Liquid purification or separation – Processes – Ion exchange or selective sorption
Patent
1993-02-09
1994-01-25
Silverman, Stanley S.
Liquid purification or separation
Processes
Ion exchange or selective sorption
210688, 210691, 210917, C02F 128
Patent
active
052813380
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method of decolourising water comprising humic or fulvic acid, for example moorland runoff water.
Water, such as that which runs off moorland, is coloured and as a result is aesthetically undesirable and unacceptable to customers. In addition humic substances may react with halogens, e.g. chlorine, during water treatment to produce trihalomethanes or other organohalogens (organhalons) which may represent a health hazard. Humic substances also reduce the effectiveness of chlorine disinfection. Colouration of water can be particularly pronounced following heavy rain after a drought. It is known that the colour may be removed from such water by chemical precipitation methods using for example aluminium sulphate and hydrated lime to adjust pH, followed by mixing, flocculation and physical separation of the flocs by for example air flotation. It is also known that activated carbon may be used to remove colour from water but this is expensive to regenerate and relatively inefficient and so activated carbon is generally only use for removal of odour/taste and pharmaceuticals such as unmetabolised drugs or their breakdown products. A further way to remove colour from water involves the use of ion-exchange resins. However, this is relatively expensive since the resins are expensive to regenerate.
It has now been found that colour may be effectively removed from such coloured water by adsorption of colouring components onto chitin or alginic acid. Chitin and alginic acid are low cost biomass materials which are readily available in large quantities.
The present invention therefore provides a method of decolourising water coloured by humic or fulvic acid, which method comprises bringing the water into contact with chitin or alginic acid as adsorbent. The invention also provides the use of chitin or alginic acid to decolourise such water. In this way the level of colour in the water can be reduced to an acceptable level.
An acceptable level of colour in the water may, for example, be a level of less than 20 Mazen units. Alternatively an acceptable level of colour may be such that the water may be mixed with uncoloured water to provide water with a colour level of less than 20 Hazen units. For example water with a colour level of less than 40 Hazen units may be mixed with equal volumes of uncoloured water to provide water with a colour level of less than 20 Haze units.
The colour of water is expressed in terms of Hazen units and one Hazen unit is defined as the colour produced by 1 mg/l of platinum in the form of chloroplatinic acid in the presence of 2 mg/l of cobaltous chloride hexahydrate. Samples are compared against standards either visually, or photoelectrically using a previously constructed calibration graph.
The water to be decolourised by the method of the present invention comprises humic and/or fulvic acid. These are polyphenolic acids found in the "humic fraction" of soils. The acids are formed as products of the anaerobic digestion of lignin and are resistant to further breakdown. They are formed as breakdown products of peat and produce colouration in for instance moorland runoff waters, e.g. acidic or neutral moorland runoff waters.
The coloured water may also contain additional contaminants such as other polyphenolic acids including those found in industrial waste and such as particulate material as turbidity and metal ions, e.g. aluminium, manganese or iron. Such additional contaminants may also be adsorbed by the adsorbent. Alternatively the coloured water may be substantially free of other contaminants such as metal ions.
The coloured water used in the method of the present invention is typically naturally neutral or acidic and has a pH from 5 to 7. The pH may however be specifically adjusted to optimise a particular step in water treatment such as flocculation, or aluminium or iron salt precipitation and may be outside this range.
The adsorbent used in the method of the present invention adsorbs coloured compounds, such as humic or fulvic acid, present in the water and s
REFERENCES:
patent: 3032496 (1962-05-01), Griffith
patent: 3533940 (1970-10-01), Peniston et al.
patent: 3635818 (1972-01-01), Muzzarelli
patent: 4125708 (1978-11-01), Masri
patent: 4402920 (1983-09-01), Lopez et al.
patent: 4775650 (1988-10-01), Portier
patent: 4882066 (1989-11-01), Portier
Muzzarelli, R. A. A., Chitin (Pergamon Press) pp. 62-63.
Brown Melanie
Buchan Alexander
Harris Ralph
Jacques Anne M.
Archaeus Technology Group Limited
Nessler Cynthia L.
Silverman Stanley S.
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