I’m going to build a digester specifically for dog poop. I will be using a salvaged approx 60 gallon tank from an old air compressor. I’ll add lots of gravel under it to ensure good drainage and will figure out a way to have the lid air tight.
So great that you’re looking at handling the dog poop yourself rather than sending it to the landfill. Extra points for recycling the old air compressor. I’m going to address your questions one by one and then make some design suggestions for you
1. If it’s in a sunny area and painted black will the extra heat help the breakdown?
You will be burying the compressor so painting it black won’t be useful except perhaps for the lid.
2. With a 70lb dog how long would it last before it would have to be emptied? I’m hoping it will last a long time.
Your design needs to have a way for the material to move into the soil as it breaks down. Depending on the situation soil wise in your yard you would have numerous holes along the side and bottom or you would rig up an overflow system like is used in the doggie dooley system. I think your system would last a very long time provided it doesn’t get overloaded during cold weather or clogged with “compostable” and “biodegradable” bags.
3. I will be shovelling in a lot of snow in the winter in hopes of getting rid of as much of the dirty snow as
possible. It will melt in the spring anyway so space should not be an issue. That and we get the odd warm day so it might melt before summer. The system relies on microbes to function. Extended cold weather where temperatures are below 5˚C or 40˚ F will stop the system. In Edmonton that means you will have issues through the coldest months and could very easily overload your system.
4. Would it be necessary to add septic starter? If so when should I add it. When the tank is 1/2 full? 3/4 full? When I add it how fast and to what degree will it break down and reduce the volume?
Septic starter would be used from the beginning. You’d add the septic starter every couple of weeks. You also need to give it some water to facilitate getting the material out into the soil.
This is a lot of work if it’s not going to be effective. I also don’t want to stink up my yard.
I want you to have a close look at the doggie dooley FAQ page before you get too much further along. They’ve created two different products, one a septic tank with an overflow tube and the other a leach system. This will give you food for thought on how you might adjust your project.
A second design to have a look at this city farmer video. It’s worth keeping in mind that this system works well in Vancouver where temperatures below 5˚C or 40˚F are rare and usually short lived.