Composting can take place in the presence of air (aerobic) or without air (anaerobic). In composting toilets we prefer aerobic composting because this gives faster breakdown,  faster metabolic rates and higher temperatures (to kill pathogens) and importantly no foul smells. Anaerobic breakdown is much slower, creates no heat, and produces foul smells. This means that if we aerate the compost properly we don’t get foul smells, guaranteed.

Aerobic breakdown the bacteria “breathe” oxygen and consume the carbon in the waste. Just the same as we breathe Oxygen and get our energy from Carbon, sugar for example. In both, Humans and bacteria, what is released from the respiration process is carbon dioxide which is odourless and water vapour. But unlike humans, who must have air, there are bacteria that can operate  in the absence of air – anaerobically. So since there is no oxygen going in no oxygen can come out so instead of releasing CO2 (Carbon Di Oxide) which happens in aerobic respiration it releases CH4 (Methane). So here we see that the absence of Oxygen causes a different gas to be created. Although it is too complicated, and unnecessarily, to go through every chemical reaction in the anaerobic composting process we will look at the production of Hydrogen Sulphide (H2S) which is a very smelly gas. Sulphur enters the human digestive system in broccoli and meat.  In an anaerobic environment bacteria “breathe” sulfate rather than oxygen in the thus releasing Hydrogen Sulphide (H2S).

Putrefactive breakdown of organic material takes place anaerobically. Organic compounds break down by the action of living organisms that do not require air in the normal sense. These organisms use nitrogen, phosphorus, and other nutrients to live and to develop cell protoplasm, but they reduce the organic nitrogen to organic acids and ammonia which smells. The carbon from the organic compounds which is not utilized in the cell protein is liberated mainly in the reduced form of methane (CH4).

So we can see how important aeration is in composting toilets. This is why the 360 degree rotating BioDrum from Sun Mar is so effective. This simple but unique design ensures that the compost is aerated and thus smelly gases are not created.