Practices to Reduce Ammonia

Tag : Superphosphate
Covering a manure storage area with an impermeable cover preventsthe release of gases into the atmosphere, and eliminates theeffects of wind and radiation on emission rates. Odor reductionefficiencies of 70 to 85 percent have been observed when surfacesare completely covered by impermeable covers.

Although undocumented, ammonia reductions may be similar.Polyethylene covers typically range in price from $1.00 to $1.40per square foot, installed. Wind and snow-load damage present thegreatest challenges with respect to implementation and extended useof impermeable covers. Damage due to weather alters the life of thecover and impacts the requirements for capital investment overtime. Many manufacturers list a useful life of 10 years forfacilities constructed to prevent snow accumulation on the cover,but do not provide any guarantee against wind damage. Permeable Covers
Permeable covers, or biocovers, act as biofilters on the top ofmanure storage areas. Materials often used as covers include straw,cornstalks, peat moss, foam, geotextile fabric, and Leka rock.

Permeable biocovers reduce emissions, in part, by reducing both theradiation onto the manure storage surface and the wind velocityover the liquid surface of the storage area. At the solution/airinterface, humidity is relatively high, which creates a stabilizedboundary that slows the emission rate of odorous volatiles. Theaerobic zone within the biocover allows the growth of aerobicmicroorganisms that utilize the carbon, nitrogen, and sulfur fromthe emissions for growth.

By further degrading and making use of these compounds prior toexiting the biocover, odors emitted from the biocover are alteredand reduced. Reports of odor reductions of 40 to 50 percent arecommon whenever various straw materials are used. An odor reductionefficiency of 85 percent has been noted following the use of afloating mat or corrugated materials. Although ammonia emissionreductions are undocumented, the processes that occur in thebiocovers suggest that ammonia emissions may be reduced to the sameextent.

Costs for biocovers vary widely depending on the material used andthe method of application. In Minnesota, an operation employed a1.8-inch thick geotextile material that cost $0.25 per square foot,plus installation costs. Straw was added on top of the geotextilecover for additional odor control. Straws and cornstalks costapproximately $0.10 per square foot, applied; peat moss and foamcost about $0.26 per square foot, and Leka rock is approximately$2.50 per square foot for a 3-inch depth.

All costs depend on the depth of the material used. Leka is aproduct of Norway, thereby requiring considerable shipping costs of$5.$6 per cubic foot. The cost to cover a 1.5-acre earthen storagewas $6,000 whereas an above ground tank over 0.2 acre was $500, forthe same material.

Most recommendations suggest a minimum of 8-inch and preferably 10-to 12-inch depth of coverage on a manure storage surface. Newcovers (except Leka rock) may need to be applied at least annually,and one study showed that only 50 percent of the straw coverremained four months after installation.

Therefore, management and re-investment costs need to beconsidered. Removal of large, fibrous material during storagecleanout must also be considered before selecting this option. Onedisadvantage of both permeable and impermeable covers is a probableincrease in ammonia emissions and odors during land application. Urine/feces Segregation
Because ammonia results from the interaction of urine and feces inswine and ruminants, efforts to separate them immediately uponexcretion have reduced ammonia emissions successfully. Manurehandling systems designed to prevent urease from coming in contactwith urea are under investigation.

Most systems employ a separator or a belt conveyor whereby feces,containing urease, are captured on the belt and urine is storedbelow. As much as 80 percent reduction in ammonia emissions isexpected from using this system but the practice has not yet beencommercially implemented. However, several urine/feces segregationsystems are in the developmental phase at this time. Acidification
Depending on the pH, N can exist in different forms. Reducing thepH maintains more nitrogen in the form of ammonium, which is notreleased as a gas. Therefore, strategies that acidify manure(reducing the pH) can be used to trap ammonium and prevent itsrelease as ammonia. Among these strategies are dietary practicesused to acidify urine by including phosphoric acid. However,ammonia emissions are more related to the buffering capacity, oralkalinity, of the manure than to pH, suggesting that pH ofexcretions may increase during storage, therefore reducing theeffectiveness of this strategy.

A disadvantage of acidification is that although it traps ammonia,the reduced pH is conducive to volatilization of hydrogen sulfide,another odorous compound produced from the anaerobic decompositionof manure. Costs associated with this practice include the acid andthe equipment to apply and mix the acid with the stored manure. Additives
Additives to control ammonia emission predominantly function byeither binding ammonia or by inhibiting urease, the enzyme thatbreaks urea down to ammonia. Two inhibitors, thiophosphorictriamide and cyclohexylphosphoric triamide, restrained theproduction of urease following application to cattle feedlot pens(0.32 oz. per pound of manure). Similarly, weekly additions ofphenyl phosphorodiamidate to cattle and swine slurries preventedthe urea from being hydrolyzed up to 70 and 92 percent,respectively. Because urease occurs widely in nature, the inhibitormust be applied routinely to prevent future emissions.

Routine application, however, may pose problems once the manure island-applied, unless plants can quickly use the nitrogen. Ureaseinhibitors are not widely available commercially, and theabove-mentioned compounds are chemical rather than products.However, one product, manufactured by Agrotain, is distributedthroughout the United States.

Mineral and chemical amendments have been used to reduce ammoniaemissions from animal manures. Phosphates and gypsum reducedammonia losses from dairy manure storage by 28 and 14 percent,respectively. Triple superphosphate, superphosphate, calciumchloride, and gypsum treatments reduced ammonia losses by 33, 24,13, and 8 percent, respectively, when surface-applied to dairymanure.

All additives involve the cost of the products themselves and theapplication equipment associated with them. Continuous applicationis likely needed in manure storage whereas a single application ofthe additive may suffice during manure application if manure isthen incorporated. Dry Manure Storage
In open lot facilities and facilities that store dry manure,ammonia control can be a greater challenge. Ammonia loss duringcomposting depends on the carbon to nitrogen (C:N) ratio: ammoniavolatilization is significant below 15:1. Increased use of beddingwill help maintain a higher C:N ratio but also results in a dryerproduct that will not compost as readily without the addition ofmoisture. Application of a layer of 38 percent zeolite, placed onthe surface of the composting poultry manure, reduced ammonialosses by 44 percent.

Strategies that focus on source reduction, such as dietmanipulation, are applicable and may prove to be the best controlmeasure. Covering manure can be effective as well. Similarly,practices that involve binding ammonia or altering the pH, so thatammonia is less volatile, can control its emission.

Calcium chloride and triple superphosphate treatments are effectivein reducing losses when surface applied to poultry manure (19 and17 percent, respectively). Strategies to Reduce Ammonia Emissions During Land Application
Estimates of whole-farm ammonia emissions suggest that as much as35 percent of the total ammonia emissions may occur during landapplication of manure. Therefore, control strategies beyond thoseimplemented in housing and manure storage areas should beconsidered, as reported below for injection and manure amendments. Injection or Incorporation
Injecting or incorporating manure shortly after surface applicationcan best prevent nitrogenous emissions that result from landapplication, in addition to reducing odorous emissions. Costs toinject manure are estimated to be $0.003 per gallon above the costto haul and spread liquid manure. A portion of the added cost canbe recaptured, agronomically, in the form of reduced nitrogenlosses for injected manure versus broadcast application. Thebenefits of reduced nitrogen losses through volatilization can alsobe realized by incorporation, after broadcast application. Manure Amendments
Research has demonstrated that some products can effectively reduceammonia losses through either a binding or a pH effect. Ureaseinhibitors may also prove effective. Costs are productspecific, andoften determined as much by application rate and frequency as bythe cost per unit weight. Following land application of freshchicken slurry amended with calcium chloride, a reduction inammonia losses of 37 percent was found. Aluminum sulfate, ferroussulfate, and phosphoric acid reduced ammonia volatilization fromlitter by 96, 79, and 93 percent, respectively.

Aluminum sulfate is often recommended as amendment, due to theenhanced phosphorus content of litter following addition ofphosphoric acid, and to toxicity concerns associated with additionof ferrous sulfate. Conclusions
Employing specific practices can reduce ammonia emissions. A numberof practices are available but not all are suited for alloperations. Careful consideration and selection will help ensurethat you achieve the desired results. Neither endorsement ofcompanies or products mentioned is intended, nor is criticismimplied of similar companies or products not mentioned.

Source: Iowa State University - July 2004