
p-cymene
Tridekane
5 %
2-butanone
40%
Siloxane D4

11. Material and methods Inhibition of the biogas process by VOC
Description
Substrate
Added amount of prepared process water
Volume in BMP-bottle
Series 1
Control
Cellulose, starch, fat, gelatin -
500 ml
Series 2
+ addition of VOC-solution in a high amount
11.6 mg VOC/L
liquid in BMP-bottle
Series 3
+ addition of VOC-solution in a very high amount
238 mg VOC/L

12. Material and methods Adsorption of VOC for activated carbon and peat
Filter material
Flow
Amount of filter material
cm3, g
Process water bypassed through filter
Concentration of process water
Reference
≈ 1 l/h
None
1 l
24 and 483 mg VOC/l
Activated carbon
≈ 0,7 l/h
4,5 cm3/
2,45 g
2,8 l
Peat
≈ 0,6 l/h
2,15 g

13. Results - characterization of process water
Results from the plants are divided into three categories with respect to main substrate used at the plant:
Waste (food- and slaughterhouse waste)
Sewage sludge (WWTP)
Agriculture (manure, silage, grain)
At all plants except one, >10 % of the substrate mix consisted of waste.

14. Results – characterisation of process water
Average content of mg VOC in process water from upgrading of biogas with respect to m3 treated biogas

15. Results – characterisation of process water
Average share of most common VOCs in process water from upgrading of biogas
Average share of total amount VOC

16. Results – characterisation of process water
Average share of most common VOCs in process water from upgrading of biogas
Average share of total amount VOC

17. Results – characterisation of process water
Average share of most common VOCs in process water from upgrading of biogas
Average share of total amount VOC

18. Results – characterisation of process water
Average share of most common VOCs in process water from upgrading of biogas
Average share of total amount VOC

19. Results - Characterization of process water
Waste biogas plants

20. Results - Characterization of process water
Sewage biogas plants

21. Results - Characterization of process water
Agriculture biogas plants

22. Results - BMP-test with addition of VOC-solution
No inhibition for addition of VOC-solution in realistic and high amount

23. Results - Filter trials for adsorption of VOC
Both materials adsorbed VOC, more VOC adsorbed by active carbon.

24. Conclusions
Content and most common VOCs are dependent of substrate, but high variations indicating site specific conditions are important for the results
Highest levels of VOCs in process water when waste is main substrate and lowest levels when agricultural residues is main substrate
Varying VOC content at the two plants where sewage sludge is main substrate. One plant in line with waste and the other plant in line agricultural residues
Laboratory trials showed no inhibition for process water in a realistic amount in BMP-test and activated carbon and peat can adsorb VOC if used in a filter