How to Use Manure for Small-Scale Biogas Production

Introduction

Manure can be a great resource for producing biogas on a small scale. Biogas is a renewable fuel produced from organic matter like manure through a process called anaerobic digestion. The gas produced is mostly methane and carbon dioxide, which can be used similarly to natural gas for cooking, heating, and generating electricity. Using manure for biogas has many benefits, especially for small farms or homesteads with livestock.

Benefits of Small-Scale Biogas from Manure

• Provides renewable energy source - Biogas can displace use of unsustainable fossil fuels and provide energy independence.

• Reduces manure waste - Anaerobic digestion reduces volume of manure while creating useful biogas fuel.

• Produces high-quality fertilizer - Digested manure is an excellent organic fertilizer for crops and gardens.

• Lowers greenhouse gas emissions - Manure emits less methane when digested in a closed system compared to decomposing in the open.

• Requires small initial investment - Small-scale systems can be built affordably using simple designs and local materials.

• Provides local fuel source - Biogas production uses feedstocks available onsite, eliminating transportation costs.

Key Components of a Small Biogas System

A simple biogas plant for manure has four main components:

Input Materials

• Manure - Main feedstock loaded into the digester. Cow, pig, chicken, and other manures can be used.

• Water - Used to create slurry with the manure to pump into digester.

Anaerobic Digester

• Sealed tank - Holds manure slurry while microbes break down organic matter, releasing biogas. Can use concrete, plastic, or metal tank.

• Heating system (optional) - Heating the digester accelerates biogas production in colder climates.

• Mixing method - Mixing prevents solids from settling and maintains even temperature.

Biogas Collection/Storage

• Pipes - Transport biogas from digester to storage.

• Gas holder - Stores the produced biogas before consumption. Could be tank, bag, or floating drum.

Biogas Use

• Burner or appliance - Simple stoves or lamps use biogas for cooking/lighting needs.

• Generator (optional) - Converts biogas into electricity. Requires more investment.

Choosing a Digester Design

There are several types of simple backyard digesters to consider:

• Fixed dome - Masonry or concrete dome attached to digester tank.

• Floating drum - Metal drum floats in tank to collect rising gas.

• Plastic tubular digester - Flexible plastic tubes or bags can act as digester and gas holder.

• Above-ground plastic tank - Low-cost pre-made tanks like troughs or IBCs can be repurposed.

The design choice depends on factors like cost, weather, number of animals, and construction skills. Fixed domes are more permanent while floating drums, plastic digesters, and tanks offer flexibility. Consult with experts to choose the optimal system.

Sizing the Biogas System

To size the system properly:

• Estimate total daily manure input based on number and type of animals.

• Choose digester volume to hold at least 15-30 days' worth of manure.

• Select biogas storage to hold 1-2 days of fuel use.

Right-sizing for the manure load ensures adequate retention time in the digester for gas production. Undersizing causes problems with overflow or clogging.

Operating and Maintaining the Digester

Routine maintenance is key to a well-functioning digester:

• Load manure and feed digester daily. Remove compost regularly.

• Monitor temperature and mixing. Keep digester contents at 25–40°C.

• Inspect piping for leaks. Repair any cracks or malfunctions immediately.

• Clean out any solids settled in pipes or digester with water pressure.

• Check biogas appliances frequently for safety. Burn biogas cleanly for best performance.

Perform maintenance actively and the system will produce abundant biogas with steady feedstocks.

Safety Considerations

Anaerobic digestion is generally safe but consider these precautions:

• Methane gas is explosive so keep flames/sparks away from biogas system.

• Use gas valves and ensure piping is airtight to avoid leaks.

• Wear gloves and wash hands when handling digester inputs and outputs.

• Monitor digester pressure and do not open if over-pressurized.

With training and safe operation, household biogas from manure can provide clean, renewable energy without health risks.

Conclusion

Producing biogas from manure at home provides an excellent source of energy while responsibly managing waste. Carefully designed and sized small-scale digesters can convert manure into lighting, cooking fuel, electricity, and organic fertilizer. With simple construction and routine maintenance of the digester and biogas system, a small farm or homestead can utilize this sustainable energy solution. Biogas production helps reduce fossil fuel usage and manage manure effectively for economic and environmental benefits.