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United States Department of Agriculture

Agricultural Research Service

2010 Annual Report

1a.Objectives (from AD-416)
Develop and evaluate algal systems for the treatment of dairy and swine manure effluents with respect to: a) capturing N and P from raw and anaerobically digested dairy manure effluents; b) utilization of the algal biomass as an organic fertilizer; and c) overall system nutrient uptake efficiency, operational costs, and potential returns of integrated farm-scale systems. Determine levels and biological effects of oxytetracycline and chlorotetracycline in manure from treated animals on biological treatment processes. Determine levels of antibiotic resistant bacteria in treated manures from animals treated with oxytetracycline and chlorotetracycline. Develop technology and management practices that improve anaerobic digestion of dairy and other animal manure by: a) increasing yield of methane gas; b) increasing energy efficiency of the conversion system; and c) reducing cost. Develop technology to increase the efficiency with which the methane is used to economically meet the energy needs of the farm.

1b.Approach (from AD-416)
Laboratory and pilot-scale field studies will be used to evaluate treatment efficiency and cost of microalgal-based treatment technologies at different loading rates of raw and anaerobically digested manure effluents. Dried algal biomass from manure treatment will be tested in growth chamber studies to evaluate the value of the biomass as an organic fertilizer capable of meeting plant nutrient requirements. Laboratory-scale composting, soil incubation, and anaerobic digestion studies will be used to determine the fates of the antibiotics oxytetracycline, chlorotetracycline, and antibiotic-resistant bacteria in manures from therapeutically treated beef calves. Laboratory and pilot-scale field studies will be used to quantitate effects on methane yield of co-digesting dairy manure with agricultural and industrial by-products. Additional studies will focus on use of cold tolerant microbial consortia to improve the rate and yield of methane production during anaerobic digestion of dairy manure at 10-25 C.

3.Progress Report
Although composting is an effective practice for stabilizing manure nutrients prior to land application, emissions of ammonia, methane, and nitrous oxide during composting, there are negative environmental consequences of this process. There is a need to determine the emissions of these gases during typical farm-scale composting operations and to test the effectiveness of different management measures to reduce emissions. Pilot-scale dairy manure composting studies were completed using a photoacoustic gas analyzer for measuring ammonia, methane, carbon dioxide and nitrous oxide emissions.

There is a global need to reduce dependency on fossil energy and to make use of sustainable energy feedstocks. Current anaerobic digestion technology in the U.S. is focused on large-scale dairy farms (greater than 500 cows). However, the vast majority of dairies (in the U.S. and elsewhere) have less than 200 cows. There is an urgent need to develop and support inexpensive anaerobic digestion systems for these small farms. One approach to increase potential biogas production at small dairies is to supplement manure with digestable agricultural residues such as switchgrass. Laboratory-scale studies aimed at improving biogas yield were conducted using mixtures of dairy manure and switchgrass.

1. DETERMINING WHETHER BIOGAS YIELD FROM SWITCHGRASS IS AFFECTED BY ITS STAGE OF GROWTH AT HARVEST. A variety of agricultural feedstocks have been proposed as potential supplements to dairy manure to increase biogas production through anaerobic digestion. Previous studies have shown that addition of switchgrass to dairy manure in high solids anaerobic reactors significantly increases biogas yield. However, there has been no information on whether the growth stage of switchgrass affects its digestibility or ultimate biogas yield. Results show that the timing of biogas production differs between anaerobic reactors containing green switchgrass (harvested in July) and reactors containing brown, senescent switchgrass (harvested the following January). However, the different reactors showed no significant difference in the amount of biogas produced. These results are important because the environmental benefits of this deep-rooted plant will be affected by its production cycle. The costs of harvest and production yield will also be affected by the harvest cycle.

2. GREENHOUSE GAS EMISSIONS FROM DAIRY MANURE COMPOSTING OPERATIONS. The effect of pile mixing on greenhouse gas (GHG) emissions from stored dairy manure was determined using large flux chambers designed to completely cover pilot-scale manure piles. GHG emissions from piles that were mixed four times during the 80 day trial were about 20% higher than unmixed piles. Carbon dioxide, methane, and nitrous oxide accounted for about 75%, 20%, and 3% of GHG emissions, respectively. Approximately 70% of carbon dioxide and methane emissions from all piles occurred within first 23 days. In contrast, 60-75% of nitrous oxide emissions occurred during the later stages of composting. These results suggest that with respect to minimizing GHG emissions, farmers should store manure in undisturbed piles or, at the very least, delay the first turning of manure piles for at least four weeks.

3. BENEFICIAL USES FOR MANURE BYPRODUCTS. Determined efficacy of synthetic fabric socks filled with mature compost (compost socks) in capturing contaminants present at low levels in stormwater. Previous results showed that compost socks efficiently captured nutrients, motor oil, and diesel fuel from single batches of stormwater contaminated with high concentrations of these materials. Results from recent laboratory-scale experiments showed compost socks that were also effective in capturing >95% of motor oil from repeated batches of water contaminated with low levels (about 15 milligrams per kilogram) of diesel fuel. These results are important since these experiments simulated conditions and oil concentrations similar to those in actual field conditions.

Review Publications
Lozano, N., Rice, C., Ramirez, M., Torrents, A. 2009. Fate of triclosan in agricultural soils after biosolid applications. Chemosphere. 78:760-766.

Mulbry III, W.W., Kangas, P., Ingram, S.K. 2010. Scrubbing the Bay: Nutrient Removal Using Small Algal Turf Scrubbers on Chesapeake Bay Tributaries. Ecological Engineering. 36:536-541.

Loyo-Rosales, J.E., Rice, C., Torrents, A. 2009. Fate and Distribution of the Octyl- and Nonylphenol Ethoxylates and Some Carboxylated Transformation Products in the Back River, Maryland. Journal of Environmental Monitoring. 12:614-621.

Last Modified: 3/2/2015
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