Applying target costing in the development of marketable and environmentally friendly products from swine waste

Engineering Economist, April-June, 2008 by Yuang-Sung Al Chen, Gilroy J. Zuckerman, Kelly Zering

The main constraint in biomethanol Process II is the high cost of solids separation and storage. Separation and storage costs are approximately half of the total cost of Process II. Additional concerns are that trucking costs rise proportionally to trucking distance and rising fuel costs, and that transportation of swine manure using public roads must comply with all biosecurity and public safety regulations at local and federal government levels. Manure trucking also likely becomes a contentious issue in the local community due to the concerns about odor, pathogens, and environmental pollution, among others. A future design element of this system will be to select truck containers that eliminate any emissions from manure being transported.

Thus, the focus of redesigning Process II to yield Process III is on finding a lower cost solids separation and storage system while limiting trucking distance to the extent possible.

The cost deployment flowchart in Figure 2 illustrates the general system design and some of the calculated design parameters.

DESCRIPTION OF BIOMETHANOL PROCESS III: TRUCKING CENTRIFUGE SEPARATED SOLIDS TO CENTRALIZED MESOPHILIC DIGESTERS AND BIOMETHANOL PLANT

Process III involves separating solids at the farm using a system of mobile centrifuge separators and on-farm storage tanks and transporting the separated solids to a centralized digestion/biomethanol facility. Based on pilot-scale belt systems, economic analysis of belt systems for manure removal indicates a high initial cost of construction costs at farm level that include material costs, retrofitting costs, and installation costs. Trailer-mounted centrifuge separation technology is used to capture solids at the farms and to reduce the significant investment needed to retrofit farm buildings with the belt separating system (Zering 2005).

In addition, a centralized, in-ground, mesophilic (medium temperature) digester was incorporated in this process. Using a mesophilic or heated digester allows bacteria to work much more expediently at higher temperatures. Thus, the digestion occurs at a much faster rate than when the digester is left at ambient-temperature. This means that a smaller but heated digester can handle the same flow of manure as a larger but unheated digester. In sum, biogas production efficiency per cubic foot is improved by using heat and smaller digesters.

[FIGURE 2 OMITTED]

Critical assumptions include (a) the minimum size of biomethanol production plant to keep costs within a feasible range, (b) quantity of manure volatile solids produced by pigs, (c) the quantities of separated solids captured by the separators, (d) the locational distribution of pig farms around the centralized digesters, (e) the cost of managing separated solids to the centralized digesters, (f) the cost of dispersing residual sludge and liquid from the digesters, g) the quantities of methane produced from anaerobic digesters, and (h) the amount of biomethanol that can be manufactured from a given volume of methane contained in biogas.