Stabilization of water

Details Stabilization of water Stabilization of water

1997-10-24

1999-11-30

McKane, Elizabeth

Chemical apparatus and process disinfecting, deodorizing, preser

Process disinfecting, preserving, deodorizing, or sterilizing

Maintaining environment nondestructive to metal

422 12, 422 13, 422139, 422211, 422900, 210724, 210749, 210750, C02F 166, C02F 168

Patent

active

059937378

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND TO THE INVENTION

THIS INVENTION relates to the stabilization of water. More particularly, the invention relates to a process for the partial or total stabilization of water, which may be potable water or non-potable water intended for industrial, agricultural or other use.


SUMMARY OF THE INVENTION

According to the invention there is provided a process for the stabilization of raw water having a pH of 2,5-9, an Alkalinity of at most 150 mg/l expressed as calcium carbonate, a calcium content of at most 100 mg/l expressed as calcium carbonate, and a positive calcium carbonate dissolution potential, the process comprising: part to increase its calcium carbonate dissolution potential; carbonate where said water consumes part of the calcium carbonate of the particles before issuing from the bed, which consumption is associated with an increase in the calcium content of the water and with an increase in the Alkalinity of the water as it passes through the bed; and thereby to obtain a product water having a positive calcium carbonate dissolution potential which is at least 2 mg/l calcium carbonate less than that of the raw water, and is at least partially stabilized.
By stabilized water is meant broadly a water where the chemistry is such that the water has a calcium carbonate precipitation potential of between 0 mg/l and 5 mg/l at ambient temperature, and where the water is stable with regard to gaseous and aqueous carbonate species.
Usually the acidified part will be fed in an upflow manner through the bed of particles.
By calcium carbonate dissolution potential of a water is meant mass in mg of calcium carbonate which must be dissolved in a litre of the water to saturate the water with regard to dissolved calcium carbonate, and it is expressed as mg/l calcium carbonate or mg/l CaCO.sub.3.
Preferably sufficient calcium carbonate from the particles is consumed to reduce said dissolution potential of the product water to as low a value as possible, e.g. between 10 mg/l of CaCO.sub.3 and 0 mg/l of CaCO.sub.3, and typically to about 2 mg/l CaCO.sub.3, partially to stabilise the water. Usually, the raw water will have a dissolution potential of at least 10 mg/l CaCO.sub.3. In other words, sufficient calcium carbonate from the particles may be consumed to obtain, after mixing of the water issuing from the bed with the remainder of the water, the product water having a calcium carbonate dissolution potential of between 0 mg/l calcium carbonate and 10 mg/l calcium carbonate, or indeed less, so that the dissolution potential can be negative.
It follows that the dissolution potential may thus be reduced to a value less than 0 mg/l CaCO.sub.3, ie a positive precipitation potential is created. Accordingly, sufficient calcium carbonate from the particles may be consumed to obtain a product water having a positive precipitation potential of 0-5 mg/l calcium carbonate in the water, thereby to stabilize the water fully.
By Alkalinity (also known as total alkalinity) is meant the total concentration, expressed in mg/l as calcium carbonate (CaCO.sub.3) in the water, of dissolved CO.sub.3.sup.2-, HCO.sub.3.sup.- and OH.sup.- ions, less the concentration of dissolved H.sup.+ ions. This can be expressed by: -H.sup.+.
When water is partially stabilized, it becomes less aggressive to cementitious conduits, containers and structures and less corrosive with regard to metals. When water is fully stabilized it is non-aggressive and will not attack cementitious concrete, and it is significantly less corrosive with regard to most metals. A fully stabilized water is slightly supersaturated with regard to calcium carbonate.
By potable water is meant a water having the properties set forth in the following Table:


TABLE ______________________________________ Typical Properties Units Values Values ______________________________________ pH pH units 4.0-9.5 4.5-8.0 conductivity mS/m .ltoreq.300 5-70 magnesium mg/l as Mg .ltoreq.100 5-70 content calcium content mg/l as Ca .ltoreq.300 1-50 sodium content mg/l as Na

REFERENCES:
patent: 3839199 (1974-10-01), Weiss et al.
patent: 4153556 (1979-05-01), Riedinger
patent: 4188291 (1980-02-01), Anderson
patent: 4814074 (1989-03-01), Auchincloss
patent: 5156746 (1992-10-01), Maree et al.
patent: 5174901 (1992-12-01), Smith
patent: 5695646 (1997-12-01), Graf

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