Encyclopedia of Environmental Science and Engineering, Volume I and II

DISINFECTION 239

PRACTICAL USES

This final section brings together some of the data presented

in the preceding sections, and also provides information in

certain specific instances. Disinfectants will be considered

from two points of view, first their medical, and second their

nonmedical uses. Some brief information on antiseptic and

preservative use will also be supplied.

Medical Uses

The use and choice of disinfectants in hospitals have been

extensively considered in the last decade in Britain by a spe-

cial committee (Report, 1965) set up for this purpose. Our

comments here are thus based on the recommendations of this

report and on the findings presented by Kelsey and Maurer

(1967). The Report (1965) recommended that two classes

of disinfecting agents were needed, (a) for general disinfec-

tion and (b) for surface disinfection of clean objects. Agents

for general disinfection should have a wide spectrum, and at

appropriate dilutions should remain active in the presence of

organic matter; the main purpose of such disinfectants, e.g.,

phenolic disinfectants based on coal-tar acids, is not neces-

sarily to kill all bacteria but to ensure that an object is free

of significant numbers of organisms. Chemicals for surface

disinfection must be quick-acting, have a wide spectrum, be

non-harmful to materials and leave no objectionable odours.

Such disinfectants, e.g., hypochlorites, should be used for

the rapid disinfection of clean surfaces such as trolley tops,

kitchen tables and clinical thermometers.

Kelsey and Maurer (1967, 1972) have presented a list

of the steps to be taken in drawing up a policy for the use

of general purpose disinfectants in hospitals, and among the

points they make is the non-usage of disinfectants in cer-

tain cases, especially where sterilization is the objective or

where other more reliable means are available. For further

information, see Lynn (1980), Ayliffe and Collins (1982)

and Lowbury (1982). Preoperative disinfection of the skin

(including surgeon’s hands), disinfection of operation sites

and topical prophylaxis, i.e., antisepsis in burns, are dis-

cussed by Lowbury (1982). Ayliffe and Collins (1982) pro-

vide a rational approach to hospital disinfection.

Nonmedical Uses

The main nonmedical uses of disinfectants occur in the

food, dairy, brewing and fermentation industries (Foster

et al. , 1958; Frazier, 1967). The maintenance of equipment

for use in these industries in a proper sanitary condition

cannot be overemphasized. This therefore means that the

cleaning of such equipment is of considerable importance,

since the presence of organic matter can reduce or virtually

eliminate the effect of many disinfectants (page 164). In the

dairy industry, milk stone—resulting from milk drying on

equipment, and thus consisting of fat, protein and minerals—

and milk film are a well-known problem in disinfection

(Clegg, 1967). Chemicals which are of use against micro-

organisms in liquid suspension in laboratory tests may be of

little use against such organisms on a soiled surface if they

are poor detergents (Cousins, Hoy and Clegg, 1960).

To counteract the unwanted effects of organic matter,

one of the following two methods may be employed (see

also Davis, 1972a,b and BSI 1977):

1) detergent first, followed by a disinfectant;

2) combination of detergent and disinfectant (this

corresponds to a sanitizer, or to the detergent-

sterilant of Davis (1968), as described in the

Introduction).

Harris (1969) stresses the need for using two operations,

i.e., the use of cleaning before disinfection. Cleaning is the

first essential in the sanitary care of food equipment, and

approximate sterility the last (Foster et al. , 1958). Steam

under pressure is an obvious method of sanitization, but

this is limited only to closed systems which can withstand

pressure (Frazier, 1967). Theoretically, separate procedures

would be expected to give a better result (Clegg, 1970),

because of the inactivating effect of organic matter on disin-

fectants; however, a finding made several years ago (Neave

and Hoy, 1947) suggests that a detergent-disinfectant com-

bination would be of greater use, because “the effect of the

detergent on milk solids more than outweighs the effect of

milk residues inactivating the disinfectant” (Clegg, 1970).

An effective detergent should dissociate organic and inor-

ganic solids, emulsify, saponify or suspend grease, fats and

oils, have good wetting ability, be easily rinsed and be non-

corrosive (Olivant and Shapton, 1970). Detergents are thus

of considerable importance in this field, because they can

also be responsible for the mechanical removal of bacteria

(Gilbert, 1969). The most commonly used detergents are

strong and mild alkalis, alkali salts, strong acids, anionic

alkyl sulphates and aryl sulphonates and non-ionic conden-

sates (Davis, 1968). An excellent descaling agent is nitric

acid which can be used hot at concentrations of 0.25–0.5%

or cold at 0.5–1%, and which is, in addition, a powerful

disinfectant. It is, however, less effective than alkali in the

removal of hardened protein films, and is normally employed

with a corrosion inhibitor. In actual fact, many detergents are

good disinfectants and vice versa, e.g., a detergent such as

sodium hydroxide possesses considerable germicidal power

(Whitehouse and Clegg, 1963), whereas hypochlorites have

a useful detergent effect by disintegrating protein matter

(Davis, 1968). Cleaning is an essential first part in high-

speed food and beverage processing plant, and considerable

economic benefit is achieved as a result of the production of

stable liquid detergents and disinfectants which can be deliv-

ered by tanker and then distributed to the cleaning areas by

pipeline (Hill, 1969). However, even with good precleaning,

traces of inactivating protein material may remain on equip-

ment, and it is thus important to choose a disinfectant which

has a high protein tolerance (Harris, 1969). The design of

equipment to facilitate cleaning must also be stressed, and

stainless steel is an obvious example, with glass pipelines to

give a high degree of visual cleanliness (Harris, 1969).

C004_002_r03.indd 239C004_002_r03.indd 239 11/18/2005 10:19:31 AM11/18/2005 10:19:31 AM