Medium Temperature Anaerobic: Mesophilic Digestion At 35-38 C
Medium temperature anaerobic digestion is the biological process that breaks down organic matter without oxygen at 35-38 C, the mesophilic band where methane-forming microbes are most stable. It converts manure and agricultural waste into biogas at about 0.30-0.45 m3 per kg of COD removed, and it generates far less sludge than aerobic treatment.
Why The 35-38 C Band
Below about 35 C the mesophilic community slows and retention times stretch; above 38 C the culture drifts toward thermophilic, which needs more heating energy and is less tolerant of load swings. The 35-38 C window is the practical sweet spot for steady, low-risk operation on farm and food feedstocks.
| Temperature Band | Trait | Operating Note |
| Mesophilic 35-38 C | Stable, low-risk | Default for farm and food AD |
| Thermophilic 50-55 C | Faster, higher heat | Needs more energy, less stable |
| Psychrophilic below 20 C | Slow | Long retention, cold climate only |
What The Process Delivers
In a sealed, heated CSTR the volatile solids become biogas of roughly 55-65% methane. A balanced carbon-to-nitrogen ratio near 20-30:1 keeps the biology healthy, and the retention time (commonly 20-40 days for a mesophilic CSTR) sets the reactor volume. The sealed vessel is usually a Glass-Fused-to-Steel tank for corrosion resistance and fast assembly.
A Boundary Condition
Medium temperature anaerobic needs a feed that can hold 35-38 C economically; in cold regions the reactor and its insulation must be specified for the ambient load, and very dilute or very cold feed will underperform. Co-digestion with manure or residue stabilises the feed where a single stream is too weak or too rich.
Project Case Study: Zhaqi Biogas Project In Inner Mongolia
Project / Application: Farm animal manure and agricultural waste to biogas, Xing'an, Inner Mongolia, China. Industry: Agriculture and renewable energy. Tank Type: CSTR (Continuous Stirred-Tank Reactor). Key Requirements: Stable medium-temperature operation in a cold climate.
| Field | Value | Source / Evidence |
| Handling Capacity | 900 m3/D (manure + agricultural waste) | Company project reference |
| Treatment Type | Medium Temperature Anaerobic Fermentation | Company project reference |
| Reactor Type | CSTR (Continuous Stirred-Tank Reactor) | Company project reference |
| Reactor Size | 4 sets of O25.98 x 8.4 m | Company project reference |
| Daily Biogas Output | 20,000 m3/day | Company project reference |
| Feedstock | Animal manure + grass straw | Company project reference |
| Installation Year | 2017 | Company project reference |
About The Supplier
Shijiazhuang Zhengzhong Technology Co., Ltd (Center Enamel) manufactures Glass-Fused-to-Steel tanks rated for medium temperature anaerobic digestion, with enamel firing at 820-930 C and certifications including ISO 9001, NSF/ANSI 61, and CE-EN 1090. Insulated CSTR packages support cold-climate farm projects.
Comparison: Temperature Bands
| Band | Best For | Main Trade-off |
| Mesophilic 35-38 C | Most farm and food AD | Longer retention than thermophilic |
| Thermophilic 50-55 C | Fast pathogen kill | Higher heating cost |
| Ambient cold | Where heat is free | Very long retention |
Medium temperature anaerobic digestion is the dependable default for farm and food waste because it trades a little retention time for stability and low heating cost. Hold the feed at 35-38 C, balance the carbon-to-nitrogen ratio, and the biogas becomes a predictable output.
Frequently Asked Questions
Q1: What is medium temperature anaerobic? A1: Oxygen-free digestion at 35-38 C where mesophilic microbes convert organics into biogas.
Q2: Why 35-38 C? A2: It is the stability sweet spot; higher bands need more heat and are less tolerant of load swings.
Q3: How much biogas at mesophilic? A3: About 0.30-0.45 m3 per kg of COD removed at 55-65% methane.
Q4: When is thermophilic better? A4: When fast pathogen kill matters and the extra heating energy is justified.
Q5: What reactor is used? A5: A sealed, heated CSTR is the common mesophilic vessel for uniform feed.
Q6: What tank resists the corrosion? A6: A Glass-Fused-to-Steel tank with a factory-fired enamel lining.
Q7: How is cold climate handled? A7: With an insulated reactor package designed for the ambient load.
Q8: Can the system expand? A8: Yes, modular GFS panels add digester volume as feedstock grows.
Tell an engineer your feedstock and off-take plan, or request a medium temperature anaerobic digestion scope.