Andrew C. VanderZaag

Floating Covers to Reduce Gas Emissions from Liquid Manure Storages: A Review

Liquid manure (slurry) storages are sources of detrimental gases. Floating covers are a potential mitigation measure that can be implemented on many storage facility types. This article reviews the use of floating covers to reduce the emissions of odors, hydrogen sulfide (H2S), ammonia (NH3), and greenhouse gases (GHGs) including carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Covers have been established with materials of natural origin (e.g. natural crusts, straw, peat, and light expanded clay aggregates), synthetic origin (e.g. geotextile, plastic, and rubber), and composites of both. Nearly all cover types have been capable of substantially reducing NH3 emissions (compared to uncovered controls). Reductions of odor and H2S have also been good, though fewer cover types have been assessed with respect to these parameters. When used alone, oil covers can produce foul odors and should not be used. Less information is available on the influence of covers on GHG emissions. In studies >2 weeks long, covers generally increased CH4 and CO2 emissions. All studies where N2O was measured found that permeable covers increased its emission. There is some difficulty comparing laboratory and field observations, which may be due to study duration, hydrologic influences, or slurry characteristics. Principles of mass transfer are discussed with respect to the mechanisms of cover operation. Though evidence of microbial gas consumption in permeable covers exists, its relative importance is unclear. Currently, information on many cover materials is limited to one or two studies, and simultaneous assessments of the effects on all aforementioned gases is lacking for all covers.

Carbon footprint of Canadian dairy products: Calculations and issues

The Canadian dairy sector is a major industry with about 1 million cows. This industry emits about 20% of the total greenhouse gas (GHG) emissions from the main livestock sectors (beef, dairy, swine, and poultry). In 2006, the Canadian dairy herd produced about 7.7 Mt of raw milk, resulting in about 4.4 Mt of dairy products (notably 64% fluid milk and 12% cheese). An integrated cradle-to-gate model (field to processing plant) has been developed to estimate the carbon footprint (CF) of 11 Canadian dairy products. The on-farm part of the model is the Unified Livestock Industry and Crop Emissions Estimation System (ULICEES). It considers all GHG emissions associated with livestock production but, for this study, it was run for the dairy sector specifically. Off-farm GHG emissions were estimated using the Canadian Food Carbon Footprint calculator, (cafoo)(2)-milk. It considers GHG emissions from the farm gate to the exit gate of the processing plants. The CF of the raw milk has been found lower in western provinces [0.93 kg of CO2 equivalents (CO2e)/L of milk] than in eastern provinces (1.12 kg of CO2e/L of milk) because of differences in climate conditions and dairy herd management. Most of the CF estimates of dairy products ranged between 1 and 3 kg of CO2e/kg of product. Three products were, however, significantly higher: cheese (5.3 kg of CO2e/kg), butter (7.3 kg of CO2e/kg), and milk powder (10.1 kg of CO2e/kg). The CF results depend on the milk volume needed, the co-product allocation process (based on milk solids content), and the amount of energy used to manufacture each product. The GHG emissions per kilogram of protein ranged from 13 to 40 kg of CO2e. Two products had higher values: cream and sour cream, at 83 and 78 kg of CO2e/kg, respectively. Finally, the highest CF value was for butter, at about 730 kg of CO2e/kg. This extremely high value is due to the fact that the intensity indicator per kilogram of product is high and that butter is almost exclusively fat. Protein content is often used to compare the CF of products; however, this study demonstrates that the use of a common food component is not suitable as a comparison unit in some cases. Functionality has to be considered too, but it might be insufficient for food product labeling because different reporting units (adapted to a specific food product) will be used, and the resulting confusion could lead consumers to lose confidence in such labeling. Therefore, simple units might not be ideal and a more comprehensive approach will likely have to be developed.

Gas emissions from straw covered liquid dairy manure during summer storage and autumn agitation.

This study evaluated the effect of straw covers on emissions from liquid manure during storage and agitation. Emissions of carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and ammonia (NH3) were measured from six tanks (6.6 m2 each) containing batch-loaded liquid dairy manure. This was conducted between June and October 2007 in Nova Scotia, Canada. Straw was added to four of the tanks at two thicknesses (15 and 30 cm), while two tanks remained uncovered. Gas concentrations were measured using tunable diode lasers, an infrared gas analyzer, and acid traps. Fluxes were measured using steady-state chambers. At the end of the study, one tank from each treatment was agitated. During 122 d of undisturbed storage, the covers increased emissions of CO2 and N2O. However, the 15 and 30 cm covers reduced CH4 emissions by 24% and 28% and reduced NH3 emissions by 78% and 90%, respectively. During 5 d of intermittent agitation, substantial releases of CO2, CH4, and NH3 were observed from all treatments. In this period, greenhouse gas emission reductions were relatively unchanged because releases from the control and covered tanks were similar. However, emissions of NH3 during agitation were highest from tanks that had been covered, thereby decreasing the overall emission reduction provided by the 15 and 30 cm covers to 68% and 76%, respectively. Despite elevated emissions during agitation, the results suggest that straw covers provide an overall reduction of CH4 and NH3 emissions compared to the control.

Greenhouse gas emissions from surface flow and subsurface flow constructed wetlands treating dairy wastewater.

Agricultural wastewater treatment is important for protecting water quality in rural ecosystems, and constructed wetlands are an effective treatment option. During treatment, however, some C and N are converted to CH(4), N(2)O, respectively, which are potent greenhouse gases (GHGs). The objective of this study was to assess CH(4), N(2)O, and CO(2) emissions from surface flow (SF) and subsurface flow (SSF) constructed wetlands. Six constructed wetlands (three SF and three SSF; 6.6 m(2) each) were loaded with dairy wastewater in Truro, Nova Scotia, Canada. From August 2005 through September 2006, GHG fluxes were measured continuously using transparent steady-state chambers that encompassed the entire wetlands. Flux densities of all gases were significantly (p < 0.01) different between SF and SSF wetlands changed significantly with time. Overall, SF wetlands had significantly (p < 0.01) higher emissions of CH(4) N(2)O than SSF wetlands and therefore had 180% higher total GHG emissions. The ratio of N(2)O to CH(4) emissions (CO(2)-equivalent) was nearly 1:1 in both wetland types. Emissions of CH(4)-C as a percentage of C removal varied seasonally from 0.2 to 27% were 2 to 3x higher in SF than SSF wetlands. The ratio of N(2)O-N emitted to N removed was between 0.1 and 1.6%, and the difference between wetland types was inconsistent. Thus, N(2)O emissions had a similar contribution to N removal in both wetland types, but SSF wetlands emitted less CH(4) while removing more C from the wastewater than SF wetlands.

Permeable Synthetic Covers for Controlling Emissions from Liquid Dairy Manure

Liquid manure storages emit greenhouse gases (GHGs) and ammonia (NH3), which can have negative effects in the atmosphere and ecosystems. Installing a floating cover on liquid manure storages is one approach for reducing emissions. In this study, a permeable synthetic cover (Biocap™) was tested continuously for 165-d (undisturbed storage + 3-d agitation) in Nova Scotia, Canada. Covers were installed on three tanks of batch-loaded dairy manure (1.3 m depth × 6.6 m2 each), while three identical tanks remained uncovered (controls). Fluxes were measured using steady-state chambers. Methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O) were measured by absorption spectroscopy, and NH3 was measured using acid traps. Results showed covered tanks consistently reduced NH3 fluxes by approximately 90%, even though a surface crust formed on controls after about 50 days. Covers continued to reduce NH3 flux during agitation. Covered tanks also emitted significantly less CO2 and N2O than the controls (p-value <0.01). However, CH4 fluxes were not reduced, and therefore overall GHG fluxes were not substantially reduced. Short-term trends in CH4, CO2, and N2O flux provided insight into cover function. Notably, bubble fluxes were a key component of CH4 emissions in both treatments, suggesting the covers did not impede CH4 transport.

Towards an inventory of methane emissions from manure management that is responsive to changes on Canadian farms

Methane emissions from manure management represent an important mitigation opportunity, yet emission quantification methods remain crude and do not contain adequate detail to capture changes in agricultural practices that may influence emissions. Using the Canadian emission inventory methodology as an example, this letter explores three key aspects for improving emission quantification: (i) obtaining emission measurements to improve and validate emission model estimates, (ii) obtaining more useful activity data, and (iii) developing a methane emission model that uses the available farm management activity data. In Canada, national surveys to collect manure management data have been inconsistent and not designed to provide quantitative data. Thus, the inventory has not been able to accurately capture changes in management systems even between manure stored as solid versus liquid. To address this, we re-analyzed four farm management surveys from the past decade and quantified the significant change in manure management which can be linked to the annual agricultural survey to create a continuous time series. In the dairy industry of one province, for example, the percentage of manure stored as liquid increased by 300% between 1991 and 2006, which greatly affects the methane emission estimates. Methane emissions are greatest from liquid manure, but vary by an order of magnitude depending on how the liquid manure is managed. Even if more complete activity data are collected on manure storage systems, default Intergovernmental Panel on Climate Change (IPCC) guidance does not adequately capture the impacts of management decisions to reflect variation among farms and regions in inventory calculations. We propose a model that stays within the IPCC framework but would be more responsive to farm management by generating a matrix of methane conversion factors (MCFs) that account for key factors known to affect methane emissions: temperature, retention time and inoculum. This MCF matrix would be populated using a mechanistic emission model verified with on-farm emission measurements. Implementation of these MCF values will require re-analysis of farm surveys to quantify liquid manure emptying frequency and timing, and will rely on the continued collection of this activity data in the future. For model development and validation, emission measurement campaigns will be needed on representative farms over at least one full year, or manure management cycle (whichever is longer). The proposed approach described in this letter is long-term, but is required to establish baseline data for emissions from manure management systems. With these improvements, the manure management emission inventory will become more responsive to the changing practices on Canadian livestock farms.

Effects of winter storage conditions and subsequent agitation on gaseous emissions from liquid dairy manure

An understanding of emissions from liquid manure facilities during winter, spring thaw and agitation is needed to improve national emissions inventories in Canada. In this study, liquid dairy manure was stored in six pilot-scale tanks (1.8 m deep × 6.6 m2 surface area) covered by steady-state chambers that enabled greenhouse gas (GHG) and ammonia (NH3) flux measurement. After 158 d of undisturbed storage, three tanks were agitated for 5 d (8 h per day) consecutively. During storage, methane (CH4) flux was correlated with manure temperature at 30 cm depth (P < 0.05). Nitrous oxide (N2O) fluxes occurred only during spring thaw - at rates comparable with agricultural soil during spring thaw. On a carbon dioxide (CO2) equivalent basis, however, cumulative N2O fluxes were negligible compared with CH4 fluxes. Flux of NH3 was correlated positively with manure temperature near the surface and negatively with the presence of ice or a surface crust (P < 0.01). Agitation did not affect N2O and NH3 fluxes, whereas CO...

Survival of Escherichia coli in agricultural soil and presence in tile drainage and shallow groundwater

Animal agriculture and the use of manure as a soil amendment can lead to enteric pathogens entering water used for drinking, irrigation, and recreation. The presence of Escherichia coli in water is commonly used as an indicator of recent fecal contamination; however, a few recent studies suggest some E. coli populations are able to survive for extended time periods in agricultural soils. This important finding needs to be further assessed with field-scale studies. To this end, we conducted a 1-yr study within a 9.6-ha field that had received fertilizer and semi-solid dairy cattle manure annually for the past decade. Escherichia coli concentrations were monitored throughout the year (before and after manure application) in the effluent from tile drains (at approximately 80 cm depth) and in 5- to 8-m-deep groundwater wells. Escherichia coli was detected in both groundwater and tile drain effluent at concentrations exceeding irrigation and recreational water-quality guidelines. Within two of the monitoring w...

Ammonia Emissions from Surface Flow and Subsurface Flow Constructed Wetlands Treating Dairy Wastewater

Agricultural wastewater treatment is important for maintaining water quality, and constructed wetlands (CW) can be an effective treatment option. However, some of the N that is removed during treatment can be volatilized to the atmosphere as ammonia (NH(3)). This removal pathway is not preferred because it negatively impacts air quality. The objective of this study was to assess NH(3) volatilization from surface flow (SF) and subsurface flow (SSF) CWs. Six CWs (3 SF and 3 SSF; 6.6 m(2) each) were loaded with dairy wastewater ( approximately 300 mg L(-1) total ammoniacal nitrogen, TAN = NH(3)-N + NH(4)(+)-N) in Nova Scotia, Canada. From June through September 2006, volatilization of NH(3) during 12 or 24 h periods was measured using steady-state chambers. No differences (p > 0.1) between daytime and nighttime fluxes were observed, presumably due in part to the constant airflow inside the chambers. Changes in emission rates and variability within and between wetland types coincided with changes in the vegetative canopy (Typha latifolia L.) and temperature. In SSF wetlands, the headspace depth also appeared to affect emissions. Overall, NH(3) emissions from SF wetlands were significantly higher than from SSF wetlands. The maximum flux densities were 974 and 289 mg NH(3)-N m(-2) d(-1) for SF and SSF wetlands, respectively. Both wetland types had similar TAN mass removal. On average, volatilization contributed 9 to 44% of TAN removal in SF and 1 to 18% in SSF wetlands. Results suggest volatilization plays a larger role in N removal from SF wetlands.

Methane emissions from digestate at an agricultural biogas plant.

Methane (CH4) emissions were measured over two years at an earthen storage containing digestate from a mesophilic biodigester in Ontario, Canada. The digester processed dairy manure and co-substrates from the food industry, and destroyed 62% of the influent volatile solids (VS). Annual average emissions were 19gCH4m(-3)d(-1) and 0.27gCH4kg(-1)VSd(-1). About 76% of annual emissions occurred from June to October. Annual cumulative emissions from digestate corresponded to 12% of the CH4 produced within the digester. A key contributor to CH4 emissions was the sludge layer in storage, which contained as much VS as the annual discharge from the digester. These findings suggest that digestate management provides an opportunity to further enhance the benefits of biogas (i.e. reducing CH4 emissions compared to undigested liquid manure, and producing renewable energy). Potential best practices for future study include complete storage emptying, solid-liquid separation, and storage covering.