Trials running pig manure through our KP presses have been run in the States and Canada, and KP-6 presses have been sold to pig farmers in Costa Rica and Sri Lanka. In all cases the press has done its job of separating solids and liquids, but machine sales did not result in the States.
Pig Manure is highly digested and contains a large portion of the solids in the form of very small particles. The larger particles are basically undigested food. Typically pig manure is pumped to a KP press with a dilute inbound solids consistency in the range of 1% to 6%. At the lower solids content, the gpm capacity of the press goes up, reaching 100 gpm in the KP-10.
However there are two problems that can occur when very low consistency flows are pumped to a press. Either the solids capture rate goes down, or the screen of the screw press tends to blind. For that reason, Vincent insists that flows of pig manure be pre-thickened with a sidehill screen before being admitted to the press.
Regardless of inbound solids content, the cake produced by the press will have a moisture content of about 70%. This cake material is quite dry to the touch, and it composts very readily. Remarkably, it has almost no odor.
Since the cake is essentially undigested animal feed, it provides a good feed additive. Our Costa Rican customer sells his press cake, in 50-pound bags, to nearby cattle ranchers. The investment in the press has significantly reduced a pond odor problem while paying for itself in by-product sales.
Testing sponsored by A.O. Smith ESPC (Harvestore) was conducted by the Dairy Forage Research Department at the University of Wisconsin. They found that the capture rate for the KP press was in the range of 20% to 25%. This means that at least three quarters of the inbound solids go through the screen and are carried away with the filtered liquid.
Advanced animal husbandry practices in North America result in a higher proportion of the feed being digested. Overseas it is typical for coarser ground material to be feed, and for less complete digestion to take place. Thus the solids capture rate is higher outside of North America.
The low capture rate is the reason that sales were not achieved in the States and Canada. In these countries the reason for pressing manure was the hope that most of the solids would be separated from the liquid and that the odor and wastewater treatment problems associated with hog farms would be addressed. A belt press would be better suited for this task than a screw press.