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BackgroundEnteric methane (CH4) accounts for about 70% of total CH4 emissions from the ruminant animals. Researchers are exploring ways to mitigate enteric CH4 emissions from ruminants. Recently, nano zinc oxide (nZnO) has shown potential in reducing CH4 and hydrogen sulfide (H2S) production from the liquid manure under anaerobic storage conditions. Four different levels of nZnO and two types of feed were mixed with rumen fluid to investigate the efficacy of nZnO in mitigating gaseous production.MethodsAll experiments with four replicates were conducted in batches in 250 mL glass bottles paired with the ANKOMRF wireless gas production monitoring system. Gas production was monitored continuously for 72 h at a constant temperature of 39 ± 1 °C in a water bath. Headspace gas samples were collected using gas-tight syringes from the Tedlar bags connected to the glass bottles and analyzed for greenhouse gases (CH4 and carbon dioxide-CO2) and H2S concentrations. CH4 and CO2 gas concentrations were analyzed using an SRI-8610 Gas Chromatograph and H2S concentrations were measured using a Jerome 631X meter. At the same time, substrate (i.e. mixed rumen fluid+ NP treatment+ feed composite) samples were collected from the glass bottles at the beginning and at the end of an experiment for bacterial counts, and volatile fatty acids (VFAs) analysis.ResultsCompared to the control treatment the H2S and GHGs concentration reduction after 72 h of the tested nZnO levels varied between 4.89 to 53.65%. Additionally, 0.47 to 22.21% microbial population reduction was observed from the applied nZnO treatments. Application of nZnO at a rate of 1000 μg g− 1 have exhibited the highest amount of concentration reductions for all three gases and microbial population.ConclusionResults suggest that both 500 and 1000 μg g− 1 nZnO application levels have the potential to reduce GHG and H2S concentrations.

Greenhouse gas (GHG) emissions from agricultural production operations are recognized as an important air quality issue. A new technique following the U.S. Environmental Protection Agency Method TO-14A was used to measure GHG emissions from ground-level area sources (GLAS) in a free-stall dairy operation in central Texas. The objective of this study was to quantify and report GHG emission rates (ERs) from the dairy during the summer and winter using this protocol. A weeklong sampling was performed during each season. A total of 75 and 66 chromatograms of air samples were acquired from six delineated GLAS (loafing pen, walkway, barn, silage pile, settling basin, and lagoon) of the same dairy during summer and winter, respectively. Three primary GHGsmethane (CH 4 ), carbon dioxide (CO 2 ), and nitrous oxide (N 2 O)-were identified from the dairy operation during the sampling periods. The estimated overall ERs for CH 4 , CO 2 , and N 2 O during the summer for this dairy were 274, 6005, and 7.96 g head Ϫ1 day Ϫ1 , respectively. During the winter, the estimated overall CH 4 , CO 2 , and N 2 O ERs were 52, 7471, and 3.59 g head Ϫ1 day Ϫ1 , respectively. The overall CH 4 and N 2 O ERs during the summer were approximately 5.3 and 2.2 times higher than those in the winter for the free-stall dairy. These seasonal variations were likely due to fluctuations in ambient temperature, dairy manure loading rates, and manure microbial activity of GLAS. The annualized ERs for CH 4 , CO 2 , and N 2 O for this dairy were estimated to be 181, 6612, and 6.13 g head Ϫ1 day Ϫ1 , respectively. Total GHG emissions calculated for this dairy with 500 cows were 2250 t of carbon dioxide equivalent (CO 2 e) per year.

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Although there are more than 200 odor-causing volatile organic compounds (VOCs), phenol and p-cresol are two prominent odor-causing VOCs found downwind from concentrated animal feeding operations (CAFOs). The VOC emissions from cattle and dairy production are difficult to quantify accurately because of their low concentrations, spatial variability, and limitations of available instruments. To quantify VOCs, a protocol following U.S. Environmental Protection Agency (EPA) Method TO-14A has been established based on the isolation flux chamber method and a portable gas chromatograph (GC) coupled with a purge-and-trap system. The general objective of this research was to quantify phenol and p-cresol emission rates (ERs) from different ground-level area sources (GLASs) in a free-stall dairy during summer and winter seasons using this protocol. Two-week-long sampling campaigns were conducted in a dairy operation in central Texas. Twenty-nine air samples were collected during winter and 37 samples were collected during summer from six specifically delineated GLASs (barn, loafing pen, lagoon, settling basin, silage pile, and walkway) at the free-stall dairy. Thirteen VOCs were identified during the sampling period and the GC was calibrated for phenol and p-cresol, the primary odorous VOCs identified. The overall calculated ERs for phenol and p-cresol were 2656 AE 728 and 763 AE 212 mg hd À1 day À1 , respectively, during winter. Overall phenol and p-cresol ERs were calculated to be 1183 AE 361 and 551 AE 214 mg hd À1 day À1 , respectively, during summer. In general, overall phenol and p-cresol ERs during winter were about 2.3 and 1.4 times, respectively, higher than those during summer.Implications: Concentrated animal feeding operations contribute a considerable amount of VOCs to the atmosphere. The phenol and p-cresol are two VOCs recognized as potential odor-causing compounds emitted from livestock operation. To develop effective strategies for mitigating livestock odorous VOC emissions, relative emissions from different GLAS in a livestock operation under different climate conditions should be quantified. It is also important to obtain direct estimates of VOC emissions from different GLAS in CAFOs to compile emission inventories. This research determined phenol and p-cresol emissions from different GLAS in a free-stall dairy and also identified areas in a dairy operations that have the highest phenol and p-cresol emissions.

Swine effluent with high organic strength need to be treated to make it suitable for applying to crop/pasture fields, or discharging to any waterways. Electrocoagulation is a relatively simpler and cheaper technique over biological and chemical treatment methods currently used to treat high-strength industrial and municipal wastewater. The performance of an electrocoagulation system mainly depends on the pH, Electrical Conductivity (EC) of the medium, Chemical Oxygen Demand (COD) loading rates and catalytic activity of the electrodes used. In this research, a study was conducted to compare the pollutant removal efficiencies of three electrodes (Fe-Fe, Al-Al and Fe-Al) with three electric current levels (500, 1000 and 2000 mA) while treating swine manure effluents. The electrochemical cell consisted of two parallel rectangular plates (90×25×1.5 mm) of Iron (Fe-Fe), Aluminum (Al-Al) and Iron-Aluminum (Fe-Al, later on described as hybrid) electrodes; immersed in a beaker with 550 mL swine effluents and powered by a Direct Current (DC) supply. All studies were conducted in batches at room temperature. In general, removal efficiencies were increased with increasing current densities and electrolysis times for electrodes evaluated. Aluminum electrodes outperformed iron and hybrid (iron-aluminum electrodes) in removing Total Phosphorus (TP) at all current density levels tested. Overall, use of hybrid electrodes resulted in better COD removal. For the same treatment times (1200 s) at higher current density (21 mA cm −2 ), hybrid electrodes removed about 100% COD, which are about 1.9 and 1.3 times higher than those of aluminum and iron electrodes, respectively. Iron electrodes showed the highest removal efficiency (85%) for Total Organic Carbon (TOC) at 21 mA cm −2 current density and 1200 s treatment time. Overall, lower Specific Electrical Energy Consumptions (SEECs) per kg of Pollutants (TP, COD and TOC) were estimated for the aluminum electrodes than the other electrodes combination.