Liquid purification or separation – Processes – Chemical treatment
Patent
1998-02-23
1999-10-12
Woo, Jay H.
Liquid purification or separation
Processes
Chemical treatment
210764, 210916, 422 5, 422 28, C02F 172
Patent
active
059650338
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
The invention relates to a process for the disinfection of aqueous solutions by using a disinfectant containing peracetic acid (PAA) and hydrogen peroxide (H.sub.2 O.sub.2), the invention achieving not only effective germ reduction but also a retarded reappearance of germs.
Effective disinfection processes are necessary for the treatment of aqueous solutions, especially domestic sewage, surface waters and industrial circulating waters and effluents, containing microorganisms which cannot be discharged untreated for hygienic, operational or environmental reasons. Effective disinfection processes which are environmentally compatible at the same time are based on the use of active oxygen compounds, such as hydrogen peroxide in particular, and lower percarboxylic acids, especially peracetic acid, as disinfectants.
The report by J. A. L. Fraser et al. on the Desinfection (sic) of Water Conference of Jan. 22, 1992, London (SCI Water and Environment Group), gives a comparative survey of the biocidal properties, the handling and the use of hydrogen peroxide and peracetic acid in a variety of application areas:
Hydrogen peroxide is a moderately active, mild disinfectant with bacteriostatic properties. Although H.sub.2 O.sub.2 concentrations of 25 mg/l inhibit the growth of some bacteria, an effective reduction of the germ count, even at a much higher H.sub.2 O.sub.2 concentration, takes many hours or requires additional UV irradiation. In the case of the disinfection of large quantities of water, for instance for the treatment of water in sewage works and their outputs, such measures are inadequate and also uneconomic.
Peracetic acid is a highly effective disinfectant which is used to effect rapid germ reduction. Accordingly, peracetic acid is used for sterilization in the food industry and for the disinfection of bottles and hospitals. The use of peracetic acid for water treatment has hitherto been subordinate or non-existent. Due to the process for the manufacture of such solutions, they contain not only peracetic acid and water but also hydrogen peroxide and acetic acid, together with one or more stabilizers; the concentration of peracetic acid (PAA) and hydrogen peroxide (H.sub.2 O.sub.2), and the molar ratio of PAA to H.sub.2 O.sub.2, can vary within wide limits.
Commercially available peracetic acid solutions described in the cited conference report contain 15 wt. % of PAA, 14 wt. % of H.sub.2 O.sub.2 and 28 wt. % of acetic acid, or 38 wt. % of PAA, 4 wt. % of H.sub.2 O.sub.2 and 44.7 wt. % of acetic acid. Because of their caustic and fire-promoting properties, the use of such highly concentrated peracetic acid solutions creates handling, storage, material and transport problems. The disproportionately high acetic acid content is also responsible for increasing the chemical oxygen demand (COD) of the water to be treated. A much greater problem, however, is the fact that this extremely high proportion of freely available acetic acid--additional acetic acid is formed from the decomposition of the peracetic acid--forms the basis for a renewed and possibly explosive proliferation of the germs.
Peracetic acid solutions which are easier to handle, with a lower peracetic acid content, for instance 0.5 to 12.5 wt. % of peracetic acid, can be prepared by diluting more concentrated solutions with water and requisite amounts of acetic acid and/or hydrogen peroxide--cf. WO 91/12058. Such solutions are proposed in said document for domestic hygiene purposes. This document does not suggest the idea of also using peracetic acid solutions diluted in this way for the disinfection of large quantities of water, instead of the more highly concentrated solutions mentioned above. Also, there is no suggestion of using solutions with a very low peracetic acid content and at the same time a high H.sub.2 O.sub.2 content for such a purpose.
WO 94/16110 teaches a process for the disinfection of aqueous sugar solutions or similar solutions. The peracetic acid solution used here contains 0.5 to 5 wt. %, preferably 2 to 3 wt.
REFERENCES:
patent: 5393781 (1995-02-01), Vegega et al.
patent: 5409713 (1995-04-01), Lokkesmoe et al.
patent: 5565231 (1996-10-01), Malone et al.
patent: 5733474 (1998-03-01), Kagermeier et al.
Peroxygens in Water Disinfection, Fraser et al., Jan. 22, 1992.
Bactericidal Properties of Peracetic Acid and Hydrogen Peroxide, Alone and in Combination, and Chlorine and Formaldehyde Against Bacterial Water Strains, Anouar Alasri et al., (1992), Can. J. Microbiol. Vol. 38, pp 635-642.
Del Grosso Birgit
Huss Michael
Schneider Roland
Degussa-Huls-Aktiengesellshaft
Morrison Betsey J.
Woo Jay H.
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