Livestock manure used to be considered waste. Today, landowners have many choices for handling manure using traditional waste storage structures, on-farm manure application and innovative manure management and treatment systems. The manure management needs and local regulations are unique to every farm.
Whether choosing a new system or upgrading an existing system, considerations include:
• Landowner goals and objectives
• Manure handling practices
• Operation’s impact on air and water quality (resource concerns)
• Alternate uses or market for manure or post-handling by-product
• Plan for potential excess of nitrogen and phosphorous
• Alternative(s) if insufficient land is available for land application
• Nutrient utilization by crops and application method
• Payback period and funding availability
A webinar called “Evaluation of Manure Management Systems” was offered by Jeff Porter, P.E., team leader, USDA NRCS National Manure Management Team, to evaluate current or proposed manure handling processes.
Whether working with small or giant farms, seek peak performance for manure handling systems. The Natural Resources Conservation Service (NRCS) offers guidelines on manure application for cropland or pasture through the nutrient management conservation practice standard. Farms with small herds often have capacity to spread their manure on site seasonally and store it during cold months. Giant, Concentrated Animal Feeding Operations (CAFO) often generate more manure than they can effectively spread on their own lands. Some may contract with neighbors for nutrient disposal.
To evaluate manure-handling systems, Porter advised looking at the whole picture. Study what goes in, what comes out and what happens inside the handling operation. He recommends evaluating each system and process separately.
Physical systems treat suspended pollutants by letting them settle, float and/or filter the remaining slurry. Some operators recycle sand or manure solids as bedding. System processes may include separating liquids from solids for separate waste streams. Screw presses can remove liquids to concentrate solids.
Chemical processes change the properties of the waste and waste stream. Adding metal salts or polymers can convert dissolved solids to suspended solids to aid settling or filtering. Gasification or heating manure can create syn-gas or other products while reducing waste volume. Other chemical processes may modify waste’s chemical make-up for alternate uses or destroy organic chemicals through oxidation or other processes.
Biological processes are similar to what happens in natural settings. Bacteria and other organisms break down manure and other materials into various byproducts. Compost operations, anaerobic digesters or other controlled environments may speed these processes. Digesters produce biogas, which can be used to generate heat or electricity. Digester byproducts may be applied to farmland.
When choosing a system, be sure to consider local regulations, labor availability and skills, current and potential market for byproducts, the time needed to develop markets, connection to a grid for electricity generation, the need for heat or hot water and system implementation costs.
When evaluating manure treatment systems, Porter reviews every process that changes manure characteristics whether it will separate, convert or digest manure. He likes to follow the same path as the manure, guided by farm operators. Porter is careful with biosecurity. At a minimum, he recommends cleaning boots and equipment between site visits. Additional biosecurity steps may also be required.
1. Diagram the current/planned system. Include all components in order. Do not skip any processes, including short-term and long-term storage. Storage may lead to crust formation, anaerobic activity, nitrogen breakdown, carbon dioxide or ammonia emissions, concentration by evaporation or dilution by rainfall. Any of these factors may cause a system to run below peak performance. The process order matters and depending on the component arrangement can give different results. Include manure, liquid or byproduct land application and methods, and note any emissions. Analyze soils and describe other practices that may affect potential crop/plant uptake.
2. Identify all system components, including inputs and outputs for each process. Often the output of one process becomes the input for the next process. Be sure to include every component when a site has multiple waste streams and/or multiple buildings. Review all manure handling and processing steps, and seek potential leaks or emissions that may need to be prevented. Consider potential value added products for on-farm use or sale as well as any by-products/residues for on-farm land application. Value added products may shorten the payback period for handling system upgrades and increase farm profitability.
3. Characterize input manure and output byproducts. Seek lab analysis of TS, COD/BOD, N, K, P, pH, salts, pathogens and other components as needed. Manure with bedding material or diluted manure will have different characteristics than excreted manure. Manure characteristics will affect all processes. Various forms of nutrients need different handling. For example, the type of anaerobic digester used is dependent on the manure waste stream solids content. Too much ammonia may shut down a digester. Use accurate soil tests for planning land applications. Soil conditions will affect plant and soil nutrient capacity. Estimate manure production volume.
4. Track the form and fate of the nutrients through each process (in order).
5. Identify system nutrient outputs and forms. Operators should select their preferred outputs: value added products, soil amendments, compost and/or spreadable residues. Some operators used composted, dried solids as bedding keeping materials in the system.
Nutrient-laden liquids need to be handled or further processed. Gaseous emissions include carbon dioxide, ammonia, odors and other air pollutants. Potential pathogens may affect value added opportunities.
For new sites, estimate input characteristics and volume with the most accurate data possible. Analyze manure from nearby sites using similar feeds, bedding and water sources and livestock whenever possible.
Separating liquids from solids can significantly reduce handling and/or spreading costs. Thermo-chemical processes, such as gasification, can be used to create energy for heating or electricity and reduce manure volumes 80-90 percent. Remaining byproducts have low nitrogen levels and are more economical to move offsite. Combustion systems may produce high NOX levels and should be evaluated.
When considering new or upgraded manure handling technologies, initial costs can run in the tens or hundreds of thousands of dollars. Use careful analysis to ensure technologies offer effective returns. Many, but not all, operations find a market for excess nutrients (as value added products) to offset some of their new system costs.