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

Tekniska verken i Linköping AB and Svensk Biogas 2019-01-02 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)

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

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

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

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)

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

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

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

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

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

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

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.

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

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

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

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

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

Results - Characterization of process water Waste biogas plants

Results - Characterization of process water Sewage biogas plants

Results - Characterization of process water Agriculture biogas plants

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

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

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