No, urine should not be added into the HOTBIN. Many gardening and composting sites recommend adding urine onto cold compost heaps to help speed things up. With cold composting this provides the bacteria with a source of food which can be digested quickly to produce heat quickly.
Why Is Urine Recommended in Cold Composting?
Urine is about 98% water and the rest is mainly a chemical called urea. (Although there can sometimes be small amounts of amino acids and other things like antibiotics if you are taking certain medications). Urea is a source of food (nitrogen) for the bacteria, it is made up of lots of small molecules in a water solution – these properties allow urine to be digested very quickly which means fast growth and heat. Composting bacteria digest the sugars and carbohydrates leaving carbon dioxide and water. This water then has to be removed to create crumbly rich compost and there are two places the water can go – it can drain into the soil or evaporate into the air.
How Is the HOTBIN Different?
In hot composting and specifically the HOTBIN, significant heat energy has to go into removing the excess water from waste, especially food waste and grass both of which are more than 80% water. Adding additional liquid such as urine should be avoided because more water is being added to benefit from just a few grams of urea (food) which in comparison to the kitchen/garden waste being added will have very minimal value to the bacteria.
What If It's Added By Way of Straw / Hay?
Another common method of adding urine into a compost heap is if straw or hay has been urinated on. This method is also not recommended, although small amounts of straw can go into the HOTBIN, too much can cause problems. Straw will also not replace the job of shredded paper and/or bulking agent.