Composition having bacteriocidal or bacteriostatic acitivity

A composition which has bacteriocidal or bacteriostatic properties which comprises humic acid or a salt or a derivative thereof as active ingredient in a suitable carrier. The active ingredient is preferably an alkali metal salt of humic acid and the carrier is preferably water.

BACKGROUND OF THE INVENTION 
This invention relates to a composition which has bacteriocidal or 
bacteriostatic activity. 
There is a great demand both in industry and elsewhere for agents which 
have bacteriocidal activity or bacteriostatic activity or both. An agent 
which has bacteriocidal activity will destroy bacteria whereas an agent 
which has bacteriostatic activity will inhibit the growth of bacteria 
without destroying them. Examples of industrially used bacteriocidal 
agents are phenol and its derivatives, hypochlorite, mercuric chloride and 
organic mercury compounds. Many of these agents are specialist chemicals 
which are expensive. Humic acids occurring naturally in materials such as 
sewage sludge or decomposed plant material (compost) have been shown in 
literature to have some anti-microbial action. 
Reference to this regard may be had, for example to Hasset et al. 
Bacteriocidal Action of Humic Acids, Soil. Biol. Biochem. 19, 111-113, 
(1987). 
However, due to the divergent origins of these natural sources it is 
difficult, if not impossible, to produce a uniform and consistent natural 
humic acid product. It is also difficult and expensive to extract humic 
acids from these natural sources because of their low humic acid content. 
SUMMARY OF THE INVENTION 
According to the present invention, there is provided a composition having 
bacteriocidal or bacteriostatic activity comprising an agent selected from 
coal-derived humic acid, salts and derivatives thereof, and a suitable 
carrier. 
Further according to the invention, there is provided a method of reducing 
the bacterial activity of a locus including the step of applying a 
composition as described above to that locus.

DETAILED DESCRIPTION OF THE INVENTION 
Essential to the invention is that the humic acid is derived from coal. 
Coal, as is known, is a carbonaceous rock originating from plant organic 
material which has been formed by temperature and pressure, and a variety 
of chemical processes during a so-called "coalification" period. 
Preferably, the coal is one with a rank ranging from lignite/brown coal 
and bituminous hard coal. Coal-derived humic acid has several advantages 
over humic acid derived from other natural sources, e.g. plant derived 
organic material. 
1. Coal enables humic acid to be produced in a stable form and with uniform 
and reproducible consistency. Consistency of product is vital for 
commercial applications. Humic acids derived from natural plant materials 
or sewage sludge will vary in biological activity due to factors such as 
their divergent origins and consequent structures. 
2. Humic acid derived from coal and its salts and derivatives have been 
shown to have biocidal efficacy at low concentrations, e.g. 350 ppm. The 
literature shows that humic acid derived from natural sources does not 
have biocidal activity or efficacy at such low concentrations. 
3. It is difficult to extract humic acids from their natural plant 
materials and sewage sludge because of low humic acid. Consequently, humic 
acid derived from such sources is expensive. 
Coal-derived humic acid will generally have the following elemental 
analysis: 
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Element Range (percent) 
______________________________________ 
Carbon 45-70 (typically 60-65) 
Oxygen 20-40 (typically 25-35) 
Hydrogen 2-6 (typically 3-4) 
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The coal-derived humic acid will also contain sulphur and nitrogen. The 
sulphur will generally be present in an amount of up to 5% (typically 
0,5-2%) while the nitrogen will generally be present in an amount of 1-2% 
(typically 1,5%). 
Coal-derived humic acid may also be distinguished from humic acid derived 
from natural sources by the fact that it contains a higher aromaticity and 
a higher ratio of phenolic to carboxylic groups. By way of example the 
average ratio of phenolic to carboxylic groups in a coal-derived humic 
acid is 1,46 in contrast to a ratio of about 1,08 for humic acid derived 
from a natural plant origin. 
The humic acid may be in the form of the free acid or in the form of a salt 
or other suitable derivative. It is preferable that the humic acid be in 
the form of a water-soluble salt such as an alkali metal salt. 
The composition may take a liquid or solid form, depending on the carrier. 
When the carrier is liquid, it is preferably an aqueous carrier. In this 
form, the composition may be used as a household or industrial 
disinfectant. The composition with an aqueous carrier has been found to be 
particularly suitable in disinfecting water in cooling towers or the 
cascade plates over which water in such towers passes. The composition may 
also be used in the form of a soap or other suitable solid form. 
When an aqueous medium is used, the pH of that medium will generally be in 
the range 2-12, preferably 7-8,5. 
The concentration of the agent, in the composition will vary according to 
the nature of the application. Generally, the concentration of the agent 
will be in the range 4-25% by weight. For aqueous carriers, the upper 
limit of the concentration of the humic acid will generally not exceed 17% 
by weight for at higher concentrations gelling tends to occur. 
The composition can be used to reduce the bacterial activity of a locus to 
which it is applied. The action of the composition will be bacteriocidal 
at higher concentrations of the agent and bacteriostatic at lower 
concentrations. In both situations, the bacterial activity of the locus is 
reduced. 
The humic acid will be recovered from coal which has been oxidised. Various 
oxidation routes for coal have been described in the literature. Some of 
these processes involve the dry air-oxidation of coal and others involve 
the wet oxidation of coal. 
The humic acid is preferably derived from a coal which has been oxidised by 
the process described and claimed in European Patent Publication No. 
0298710 (Application No. 88306134.3). The method of this European Patent 
Publication involves mixing coal with an aqueous medium to produce a 
slurry having a pH in the range of 4-9, reacting the slurry with a gaseous 
oxidant selected from oxygen, air and mixtures thereof under conditions of 
temperature and pressure and for a period to cause the oxidation of coal 
thereby producing oxidised coal containing humic acids, and separating the 
oxidised coal containing humic acid from the aqueous medium. This process 
has the particular advantage that it achieves high humic acid yields and 
selectivity. 
The humic acid may be recovered from the oxidised coal by extraction with 
aqueous alkali. This produces a solution containing the humic acid in the 
form of a soluble alkali salt. The free humic acid may be generated from 
such solutions by acidification. 
The invention will be illustrated by the following non-limiting examples. 
The first example describes a particular method of producing humic acid. 
The second example describes certain efficacy studies carried out using 
humic acid. 
EXAMPLE 1 
20 g of a Sourth African coal with a mean particle size of 10 microns was 
slurried in 400 ml water and quantitatively transferred to a stirred 
autoclave of 2 liter capacity. The autoclave was charged with oxygen to a 
pressure of 4,0 MPa (cold) and sealed. 
The turbine stirrer, running at 1500 rpm, and the bar type heaters were 
simultaneously started. The temperature was controlled at 150.degree. 
C..+-.2.degree. C. for the desired period after which the reaction was 
terminated by cooling the reactor with a jet of compressed air and 
allowing the pressure to drop to atmospheric, by opening a valve. 
The humic acid content of the oxidised coal was then determined as follows: 
The coal slurry, quantitatively transferred to a round bottom flask, was 
mixed with 20 g of sodium hydroxide pellets and refluxed for five hours 
after which the reaction mixture was cooled and centrifuged to separate 
the residue. 
The residue was washed twice with 0,1N NaOH solution and twice with water. 
All the washings were added to the solution obtained after centrifuging. 
The residue was dried, weighed and the organic content determined. 
The humic acid contained in the solution was recovered by precipitation, 
after acidification with hydrochloric acid to a pH value of 2. The now 
insoluble humic acid was centrifuged, washed with 0,1N HCl solution and 
water. After drying to constant mass the solid humic acid was weighed and 
analysed for organic content. 
Summary of reaction conditions: 
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Temperature 150.degree. C. 
Oxygen partial pressure 
4,0 MPa (cold) 
Slurry concentration 5% 
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The result obtained are tabulated below: 
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Reaction C recovered 
period as % 
(minutes) humic acid 
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60 45,5 
120 52,5 
180 63,5 
240 45,7 
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The humic acid figures relate to the carbon content of the starting coal. 
The elemental analysis of the humic acid was as follows: 
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Element Percent 
______________________________________ 
Carbon 63,3 
Oxygen 31,3 
Hydrogen 
3,4 
Sulphur 0,4 
Nitrogen 
1,6 
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EXAMPLE 2 
The ability of coal-derived humic acid as produced by Example 1 to inhibit 
the growth of bacteria was examined. The typical procedure followed was as 
follows: 
Three Erlenmyer flasks equipped with side-arms were filled with a sterile 
growth medium (nutrient broth). All the media in the flasks were 
inoculated with the organism on which the effect of humic acid was being 
evaluated. To two flasks of humic acid were added to obtain concentrations 
of 0,01% and 0,1% (on a mass per volume basis) humic acid, respectively. 
The addition of humic acid was omitted to the third flask with the 
intention to use it as a control. The flasks were incubated at 27.degree. 
C. and the growth of the organism was monitored by reading the absorbance 
at 540 nm in an ultra violet/visible spectrophotometer during the 
incubation period. 
Abovementioned procedure was done in duplicate for every organism tested. 
The following five organisms, i.e. bacteria selected to cover a large 
spectrum, were tested: 
Pseudomonas aeruginosa 
Staphylococcus aureus 
Escherichia coli 
Bacillis subtillis 
Acinetobacter calcoaceticus 
The results obtained were as follows: 
(a) With P. aeruginosa 
The period needed for the control's organisms to double in number (flask 
containing growth medium and organism but no humic acid) was determined to 
be 2,4 hours. In the flasks containing 0,01% m/v humic acid and 0,1% m/v 
humic acid the periods needed to double the number of organisms were found 
to be 8,6 and 11,55 hours respectively. 
Thus, concentrations of both 0,1% and 0,01% m/v humic acid exhibited an 
inhibitory effect under ideal conditions for growth on P. aeruginosa. 
(b) With S. aureus 
The periods needed for the organisms to double in number in the control 
medium and media containing 0,01% and 0,1% m/v humic acid were found to be 
1,22, 1,68 and 8,21 hours respectively. 
Thus, humic acid at a concentration of 0,1% m/v inhibited the growth of S. 
aureus under ideal conditions for growth. 
(c) With E. coli 
The periods needed for the organisms to double in number in the control 
medium and media containing 0,01% and 0,1% m/v humic acid were found to be 
1,28, 1,58 and 4,06 hours respectively. 
Thus, humic acid at a concentration of 0,1% inhibited growth of E. coli 
under ideal conditions for growth. 
(d) With B. subtillis 
The periods needed for the organisms to double in number in the control 
medium and the medium containing 0,01% m/v humic acid were found to be 
1,79 and 3,07 hours respectively. 
No definite conclusion can be drawn as no result for a medium containing 
0,1% m/v humic acid was obtained. 
(e) With A. calcoaceticus 
The periods needed for the organisms to double in number in the control 
medium and media containing 0,01% and 0,1% m/v humic acid were found to to 
2,87, 2,54 and 12,15 hours respectively. 
Thus, humic acid, at a concentration of 0,1% m/v, inhibited growth of A. 
calcoaceticus under ideal conditions for growth. 
EXAMPLE 3 
The efficacy of coal-derived humic acid as produced by Example 1 was 
compared with naturally occurring sewage sludge humic acid. 
METHODOLOGY 
Test organisms: 
Klebsiella pneumoniae 
Pseudomonas aeruginosa 
P Fluorescens 
B cereus 
A calcosceticus 
BIOCIDE USED 
Coal-derived humic acid concentration: 350 ppm. 
The test organisms were exposed to the above humic acid concentration for 6 
hours. The initial bacterial number was determined and again 6 hours after 
the addition of the humic acid. The percentage kill was calculated as 
follows: 
##EQU1## 
RESULTS 
TABLE 1 
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The effect of humic acid on the test organisms 
Test organism % Kill 
______________________________________ 
P fluorescens 86 
P aeruginosa 85 
B cereus 96 
A calcoacelicus 66 
Klebsiella pneumoniae 
99 
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By comparing the results in Table 1, with published data (Hassett, et al 
Soil. Biol. Biochem. 19, 111-113, (1987)), it is clear that the humic 
acids derived from coal were significantly more effective than humic acid 
derived from plant sources. A much lower concentration i.e. 350 ppm 
-vs-700 ppm gave a better kill percentage (86%) in 6 hours than that 
obtained with natural humic acids (obtained from sewage sludge) over a 
period of 24 hours.