Cleaning and disinfection 401 Soiling of surfaces is a natural process which reduces the free energy of the system. To implement a sanitation programme, therefore, energy must be added to the soil to reduce both soil particle-soil particle and soil particle-equipment surface interactions. The mechanics and kinetics of these interactions have been discussed by a number of authors (Jennings 1965, Schlussler 1975, Loncin 1977, Corrieu 1981, Koopal 1985, Bergman and Tragardh 1990), and readers are directed to these articles since they fall beyond the scope of this chapter. In practical terms, however, it is worth looking at the principles involved in basic soil removal, as they have an influence on the management of sanitation programmes Soil removal from surfaces decreases such that the log of the mass of soil per nit area remaining is linear with respect to cleaning time(Fig. 14.1(a)and thus follows first-order reaction kinetics (Jennings 1965, Schlusser 1975). This approximation,however, is only valid in the central portion of the plot and, in practice, soil removal is initially faster and ultimately slower(dotted line in Fig 14.1(a)than that which a first-order reaction predicts. The reasons for this unclear, though initially, unadhered, gross oil is usually easily removed ( Loncin 1977)whilst ultimately, soils held within surface imperfections, or otherwise protected from cleaning effects, would be more difficult to remove(Holah and Routine cleaning operations are never, therefore, 100% efficient, and over a course of multiple soiling/cleaning cycles, soil deposits(potentially including microorganisms)will be retained. As soil accumulates, cleaning efficiency will decrease and, as shown in plot A, Fig. 14.1(b), soil deposits may for a period grow exponentially. The timescale for such soil accumulation will differ for all 品E0 Cleaning time→> Number of periodic cleans Fig 14.1 Soil removal and accumulation. (a) Removal of soil with cleaning time. Solid line is theoretical removal, dotted line is cleaning in practice.(b) Build up of soil(and/or microorganisms); A, without periodic cleans and b, with periodic cleans. (After Dunsmore et al. 1981)Soiling of surfaces is a natural process which reduces the free energy of the system. To implement a sanitation programme, therefore, energy must be added to the soil to reduce both soil particle-soil particle and soil particle-equipment surface interactions. The mechanics and kinetics of these interactions have been discussed by a number of authors (Jennings 1965, Schlussler 1975, Loncin 1977, Corrieu 1981, Koopal 1985, Bergman and Tragardh 1990), and readers are directed to these articles since they fall beyond the scope of this chapter. In practical terms, however, it is worth looking at the principles involved in basic soil removal, as they have an influence on the management of sanitation programmes. Soil removal from surfaces decreases such that the log of the mass of soil per unit area remaining is linear with respect to cleaning time (Fig. 14.1(a)) and thus follows first-order reaction kinetics (Jennings 1965, Schlusser 1975). This approximation, however, is only valid in the central portion of the plot and, in practice, soil removal is initially faster and ultimately slower (dotted line in Fig. 14.1(a)) than that which a first-order reaction predicts. The reasons for this are unclear, though initially, unadhered, gross oil is usually easily removed (Loncin 1977) whilst ultimately, soils held within surface imperfections, or otherwise protected from cleaning effects, would be more difficult to remove (Holah and Thorpe 1990). Routine cleaning operations are never, therefore, 100% efficient, and over a course of multiple soiling/cleaning cycles, soil deposits (potentially including microorganisms) will be retained. As soil accumulates, cleaning efficiency will decrease and, as shown in plot A, Fig. 14.1(b), soil deposits may for a period grow exponentially. The timescale for such soil accumulation will differ for all Fig. 14.1 Soil removal and accumulation. (a) Removal of soil with cleaning time. Solid line is theoretical removal, dotted line is cleaning in practice. (b) Build up of soil (and/or microorganisms); A, without periodic cleans and B, with periodic cleans. (After Dunsmore et al. 1981). Cleaning and disinfection 401