Everything you need to know about biodigester septic systems.

What is a biodigester?

A biodigester is a system that uses microbes and bacteria to digest organic material (like food or pee and poop) and convert them into treated water, methane gas (also known as biogas), and phosphorus.

The CITIJAL Easy-Clean Biodigester is a dual tank septic system that you can use with a regular toilet, so you can have the comforts of indoor plumbing, with the independence of an off-grid system. Each tank is made from high-quality polymer plastics using a rotating moulding technique that leaves them smooth and easy to clean. They are incredibly durable, lightweight and practical. Unlike most composting toilets, the closed system keeps them from smelling or attracting flies or wildlife.

What size to get

CITIJAL has biodigesters in a range of sizes. Most households probably only require the smallest size, which serves a household of about 5 people. Other sizes are available for larger households, including those with guest homes or Airbnb rentals, all the way up to larger resorts or hotels. Our technicians can help you determine the best size for your needs.

How to install it

Gravity plays an important role here, for drainage, so if you can choose a location downhill for best results. Either way, you will need to excavate as the system needs to be below ground. You’ll need a location with good soil and a slope of at least 3 percent. As mentioned, the system produces biogas, phosphorus and treated water.

In large scale farm-based biodigester systems, enough biogas is produced that it can be repurposed as an energy source, but the average household biodigester produces very little gas. It will just evaporate. The solids, now mostly phosphorus, will be retained in the secondary tank and can be used as fertilizer. There treated water can be drained through an absorption well, oxidation field or wetland.

Absorption well

The absorption well makes it easier for the treated water to drain into the subsoil. It should be located at least 30 meters from any water well and at a distance from any building. It needs to drain into permeable subsoil, so  test your soil for permeability before installing. Do not install an absorption well in clay or other ground conditions where water pools. The absorption well also can’t be too close to trees or other plants with broad root systems, as they risk clogging or breaking they system.

Create the natural filtration system by filling the excavation with a base gravel bed, a sand bed, another gravel bed and then larger stones that should make direct contact with the water outlet line. The whole well should remain below ground level.

Oxidation field

An oxidation field is a series of perforated pipes, placed at a distance of at least 1.8 meters and with a recommended depth of between 30 to 60 cm. Again, don’t build it too close to trees, since the roots can obstruct or lift pipes. In the perforations you should place tar paper to prevent the filling material from entering the tubes, increasing humidity. The more porous the soil, the bigger the slope of the tubes should be, up to a slope of 10 percent.


A wetland is a surface that floods permanently or intermittently. It works like a sponge where water accumulates or circulates inside slowly. Wetlands are beneficial because they help regulate floods and droughts and maintain water quality by retaining sediment and nutrients removing contaminants. They act as water reserves, stabilize microclimates, and support carbon retention! To use a wetland for your biodigester drainage, you need to pick a good location where these conditions will exist. Our technician can help!

How it works

The first tank uses all the existing bacteria to digest the poops. Since it’s an airtight, closed system, it is anaerobic bacteria that do most of the work. Solids sink to the bottom of the tank where they are slowly treated by the bacteria. Anaerobic digestion works in a two-stage process to decompose organic material in the absence of oxygen. In the first stage, the solids are converted into fatty acids by anaerobic bacteria known as “acid formers.” In the second stage, the acids are further converted into bio-gas by more specialized bacteria known as “methane formers.” The solids remaining after the digestion process can be used as a soil amendment, applicable on-farm or made available for sale to other markets.

Meanwhile, the liquids are drained out through tubes and into a filtration system as described above. The final product is clean enough that it won’t harm your wetlands, plus it’s high nitrogen so it will also feed the plants in the area.

Keeping it clean

The CITIJAL Easy-Clean Biodigester really lives up to it’s name. It requires very little maintenance, and no specialized equipment like pumps or anything. Once a year you just empty the first tank by turning a faucet. The digested poop will have become a sludge by this point, almost entirely digested by all the bacteria. It will drain out into the second tank. Let it dry there for about two months to further evaporate any nitrogen (pee) or methane (farts). After that, it’s basically good to go in the garden – it’ll be really high phosphorus – almost 100% – so it’s best to mix it with a little garden lime so it doesn’t burn your plants.

The benefits

Low carbon solution

Of course, one of the great benefits of biodigesters is they are eco-friendly and will reduce a household’s carbon footprint significantly. Instead of contributing to sewage outfall or other potentially flawed systems, biodigester septic systems convert poop into phosphorus.

High nutrient fertilizer

It’ll be such a highly concentrated fertilizer that we recommend mixing it with a little common garden lime before adding it your gardens so it doesn’t burn your plants with an overdose of a singular nutrient.

The drainage field also benefits the land with its nitrogen content, and if you can put in the wetland option, you’ll enjoy the added ecosystem development too.


Traditional septic systems or gaining access to municipal sewage can be pricey and limiting. CITIJAL biodigesters are so much easier to install than traditional septic systems that they are much cheaper, plus you don’t need to pay to get them professionally pumped because they are so easy to clean yourself. With all the nutrients being repurposed as fertilizer, you’ll also save money on garden amendments!


With our biodigesters, you don’t need road access because you don’t need to hire a septic pumper, and you don’t need to be within reach of a municipal system. You can be fully self-reliant, independent and off-grid.

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