This is a great question and something I see a lot!
I am not a Soil Scientist, or a Scientist of any official kind for that matter. But I am an expert at Compost operations because I lived it!
For some reason these Scientific types, whom study the science of the compost process, invariably suggest a large material grind size of bulking agent to blend with Sludges or food wastes. This makes perfect sense for making windrows or static piles to allow airflow through the pile and create a perfect environment for composting. Aerobic Composting takes water and oxygen and continued airflow increases the speed of the compost process. But you need to earn a living from the compost, so the more of it the better.
The objective of a Compost Facility is to make Compost, not make overs. If you are mixing 8”-12” material with your food wastes or sludges, airflow through the pile will be great, but if you are screening out the composted material at ½”, your split of finished product to overs will be about 1:5.
So if you compost 10,000 yards per year, then the next year you will have 18,000 yards because of all the overs you are adding back in. Then the following year, you will have 25,000 yards to compost. Obviously the reduction in volume from composting reduces these numbers, but you get the picture.
When I first started composting, I thought I was smarter than everyone and mixed sawdust with all the wet sludges and food wastes. It worked great in drying the materials and made them able to be windrowed. Of course, after the first time I turned these piles, I had odor complaints from about 3 different Counties.
So, what do you do? Try these options and see if you can decrease your composting time, reduce your overs and create great looking compost:
· Start reducing your bulking agent size. The smaller your bulking agent is, the more fines you have and the faster they break down to a usable compost size.
· Keep a nose out for odor. The finer the material, the less airflow and the more potential for odor when you break into the piles.
· Use a windrow turner or turn the windrows more often. You have reduced the airflow with the finer material so you need to add more oxygen more often than previously.
· Watch the temperatures. With the finer materials, the heat will generate much more quickly which means you need to turn more often.
Over time, you will figure out the best grind size and turn schedule to accommodate your operations. Shoot for a 65%-75% finished product to 25%-35% overs. This will be enough overs to work back into your new windrows to kick start your compost process. Good Luck.
Questions, Dave Whitelaw Grinderguy@askthegrinderguy.com