Manure Separator Boosts Efficiency of Aeration Treatment

Using a solids-liquid manure separator will vastly improve the efficiency of aeration treatment of swine manure, according to a research trial from the University of Minnesota-Waseca.

That conclusion was based on the assessment of one parameter of the aeration process: oxygen transfer coefficient (OTC).

When the amount of manure solids increased from 0.5% to 4%, it led to a reduction in OTC from 0.59/min. to 0.15/min. This means that OTC in manure at 4% solids is reduced to about _ the level of efficiency of what it would be in manure at 0.5% total solids level (0.59/min. divided by 0.15/ min.).

Put another way, the energy consumption for manure with 4% total solids is nearly four times that for manure with 0.5% solids content, in order to achieve the same treatment results.

In the study, a pilot-scale aeration system was used to evaluate the impact of manure solids content on aeration efficiency. Four different solids levels of swine manure were tested: 0.5%, 1.0%, 2.0% and 4.0%. Aeration was applied at the same rate for each solids category. The dissolved oxygen (DO) concentration in the manure was recorded every six minutes until it reached the saturation level. After saturation, the aeration was stopped, but the DO monitoring continued for one hour to observe the effects of solids content on oxygen-holding capacity of the treated manure.

As summarized, the level of manure solids had a profound effect on the OTC in manure by aeration. Increasing the concentration of manure solids had a direct, negative correlation on the efficiency of the aerator.

And when aeration stopped, the DO concentrations decreased as expected, but decreased based upon the solids content in the manure. For the manure with 4.0% total solids content, the DO concentration neared zero about 30 minutes after aeration stopped. For the two lowest levels of solids content, only slight decreases in the DO concentration were seen during the same time period.

These results bear out that high solids content in swine manure not only reduce the efficiency of the oxygen transfer process, but also the oxygen-holding capacity of the treated manure — both necessary for efficient aeration of swine manure.

Use of a solids-liquid separator prior to aeration of liquid swine manure holds potential for greatly lowering aeration time, thus saving energy.

For producers who don't have a separator, a settling tank to reduce manure solids before aeration also would help reduce aeration time.

Researcher: Jun Zhu, University of Minnesota-Waseca. Phone Zhu at (507) 835-3620; fax (507) 835-3622; or e-mail

Manure Collection System May Provide Ultimate in Recycling

Researchers at North Carolina State University (NCSU) have developed a unique belt system for collection of swine manure and urine. Combusting the fecal material into ash converts a by-product into a valuable energy source and a promising mineral source for use in swine diets.

Instead of collecting manure in a standard holding pit, NCSU researchers designed an inclined conveyor. Waste falls through slotted floors onto the conveyor belt. Urine rolls off immediately and is removed from the barn. Feces remain on the belt to air dry.

Separating urine and feces in the barn has a big impact on odor and ammonia production, reducing ammonia levels by 65% to 80%. Bacterial action is also lessened, cutting overall odor emissions.

In this modified housing system, pig feces are harvested daily to a dry matter content of 50% to 60%. The high-energy product is combusted in a small-scale gasification system. The end products are energy and sterile ash.

The energy can be captured in the form of steam, electricity or a liquid fuel such as ethanol or diesel. Revenue from the sales of this energy is expected to make this pig and energy production system more economical than conventional pig production, especially if environmental legislation becomes more costly.

This thermal decomposition process also destroys bacteria and antibiotic residues.

For every 1,000 lb. of dry fecal material, about 130 lb. of ash is harvested. The ash is high in calcium (11.5%) and phosphorus (13.3%), making it a good candidate for mineral supplementation in swine diets.

To test digestibility, pigs were given a ration supplemented with minerals vs. a ration supplemented with ash and other ingredients.

Results were promising, indicating that mineral digestibility of the ash is very comparable to that of the commercial mineral products.

Next, NCSU researchers plan to use different sources of ash to evaluate them for nutrient content and digestibility. If results are encouraging, it may solve the environmental problem of ash disposal, which is also a by-product of incineration of mortalities. And, it may reduce the need for supplemental minerals.

Urine removed from the hog barn can be converted into harmless nitrogen gas. The ammonia can also be captured and converted into nitrogen fertilizer.

Researcher: Theo van Kempen, North Carolina State University. Phone van Kempen at (919) 515-4016; fax (919) 515-7780; or e-mail