In the RESTORE project, SINTEF has calculated the climate effects of different treatments of residual flows from a farm. Different residual materials have been looked at and whether they can be composted, incinerated or used in biochar production. A spreadsheet model has been created that provides some answers on the economics, quantity produced and climate footprint of different alternatives.
Here is an example of the calculation for composting materials from the farm at Mære. What we choose to compost is manure from the stable and from the calf department, leftover feed, park waste and waste from the greenhouse. Below is a table of the quantities that were calculated in m3 and in tons.
Fixed and variable costs can be entered, here is an example of costs for establishing a compost area with a fixed cover, catch ponds and a compost turner. It is possible to do this more cheaply and perhaps also save by joining forces with other farms. Work is stipulated for a 10% position and 100 tractor hours with a diesel consumption of 20 liters/hour when the turner is running.
The spreadsheet calculates the amount of finished compost we can get out to 200 tons. It also calculates the climate footprint divided into primary (directly from the compost) and secondary emissions (diesel) and CO2 in organic material bound in the compost.
Here we see that over half of the carbon remains in the compost (156 tonnes CO2e) and that diesel accounts for little (1.6 tonnes CO2e). On the other hand, diesel use is the only fossil emission, while the others are biological. We usually think that biological emissions are part of the cycle and can therefore be counted as zero.
The question may be whether we are able to permanently increase the content of organic matter (mold) in the soil when we use compost. If we are able to bind carbon in the soil in this way, it is a plus in the climate accounts, the uncertainty is how long it stays in the soil before it breaks down again. The effect on better plant growth is not included in the calculations
On the negative side, we know that composting can lead to runoff of nutrient-rich water. That is why we have installed catch ponds at the compost site. During the composting process, methane and nitrous oxide can also be produced. This is what the model tries to calculate.
No comparison has been made here, but the alternatives for these materials are not necessarily better. Some materials can be dried a little and then burned. Some can be spread on the field and worked directly into the soil.
We have also calculated combustion (wood chip firing) and production of biochar. (and you can see this here)
The spreadsheet prepared by Sintef is available by contacting us.
