Application: to reduce emission of odors and gases from the manure storage by altering the manure’s chemical or microbial properties
- Can be implemented with little change to current manure system.
- Typically little scientific information on performance of additives.
A large assortment of additives exist, some are added directly to manure, some are fed to the animal, while others are sprayed in the air. Within this factsheet, the focus will be on additives that are either directly added to the manure, or incorporated into the diet with the intension of being delivered to the manure to alter manure properties. Of the numerous products available, it is probable that some may be capable of altering the manure odor intensity in some conditions, but may not be as successful in other situations. Differences in how an additive performs on one farm as compared to another may be related to things like the type of animal, how the manure is handled (frequency of scraping, flushing, or removal), the amount of wasted feed, how or where the manure is stored, or even differences in the amount of water added to the manure.
|Figure 1. Manure additive testing set-up at Iowa
In general, manure additives can be classified into one of three broad categories, microbial additives, adsorbents and absorbents, and other chemical additives. Microbial additives are either some sort of mixed culture of enzymes, mixed culture of microorganisms, or some combination of the two that are added to the manure at some set frequency. Adsorbents and absorbents are compounds that collect odorous compounds either on their surface or interior, preventing their loss from the manure. Other chemical additives are a class of chemicals that act by altering odorous compounds and include oxidizing agents, precipitants, electron acceptors, or even pH altering chemicals.
Microbial additives, or digestive additives, are either enzymes or microbes that are added to the manure with the intension of increasing breakdown of solids or reducing the emission of ammonia, hydrogen sulfide, or odor. In general, the odors associated with manure tend to be partially decomposed organic compounds. Complete microbial breakdown of these compounds result in the formation of carbon dioxide and methane, both of which are odorless. However, in some cases sufficient microbes to completely process these compounds into methane and carbon dioxide, as quickly as the compounds are formed, may not exist. In these cases, adding certain microbes or enzymes may accelerate certain steps in the decomposition process, reducing the loss of the most odorous compounds from the manure. Often times these microbial additives have to be added frequently;this suggests that the added microbes may not readily adapt to the natural conditions in the manure handling system.
|Figure 2. Manure treatment testing set-up at
In the case of enzymes, these can be either fed to the pig or applied directly to the manure. In either case, the objective is to provide enzymes that are specifically targeted to break down certain types of solids in the manure, such as cellulose, which is typically harder to break apart. In many ways these enzymes are similar in concept to these used in cellulosic ethanol plants; however, there are several differences. In particular, with manure we are often dealing with a much more eclectic material that is not as uniform in composition as that at the ethanol plant, and that naturally has a much wider assortment of microbes present within the material. This can impact enzyme effectiveness as often times the enzymes only operate on very specific materials.
If the additive is a microbial culture it will most likely be added directly to the manure. In this case, the manure is being seeded with microbes that were selected to perform specific functions. In all cases, the added microbes must compete with microbes already present in the manure for food and resources to survive. It is possible that the supplemental microorganisms may not readily adapt to the natural conditions in the manure, which may limit their effectiveness. In other cases, the manure may be suitable for colonization by these microbes, which would improve effectiveness. At this time, very few university studies are available on the effect of different microbial additives and their ability tomodify the bacteria population within the manure.
Adsorbents and Absorbents
Adsorbents and absorbents are biological or chemical materials that can collect the odor compounds on their surface or interiors. A practical example of this that you may be familiar with, is the use of charcoal filter for water purification (like used in the Brita water purification systems). The idea is to provide a material with lots of surface area that will react with, and either chemically or physically capture and hold certain compounds. An example of this that has been used in manures are zeolites or clinoptilolites. Alternative examples may include synthetic organic polymers that can react and bind with either ammonium ions or organic matter.
Zeolites are naturally occurring and mineralize with a high affinity to chemically interact with positively charged ions, such as ammonium. This means they have the potential to reduce ammonia emissions from the manure. A 1997 study by Miner et al. found that application of 1 to 4% clinoptilolite (a type of zeolite) to dairy slurry immediately before surface application reduced ammonia emission by 60%. Similarly, the high adsorption capacity of these compounds can reduce odor emissions. A study of zeolites as an amendment for poultry litter recently demonstrated a 50 to 70% reduction in odorants from the manure (Cai et al., 2007).
Another example of an absorbent aresaponins from yucca. Saponins a high-molecular-weight glycosides extracted from the yucca plant. A 1995 study by Amon et al. reported a 26% reduction in ammonia emissions from a swine barn using saponins while Kemme et al. (1993) reported a 23% reduction. However, Johnston et al. (1981)and Martinez et al. (1997) all reported no effect of saponins on ammonia emissions.
Other Chemical Additives
The final class of additives are other chemical additives. These compounds act by altering the characteristics of the manure in some manner to alter odor emission properties. This could be done by killing certain bacteria, changing a characteristic to encourage proliferation of a different bacteria, or digesting organic matter in the manure. Often times when dosing chemicals into the manure, side reactions will occur in addition to the desired reaction. This makes determining the application rate somewhat challenging, and could help explain why a treatment observed to be effective at one manure storage may be found to be less effective in different conditions.
As discussed, there are several types of products that can be used, including oxidizing agents. Oxidizing agents help break down organic matter in the manure and limit the formation of hydrogen sulfide. In particular, the oxidizing agents are most effective if they are utilized in such a way that they can oxidize the released odorous organic compound into less odorous products. These products also destroy odor-producing bacteria, including those that produce hydrogen sulfide and ammonia. Researchers have found that different oxidizers reduces odor by 25 to 50%, with a cost of $2.65 per 100 gallons of manure estimated for use of ozone was used as the oxidizer.
In many ways, these compounds share similarities to the use of aeration, but rather than relying on the introduction of oxygen into the manure, a different chemical is being used. Example chemicals include chlorine (such as sodium hypochlorite or bleach), potassium permanganate, hydrogen peroxide, or ozone. Although these additions can be effective, due to the higher amounts of organic matter in the manure, these compounds generally haven’t been cost effective in real world situations.
One example of this type of compound that was recently tested was the use of soybean peroxidase as an additive for swine manure. The soybean peroxides were added as a topical amendment to the manure with testing performed at both the lab and barn scales. In this study, the soybean peroxidase was mixed with calcium oxide and applied; resulting in some partial crusting. This product was estimated to cost around $2.62 per pig marketed, but its application resulted in 20% less ammonia, 80% less hydrogen sulfide, and 30 to 40% reduction in volatile organic carbon emissions. This product, as utilized, had two potential mitigation methods; it acted as a permeable cover on the surface of the manure, as well as an oxidizing agent for odorants from the manure.
A second class of compounds is precipitants. Precipitants are chemicals that react with substances in the manure to form a solid. Examples used to treat manure include both iron and zinc salts, which will first dissolve and then react with sulfides to from a precipitate. In many cases these reactions are pH dependent and often times additional side reactions, i.e., reactions in addition to the one we were striving for, will occur. The final class of additives is electron acceptors. Typically,these compounds interact with the sulfate ion and then inhibit sulfide formation.
In general, research work on manure additives have shown inconsistent results, potentially due to differences in methodologies used by the researchers as well as differences in manure properties used in the testing.When considering the different additives available, asking about what work they have performed, and the additives that were used (microbial, adsorbents, oxidizers, acidifiers, others), is a good method to evaluate the products effectiveness.
|NH3||0 to 60%||varies greatly depending on the product|
|H2S||0 to 80%||varies greatly depending on the product|
|Odor||0 to 20%||varies greatly depending on the product|
|Volatile Organic Compounds (VOC)||10 to 40%||varies greatly depending on the product|
|Greenhouse Gases||0 to 10%||varies greatly depending on the product|
|Cost||$||varies with the additive used and dosing frequency required|
Amon, M., M. Dobeic, T.M. Misselbrook, B.F. Pain, V.R. Phillips and R.W. Sneath. 1995. A farm scale study on the use of De-Odorase for reducing odour and ammonia emissions from intensive fattening piggeries. Bioresources Technology 51: 163-169.
Cai, L., J.A. Koziel, Y. Liang, A.T. Nguyen, and H. Xin. 2007. Evaluation of zeolite for control of odorants emissions from simulated poultry manure storage. Journal of Environmental Quality 36(1)(: 184-193.
Johnston, N.L., C.L. Quarles, D.J. Fagerberg, and D.D. Caveny. 1981. Evaluation of yucca saponin on performance and ammonia suppression. Poul. Sci. 60: 2289-2295.
Miner, J.R., S.N. Raja, and W. McGregor. 1997. Finely ground zeolite as an odour control additive immediately prior to sprinkler application of liquid dairy manure. P 717-720. In Proc. Of the Int. Symp. On Ammonia and Odour emissions from Animal Production, Vinkeloord, the Netherlands. Rosmalen, the Netherlands.
McCrory, D.F. & P.J. Hobbs. 2001. Additives to reduce ammonia and odor emissions from livestock wastes: a review. Journal of Environmental Quality 30:345-355.
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