How to Build a Biodigester in 6 Simple Steps

A comprehensive guide to biodigester construction

If you’re considering building a biodigester for your home, then this article will provide you with a step-by-step guide on how to construct a biodigester; from selecting the ideal location to sealing it airtight. Whether you’re a DIY enthusiast or seeking expert assistance, this guide has you covered.

1. Site Selection

When it comes to constructing a biodigester, selecting the right site is crucial for its effectiveness and functionality. The first step in site selection is to assess the plumbing system and determine the number of toilets and pipes in the building.

This information will help you decide where to place the biodigester, taking into consideration factors such as the location of the pipes and the gradient and slope of the waste pipelines.

It’s also important to consider homeowner preferences when choosing the site for the biodigester. Some homeowners may prefer to have it hidden at the back of the building, while others may want it to be more visible as part of the overall design. Discussing these preferences with the homeowner and considering practicalities like accessibility and aesthetics will ensure that the biodigester is placed in an ideal location.

2. Digging the Ground

Once you have selected the site for your biodigester, the next step is to dig the ground according to the recommended dimensions. A rectangular shape is often preferred for biodigesters as it allows for better functionality and maintenance. The length of the biodigester should be around six feet, while the width can be 2 1/2 to 3 feet. The depth should be approximately 2 to 2 1/2 feet.

When digging the ground, it is important to create a gradient that leads to the soakhole pit or soakaway. This ensures that any water that enters the biodigester is drained immediately, allowing for rapid separation of wastewater from human waste.

It is crucial to consider the slope and gradient of the ground to prevent any backflow or blockage in the system.

Rectangular shapes are preferred over circular or square ones as they provide better space utilization and allow for easier installation of filtration materials and bedding materials.

Additionally, rectangular biodigesters are more efficient in terms of separating wastewater from human waste, leading to improved biodegradation processes.

3. Constructing a Soakhole Pit (Soakaway)

After digging the ground and creating the biodigester, the next step is to construct a soakhole pit for wastewater drainage. There are two options for this: a soakaway or a soakhole pit.

A soakaway involves building blocks and connecting a leachate pipe, while a soak hole pit requires laying stones and covering them with rubber or carpet before burying them in the ground.

The choice between a soakaway and a soak hole pit depends on the condition of the ground and its ability to effectively drain the wastewater.

A soakhole pit is suitable when the ground has good drainage capabilities, ensuring that the wastewater is properly soaked into the surrounding soil.

On the other hand, a traditional soakaway is preferred when the ground conditions are not ideal for drainage, as it allows for better containment of the wastewater within the pit.

**Traditional soakaway constructed for greywater treatment. This can also be used for black water treatment**

Regardless of which option you choose, it is crucial to consider the gradient of the ground to prevent any water from flowing back into the biodigester.

The gradient should be carefully planned to ensure that there is proper flow and drainage of wastewater towards the soak pit or soakaway. This will help maintain the functionality and efficiency of the biodigester system.

4. Laying Blocks or Prefabricated Slabs:

When it comes to constructing the walls of the biodigester, there are two main options to consider: laying blocks or using prefabricated slabs. Both options have their advantages and disadvantages, depending on the specific needs and preferences of the project.

If you choose to lay blocks, it is recommended to use quarried earth blocks for their firmness and ability to contain moisture. These blocks have been pressed and are more suitable for retaining any water that may be present in the biodigester.

Laying the blocks requires some technical understanding, so if you are a beginner in biodigester construction, it may be best to seek expert assistance or guidance.

On the other hand, using prefabricated slabs can offer a quicker and more efficient construction process. These slabs can be easily fitted to match the size of the hole that has been dug for the biodigester.

They also allow for better space utilization and can be cast with perforations for filtration purposes. If you have experience casting these slabs or have access to precast slabs, this option can be a viable choice.

Regardless of which option you choose, it is important to consider the placement of filtration materials and bedding materials within the biodigester. This will ensure the proper functionality and efficiency of the system.

5. Preparing the Biodigester Bed:

Once the biodigester has been constructed, the next step is to prepare the biodigester bed. This involves casting slabs with perforations that will serve as bedding materials for the biodigester. These slabs are essential for facilitating rapid separation, a key characteristic of biodigesters.

Rapid separation is what sets biodigesters apart from septic tanks. In a biodigester, the wastewater is immediately drained out, separating it from human waste.

This allows for efficient biodegradation processes to take place. To aid in this process, bulking materials such as fibre nets and coconut fibre can be used as filtration materials in the biodigester bed.

These materials help to separate water from human waste and promote the growth of beneficial microorganisms that aid in biodegradation.

The use of fibre nets and coconut fibre also helps to prevent clogging and ensure the proper functioning of the biodigester system.

By preparing the biodigester bed with these materials, you can ensure the optimal performance and longevity of your biodigester.

6. Cover Biodigester Sealing it Airtight

When it comes to sealing the biodigester with a top slab, there is often a debate about whether a vent pipe is necessary. Some argue that a vent pipe is needed to allow for the release of air and gases from the biodigester.

However, I believe that using a vent pipe can lead to potential issues with flies and water ingress, compromising the effectiveness of the biodigester.

Instead of relying on a vent pipe on the biodigester itself, it is more practical and aesthetically pleasing to utilize the vents already present in the house.

These vents are designed to allow for proper air circulation and odour control within the plumbing system.

By ensuring that the house has adequate venting, you can prevent any potential problems associated with flies or water entering the biodigester through a vent pipe.

Additionally, considering factors such as the level of the house when the groundwork is completed and any aesthetic preferences of the homeowner will help create a biodigester that is both effective and visually appealing.