How Biogas Generators Work: Types, Efficiency & Complete Guide
Every year, millions of tons of organic waste end up in landfills, releasing methane—a greenhouse gas 25 times more potent than CO₂. But what if that waste could become your most reliable energy source? Biogas generators turn animal manure, food scraps, crop residues, and wastewater sludge into renewable electricity and heat, cutting emissions and energy costs at the same time.
In this guide, you’ll learn exactly how biogas generators work, the different types available (from home digesters to industrial 2 MW power plants), what biogas generator efficiency really means, and how to choose a commercial biogas generator set for your farm, factory, or facility. By the end, you’ll know what to look for in a high-performance biogas power generation system — including our industrial generator sets (400 kW to 2000 kW) that we manufacture for real-world applications.
1. What Is a Biogas Generator?
A biogas generator (often called a biogas generator set or biogas gen-set) is a system that converts organic waste into electricity and usable heat. It combines two main parts:
Anaerobic digester – an airtight tank where bacteria break down organic matter without oxygen, producing raw biogas (mainly methane and CO₂).
Gas engine + alternator – a combustion engine specially designed to run on biogas, which drives a generator to produce electricity.
When heat from the engine coolant and exhaust is recovered, the system becomes a biogas CHP generator (combined heat and power), achieving total efficiency above 85–90%.
2. How Does a Biogas Generator Work? (Step-by-Step)
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Step 1 – Feedstock Preparation
Organic waste (manure, food waste, crop residues, sewage sludge) is mixed with water to create a pumpable slurry. Large solids should be pre-shredded to increase the surface area for bacteria.
Step 2 – Anaerobic Digestion (Four Key Phases)
The slurry enters a sealed, oxygen-free digester where multiple groups of bacteria work in sequence. This process has four distinct phases:
| Hydrolysis | Complex molecules (fats, proteins, carbohydrates) are broken down into simpler sugars, amino acids, and fatty acids. |
| Acidogenesis | Simple organic compounds are further converted into volatile fatty acids, alcohols, hydrogen, and CO₂. |
| Acetogenesis | Fatty acids are converted into acetic acid, along with additional hydrogen and CO₂. |
| Methanogenesis | Methanogenic archaea convert acetic acid, hydrogen, and CO₂ into methane (CH₄) and CO₂ – this is the biogas. |
The gas collected at the top of the digester is raw biogas, typically containing 50–70% methane (CH₄), 30–50% CO₂, plus trace amounts of hydrogen sulfide (H₂S) and water vapor. For comparison, natural gas has about 1000 BTU/ft³, while biogas ranges from 500–700 BTU/ft³, which is why engines must be specifically adapted.
Step 3 – Gas Cleaning (Recommended)
Raw biogas should be treated before entering the generator engine:
Dehydration – removes water vapor to prevent corrosion.
Desulfurization – removes corrosive H₂S (target below 200–500 ppm for engine safety).
Particulate filtration – removes fine solids.
Step 4 – Combustion & Power Generation
Cleaned biogas is fed into a spark-ignited gas engine (lean-burn or rich-burn). The engine turns an alternator to produce electricity. Modern industrial engines use electronic controls (e.g., Woodward) and pre‑chamber lean‑burn technology to achieve high electrical efficiency. Our 190 and 300 series (400 kW to 2000 kW) employ this exact technology, reaching up to ≥40% electrical efficiency in the 300 series.
Step 5 – Heat Recovery (CHP)
Up to 50% of the energy in biogas can be recovered as heat from the engine jacket water and exhaust. This thermal energy can warm digesters, heat buildings, or supply process heat, turning a simple power plant into a biogas CHP generator with combined efficiency over 85%.
Step 6 – Byproduct: Digestate as Fertilizer
The residue leaving the digester is called digestate. It is rich in nitrogen, phosphorus, and potassium – essential plant nutrients – and has greatly reduced odor and pathogens. Digestate can be separated into a solid fraction (used as bedding or compost) and a liquid fraction (used as liquid fertilizer). This closes the nutrient loop and adds another revenue stream for farms and waste treatment plants.
3. Types of Biogas Generators (By Scale)
Not all biogas generators are the same. The right type depends on your waste volume and energy demand.
| Home / Mini Biogas | 1–20 kW | Households, small farms (cooking, lighting) |
| Small Commercial | 30–200 kW | Medium dairy, food processing, local waste |
| Industrial Biogas Generator Sets | 400 kW – 2 MW+ | Large farms, wastewater treatment, landfill, industrial CHP |
For applications above 400 kW, you need a robust, containerized solution that can run 24/7, handle varying methane content, and meet grid codes. That’s exactly where our generator sets – the 190 series (400–1000 kW) and 300 series (1000–2000 kW) – are designed to excel.
4. Key Applications of Biogas Generators
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Agricultural farms – dairy, pig and poultry manure → electricity + bedding/fertilizer.
Food & beverage plants – fruit/vegetable waste, brewery effluent → power for own facility.
Municipal wastewater treatment – sewage sludge digestion to power plant operations.
Landfill gas recovery – converting fugitive methane into grid electricity.
Industrial CHP – replace diesel or propane boilers with biogas-fired engine + heat recovery.
An onsite gas generator for biogas means you don’t need a pipeline – you generate power right where you have the waste.
5. Biogas Generator Efficiency: What You Need to Know
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Efficiency is usually expressed as “electrical efficiency” (how much fuel energy becomes electricity) and “total CHP efficiency” (electricity + useful heat).
Typical spark-ignited biogas engines: 35–42% electrical efficiency.
Lean-burn engines with pre-chamber (our 300 series): ≥40% electrical efficiency at full load.
CHP efficiency: adding heat recovery pushes total efficiency to 85–92%.
Fuel consumption estimate: roughly 0.5 Nm³ of biogas (55% CH₄) produces 1 kWh of electricity. Higher methane content improves efficiency.
Efficiency comparison table (industrial class)
| 190 series (naturally aspirated) | 400–550 | ~36–38% | ✓ |
| 190 series (turbocharged) | 600–1000 | ~38–40% | ✓ |
| 300 series (L-8, intercooled) | 1000–2000 | ≥40% | ✓ |