Homes and gardens

Switch to a bio-digester

In light of recurring tragedies — involving workers losing their lives while cleaning septic tanks — it is time to question the safety and functioning of the ubiquitous septic tank.

These tanks treat wastewater by separating the sludge (solid waste) from the blackwater (liquid waste) in a closed chamber without any accelerated action. The resulting untreated liquid, once separated is allowed soak into the soil where it slowly disperses hopefully treated by organic matter in the soil at some point in time.

The problem with this arrangement for waste disposal is the possibility of water overflowing if there is an increase in water use. The overflow would then end up having to be collected and disposed of manually, not a very environment-friendly practice. Another issue with the septic tank is the sedimented sludge needs to be cleaned out periodically, thus requiring manual intervention.

Finding options

The good news is that today we have improved options for the conventional septic tank. One such option is the use of a biodigester. This technology was developed by DRDO (Defence Research Development Organization).

A biodigester degrades and converts human waste into usable water and gases. This ongoing treatment is achieved by introducing bacteria into the tank that is built for collection of waste. The bacteria decompose the faecal matter anaerobically. The resulting water is treated well enough to be used for irrigation.

Further treatment of this water can enable its reuse for flushing, washing vehicles, etc. The resulting gas is minimal and is vented out. However, it is important to monitor the quality of the treated water at regular intervals.


For a single-family home, a biodigester tank as small as 4’ x 4’ x 3’ is adequate. When compared to the standard septic tank, there is no need for any removal of sludge and no odour. Compact in size, this pre-made system can be installed underground. It is also cost effective when compared to the septic tank.

Due to its many advantages, it is time to consider switching to biodigesters as a modern, convenient, safe and environmentally friendly version of the conventional septic tank.

The author is the founder of Green Evolution, a sustainable architecture firm

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Printable version | Sep 16, 2021 3:38:01 AM |

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