A Cost Comparison of Composting and Incineration as Methods for Mortality Disposal
All poultry production operations have to determine how they will deal with the issue of disposal of mortality. There are numerous methods used to dispose of the mortality and the method selected should be based upon the situation of each particular farm and by restrictions placed upon them by regulatory agencies. Generally, these restrictions are based upon the method's impact upon disease control, air, and water quality. In addition, some states have passed legislation prohibiting burial or pit disposal methods.
The most common methods of disposal are:
An additional method of disposal is extrusion of the mortality to produce a value added protein product. Other procedures such as fermentation, acid preservation and refrigeration are used temporarily to maintain the mortality before it is rendered. These methods are not used frequently because of the monetary investment in labor and equipment.
Burial is very common and can be as a disposal pit or trench burial. Trench burial is generally utilized when there are catastrophic losses and disposal pits are typically used for normal daily mortality. The major concern with burial disposal is the potential impact upon ground and surface water contamination.
Rendering is a good method which converts mortality to an added value product as a protein feed stuff. The major disadvantage to rendering is the potential for spread of disease organisms through an inadvertent mistake or a lack of biosecurity during the transportation of carcasses to the rendering plant.
Composting is a more recent procedure developed for the disposal of poultry mortality. The method uses naturally occurring microorganisms (bacteria and fungi) to convert mortality and litter into a product which can be used as a soil amendment on the farm. It is important to note that the final composition of the compost can be highly variable depending upon the management of the process.
Incineration is the most biologically safe method of all disposal methods because it reduces the carcasses to ash using very high temperatures. There is no threat to water quality and is safe from the threat of spreading disease. Incineration also will not promote problems of insects or vermin. There may be some concern for air quality if the incinerators are not properly designed or if they are improperly managed.
Criteria for Selection of Disposal Method
The criteria a person must use to determine the most suitable disposal method needs to include the economics of each method, the reliability of the procedure, the degree of biosecurity the method offers, and the way the method will fit into one's particular operation.
The cost of labor, the availability of needed equipment, and the amount of mortality which needs to be disposed of all have to be considered in the disposal assessment. The pattern of mortality is also important. Carcass mass is rather consistent in a breeder or layer operation but a grow out operation will have a varied amount as body size increases with age. Catastrophic losses can create havoc with any disposal method and alternative procedures should be in place in case of a severe disease outbreak or a management problem such as ventilation failure which may cause high losses. When evaluating the disposal methods, one should examine carefully the most recent information available. Technology has been changing rapidly and sound management decisions should not be made from inappropriate or outdated information data.
Incineration was a very popular method until the 1970's when fuel prices escalated and made the method costly. Most information on the efficiency of incineration is based upon the older styles of incinerators and not the newer designs. The newer designs utilize an improved single burner in combination with a redesigned fire box which enhances combustion. Newer incinerator design was evaluated in a recent study at NCSU for its efficiency. During these studies carcasses from the following groups were used to evaluate the incinerators: 3-week old broilers, 7 week-old broilers, 65 week-old broiler breeders, 72 week-old commercial layers and 18 week old turkey toms. A new style incinerator1 was used having a capacity of 250 pounds for the smaller carcasses and 200 pounds for the larger carcasses. Five loads from each class of bird were incinerated and there were no differences noted in fuel efficiency between the first burn and subsequent burns. The results were calculated on a carcass mass of at least 1000 pounds. It was evident from the data gathered that the carcass fat acted as a fuel for the incineration which increased the efficiency of the incinerator. The broilers, which were incinerated when three weeks-old, had little or no carcass fat while the seven week-old broilers, the broiler breeder, commercial layer and turkey had substantial body fat. The labor required to properly manage the incinerator was recorded. Results of the fuel efficiency for the new design incinerator are shown in Table 1. Additionally, an older design incinerator2 with 2 burners was tested at the same time that the 3 week-old broilers and the 72 week-old layers were incinerated to evaluate the extent of the efficiency gained with the newer designs.
The results between the older model and the newer model show that increased efficiency has been attained. Thus, the economics of incineration may make it again a viable alternative for disposal of poultry mortality on some farms.
Composting of mortality was developed a number of years ago as an alternative to disposal pits due to the concern with the possibility of ground water contamination in areas of high water tables. Composting consists of the layering of a carbon source such as litter with carcasses combined with the proper amount of moisture and air introduction for maintenance of aerobic conditions to provide the optimal environment for the microbial degradation. Composting requires the monitoring of the compost temperature as an indicator of the microbial activity within the bin. The compost bin must be aerated by physically turning the compost material introducing oxygen, thus starting another heat cycle when the compost temperature declines. Previous work by the authors with forced aeration of the compost bin demonstrates that the mechanical turning of the compost is essential. It appears that the mechanical turning helps to mix the compost bin and eliminate micro environments established in the bins. This makes having a front-end loader essential for operation of a composter. The composting carcasses need to go through three heat cycles to insure complete decomposition and destruction of potential pathogens.
Comparison of Costs for Incineration and Composting
Incineration and composting were compared as mortality disposal methods in this study for three types of poultry. The types included were broilers, broiler breeders, and commercial layers. It would be inappropriate to use the same cost efficiencies of a particular method for all types of poultry as different body compositions exist. The following cost analysis is based upon data collected for each poultry type with regards to fuel consumption, composter capacities needed, and labor evaluations. Certain assumptions will still have to be made with regards to the amount of mortality and some fixed and variable costs that are specific for a farm. However, as long as an individual is aware of these assumptions, adjustments can be made when evaluating one's own operation (i.e. cost of building materials, fuel, etc.). The size of the incinerator purchased and composter built is varied to best suit a farm based upon the type of poultry and the mortality expected.
A few assumptions to be made in the case of composting are whether a front-end loader is available, how the cost is assessed for time used and the labor involved. It is imperative that a front-end loader be used to turn the compost bin at the appropriate time to insure proper composting. Labor criteria will not include the cost of gathering carcasses but rather the cost of moving them from the house and disposing by the indicated method. Composting trials were conducted concurrently with the incineration trials to assess the labor costs to properly compost carcasses.
Assumptions to be made use a 100,000 hen production unit and are based upon an expected death rate of 0.5% per month. Using an average weight of 3.75 pounds will result in approximately 62 pounds per day or 22,500 pounds per year.
The assumptions to be made use a 10,000 breeder facility which has an average mortality for the hens of 0.35%/week and 1.5%/week for males. This will produce approximately 32 hens/week (8 lb.) and 15 males/week (11.5 lb.) for a total of 434 pounds of carcass mass (62 pounds per day) per week for 45 weeks (315 days) during the year (19,530 pounds).
The assumptions to be made use a broiler farm having a capacity of 100,000 broilers, raised to 7 weeks of age and having 6 flocks per year. A broiler operation having a capacity of 100,000 may demonstrate a mortality profile much like the one in Table 4. This data is a compilation of normal mortality figures on two farms for 5 flocks each.
It is rather apparent that with increasing the bird's age, disposal becomes more of a concern and time consuming aspect. Because of the variability in a grow out operation, disposal method must be adequate to handle the maximum mortality.
The results of this study indicate that incineration of poultry mortality can be a viable alternative for an operation. It is true that a case could be made to alter the assumptions made in our study for either incineration or composting, but the assumptions were made based upon actual costs experienced in a poultry operations. The actual decision as to which method is best for a particular farm should be based upon the individual circumstances on each farm and the restrictions they must adhere to. One of the first steps in developing information from which to make an informed decision is to develop a budget similar to the ones presented, using a producer's own cost information.
1 New design incinerator used in the trials was a Shenandoah A-10.
May 30, 2007