Urban agriculture has been growing as the movement of population to the urban centers is increasing. According to FAO (2008), by 2030 majority of the population in sub sahara Africa (SSA) would be living in the urban area. Pollution from animal manure is a global concern and is much more acute and serious in countries with high concentrations of animals on a limited land base for manure disposal (Roderick, Stroot and Varel, 1998), this is the case with urban livestock production. Environmental pollution and odor complaints related to animal production have increased dramatically during the past decade (Ernest and Ronald, 2004). These odors potentially interfere with quality and enjoyment of life (Mauderly, 2002 and Albert, 2002). According to Pfost, Fulhage and Hoehne, 1999, odor complaints are more common when the humidity is high and the air is still or when the prevailing breezes carry odors toward populated areas. Inspite of the role that urban agriculture can play in pursuing the Millennium Development Goals, more specifically those, related to poverty reduction, food security, and environmental sustainability, odor from livestock still remains a major obstacle to future development. According to Obayelu 2010 there has been public's increasing intolerance of livestock odors, hence the need to find solutions which will be ecosystem friendly. This paper will review some methods of odor control focusing on natural solutions to this problem.
For an odor to be detected downwind, odorous compounds must be: (a) formed, (b) released to the atmosphere, and (c) transported to the receptor site. These three steps provide the basis for most odor control. If any one of the steps is inhibited, the odor will diminish. (Chastain, 2000)
There are four general types of compounds for odor control: (1) masking agents that override the offensive odors, (2) counteractants that are chemically designed to block the sensing of odors, (3) odor absorption chemicals that react with compounds in manure to reduce odor emission, and (4) biological compounds such as enzymatic or bacterial products that alter the decomposition so that odorous compounds are not generated (Chastain, 2000). Some of these compounds are added directly to the manure while others are added to the feed. Yucca schidigera is a natural feed additive for livestock and poultry used to control odors, ammonia and other gas emissions, which can be detrimental to livestock performance. Essential oils are being promoted as effective and safe antimicrobial or antiviral (disinfectant) agents that also act as masking agents in the control of odor examples are thymol and carvacrol. Natural zeolite, clinoptilolite (an ammonium-selective zeolite), has been shown t o enhance adsorption of volatile organic compounds and odor emitted from animal manure due to its high surface area. Cai et al. (2007) reported reduction >51% for selected offensive odorants (i.e. acetic acid, butanoic acid, iso-valeric acid, dimethyl trisulfide, dimethyl sulfone, phenol, indole and skatole) in poultry manure with a 10% zeolite topical application. Treatment of broiler litter with alum was originally developed to reduce the amount of soluble phosphorous in poultry litter. However, it was also observed that using alum reduced the pH of the litter to below 6.5, and as a result, reductions in ammonia emissions from the litter have been observed.
Amendment of manure with alkaline materials such as cement kiln dust, lime, or other alkaline by-products can increase the pH to above 12.0, which limits the vast majority of microbialactivity, including odor producing microorganisms (Veenhuizen and Qi, 1993, Li et al., 1998). The effect of the addition of lime and other ONAs that alter the pH and moisture content of the waste and bedding requires further scientific research (McGahan, et al., 2002).
Dust particles can carry gases and odors. Therefore, dust control in the buildings can reduce the amount of odor carried outside. Management practices that can greatly reduce the amount of dust in poultry buildings are Clean interior building surfaces regularly, Reduce dust from feed, this can be by addition of oil to dry rations, proper and timely maintenance of feeders, augers, and other feed handling equipment. Also managing the relative humidity (RH) in poultry houses. Planting just three rows of trees around animal farms has also been proven to cut nuisance emissions of dust, ammonia, and odors from poultry houses. The use of tress around livestock facilities to mitigate odour and improve air quality has been recently reviewed by Tyndall and Colletti (2000). They concluded that trees have the potential to be an effective and inexpensive odor control technology particularly when used in combination with other odour control methods. Trees ameliorate odours by dilutio n of odour, encourage dust and aerosol deposition by reducing wind speeds, physical interception of dust and aerosols, and acting as a sink for chemical constituents of odour.
The use of indigenous microorganisms for odor reduction related to livestock is being promoted under Natural farming, in this instance cultured mixtures of microorganisms consisting mainly of lactic acid bacteria, purple bacteria and yeast are used. This is already made into commercial product and marketed as effective microorganism activated solution (EMAS).
Interestingly, there is paucity of information on ethnobotanicals that are useful for odour control. Most literatures on ethnobotany focused of treatment and control of animal diseases but not on traditional control of the environment of livestock. As scientists are still working hard to develop chemical or biological additives which will eliminate or reduce odors associated with poultry wastes there is the need to survey traditional livestock owners for information that can serve for development of effective,inexpensive, efficient and suitable agent for odor control in poultry management.
Oyebanji Bukola, Department of Animal Sciences, Obafemi Awolowo University, Ile-Ife, Nigeria
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