Valorisation of Effluents from Anaerobic Digestion as Single Cell Protein Focus on Safe Gas. Supply

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1 Valorisation of Effluents from Anaerobic Digestion as Single Cell Protein Focus on Safe Gas Borja Valverde Pérez Supply Bioenergy and Microbial Ecology and Technology Laboratory (Metlab) research groups August Z. Zachariae, Astrid F. Kjeldgaard, Zahra Rasouli, Wei Xing, Alejandro Palomo, Martina D Este, Davide De Francisci, Mathias L. Pape, Barth F. Smets, Irini

2 Agenda Microbial protein and its impact on nitrogen cycle Co-cultivation of green microalgae and methanotrophic bacteria Bubble-free membrane bioreactor 2

3 Microbial protein and Methane Oxidizing Bacteria (MOB) What is microbial protein?:protein produced by microbes, which can be used as feed ingredient (EU approved!) Why MOB?: Bacteria have high growth rates and crude protein content compared to algae and fungi. Compared to algae, the cultivation of MOB s is less space demanding. 1 st generation process already exists: natural gas and synthetic nitrogen resources [ ] Methane can be produced from most organic waste at a relatively low cost.

4 Anthropogenic nitrogen cycle Atmosphere Consequences include: N GHG s 2 GHG s Climate change Synthetic N 2 Manure GHG s Animal GHG s Eutrophication and other chemical pollution of aquatic Livestock ecosystems Acid products N-Fertilizer Land-use change deforestation and other habitat ~145 Mt/y losses WWTP Haber-Bosch Croplands Natural resources depletion N-fixation >1 % of global energy consumption Leaching/run-off of reactive N Surface and ground water Consumers N 2

5 Closing the nitrogen drain SCP production Atmosphere Manure GHG s N 2 GHG s N 2 SCP GHG s GHG s N 2 Livestock Synthetic N-Fertilizer Animal products Haber-Bosch N-fixation Croplands Leaching/run-off of reactive N WWTP CH 4 Surface and ground water Consumers SCP SCP production

6 Nutrient Management Traditional approach Manure Biogas energy Nutrients fertilizer 6

7 Nutrient Management Nutrient Upcycling and Reuse in Agriculture Single Cell Protein Biogas Manure Fermenter Nutrients Plant Growth Promoters 7

8 Focus on Safe Gas Supply

9 Co-cultivation of algae and methanotrophs Rasouli et al., 2018 (BEJ) 9

10 Co-cultivation of algae and methanotrophs Blue: CH 4 Red: CO 2 Green: O 2 o o o The consortium effectively removed organic carbon and nutrients Imbalance between photosynthesis and methane oxidation o Level of explosion is achieved! Further optimization is needed 10

11 Co-cultivation of algae and methanotrophs Contains the essential amino acids for chicken 11

12 Bubble-free membrane bioreactor Cultivation of a mixed culture of methane oxidizing bacteria First experiences: Suboptimal supply of gasses leads to biofilm formation Leakage of gases and building of headspace Progressive lose of methanotrophs

13 Bubble-free membrane bioreactor Progressive lose of methanotrophs Methylococcales (pink) Methylophilales (light green) 13

14 Bubble-free membrane bioreactor After gas supply optimization good oxygen to methane ratio Biomass grows in suspension Microbial protein content increased potential recovery of methanotrophic biomass Minimization of gas leakage and avoidance of head space 0,08 0,07 After optimization Before optimization g amino acid/g DW 0,06 0,05 0,04 0,03 0,02 0,

15 Take home message Both proposed options can produce biomass suitable as feed ingredient Co-cultivation of green microalgae and methanotrophs o Challenges Photosytensis and methane oxidation need to be balanced Complex process control is needed o Opportunities Valorization of the carbon dioxide from biogas Bubble-free membrane bioreactor o Challenges Risk of carbon dioxide accumulation from biogas and methane oxidation o Opportunities Operation below the low explosive limit 15

16 @Metlab_DTU

17 What happens with the real pollutants? Who are the bad guys? Heavy metals Impurities Pathogens Pharmaceuticals Antibiotic resistance genes How do we get read of them? Membrane filtration Bio-electrochemical systems