Dandora estate in eastern Nairobi hosts one of Africa’s largest rubbish dump site. And what’s more startling is that there are communities which not only thrive around this resource of rubbish but can defend their claim to it with their lives. To them, the rubbish is not just a smelly site but a means of sustenance. For many of them, poverty has pushed them to the brink. The dirt we see holds solutions for them in terms of food and sustenance. But such a landfill holds a resource we seldom think of tapping: Energy.

Domestic waste is a rich source of organic matter which easily converts into gases such as methane and carbon dioxide over time. If well managed and utilized, organic waste (aka rotting waste) can be used very efficiently for energy production for domestic needs. But what is the most conducive environment for this to happen? How could one generate a good amount of natural gas just from rotting waste at home?

1. SEPARATE THE BIODEGRADABLE FROM THE NON-BIODEGRADABLE WASTE
Plastics are not biodegradable. For starters, it pays to have separate waste containers to throw away plastics and other slowly degrading waste such maize cobs in order to handle rotting matter separately. Rotting matter consists of all food related kitchen wastes. These wastes are richest in biodegradable organic matter useful in the production of methane gas, a biofuel.

2. CONVERSION IN THE REACTION CHAMBER

The reaction chamber should be isolated from the atmosphere in order to reduce the activity of oxygen. It must therefore be sealed tightly. Several factors need to be considered during handling of the waste matter:

Size
Size matters in the production of methane. By this I mean that the sizes of the waste particles must be small enough to expose maximum surface area for conversion to take place through bacteria. If possible, the waste matter should either be pulverized or broken further into smaller particles to speed up rate of reaction.

Water
Water is a key component in the conversion reaction. This is because bacteria thrive in a damp environment and are essential in driving the reaction forward.

Innoculum
The biogas production process must be initiated from the start. Innoculum consists of all types of bacteria extracted from a cow’s gut which are used to converting organic matter into methane. In this step, some cow dung may be introduced into the mound of watery kitchen waste for the conversion reaction to be initiated.
The process of biogas production usually progresses through three broad steps:

Hydrolysis involves the breakdown of large particles of organic matter into long chain fatty acids. This happens immediately the process is initiated. Its more like the way a large piece of water melon fruit is cut into small pieces. Bacteria from the gut of cows play a crucial role in this step.

Acidification happens right after the first step. This process is defined by the conversion of the fatty acids into acetic acid. Acetic acid gives off the pungent and repulsive smell that is characteristic of rotting waste. Due to this smelly step, it’s important to carry out biogas digestion in a compound such as in a farm and not in a built up residential area. However, there are emerging technologies that use enclosed digesters which retain the stench inside of them.

Methane formation is the last step in this entire process. It’s however important to note that this step produces a mixture of gases including methane, carbon dioxide and smelly sulfides. In commercial biogas production plants, the gas mixture is usually taken through a polishing step which removes the unwanted gases from the final product. A pipe could be used to tap the gas and store it in a chamber for domestic use.

3. THE REMNANTS
Biogas production starts slow before picking up towards a maxima and ultimately tapering off. The waste can be retained for a specific period of time after which it is replaced. This time differs for various types of waste. However for cow dung manure, it could take 10-14 days for the maximum biogas production to take place (biogas world.com). For food waste, around 1kg of waste will produce between 20- 80 litres of biogas over it’s entire digestion period depending on it’s organic content (electrigaz.com). After biogas production, the waste matter could be dried up then used as a soil enrichment material in a farm.

Biogas production from kitchen waste could create opportunities for reduction of domestic energy budgets for many families living especially in the rural areas. Above and beyond being a responsible solid waste management practice, kitchen biogas reduces negative climatic effects of domestic waste dumped in a land fill like the one in Dandora in eastern Nairobi.