title: Computer simulation of energy use, greenhouse gas emissions, and costs for alternative methods of processing fluid milk.
abstract: Computer simulation is a useful tool for benchmarking electrical and fuel energy consumption and water use in a fluid milk plant. In this study, a computer simulation model of the fluid milk process based on high temperature, short time (HTST) pasteurization was extended to include models for processes for shelf-stable milk and extended shelf-life milk that may help prevent the loss or waste of milk that leads to increases in the greenhouse gas (GHG) emissions for fluid milk. The models were for UHT processing, crossflow microfiltration (MF) without HTST pasteurization, crossflow MF followed by HTST pasteurization (MF/HTST), crossflow MF/HTST with partial homogenization, and pulsed electric field (PEF) processing, and were incorporated into the existing model for the fluid milk process. Simulation trials were conducted assuming a production rate for the plants of 113.6 million liters of milk per year to produce only whole milk (3.25%) and 40% cream. Results showed that GHG emissions in the form of process-related CO₂ emissions, defined as CO₂ equivalents (e)/kg of raw milk processed (RMP), and specific energy consumptions (SEC) for electricity and natural gas use for the HTST process alone were 37.6g of CO₂e/kg of RMP, 0.14 MJ/kg of RMP, and 0.13 MJ/kg of RMP, respectively. Emissions of CO2 and SEC for electricity and natural gas use were highest for the PEF process, with values of 99.1g of CO₂e/kg of RMP, 0.44 MJ/kg of RMP, and 0.10 MJ/kg of RMP, respectively, and lowest for the UHT process at 31.4 g of CO₂e/kg of RMP, 0.10 MJ/kg of RMP, and 0.17 MJ/kg of RMP. Estimated unit production costs associated with the various processes were lowest for the HTST process and MF/HTST with partial homogenization at $0.507/L and highest for the UHT process at $0.60/L. The increase in shelf life associated with the UHT and MF processes may eliminate some of the supply chain product and consumer losses and waste of milk and compensate for the small increases in GHG emissions or total SEC noted for these processes compared with HTST pasteurization alone. The water use calculated for the HTST and PEF processes were both 0.245 kg of water/kg of RMP. The highest water use was associated with the MF/HTST process, which required 0.333 kg of water/kg of RMP, with the additional water required for membrane cleaning. The simulation model is a benchmarking framework for current plant operations and a tool for evaluating the costs of process upgrades and new technologies that improve energy efficiency and water savings.
authors.affiliation: Dairy and Functional Foods Research Unit, USDA, Agricultural Research Service, Eastern Regional Research Center, 600 E. Mermaid Lane, Wyndmoor, PA 19038. Electronic address: peggy.tomasula@ars.usda.gov.
authors.forename: P M
authors.initials: PM
authors.lastname: Tomasula
authors.affiliation: Victoria University, College of Health and Bio-Medicine, Werribee Campus, PO Box 14428, Melbourne, Victoria 8001 Australia.
authors.forename: N
authors.initials: N
authors.lastname: Datta
authors.affiliation: Dairy and Functional Foods Research Unit, USDA, Agricultural Research Service, Eastern Regional Research Center, 600 E. Mermaid Lane, Wyndmoor, PA 19038.
authors.forename: W C F
authors.initials: WC
authors.lastname: Yee
authors.affiliation: Engineering and Scale-up, Process and Economics Research Support Group, USDA, Agricultural Research Service, Eastern Regional Research Center, 600 E. Mermaid Lane, Wyndmoor, PA 19038.
authors.forename: A J
authors.initials: AJ
authors.lastname: McAloon
authors.affiliation: University of Arkansas, Mechanical Engineering Department, Fayetteville 72701.
authors.forename: D W
authors.initials: DW
authors.lastname: Nutter
authors.affiliation: Center for Animal Health and Food Safety, College of Veterinary Medicine, University of Minnesota, St. Paul 55108.
authors.forename: F
authors.initials: F
authors.lastname: Sampedro
authors.affiliation: Dairy and Functional Foods Research Unit, USDA, Agricultural Research Service, Eastern Regional Research Center, 600 E. Mermaid Lane, Wyndmoor, PA 19038.
authors.forename: L M
authors.initials: LM
authors.lastname: Bonnaillie
mesh_terms: D000393:Air Pollutants / Q000032:analysis; D000818:Animals; D003198:Computer Simulation; D004736:Energy-Generating Resources; D005525:Food-Processing Industry / Q000191:economics / Q000379:methods*; D005740:Gases / Q000032:analysis; D017752:Greenhouse Effect; D008892:Milk / Q000737:chemistry* / Q000191:economics; D061352:Pasteurization / Q000191:economics / Q000379:methods
chemical_list: D000393:Air Pollutants; D005740:Gases
keywords: energy use; greenhouse gas; nonthermal milk processing; water use