| | A demand for tools which can reduce odour from livestock operations has driven the identification of several new
solutions in recent years. But like anything new and relatively untested, these new developments have also prompted several questions. What are the costs versus the benefits? What technical factors help producers achieve optimal results from the technology or practice?
The bottom line, says Ike Edeogu, a leading researcher in the field of livestock odour, is that not every solution works for every producer in every circumstance. This point is illustrated by the results of a research project conducted by a network of odour researchers throughout the province, including staff from the AgTech Centre in Lethbridge, Alberta. The study was sponsored by the Alberta Livestock Industry Development Fund (ALIDF), Alberta Agricultural Research Institute (AARI) and Alberta Agriculture and Rural Development (ARD).
"Cost-effectiveness is ultimately the factor of most concern to producers," he says. "So it’s important to carefully consider the various factors involved before adopting new odour reduction tools."
Biofiltration
Biofiltration works on the principle that odourous air can be filtered by passing it through a volume of material, or media, populated by microbial cultures that use pollutant gases in the air as food nutrients. The key to effective biofiltration is selecting biofilter media with adequate porosity, large surface areas and good moisture retention.
Wood chip and bark mulch media were tested in pig barns under a variety of water application methods, water rates and air distribution systems. The results suggested that biofilters are effective in reducing odour, particularly when using wood chips as media. However, maintaining the moist conditions necessary for effective filtration can be challenging, labour-intensive and costly.
"Although biofiltration is often touted as a quick and easy solution for odour mitigation, we found that the results do not justify the costs," says Edeogu. "Our results suggest that large expenses may be incurred and significant time spent creating and sustaining conditions favourable to the biofiltration process."
Oil sprinkling in barns
Past research suggests that sprinkling oil can reduce dust levels in pig barns by up to 95 percent. Its potential as an odour reducing tool has been driven by the possibility of a correlation between dust and odour levels.
The odour control team project did not confirm this correlation, however. Although refined, bleached and deodorized (RBD) oils emitted more pleasant, low intensity odours, and essential oils significantly improved the character of odourous air, there was little in the results to conclude that oil application reduces livestock odour.
"This confirms the outcome of some research and contradicts others," says Edeogu. "This is important information because, from a cost-efficiency perspective, RBD and essential oils can be quite costly, not to mention the set-up costs of installing spray systems. In addition, matters pertaining to the cleanup of oil deposits, the potential health risks to animals or humans from inhalation of aerosols from the oils, or risks of injury to animals from slippery floors, remain unresolved."
Diet modification
Primarily, the source of pig odour can be traced back to the incomplete digestion of dietary proteins and carbohydrates in the pig gut. Odourous compounds such as sulphides, volatile fatty acids and phenols are then produced following the partial anaerobic decomposition of undigested substrates present in the faeces. Reducing nutrient levels in pig diets may indirectly reduce odour emissions if the pig is able to utilize most of the nutrients in the diet rather than pass them out in the faeces. The downside to reducing nutrient levels in pig diets is that feed supplements will have to be added in order to sustain the animal’s nutritional needs.
Nonstarch polysaccharides (NSPs) have been said to affect manure emissions by enhancing digestion processes, in turn reducing the need for protein-reduced diets. NSPs are not digested in the pig’s small intestine but are instead passed to the hindgut, a change in process that has been reported to impact the production of odour-inducing substrates.
Experimental trials were conducted on eight pens of pigs using a range of protein levels and NSP supplements in feed. The results showed no significant effects on odour concentration or in the hedonic tone of emissions from manure. Hedonic tone is a measure of an odour’s pleasantness or unpleasantness.
"Contrary to other studies, these results did not support the use of dietary protein reduction primarily to reduce emissions from stored swine manure," says Edeogu. "Although this project focused solely on emissions from manure, it is possible that diet manipulation could have beneficial effects on other aspects of pig production such as increasing nutrient retention in the animal, therefore reducing the amount of nutrients passed out in the faeces."
Composting vs. stockpiling
The primary difference between composted and stockpiled manure is oxygen. Oxygen is a key element in the composting process. When combined with a good source of carbon, nitrogen and moisture, it produces the high temperatures required for aerobic microbial activity. Aerobic microbial activity can only occur in the presence of oxygen. These microbes digest and process the various components of manure and are said to render it less offensive.
However, little research has been conducted to compare the odour emissions from composted manure to those of stockpiled manure. Over a 107-day period, the odour concentration and hedonic tone of a compost windrow and stockpile, both containing manure from a beef cattle feedlot, were compared.
Results indicated that the emission rates from the composted manure were significantly higher than the stockpiled manure during the active composting phase (days 1 to 78). By the end of the study however, there were no significant differences between the emission rates of the two treatments following the spreading of the stockpiled and composted manure on land. Hedonic tone ratings followed a similar pattern.
"The absence of significantly lower emission rates from the compost treatment was unexpected and may be attributed to low sensitivity of the measurement procedure," says Edeogu, who says high ventilation rates through the measuring device and the influence of background odours may have played significant roles in the end result. "Because of these compromising factors, it is unclear if composting beef cattle feedlot manure reduces odour emissions compared to stockpiling."
Compost additives
The potential of phosphogypsum (PG) as a compost additive to control odour is two-fold. First is its ability to react with gaseous emissions such as ammonia, thereby retaining nitrogen in the manure, and secondly, its ability to reduce the pH of manure, consequently inhibiting the production of gases such as ammonia. PG typically retains more ammonia in compost material, lowering the pH of the compost, changing its decomposition dynamics, and in turn it may reduce odour emissions.
In a commercial farm trial, six windrows of composted beef cattle feedlot manure were compared: three mixed with 10 percent PG and three without. The project’s main objectives were to determine if feedlot manure could be effectively composted within pens housing animals and if PG would be effective in reducing odour and ammonia emissions during the composting process of feedlot manure.
The pH of the windrows amended with PG was lower and levels of ammonia-nitrogen were higher in the windrows mixed with PG compared to those without. "However, the resultsare inconclusive," Edeogu says. "The windrows were compacted as the animals trampled over them, resulting in reduced oxygen availability. This contributed to creating an environment not conducive for aerobic composting and, as a result, the product failed to compost. It was also high in moisture content, which typically inhibits the microbial activity necessary for composting by filling many voids in the windrow with moisture rather than air."
Odour is a very complex and difficult challenge for the industry, says Edeogu. "Even though the technologies evaluated did not result in a winner, it does provide producers with a basis for making decisions by knowing what doesn’t work. The challenge is measuring a significant difference with the nose. That difference has to be about a 70 percent reduction in odour emissions before the nose can detect a difference.
"Much of the research has been based on odour concentration but our findings did note a difference in character or offensiveness," he says. "For example, a bakery may emit odour concentrations equivalent to a livestock operation but most people would prefer the bakery. Being able to measure a combination of concentration and offensiveness is a recommended approach for the future." |
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