Over the last decade, Oliver stated, these goals have become more reachable, as technology has caught up to aspirations. Advanced manure treatment protocols typically begin with separation of solids and liquid, usually with a screw-press. This technique drops slurry volume anywhere from 5% to 15%. As it does, it can capture almost half of the total solids, averaging about 45%. That includes about 15% of inorganic and organic nitrogen (N) and 10% of the total phosphorus (P) and potassium.
And for some farms, this primary reduction of volume and partitioning of nutrients may be sufficient; for others, Oliver said, there are additional steps that can be taken to bridge the gap between the size of the herd and the producer’s land base. He pointed to two increasingly used methods and cited two others which are not yet advanced enough for commercial use. The methods which are appearing more on large farms include:
Fine solids separation. This process is enhanced by chemicals which clump and sort out phosphorus-rich fine suspended solids. Unlike previous iterations of this method, current systems are energy efficient and deliver stackable solids. Oliver said that the significant drawback of this method is the cost of the chemicals: up to 25 cents per cow per day, in some cases.
Ultrafiltration. Here, membranes remove phosphorus-rich fine solids. This technique offers big returns; users report rates of up to 95% phosphorus and 40% total nitrogen removal. Membranes are available to fine-tune the process for one or the other. Another pro in its favor: Ultrafiltration partners well with reverse and forward osmosis treatments and the now-clean water, which can account for up to one-third of the original manure volume, can then be used on the farm. However, the high cost of operating and maintaining ultrafiltration membrane systems can put them out of reach of all but the largest operations. Right now, Oliver said, the cost makes them practical for farms with herds of 7,000 head or more.
Vermifiltration. Just coming onboard as a feasible commercial option, vermifiltration systems send low-solids manure through wood shavings, composting worms, and other porous layers. Its large footprint and reliance on worms make it a finicky choice that’s best fit for warmer climates, but the results are impressive: Oliver stated that such a system is capable of capturing 85% of both nitrogen and phosphorus in the worm castings.
Oliver said that when considering whether an advanced manure system is something to pursue, visits to farms and discussions with vendors are vital parts of the process. Weigh the potential system’s energy demand, assess your existing manure streams, and take realistic stock of what you can live with and what you can’t live without before pursuing a particular system.
