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United States Department of Agriculture

Agricultural Research Service


Location: Sustainable Agricultural Systems Laboratory

2013 Annual Report

1a. Objectives (from AD-416):
Development and evaluation of manure treatment systems. Specific objectives: (1) Develop treatment technologies and management practices to reduce the concentrations of pharmaceutically active compounds (antibiotics and natural hormones) in manures, litters, and biosolids utilized in agricultural settings; (2) Develop management practices and technologies to minimize greenhouse gas (GHG) emissions from manure and litter storage and from composting operations by manipulating the biological, chemical, and physical processes influencing production and release of ammonia and greenhouse gases during composting; (3) Develop technology and management practices that improve the economics and treatment efficiency of anaerobic digestion of animal manures and other organic feedstocks (e.g. food wastes, crops/residues) for waste treatment and energy production.

1b. Approach (from AD-416):
Modern livestock production involves the use of large amounts of nutrient inputs as well as antibiotics. Untreated manure is either stored or immediately applied to farmland as a fertilizer. When manure is applied to fields, manure components (nutrients, microorganisms, and remaining antibiotic residues) may reach surface water by volatilization, run-off or leaching. The goal of this research is to improve our basic understanding of two common manure treatment practices (composting and anaerobic digestion) so as to maximize their benefits and minimize their economic and environmental costs. The first objective is to evaluate the efficacy of a series of minimal management options for composting manure and poultry litter on-farm to reduce concentrations of ten widely used pharmaceutically active compounds. Treatments are designed to span a range of practical management options – from the current practice of stockpiling the manure/litter to amending it with straw (to increase aeration) and adding insulating layers of straw. The second objective seeks to reduce the environmental footprint of composting by reducing methane, nitrous oxide, and ammonia emissions during composting. Greenhouse gas and ammonia emissions will be measured using replicate pilot-scale compost piles composed of manure/bedding from the BARC dairy and food/green wastes from local food processors. The first set of treatments will test the timing and frequency of compost mixing and turning. Subsequent experiments will measure and compare gas emissions from replicate piles constructed at initial bulk densities and from piles covered with 7-30 cm layers of finished compost. The third objective involves an evaluation of a relatively low-cost anaerobic digestion system that has significant potential for use on small farms. Six replicate pilot-scale plug-flow digesters, with two operational designs will be studied to provide long-term research on a system that has not been fully explored. Treatment efficiency, capital and operational costs, and gas utilization strategies will be evaluated for each type of system. Costs and benefits of different treatment strategies will be compared to existing manure management practices.

3. Progress Report:
Progress was made on two objectives, both of which fall under National Program 214, and focus on improving our basic understanding of two common manure treatment practices (composting and anaerobic digestion). Under objective 1, technologies and practices to reduce concentrations of pharmaceutically active compounds in manures, litters, and biosolids, we made progress in developing methods for analysis of three of the four pharmaceutically active compounds (PACs) targeted this year in poultry litter and dairy manure. In addition, we completed analyzing composting results for four other PACs. Under objective 3, we completed construction of six replicate pilot-scale anaerobic digesters and began field trials in May 2013 using dairy manure from the BARC digester.

4. Accomplishments
1. In the U.S., anaerobic digestion (AD) is an economically viable manure treatment option for large dairies (>500 cows). However, since roughly 90% of U.S. dairies have less than 200 cows, this technology is economically inaccessible to the vast majority of U.S. dairies. As part of a research effort focused on developing designs and strategies to make anaerobic digestion technology available to small farms, ARS and University of Maryland scientists performed an economic assessment of small-scale U.S. digesters using cost data from eight existing 100 to 250-cow dairies and eight theoretical systems. Cash flow analysis results showed that total capital costs, capital costs per cow, and net costs per cow generally decreased with increasing herd size in existing systems. Among existing revenue streams, use of digested solids for bedding generated the highest revenue ($100 per cow per year), followed by biogas use for heating and/or electrical generation ($47 to $72 per cow per year) and CO2 credits ($7 per cow per year). No system had a positive cash flow under the assumed conditions (8% discount rate, 20 year term). However, six of the sixteen systems had positive cash flows when 50% cost sharing was included in the analysis. Our results suggest that, with cost sharing, economically viable AD systems are possible on 250-cow dairies. Additional revenue streams, such as tipping fees for food waste, may reduce the minimum size to 100-cow dairies. These efforts support current efforts within the U.S. dairy industry to increase renewable energy and decrease greenhouse gas emissions on dairy farms.

2. Algal turf scrubbing (ATS) is an engineered wastewater treatment system in which lawn-like, filamentous algae are grown in shallow sloping raceways. Algae grow using the nutrients in the wastewater and are removed from the system by weekly harvesting. Beyond their practical application for wastewater treatment, ATS systems are also useful for answering much more basic questions in biology and ecology. Some species of algae grow very quickly within algal turf scrubbers. However, which species dominate and how fast they grow is partially dependent on the water flow rate through the system. The general goal of this research is to develop automated systems in which a characteristic (such as color, growth rate, or size) of the organisms being grown is used to control the system in which the organisms are grown (for example, by affecting the feeding rate, temperature, or amount of light). The specific objective of these experiments was to evaluate how well algal growth rates could be used to automatically optimize water flow rates in an ATS. Results from computer modeling experiments showed that algal growth rates could be used in concert with a feedback control system to optimize water flow rates. However, in practice, the variability of algal growth rates between weekly harvests frequently confused the feedback control system. Consequently, some experimental trials resulted in optimal flow rates but other trials were not successful. Nonetheless, these results will be useful for scientists trying to develop automated control systems and for companies seeking to grow crops of algae using the least amount of energy.

Review Publications
Blersch, D., Kangas, P., Mulbry III, W.W. 2013. Autonomous benthic algal cultivator under feedback control of ecosystem metabolism. Environmental Engineering Science. 60:53-60.

Blersch, D., Kangas, P., Mulbry III, W.W. 2013. Turbulence and nutrient interactions that control benthic algal production in an engineered cultivation raceway. Algal Research. 2:107-112.

Mulbry, III, W.W., Reeves, III, J.B., Liu, Y., Zhen, R., Liao, W. 2012. Near- and mid-infrared spectroscopic determination of algal composition. Journal of Applied Phycology. 24:1261-1267.

Olszewski, J.M., Lozano, N., Haines, C., Rice, C., Ramirez, M., Torrents, A. 2013. The effect of liming on antibacterial and hormone levels in wastewater biosolids. Waste Management and Research. 48:862-870.

Klavon, K., Lansing, S., Moss, A., Mulbry III, W.W., Felton, G. 2013. Economic analysis of small-scale agricultural digesters in the United States. Biomass and Bioenergy. 54:36-45.

Last Modified: 05/27/2017
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