Life cycle assessment of cleaning-in-place operations in egg yolk powder production
The manufacture of egg yolk powder by spray drying requires regular cleaning in order to remove fouling deposits and prevent microbiological growth on the pasteurisation heat exchanger and the spray dryer. A life cycle assessment (LCA) study on a typical powder manufacturing plant, using literature data, indicated that the egg breaking, storage and pasteurisation steps were the major contributors to the plant's environmental impacts rather than the cleaning-in-place (CIP) operations owing to their high water and electricity consumption (for refrigerated storage). CIP impacts on thermal energy and wastewater emissions were nevertheless significant, and the benefits of using intermittent flows of aqueous NaOH solution in the dryer CIP stage, reported by Yang et al. (2019), were assessed. The latter gave a 21% improvement in terrestrial ecotoxicity impact. Optimising the NaOH/temperature conditions based on experimental data gave more efficient cleaning with lower water, chemicals and energy consumption. Over-cleaning had significant impacts on terrestrial and marine ecotoxicity as well as reducing productivity. Three changes in cleaning technology were considered briefly: electrical heating, solar heating and pumping, and membrane treatment of wastewater. These gave little overall global improvement, partly due to the polluting nature of the available electricity supply (coal-fired) and local benefits to the factory being offset by impacts associated with equipment manufacture.