Abstract
The concentration of large numbers of animals in relatively small areas, high production output per animal unit, and concentration of animal excretions and air emissions are some of the staples of modern animal agriculture. Ammonia (NH3) and odors are among the most noticeable, as well as locally and regionally problematic emissions generated by concentrated animal feeding operations (CAFO) dairy production systems.
A zeolite is a mineral comprised of crystalline, hydrated aluminosilicate of alkali and alkaline earth cations having an infinite, open three-dimensional structure. Zeolites are able to further lose or gain water reversibly and to exchange cations, ammonium (NH4+) and ammonia gas (NH3) in particular, with and without crystal structure.
This dissertation presents two research projects where clinoptilolite zeolite was used to reduce NH3 emissions, retain nitrogen in compost or the clinoptilolite itself, and reduce odors. The dissertation contains a literature review, a chapter on the “Use of clinoptilolite zeolite in composting of dairy manure to reduce ammonia emissions and retain nitrogen in the compost”. Another chapter on the “Design and testing of a zeolite filter to capture ammonia and odors from dairy Manure on-farm”. A final chapter describes “Custom made designs and developments associated with this research”.
Composting is one of the most used methods to reduce volume and weight of dairy manure while stabilizing it prior to its land application or storage. As a nutrient and waste management practice, composting reduces the volume of composted wastes between 20-60% and significantly reduces their weight, which allows the materials to be much more affordable to transport than raw wastes. Most manures, including dairy manure, don’t have the proper carbon to nitrogen ratio (C:N) for composting without the loss of nitrogen as NH3 during the composting process. Due to the lack of enough carbon sources to balance the initial compost mix in arid and semi-arid regions, including southern Idaho (USA), amendments are used in an attempt to reduce the loss of nitrogen during the composting process. In many cases, these amendments provide uncertain results.
The objective of the study in chapter 2 was to demonstrate the effects of adding clinoptilolite zeolite to a dairy manure compost mix, specifically on ammonia emissions, compost nitrogen content and the quality of the final compost product.
The study was conducted on a commercial dairy in Southern Idaho. Manure stockpiled during the winter and piled after the corral cleaning was mixed with fresh pushed-up manure from daily operations, and with straw from bedding and old straw bales, in similar proportions for each windrow. Windrows were mixed and mechanically turned using a tractor bucket. Three replications of control and treatment windrows were made. The control consisted of the manure and straw mix as described. The treatment consisted of the same mix as the control plus the addition of 8% w/w on wet basis (15% dry basis) clinoptilolite zeolite during the initial mix. Windrows were actively composted for 145 to 157 days before screening, with five turns per windrow including the initial mix preparation.
Data were analyzed using ANOVA. Nitrate concentration in the treatment compost 702±127 mg/kg was three times higher than the control 223±127 mg/kg (p= 0.05). NH4+, showed a marked tendency to be lower in the treated windrows’ initial feedstock mix. These differences from the beginning of the process indicate that clinoptilolite zeolites have an immediate impact when added to the compost mix changing the NH4+ and NH3 behavior and volatilization even during the construction of the windrow. NH3 emissions showed a significant reduction in some of the measured periods. Total cumulative NH3 emissions were reduced by 14.4% in the clinoptilolite treated compost vs. control. The clinoptilolite treated compost had a cumulative value of 63.41±7.22 mg NH3-N/m3 versus the control at 74.07±7.22 mg NH3-N/m3, but such difference was not significant (p=0.2). An overall NH3 emissions reduction tendency was observed on the emissions’ fitted line of the treatment compared to the control, indicating that the total NH3 emissions from the whole process would be lower in the treated windrows. Solvita® maturity test showed a significant difference (p<0.05) indicating a higher maturity state in treated compost, with reduction in nitrogen loss potential, higher maturity index, lower estimated NH4+, phytotoxicity, noxious hazard and oxygen depletion. Volume reduction, composting temperatures, and most chemical component values had no significant differences between treatment and control. No negative effects resulted from the addition of clinoptilolite to the compost mix. The project demonstrated the feasibility of using the addition of clinoptilolite zeolites into the composting process as a Best Management Practice to improve dairy manure compost quality, reduce ammonia emissions, and change the nitrogen speciation during the composting process.
The chapter 3 study demonstrated the design and operation of a zeolite filter and air stream collection from a manure pit installed on-farm at a commercial dairy. Clinoptilolite zeolites mined in Idaho were used as the filter media. The capacity of the filter to reduce NH3 and odor emissions was tested. NH3 emissions were reduced by 92% at three days of operation and 42% after 59 days of operation of the filter. Ammonia concentration in the pre-treatment airstream from a dairy manure collection pit was relatively high. Odor concentration reduction was 45% at six days of operation with the minimum residence time of 0.85 s. The air collection roof-like structure and the zeolite filter were proven to be capable of operating in the harsh on-farm environment and to be adaptable to changing operative conditions within the dairy.
Finally, chapter 4 describes the design and construction of a cover used to capture the air over a flushed manure receiving pit, a zeolite filter, and a rotatory compost screen.