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Options For Carcass Disposal Under Emergency Conditions

by 5m Editor
19 July 2003, at 12:00am

By Dr Morgan Morrow, NCSU Swine Extension - The outbreak of foot-and-mouth disease (FMD) that hit Europe, and particularly England, in 2001 has served many purposes, not the least of which has been to demonstrate, once again, how devastating any foreign animal disease (FAD) can be to a national economy and to the animal industries directly affected.


Dr Morgan Morrow
Swine Veterinary Specialist

In the months and years following this outbreak, Great Britain has experienced a total loss of export markets, markets which may never recover because buyers were forced to find alternate suppliers with whom they now have a good working relationship. Estimates are that this situation will result in a 0.06 percent drop in GDP (equivalent to $750 million) from a 20 percent decline in livestock and dairy output for 2001 alone.

The beneficial effect of the FMD outbreak has been an awakening around the globe to the seriousness of the threat of a foreign animal disease. The governments of many countries, including the U.S., Canada, Australia, and New Zealand, have since made a major effort to be ready for such an outbreak. In North Carolina, the Veterinary Division of the state Department of Agriculture and Consumer Services has been a leader in the effort to improve national readiness.

After the alarm goes off and an FAD diagnosis is confirmed, the major activities will concentrate on euthanizing the affected animals and disposing of the carcasses. Euthanasia of hogs likely will be carried out through a variety of techniques, including fragmentation bullets (which supposedly decrease the risk to operators from bullets exiting the targeted hog), gas euthanasia (most likely with carbon dioxide until that supply is exhausted), or captive bolt pistols. In rare cases, a few well-trained people may use injectibles. All these techniques are inherently dangerous to the operator, but carbon dioxide is the safest.

As infected hogs are such major excreters of the FMD virus, it is important that they be euthanized quickly, so quickly that carcasses will probably be stockpiled and disposed of later, as time allows. However, this should not be at the expense of personnel safety. I believe that if bullets are used, fragmentation or not, some operators will be seriously injured or possibly killed in the process; and those operators are likely to be our farm workers.

In North Carolina, the Army or National Guard will not euthanize hogs, as these persons will be fully employed policing the roads and quarantine areas.

The next challenge will be disposing of the carcasses. A crucial lesson learned from the European FMD outbreak was that funeral pyres are a major turn-off. So what are the other possibilities?

The traditional method of disposal of all dead animals around the world is by burial, and that is likely to be used extensively. In many cases, a shallow trench will be dug and the carcasses deposited. However, it is unlikely that all carcasses will be placed below ground; most likely they will be mounded and covered with dirt.

If hogs are incinerated, air-curtain technology will likely be chosen. This system is environmentally friendly in that it greatly reduces emissions, can use waste product as a fuel source, has high throughput, and achieves a reduction of mass greater than 95 percent. It operates by creating a high velocity air curtain that stops the particles from escaping into the atmosphere so the particles remain under the air curtain and are re-burned. The air agitates and oxygenates the fire, resulting in a hotter and cleaner burn. Temperatures of 1,800 to 2,200oF are typically achieved.

If a firebox is used, no trench is required, as the box contains the burn. The fireboxes are generally hotter and cleaner than trench-burners because they have reflective wall panels, but the fireboxes are not as easy to move around. Both fireboxes and trench-burners can be carried over the road. Throughput can be up to 14 tons of carcass per hour, but practically, the bigger machines will probably burn only 5 to 6 tons of carcasses/hour.

A supply of wood is needed to fuel the fire, and about 1.5 to 3 gallons of diesel/hour are required for the 4- to 6-cylinder motor to drive the fan to create the air curtain. An important consideration is that supplying the fuel (e.g., wood) and diesel can be a biosecurity hazard. Therefore, the supply trucks will need to be monitored and disinfected as they leave the burn site. However, that risk is much less than the alternative of trucking carcasses off-site. Thus, air-curtain technology is a great alternative to the billowing black smoke that dominated the press reports from England and Europe two years ago.

Composting is a good alternative, but only if it is used as a storage technique. Its advantage is that it can all be done on site, but it does require a large source of carbon substrate (e.g., sawdust, straw) to use as a co-composting material.

Rendering carcasses has opportunities, but it is limited by the biosecurity risk of transporting the carcasses and by limited capacity, especially in some areas. In addition, in an emergency it could be very difficult to muster enough trucks to transport the carcasses to the rendering plants. The greatest advantage of rendering is that it kills all FADs (except prions) and it produces well-established, high-value end products. If the product can be sold to the feed industry, it can be worth approximately $240/ton. Carcasses for this method should come from noninfected pigs that are euthanized at the periphery of an infected site. If not, the fat can go as boiler fuel for about $170/ton. Or, up to 30 percent can be used as fuel to run the rendering plant.

If the outbreak should involve an exotic, transmissible spongiform encephalopathy (TSE), for example, bovine spongiform encephalopathy (BSE), then more expensive disposal methods would likely have to be used. Alkaline hydrolysis is a process developed by Drs. Gordon Kaye and Peter Weber of Waste Reduction by Waste Reduction, Inc., headquartered in Indianapolis.

It is the only process validated to destroy the prions of TSEs and was used to dispose of the two Vermont sheep herds thought to be infected with a TSE. According to the company Website (http://www.wr2.net/company.htm), the process uses alkaline hydrolysis at elevated temperature to convert the proteins, nucleic acids, and lipids of all cells and tissues, as well as infectious microorganisms, into a sterile, aqueous solution of small peptides, amino acids, sugars, and soaps.

The only byproducts of the process are the mineral constituents (ash) of the bones and teeth of vertebrates. These are soft enough after the organic matter has been degraded to be easily crushed and recovered as calcium phosphate powder. The process takes about three hours and operates at about 150oC at pH 14. Another of its advantages is that it reduces the risk inherent in transportation by on-site processing, and the end product can be discharged into the sewer or water treatment plant.

Another possibility is plasma arc technology. I just wish it were as practical as it is intriguing. Plasma can be thought of as the "fourth" state of matter, and as applied it is a form of artificial lightning.

Temperatures in a plasma torch can reach 7,000oC and therefore can gasify just about any material. Organic matter is pyrolyzed or volatized, and the residual slag is immobilized in a rock-like vitrified mass.

The technology is practical because it is used in Japanese municipal waste plants (MSW) where they can process 1 ton/hr with two 300-Kw torches. However, it is expensive (the Japanese MSW was custom-built and cost $10-12 million). This technology may have a role to play months after the outbreak when we are dealing with mounds of below- (or above-) ground buried carcasses.

A plasma torch could be brought in to vitrify that material because it can operate without disturbing the burial site and needs air to operate. However, at this stage, there is no portable system available in the U.S., and it must remain a fanciful but fascinating opportunity.

Summary

Without question (in my opinion), in an FAD emergency, a variety of techniques will be used for carcass disposal. Above-ground burial will predominate because it is relatively cheap and effective. Rendering will be used up to its capacity, which will quickly be exceeded in a large outbreak.

Composting could have a role, if only as a storage (and partial processing) technique. Trench-burning with an air curtain will certainly have a role, but again it will be limited by the availability of equipment. I doubt that plasma arc technology will come into the picture, but it yet may have a role to play, especially if some sites limit an area from being declared FAD-free.

Reproduced Courtesy

Source: North Carolina State University Swine Extension - July 2003