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Enzymes that have proven to be capable of removing toxic compounds from water and soil may also be useful in the deodorization of animal manures. Considering that pork production in the US is a $40-billion industry with over half a million workers, odor control to protect air quality in the neighboring communities must be considered an essential part of managing livestock facilities. This pilot scale (20-120 L) study tested the use of minced horseradish (Armoracia rusticana L.) roots (1:10 roots to swine slurry ratio), with calcium peroxide (CaO(2) at 34 mM) or hydrogen peroxide (H(2)O(2) at 68 mM), to deodorize swine slurry taken from a 40,000-gallon storage pit at the Pennsylvania State University's Swine Center. Horseradish is known to contain large amounts of peroxidase, an enzyme that, in the presence of peroxides, can polymerize phenolic odorants and thus reduce the malodor. Twelve compounds commonly associated with malodor (seven volatile fatty acids or VFAs, three phenolic compounds and two indolic compounds) were used as odor indicators. Their concentration in swine slurry before and after treatment was determined by gas chromatography (GC) to assess the deodorization effect. The pilot scale testing demonstrated a complete removal of phenolic odorants (with a detection limit of 0.5 mg L(-1)) from the swine slurry, which was consistent with our previous laboratory experiments using 30-mL swine slurry samples. Horseradish could be recycled (reused) five times while retaining significant reduction in the concentration of phenolic odorants. In view of these findings, inexpensive plant materials, such as horseradish, represent a promising tool for eliminating phenolic odorants from swine slurry.

Animal waste odors arising from products of anaerobic microbial metabolism create community relations problems for livestock producers. We investigated a novel approach to swine waste odor reduction: the addition of FeCl(3), a commonly used coagulant in municipal wastewater treatment, to stimulate degradation of odorous compounds by dissimilatory iron-reducing bacteria (DIRB). Two hypotheses were tested: (i) FeCl(3) is an effective source of redox-active ferric iron (Fe(3+)) for dissimilatory reduction by bacteria indigenous to swine manure, and (ii) dissimilatory iron reduction results in significant degradation of odorous compounds within 7 days. Our results demonstrated that Fe(3+) from FeCl(3) was reduced biologically as well as chemically in laboratory microcosms prepared with prefiltered swine manure slurry and limestone gravel, which provided pH buffering and a substrate for microbial biofilm development. Addition of a 1-g liter(-1) equivalent concentration of Fe(3+) from FeCl(3), but not from presynthesized ferrihydrite, caused initial, rapid solids flocculation, chemical Fe(3+) reduction, and E(h) increase, followed by a 2-day lag period. Between 2 and 6 days of incubation, increases in Fe(2+) concentrations were accompanied by significant reductions in concentrations of volatile fatty acids used as odor indicators. Increases in Fe(2+) concentrations between 2 and 6 days did not occur in FeCl(3)-treated microcosms that were sterilized by gamma irradiation or amended with NaN(3), a respiratory inhibitor. DNA sequences obtained from rRNA gene amplicons of bacterial communities in FeCl(3)-treated microcosms were closely related to Desulfitobacterium spp., which are known representatives of DIRB. Use of iron respiration to abate wastewater odors warrants further investigation.

The application of anaerobically processed animal manure to maintain adequate levels of organic matter in arid soils is becoming a common practice. The purpose of this study was to characterize two farm manure products as compared with municipal waste compost (MWC). The anaerobic processing to obtain a biogas manure (BM) product was much faster (25 d) than the aerobic composting of farmyard manure (FYM) (90 d). Drying by three different methods (solar-drying, vacuum-drying at 45 degrees C, and freeze-drying) did not affect the quality of BM. Based on the chemical characteristics, FYM and BM products were comparable, and, containing less ash (30%) and heavy metals (50 mg Pb kg(-1)), seemed superior to MWC that contained 65% ash and 108 mg Pb kg(-1). On the other hand, MWC had higher C content (69.9%), lower acidity (15.04 mol kg(-1)), and higher exothermic peaks (300-460 degrees C) than BM and FYM (50% C, 20 mol kg(-1), and 275-450 degrees C, respectively), thus showing a greater extent of humification. Also, when the organic materials were incubated with arid soils and monitored for mean residence times (MRT), MWC was slightly more resistant to decomposition (MRT 175-180 d) than BM or FYM (MRT 161-166 d). The observed differences, however, were too small to dismiss any of the products as a valuable material for land applications to improve soil quality. In view of the results obtained, MWC may be considered an adequate substitute for BM or FYM, whenever the latter are in short supply.

Public concerns about offensive odors from livestock manures are on the rise and so is the pressure to develop practical ways to reduce the odors. The use of minced horseradish (Armoracia rusticanaL) roots (1:10 w/v plant tissue to swine slurry ratio), with calcium peroxide (CaO2 at 26 or 34 mM) or hydrogen peroxide (H2O2 at 34, 52, or 68 mM) for the deodorization of swine manure, was evaluated through a series of laboratory experiments. The principle underlying this deodorization method is the oxidation of odorants by the concerted action of horseradish peroxidase (present in the plant tissue) and peroxide that serves as an electron acceptor, followed by polymerization of phenolic odorants with a possible copolymerization or adsorption of other odorant compounds. The deodorization effect was assessed by a human panel and gas chromatography (GC). In the case of the GC method, 12 compounds commonly associated with malodor (7 volatile fatty acids or VFAs, 3 phenolic compounds, and 2 indolic compounds) were used as odor indicators. Malodor assessment of the treated slurry by a human panel indicated a 50% reduction in odor intensity. GC results showed 100% removal of all phenolic odorants without reoccurrence for at least 72 h. In view of these data, using plant materials as enzyme carriers and peroxides as electron acceptors emerges as an effective approach to phenolic odor control in animal manure.

Soil fertility in organic agriculture relies on microbial cycling of nutrient inputs from legume cover crops and animal manure. However, large quantities of labile carbon (C) and nitrogen (N) in these amendments may promote the production and emission of nitrous oxide (N2O) from soils. Better ecological understanding of the N2O emission controls may lead to new management strategies to reduce these emissions. We measured soil N2O emission for two growing seasons in four corn–soybean–winter grain rotations with tillage, cover crop, and manure management variations typical of organic agriculture in temperate and humid North America. To identify N2O production pathways and mitigation opportunities, we supplemented N2O flux measurements with determinations of N2O isotopomer composition and microbiological genomic DNA abundances in microplots where we manipulated cover crop and manure additions. The N input from legume‐rich cover crops and manure prior to corn planting made the corn phase the main source of N2O emissions, averaging 9.8 kg/ha of N2O‐N and representing 80% of the 3‐yr rotations' total emissions. Nitrous oxide emissions increased sharply when legume cover crop and manure inputs exceeded 1.8 and 4 Mg/ha (dry matter), respectively. Removing the legume aboveground biomass before corn planting to prevent co‐location of fresh biomass and manure decreased N2O emissions by 60% during the corn phase. The co‐occurrence of peak N2O emission and high carbon dioxide emission suggests that oxygen (O2) consumption likely caused hypoxia and bacterial denitrification. This interpretation is supported by the N2O site preference values trending towards denitrification during peak emissions with limited N2O reduction, as revealed by the N2O δ15N and δ18O and the decrease in clade I nosZ gene abundance following incorporation of cover crops and manure. Thus, accelerated microbial O2 consumption seems to be a critical control of N2O emissions in systems with large additions of decomposable C and N substrates. Because many agricultural systems rely on combined fertility inputs from legumes and manures, our research suggests that controlling the rate and timing of organic input additions, as well as preventing the co‐location of legume cover crops and manure, could mitigate N2O emissions. [ABSTRACT FROM AUTHOR]