Getting the mulch right is a very important part of composting. There is a separate post explaining the factors that influence composting which is a good idea to read also. This post explains what are looking for in a composting mulch.
The Sun Mar units are supplied with a bag of compost sure which is made of hemp. Auboise hemp bedding is a very similar product to compost sure and it is widely available. Sun Mar recommend adding one cupful per person per day. Auboise is the soft part of the hemp plant and it absorbs 4 times more moisture than wood shavings. Because it is soft it composts easily. On the topic of moisture, if the unit is being used regularly then the storage of moisture in the compost is less of an issue as there is liquid (urine) being added all the time. In such a situation, you could thin out the auboise with some wood shavings. Shavings provide structure to the pile which creates pockets of air which are replenished each time the drum is rotated. The function of the auboise is to hold the moisture from urine between visits. Generally speaking saw dust or bark as a main ingredient are not suitable. Saw dust is too fine and does not create the air spaces required in the pile for aerobic odourless composting. Bark is too durable for the composting bacteria to break down but in Biolan units that do not have a rotatable drum, it is useful to create air spaces in the compost pile. Wood species to avoid are cedar, cypress, redwood and eucalyptus as they have sap that is antimicrobial. Peat is not considered environmentally friendly, but if you choose to use it to increase the liquid storage, the best kind of peat for composting is coarse. Fine peat moss may compact, and lose it’s porosity but you can add more shavings or chip in the mix to counter this.
Internal Composting Toilets
In Sun Mar units the drum is rolled 6 revolutions every two days. When turned the pile should not slump like mud. It should fall over itself allowing new air pockets to be formed in the pile. Although the primary purpose of turning Bio-drum is to keep the compost aerated, it also has the effect of evening out the moisture content as wet parts are mixed with dry parts. The ideal moisture content of the compost pile is 40-60%. On inspection the compost should have a sheen. If it is too dry bacteria will become desiccated and composting activity will slow. If you can see dry toilet paper then the compost is probably too dry. If that is the case just add some warm water (30-40°С). If leaving the property for a period of time as it’s recommended to soak the pile to keep composting going while you’re away. Finally coconut coir is not suitable with Sun Mar. Over time, coir creates a sticky material that will clog up the grille at the base of the BioDrum. In the Biolan composting toilets (Komplet and Eco) you need to add in pieces of bark strips which are available in most garden centres. The function of these strips is to create air spaces in the compost which is especially important as the compost is not turned in those units.
Technically speaking with a urine diverting compost toilet you don’t need to add mulch after a bowel movement because the unit does not claim to break down the waste in the unit. But if you are going to compost the waste after it comes out of the unit, having a mix of waste and mulch is essential. It is good practice to start with some mulch to line the compostable bag or container. This will soak up moisture that will inevitably get in the solids container and make changing the container more pleasant. All the guidance in the paragraphs above is relevant to composting waste from a urine diverting toilet in a compost bin. Additional things to consider are that this pile will be lacking in nitrogen and will be too dry as the urine was diverted. Adding urine is ideal but if this is not possible hydrating the pile with warm water is advised.
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