LAMBDA MINIFOR Bioreactor: A Case Study in Mesophilic and Thermophilic Continuous Anaerobic Fermentation for Biochemical Production from Organic Waste
150 Days Continuous operation | 515 mM C Peak caproate | 3.43 g/L/d Succinate productivity |
Overview of the Research
A recent study published in Green Chemistry by Hanna Prusak, Natalia Gutowska, Emilie Alaux, Mateusz Szczygiełda, Nay Yee Wint, Diana Z. Sousa, Mateusz Łężyk, and Piotr Oleskowicz-Popiel investigated how operational parameters — particularly temperature, pH, and hydraulic retention time — influence biochemical production from organic waste using mixed-culture fermentation (MCF).
The research was conducted at Poznan University of Technology (Poland) in collaboration with Wageningen University & Research (Netherlands). Using the LAMBDA MINIFOR continuous stirred-tank bioreactor over 150 days, the team systematically shifted conditions between mesophilic (37°C) and thermophilic (50°C) regimes to steer microbial communities toward target biochemicals including succinate, caproate, acetate, butyrate, propionate, ethanol, and lactate.
Figure 1. Schematic overview of the LAMBDA MINIFOR CSTR experimental setup. R1 (mesophilic, 37°C) and R2 (thermophilic, 50°C, Phase III). Gas measurement by external Ritter MilliGascounter and Shimadzu GC-2014. Original diagram.
Experimental Setup
Two LAMBDA MINIFOR 1.7 L stirred-tank fermenters (LAMBDA Laboratory Instruments GmbH, Baar, Switzerland) were operated in parallel as chemostats with a working volume of 1 litre each. Substrate was synthetic OFMSW comprising potatoes, apples, carrots, tomatoes, bread, rice, pasta, and other household organics, ground and diluted to 4% total solids.
Vessel Volume 1.7 L (1 L working volume) | Agitation Fish-tail stirrer at 2.5 rpm |
Heating IR radiation (beneath vessel) | pH Control Auto dosing with 4 M NaOH |
Substrate Feed LeadFluid BT100S peristaltic pump | Operation 150 days continuous |
NOTE: Gas volume was quantified by an external Ritter MilliGascounter, and headspace composition (H₂, CO₂, CH₄) by a Shimadzu GC-2014 with TCD three times per week. These are companion instruments — not integrated MINIFOR functions.
Figure 2. Proportional 150-day operational phase timeline for R1. Green = mesophilic (37°C); red = thermophilic (50°C, Phase III). Original diagram based on Prusak et al. (2026).
Influence of Temperature and Operating Conditions
Phase | Days | Temp | pH | HRT | Key Products |
I | 0–35 | 37°C (M) | 6.5 | 5d | Succinate, Acetate, Butyrate |
II | 35–49 | 37°C (M) | 5.5–6.0 | 5d | Acetate, Butyrate |
III | 49–77 | 50°C (T) | 5.5–6.0 | 5d | Lactate, Ethanol, Butyrate |
IV | 77–96 | 37°C (M) | 6.5 | 5d | Caproate, Acetate, Butyrate |
V | 96–114 | 37°C (M) | 7.0 | 5d | Caproate peak — 515 mM C |
VI | 114–127 | 37°C (M) | 7.0 | 2.5d | Acetate, Butyrate, Ethanol |
VII | 127–150 | 37°C (M) | 7.0 | 1.25d | Succinate peak — 118 mM C/d |
Phase I–II: pH-Driven Shifts at 37°C
Under initial mesophilic conditions (37°C, pH 6.5, HRT 5 days), succinate temporarily dominated the product spectrum, averaging 188 ± 30 mM C in R1 and 155 ± 29 mM C in R2 between days 7 and 23. Acetate and butyrate subsequently became the dominant products. Lowering pH in Phase II reshaped microbial diversity and shifted metabolism further toward acetate and butyrate, with microbial community alpha-diversity decreasing as environmental pressure increased.
MESOPHILIC FINDING: At 37°C and neutral-to-mild acidic pH (6.5–7.0), the system consistently favoured acetate, butyrate, and — under the right conditions — high-value caproate production through chain elongation driven by ethanol-consuming microorganisms.
Phase III: Thermophilic Conditions (50°C)
Raising temperature to 50°C produced a dramatic shift in both the product spectrum and microbial community. Lactate concentrations increased approximately 21-fold in R1 and 34-fold in R2 compared to Phase II. Ethanol levels also rose, while total metabolite yield fell to only 548–571 mM C — the lowest of any phase. The community simplified to just three dominant taxa accounting for ~80% of relative abundance: Weizmania coagulans and two Thermoanaerobacterium relatives.
THERMOPHILIC FINDING: At 50°C, microbial diversity collapsed and overall metabolite productivity fell significantly. However, lactate and ethanol accumulated during this phase created a rich substrate for chain elongation once mesophilic conditions were restored — priming the system for efficient caproate production in Phase IV.
Figure 3. Comparative product profiles under mesophilic (37°C, Phase V averages, R1) vs. thermophilic (50°C, Phase III averages, R1). Caproate was strongly suppressed at 50°C while lactate and ethanol dominated. Original diagram based on Prusak et al. (2026).
Phases IV–V: Caproate Production via Chain Elongation
Restoring mesophilic conditions after the thermophilic phase created an opportunity for efficient chain elongation (CE). Caproate concentrations surged 20-fold within two hydraulic retention times after the temperature shift back to 37°C. A subsequent pH increase to 7.0 in Phase V further boosted production, reaching a peak of 515 mM C on day 99 in R1.
Spearman correlation analysis confirmed a strong negative relationship between ethanol and caproate concentrations (ρ = −0.79 for R1; ρ = −0.82 for R2; p < 0.001), confirming ethanol as the primary electron donor in the chain elongation process via reverse β-oxidation. Lactate played a more limited role.
Figure 4. Conceptual illustration of the inverse ethanol–caproate relationship across 150 days (R1). When ethanol falls, caproate rises — confirming ethanol-driven reverse β-oxidation as the dominant chain elongation mechanism. Spearman ρ = −0.79, p < 0.001. Original diagram based on Prusak et al. (2026).
Phases VI–VII: Short HRT and Succinate Production
Halving the HRT to 2.5 days and then to 1.25 days shifted the system back toward acidogenic fermentation and restored succinate production. At pH 7.0, 37°C, and HRT of 1.25 days, R2 maintained relatively stable succinate output of 147 ± 19 mM C for 23 days, with a maximum concentration of 207 mM C. Succinate productivity reached 118 ± 40 mM C day⁻¹ (3.43 g L⁻¹ day⁻¹) — a ~3-fold increase versus Phase VI. RDA analysis confirmed a strong negative correlation between HRT and succinate: shorter retention times consistently favoured succinate synthesis.
Why the LAMBDA MINIFOR Suited This Study
The LAMBDA MINIFOR's design characteristics directly enabled the experimental outcomes across all seven phases and 150 days of operation.
Vessel Volume 1.7 L (1 L working volume) | Agitation Fish-tail stirrer at 2.5 Hz |
Heating IR radiation (beneath vessel) | pH Control Auto dosing with 4 M NaOH |
Substrate Feed LeadFluid BT100S peristaltic pump | Operation 150 days continuous |
Summary and Conclusions
This study demonstrates that temperature is one of the most powerful levers for redirecting mixed-culture fermentation toward different biochemicals from the same organic waste feedstock.
• Mesophilic conditions (37°C) consistently supported higher total metabolite productivity and enabled caproate production up to 515 mM C at neutral pH.
• Thermophilic conditions (50°C) reduced productivity but generated a lactate and ethanol-rich product mix that subsequently primed chain elongation upon return to 37°C.
• Short HRT (1.25 days) at 37°C and pH 7.0 was optimal for succinate, achieving 3.43 g L⁻¹ day⁻¹.
• Microbial community composition adapted predictably to each temperature and pH condition.
• The LAMBDA MINIFOR operated stably for 150 days across all seven phase transitions without process disruption.
Citation:
Prusak H., Gutowska N., Alaux E., Szczygiełda M., Wint N.Y., Sousa D.Z., Łężyk M., Oleskowicz-Popiel P. (2026). Expanding the product spectrum in mixed-culture fermentation of organic solid waste through operational control. Green Chemistry. DOI: 10.1039/d5gc05638a. Open Access — CC BY 3.0.