A 1200-hd solid-liquid separation finishing barn was built in Missouri for improved manure management and air quality. The facility has a wide V-shaped gutter below slatted flooring (Figure 1), which continuously drains away liquids. A scraper is used to collect the solids, which are then managed separately. Field sampling and research were conducted to evaluate the performance of the solid-liquid separation finishing barn in improving manure nutrient management, potential nutrient/water recycling based on filtration, and barn construction and operating costs.
What did we do?
The barn (built in 2010) was closely monitored for manure production and nutrient content, and operating costs. Laboratory-scale pretreatments and filtrations were conducted to evaluate the practicality of nutrient/water recycling from the separated liquid manure.
What we have learned?
The daily liquid manure production averaged 885 gallons and daily solid manure production averaged 299 gallons (about ¼ of the total manure volume). The separation system removed 61.7%, 41.7%, 74.8%, and 46.2% of the total manure nitrogen, ammonium, phosphorous, and potassium, respectively, with the collected solids. The filtration results indicate that the microfiltration and reverse osmosis were time and energy intensive, which was probably constrained by the relatively small-scale unit (inefficient compared with larger units), small filter surface area, and high concentration of dissolved nutrients.
The construction cost of the solid-liquid separation barn with solid manure storage was $323,000 ($269/pig-space, in 2010), 17% higher compared to the traditional deep-pit barn ($175 to $230/pig-space). It is likely that the solid-liquid separation barn will become less expensive when more barns of similar design are built, and the conveyor system can be improved and simplified for less maintenance and lower costs. Additional electricity cost was $331 per year for daily operation of the scraper and conveyor systems, and pumping the separated liquid manure fraction. The additional maintenance cost of the scraper system averaged $1,673/year. A net gain of $3,975/year was observed when considering the value of the separated manures, cost of land application, and annual maintenance cost.
A payback period of 15.1 years on the additional investment was estimated, when compared with the popular deep-pit operation. However, the payback period can be reduced by many factors, including improved conveyor system and growing popularity of the barn design in an area. When the distance to transport the slurry manure was increased from 5 miles to 7.5 and 10 miles, the payback periods became 12.7 and 11.3 years, respectively. The solid-liquid separation barn was shown to have better air quality when compared with deep-pit barns based on monthly measurements of ammonia and hydrogen sulfide concentrations.
Impacts/Implications of the Research.
This study monitored the manure production of a commercial finishing barn utilizing a solid-liquid separation system. Overall, we can conclude that the final results obtained from monitoring the total manure production rate, air quality exiting the barn fans, and the pig growth rates made sense relative to other comparative sources. The overall results indicate that the barn design can attain some valuable benefits from separating the solid and liquid streams. About a quarter of the manure volume was collected and managed as nutrient-dense solid manure (defined as ‘stackable’). The solid manure held 80% of the total solids and nearly 75% of the phosphorous.
Take Home Message
There are alternative barn designs and manure management systems (relative to lagoon and deep-pit operations) that should be considered when planning for a new operation or expansion. Considerations should include the need to better manage manure nutrients and improve air quality for human and animal occupants.
Further consideration of the manure management, including work load and major- and micro-nutrients need to be furthered analyzed. Future research may look into application of a larger-scale crossflow system to see if nutrient removal and flow rates can be improved significantly. Future research may focus on improving manure filtrate flow, and determining the cost of installation and upkeep for a filtration unit that can operate at the level of a farm operation. Extrapolating the costs off of bench-scale model does not seem remotely indicative of the true cost, due to improved efficiency and power of larger unit.
Lim, Teng (Associate Professor and Extension Agricultural Engineer, Agricultural Systems Management, University of Missouri, firstname.lastname@example.org)
Brown, Joshua (University of Missouri); Zulovich, Joseph (University of Missouri); and Massey, Ray (University of Missouri).
Please visit https://www.pork.org/research/sustainability-evaluation-solid-liquid-manure-separation-operation/ for the final report, and ASABE Paper No. 1801273 (St. Joseph, Mich.: ASABE. DOI: https://doi.org/10.13031/aim.201801273) for more information.
Funding for this research project was provided by the National Pork Checkoff and University of Missouri Extension.
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