Continuous anaerobic fermentation for 140 days in the LAMBDA MINIFOR Fermentors to study the effect of an external acetate on the lactate-based chain elongation.

For the first time, the Faculty of Environmental Engineering and Energy, Poznan University of Technology, Poland, tested the effect of an external acetate on the lactate-based chain elongation in a continuously-fed fermenter. The motive is to verify how the external acetate would affect the efficiency of carboxylate production in the presence of the microbiome which performs chain elongation of short-chain substrate (lactate-acetate) to valuable Caproate. 

In their publication - https://doi.org/10.1016/j.scitotenv.2021.149885, the author explained the experimental work of continuous anaerobic fermentation for 140 days in two MINIFOR Fermentors for the production of valuable carboxylate, primarily the Caproate by varying the feeding strategy. 

 Fig 1: Overview - Continuous anaerobic fermentation for 140 days in the LAMBDA MINIFOR Fermentors. 

Reference: doi.org/10.1016/j.scitotenv.2021.149885. Filip Brodowski, Mateusz Łężyk, Natalia Gutowska, Piotr Oleskowicz-Popiel. Effect of external acetate on lactate-based carboxylate platform: Shifted lactate overloading limit and hydrogen co-production, Science of The Total Environment, Volume 802, 2022, 149885, ISSN 0048-9697.

For this study, two 1L LAMBDA MINIFOR fermentors were run in parallel. The vessel is filled with synthetic medium. The working volume maintained in each bioreactor is 0.8L. 80ml Sludge is used as inoculum, which has a mixed microbiome. N2 gas is flushed to the Fermentors to maintain an anaerobic condition inside the vessel. The MINIFOR fermentor is inbuilt with MASSFLOW for regulated gas supply of N2 or Air.

The LAMBDA weighing module (kept at the bottom of the fermentor) was used to perform the continuous cultivation and maintain the constant volume. Whenever the weight exceeds the set value, the harvest pump activates, removes excess volume, and keeps the weight constant. 

Continuous cultures = LAMBDA MINIFOR fermentor-bioreactor + Feed Pump + Harvest Pump + Weighing module

The temperature of each bioreactor is maintained at 30 °C through an innovative infrared heating system. The pH is maintained at 5.5. The fermenters are equipped with peristaltic pumps for automatic pH regulation. Whenever pH starts to vary from the set point, either Acid pump or Base pump supplies the buffer to maintain the pH at 5.5.  Hydraulic Retention Time maintained at 5 days.

Fig 2: Schematic view of  one LAMBDA MINIFOR Fermentor system set 

Feeding strategy: 

The process was divided into different phases based on the concentration of lactate and acetate in the feedstock as shown below, 

Fig 3: The production rate profile of carboxylates with the residual substrate concentration in the bioreactor 1 (B1) and in the bioreactor 2 (B2) 

Result:

• In the bioreactor B1: as the result of the addition of an external acetate, the recovery of stable caproate production obtained is 68.9 ± 2.2 mmol C/L/d. The high hydrogen co-production observed was 748 ± 76 mLH2/d.
• In the second bioreactor, the caproate production achieved was 71.7 ± 2.4 mmol C/L/d. Also, the hydrogen gas obtained was 213 ± 30 mLH2/d.
• The microbial analysis of the mixed culture showed the Ruminococcaceae bacterium CPB6 and Acinetobacter were stable throughout the process.

Conclusion:

• Lactate as a sole carbon source destabilized carboxylate production.
• The addition of external acetate favors carboxylate production, especially Caproate.