Layer Manure

December 10, 2014
ISSUE #269

Layers (egg-laying chickens) are kept in wire cages which allow the manure to fall through. The manure can either fall into a pool of water or onto a belt conveyor.

In late 2013 we were approached by inventor Woody Cronin in regards to a system he developed for layer manure. Years before, we had tried dewatering the manure from water-bottom barns, with poor results. Because of this we were cool to the idea of running a screw press on the material from a conveyor-bottom barn.

To our surprise, with Woody's technology, it works well. Press cake with only 65% moisture content can be produced. This material is undigested food. It has very high nutritional value, and it makes an excellent feed additive for farm animals. Conceivably it could qualify as biomass fuel for a boiler.

We were told that layers digest only 40% of their feed. The operation of the screw press system results in a recovery of half of the feed found in the manure. Mathematically that calculates to a 30% recovery of the poultry feed.

Overall the operating system is as follows. The manure is first mixed with press liquor in order to fluidize and dilute it. (The system is started up with water since there is no press liquor.)

Next the flow goes through equipment which separates out the calcium (it looks and feels like sand) and the feathers. That is a gravity separation process.

From there the flow is dosed with organic polymer. Most polymers are made from natural gas, and they are not good as feed additives. However natural polymers, like those made from shrimp waste, are acceptable in feed rations.

Next the flow goes to the screw press. The flow is dilute, so pre-thickening ahead of the press may be required. This pre-thickening can be achieved with either a rotary drum or a sidehill (parabolic) screen. Prethickening can greatly increase the throughput capacity of the screw press.

The as-received manure typically had 75% to 80% moisture content. The press cake produced typically had a moisture content of 64% to 68%.

The press liquor from the press goes to the mixing pit where it is added to incoming chicken manure. High in urea, the excess press liquor is drained off for use as a liquid fertilizer.

Alternatively, with heavier dosage of polymer, the press liquor can be made very clear, with as low as 0.5% total solids.