I construct irrigation bio-digesters for locals

The road to Ndenderu in Ruaka, Kiambu County branches off Kiambu Road, cuts through banana plantations and ends on the banks of Karura River.

A team from Smart Harvest visited John Munyui who has shown resilience in farming despite the changing climatic conditions.

When it rains, Mr Munyui relies on water from Karura River and when the rains fail, he counts on technology that converts domestic waste into water.

The modern biodigester is the brainchild of Martin Gicheru, a young agri-preneur who has for long researched on ways to curb water scarcity in the thriving agricultural area.

“Ruaka has traditionally been an agricultural town. But over time, soil has become very shallow and it can’t retain water for long when it rains and so many people here have abandoned farming,” Gicheru says.

Economical water use

We find two men on Munyui’s farm, digging a trench in readiness for construction of a new biodigester.

When the 4-cubic-metre trench is done, it will hold a large water reservoir for irrigation at the farm.

Nearby is a freshly constructed biodigester that will be connected to the water reservoir once its construction is completed.

The third organic treatment plant, the first to be constructed at Munyui’s farm stands amid banana plants, succulent kales and other indigenous vegetables.

The one-cubic-meter tank is fitted with pipes that run beneath the ground to keep banana plants, kales and other vegetables nourished.

Most biodigesters do ‘soaking’ where a ditch is dug and filled with rocks to drain all waste households.

Controls wastage

Gicheru learnt about soaking when he worked at a firm that made biodigesters.

“I saw a lot of wastage at the company. A lot of water that could otherwise be put to good use would be let to soak in the ground,” Gicheru says.

He then started researching on how to tap into domestic waste to make water after he lost in his first attempt to farm in the perched Gilgil.

A biodigester has two tanks and a manhole where all the waste from households is collected. The waste comes from the kitchen, ablution blocks and water sinks.

Waste collected in the manhole is led to the second tank that is divided into two chambers.

It hits the outer chamber of the second tank forcing it to sink inside chamber. It is here that the waste is converted into water through anaerobic process.

The inside chamber is devoid of oxygen, which encourages growth and multiplication of bacteria responsible for digesting the waste. To accelerate the multiplication of these bacteria, artificial biodigester products are added to the waste.

Anaerobic process

The tank also has an outlet chamber that holds solid wastes that take longer to digest.

These include sanitary towels and plastic bags.

The tank is also fitted with a large pipe that lets out waste in form of water.

Gicheru says the water is slimy and depending on the client’s preferences, it is filtered to be used for limited domestic chores like laundry.

“The slimy product is however very rich in manure and nourishes crops,” Gicheru says.

The larger pipe is fitted with smaller pipes that run beneath the soil to wet the crops through drip irrigation.

Gicheru says the process is simple because once installed, it doesn’t require additional labour as irrigation goes on by itself.

But why biodigesters?

Unlike other septic tanks, a biodigester does not require an exhauster to get rid of sewage.

That the anaerobic process is the natural and clean process which is also attracting land developers for its affordability. Gicheru charges Sh80, 000 to install a one-cubic-metre and Sh120, 000 to install a two-cubic-metre one.

Any other one-cubic meter septic tank that do not offer alternatives to farmers cost Sh270, 000 or more to install.

However, it is indisputable that the biodigester only works where there are many residential houses.

“That is why we want to connect few residential blocks in the neighboruhood. There are more than 50 houses in the three blocks here and they will provide more than enough waste water in a day,” Munyui says.

Gicheru met Munyui in 2015 when he constructed a biodigester at the latter’s farm where he planted spinach, kales, capsicum and indigenous vegetables.

Munyui, who has been supplying residents with fresh farm produce since 2015 says he wants to have more biodigesters constructed on his farm to expand farming on the other piece of land.

“I haven’t managed to fully satisfy the local demand yet I have a lot of land that can give me more produce,” Munyui says.

With an additional biodigester on the farm, and a reservoir, the farmer aims to harvest at least 10, 000 litres of water every day to irrigate his farm.

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