Presentation Information
[P04-523]Effectiveness of Anaerobic Digestion for Wastewater Treatment in Bio-Manufacturing: Spent Biomass Reduction, COD Removal, and Methane Recovery
○Aoba Tamura1, Azumi Tomita1, Tatsunori Kiyokawa1 (1. Sumitomo Heavy Industries, Ltd. (Japan))
Keywords:
Wastewater treatment,Anaerobic digestion,Methane recovery
[Purpose]
From the perspectives of decarbonization and resource circulation, the shift towards bio-based manufacturing—producing petrochemical-derived products using biomass or carbon dioxide as carbon sources—is advancing. However, compared to upstream processes like fermentation and purification, the design and optimization of wastewater treatment and waste disposal systems have received limited attention. As the use of diverse production strains, including recombinant organisms and bacteria, is expected to expand, establishing technologies that can process waste microbial biomass cost-effectively and with high energy efficiency becomes a key challenge. This study focused on anaerobic digestion, which aims to reduce the volume and organic matter content (COD) of waste microbial biomass while recovering energy as methane. Using a model waste microbial biomass, the effectiveness of this approach was experimentally verified.
[Method]
Yeast (Saccharomyces cerevisiae) was cultivated in a nutrient medium. Harvested cells were autoclaved and used as the substrate. Anaerobic sludge from an in-house wastewater treatment facility was used as the inoculum. Batch tests were conducted in sealed 100 mL serum vials (50 mL working volume) containing sludge (10,000 mg-MLSS/L) and autoclaved yeast biomass (5,000 mg-COD/L). Nutrients (salts, trace metals, and vitamins) and a buffer were added separately. Vials were incubated at 35 degC and 80 rpm until methane production plateaued. Methane production, biomass reduction ratio, and COD reduction were measured, and methane was quantified by GC.
[Results]
In the yeast cell addition system, methane production became sufficiently small by day 27. The biomass reduction ratio was 31.4%. For an initial COD input of 5,000 mg-COD/L, dissolved COD after treatment was 1,950 mg-COD/L. GC analysis indicated a methane conversion efficiency of 49.9% for the yeast substrate.
[Consideration]
Residual dissolved COD suggests incomplete methanation of solubilized components; therefore, practical deployment should consider downstream polishing (e.g., aerobic treatment). Elemental analysis of yeast showed C/N=3.33, which is nitrogen-rich compared with the commonly recommended C/N (=25) for anaerobic digestion, implying possible ammonia inhibition at higher loading. Countermeasures to be examined include co-digestion with an external carbon source to adjust C/N and ammonia removal prior to digestion. In addition, digestion-property differences among production strains (cell-wall structure, particle size, elemental ratios) will be organized, and process calculations will be used to estimate treatment cost and energy balance.
[Conclusion]
Anaerobic digestion of spent yeast biomass enabled biomass reduction, COD reduction, and methane-based energy recovery. Incorporating anaerobic digestion as a terminal unit may improve energy efficiency and reduce disposal costs in biomanufacturing. Feasibility will be further verified through process calculations and additional experiments.
From the perspectives of decarbonization and resource circulation, the shift towards bio-based manufacturing—producing petrochemical-derived products using biomass or carbon dioxide as carbon sources—is advancing. However, compared to upstream processes like fermentation and purification, the design and optimization of wastewater treatment and waste disposal systems have received limited attention. As the use of diverse production strains, including recombinant organisms and bacteria, is expected to expand, establishing technologies that can process waste microbial biomass cost-effectively and with high energy efficiency becomes a key challenge. This study focused on anaerobic digestion, which aims to reduce the volume and organic matter content (COD) of waste microbial biomass while recovering energy as methane. Using a model waste microbial biomass, the effectiveness of this approach was experimentally verified.
[Method]
Yeast (Saccharomyces cerevisiae) was cultivated in a nutrient medium. Harvested cells were autoclaved and used as the substrate. Anaerobic sludge from an in-house wastewater treatment facility was used as the inoculum. Batch tests were conducted in sealed 100 mL serum vials (50 mL working volume) containing sludge (10,000 mg-MLSS/L) and autoclaved yeast biomass (5,000 mg-COD/L). Nutrients (salts, trace metals, and vitamins) and a buffer were added separately. Vials were incubated at 35 degC and 80 rpm until methane production plateaued. Methane production, biomass reduction ratio, and COD reduction were measured, and methane was quantified by GC.
[Results]
In the yeast cell addition system, methane production became sufficiently small by day 27. The biomass reduction ratio was 31.4%. For an initial COD input of 5,000 mg-COD/L, dissolved COD after treatment was 1,950 mg-COD/L. GC analysis indicated a methane conversion efficiency of 49.9% for the yeast substrate.
[Consideration]
Residual dissolved COD suggests incomplete methanation of solubilized components; therefore, practical deployment should consider downstream polishing (e.g., aerobic treatment). Elemental analysis of yeast showed C/N=3.33, which is nitrogen-rich compared with the commonly recommended C/N (=25) for anaerobic digestion, implying possible ammonia inhibition at higher loading. Countermeasures to be examined include co-digestion with an external carbon source to adjust C/N and ammonia removal prior to digestion. In addition, digestion-property differences among production strains (cell-wall structure, particle size, elemental ratios) will be organized, and process calculations will be used to estimate treatment cost and energy balance.
[Conclusion]
Anaerobic digestion of spent yeast biomass enabled biomass reduction, COD reduction, and methane-based energy recovery. Incorporating anaerobic digestion as a terminal unit may improve energy efficiency and reduce disposal costs in biomanufacturing. Feasibility will be further verified through process calculations and additional experiments.
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