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Biogas; an old way to make new energy savings

Arriving a few minutes after 7pm, we were ushered into the compound of a homestead with a well-manicured lawn in Maya Bukomye village, Wakiso district.

The homestead was lit in a village without electricity. The home owner, Mirabu Nakabugo, lights up her house and cooks using electricity she generates. The 56-year-old takes care of several grandchildren. She used to struggle to collect firewood, until she set up a biogas unit on her farm.

CONVENIENT: Ruth Okello has used biogas for five years

Her journey with alternative energy started in 2013. Her unit uses cow urine and dung harvested on her farm to produce biogas, which powers her rural home.

In Kirombe B zone of Luzira just outside Kampala, Ruth Okello has also taken to biogas. On her modest lot, Okello has a few zero grazing animals. She earns from the sale of milk and also uses dung for biogas production.

“I used to use up to four sacks of charcoal a month before I changed to using biogas, and that was quite expensive,” she said.

In Kampala, the cheapest sack of charcoal goes for Shs 70,000. The expanding urban population has pushed up demand/cost for charcoal.

Biogas technology has been around for some time now but it is only now that it’s being recognised as a plausible alternative energy source in parts of Uganda. What one must have is an assured source of animal or human waste.

According to the Uganda National Charcoal Survey 2015-2016, 94 per cent of Ugandans use wood biomass as cooking energy. This translates into an estimated forest loss equivalent to 115 football fields just for cooking every day.

Okello turned to SNV Netherlands Development Organisation and Biogas Solutions Uganda, a non-profit which offers training in biogas handling and connects farmers to digester fabricators. Technical advice is provided by SNV Netherlands.

Structure

At Nakabugo’s home, the biogas plant is a brick dome-like structure built near collection points for cow dung.  Inside it is a digester 10 feet deep. On the other hand, Okello has two biogas units to power her home, chicken brooder and winery. It all cost roughly Shs 4 million.

“The whole process is quite expensive but given the time I have used biogas, I have recovered the money I invested.”

How it works

Cow dung is mixed with water and fed into the digester. The digester is a sealed chamber in which microorganisms decompose the cow dung to generate gases such as methane, carbondioxide, hydrogen and hydrogen sulphate.

The gas rises into a tank placed above the digester. Attached pipes then funnel it into the house. Okello’s unit is a 7ft deep pit and 5ft in circumference. She uses two 18-litre pails of cow dung and 2,000 litres of water to mix the slur. This mixture can produce enough gas to light five bulbs in her cowshed and cook for the whole day on her two biogas stoves.

Nakabugo’s unit is bigger; 10ft deep pit and 7ft circumference. She uses three 20-litre jerrycans and 3,500 litres of water to make the slur. The resulting gas cooks for her extended family, lights eight bulbs and fires two biogas stoves.

How much energy

Moses Lubega, a biogas unit constructor with Ecosafe Company, said that a nine cubic-metre unit can produce up to 1,800 litres of gas when fed with 75kg of slur daily. A stove uses 300 litres of gas per hour. 

100 x 100 plot enough

Florence Kintu, business development and marketing manager at Biogas Solutions, says a 100x100ft plot of land is enough to set up.

“Most of the works are underground, especially where the pit is dug; others don’t require a lot of space, a 60-cubic- metre pit can fit in the plot,” she said.

Mirabu Nakabugo explains how to make the right mix of dung

Kintu says one needs roughly Shs 1.5 million to buy cement, bricks, hardcore, pipes, burners, sand and the dome for a small unit. On safety, Lubega said unlike liquefied petroleum gas (LPG), which can explode when not carefully attended to, biogas is safe at all times.

“Biogas does not have any chemicals and is not compressed to be hazardous to the user. The gas also does not expire as long as the gas chambers are tightly closed,” he told The Observer.

With Uganda’s population growing by more than three per cent each year, energy demand and costs continue rising. Experts believe that schools and institutions like prisons can reduce their spending by investing in biogas.

In Kenya, the government has started turning biogas on in prisons. Dr Johnson Byabashaija, the commissioner general of Uganda Prisons Service (UPS), last year raised the alarm about the huge and growing cost of the prisons’ dependence on wood fuel – with its devastating implications for the environment.

“UPS uses a staggering 227 tonnes of wood fuel every day to prepare meals in all the 252 prisons around the country; however, energy-saving stoves can help to reduce energy loss by up to 40 percent,” he told the press.

Frank Baine, the UPS spokesman, says energy-saving cooking stoves have since been installed in almost 50 per cent of the country’ prisons.

“We have seen a drop in consumption of firewood from three trucks to a truck a day. We have tried to benchmark on the establishment of biogas stoves but the challenge is, it’s very expensive [to set up] for us now; maybe in the future,” he said.

National Environment Management Authority estimates that up to 90,000 hectares of natural forest is lost in Uganda every year, most of it going to wood fuels.

Use in schools

Burhan Mugerwa, the head teacher, Kawempe Muslim Secondary School, said the school is planning to start using biogas in the near future.

“We have been thinking about adopting the technology and there are a few projects we are working on. When we are through, we will embark on that project,” he said.

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