Nature has been recycling animal carcasses since animals appeared on earth. Since meat processors deal with natural products, they have an advantage over processors of synthetic chemicals in disposing of process wastes. They can harness waste treatment processes that nature perfected long ago.
Meat production and processing operations do pose one challenge that nature has not faced before. Modern facilities handle animals in unprecedented concentrations. The challenge is how to let natural processes do their work safely and cleanly at a rapid turnover rate, on numbers of animals never found at such close quarters in nature.
Over the years, the meat processing industry has developed three distinct ways to handle waste disposal: rendering, incineration, and variations on the natural processes of biological decomposition.
Rendering involves the extraction of useful components of the meat. For all its unsavory reputation, rendering is actually a very sensible option from the point of view of efficiency and sustainability. It is only in the past few years, when the rendering option has come into question, that its advantages are becoming more fully appreciated. Like many extractive processes, rendering requires energy. The fact that it produces useful products that can be sold for more than the cost of producing them means that the disposal of meat processing waste products has been a profit-making opportunity, rather than an unavoidable cost.
The problem with rendering is tied to its main advantage. Instead of breaking down waste animal parts all the way to its simplest constituents, rendering must be gentle enough to remove the valuable substances intact. As a consequence, there is the possibility that the products of rendering can carry biological pathogens. For decades, that problem had been considered essentially solved. But the appearance of bovine spongiform encephalitis (BSE), or "mad cow disease" in Europe has raised questions about the safety of rendering practices, and has curtailed the use of some animal products in animal feed. Renderers may be able to accept a decreasing proportion of the total waste for an indefinite period of time.
Identifying the best alternatives to rendering is becoming a priority issue for the meat processing industry. In this guide, we will take a systematic look at the options.
Both alternatives to rendering break down meat processing wastes into much smaller molecular pieces than rendering does. But the methods used are very different.
Incineration ideally carries the breakdown process all the way to carbon dioxide, water, nitrogen, and a few other simple gases. It is rapid and, if carried out under controlled conditions, sure. No known disease-causing agents can possibly survive complete incineration.
But animals were not designed with burning in mind. Like most living tissue, meat is mostly water. To achieve complete combustion requires a hot flame, and a lot of fuel to keep it going. It is an energy intensive, and an expensive enterprise.
In addition, incineration requires a sophisticated facility to be carried out acceptably and responsibly. Images of animals burning in open fire pits, seen recently in conjunction with the recent outbreak of foot-and-mouth disease in some European countries, might be tolerated briefly as an emergency measure. But such an approach would never pass muster as a routine waste handling method.
The bottom line for meat processors is that incineration may be a possible option under special circumstances, but that a more economical alternative would be a much more preferable option.
On the surface, biological breakdown may seem to be an even gentler process than rendering, since it occurs at ambient or only slightly elevated temperatures, and generally does not require external sources of process heat. But on a microscopic level, biological breakdown works by tearing molecules into their simplest constituents, and refashioning them into substances of more interest to the microorganisms responsible for the decomposition. The low temperatures are deceptive. Nature's tools are very efficient.
In order to deal with large concentrations of waste as rapidly and efficiently as possible, methods have been devised to help nature do its work. In the composting process, the material to be decomposed is formed into a pile with bulking agents (to provide the right degree of moisture retention and air circulation) and a good balance of nutrients (chiefly nitrogen and phosphorus compounds). The pile may be turned periodically. When working properly, the center of the pile will warm up spontaneously. After a few cycles of turning and rewarming, the material is ready for land application as a fertilizer and soil conditioner.
Composting is commonly carried out on a wide variety of animal and vegetable wastes. Some facilities carry out their own composting operations. Large commercial companies also provide composting services for multiple users. Composting and land application may be viable alternative to rendering for many meat processors, depending on several factors.
Composting operations are typically regulated at the state level. Among other variables, location may be an important factor in determining the extent to which composting is a feasible alternative for a given facility. Most of this guide consists of a state-by state examination of the rules that apply to composting.
One additional note. For a long time, it has been generally assumed that the composting process is thorough enough to reduce any remaining disease-producing organisms to a safe level for land application. BSE may have changed the picture. According to the most widely accepted explanation of the disease, it is not caused by a familiar type of microorganism, such as a virus or bacterium. Instead, it is thought to be due to an unusual form of protein (called a "prion") that folds into an abnormal configuration, which somehow causes normal proteins to adopt that same mistaken configuration. That, rather than any standard reproductive process, is how the disease agent is thought to propagate. Given this novel mode of transmission, the jury is still out on the extent to which ordinary composting practices destroy the ability of the BSE agent to spread. It is possible that some state regulations may be revised in the future as more information is developed. The recent outbreaks of foot-and-mouth disease may also cause some currently accepted composting practices to be revised. Meat processors should keep this potential for change in mind when reviewing alternatives.
More details on composting for meat processors.
State by-state summary of composting rules.
Guides to composting rules for individual states: