Liquid purification or separation – Processes – Ion exchange or selective sorption
Patent
1984-12-05
1986-09-30
Cintins, Ivars
Liquid purification or separation
Processes
Ion exchange or selective sorption
210686, 2105021, 210503, 502 62, B01J 4704
Patent
active
046145915
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns a method to purify water for fish-breeding, in which the water optionally is subjected to sedimentation, subjected to sand filtration and to oxygenation and in which the water is also subjected to a treatment with a special ion-exchanger mixture consisting of clinoptilolite, an anion exchanger and a cation exchanger, the two latter being of cellulose type. The invention relates further to the mentioned ion-exchanger mixture, which do not need to be regenerated.
The world demand for animal protein has strongly increased during the last decades and in order to satisfy this increase an ever higher extent of fish protein has been used. This has i.a. resulted in a strong expansion of the sea fishing to reach a peak in the beginning of the seventies. At that time one had realized which large risks the extensive increase of the sea fishing meant for the existence of the fish, for which reason certain fishing restrictions were introduced. From that time on the interest for intensive fish-breeding has increased and the reason hereto is i.a. a more and more severe shortage of animal protein.
Fish-breeding in dams and in net compartments in lakes and in the sea has been practised during a long period of time. Such breeding is however exposed to the temperature changes of the seasons. This is inconvenient as the temperature has a great importance for the rate of growth of the fish and thereby for the production capacity of the breeding and to eliminate this inconvenience and to obtain as good growth of the fish as possible an optimal temperature during the whole year is sought (e.g. for salmon fish this temperature is about 16.degree. C.
Besides the water temperature, the oxygen content and the concentration of ammonia in the water are two important factors affecting the rate of growth of fishes.
To eliminate the inconveniences of the temperature variations the fish-breeding can be performed in completely closed water systems, which are thermally insulated against the environment and in which the temperature is regulated by thermal relays to achieve an optimum temperature. In such closed systems the water is led from the breeding tank to a purification plant, in which the oxygen content and the concentration of ammonia in the water are adjusted before it is recirculated to the breeding tank.
In purification plants hitherto there have been practised mechanical-biological purification methods of the same type as those used for sewage water from households. The demands of purification comprise (a) a reduction of the biological oxygen demand (BOD), i.e. a removal of organic substances and (b) a removal or reduction of the concentration of ammonia (NH.sub.3 and NH.sub.4.sup.+).
The concentration of ammonia is essential in this context because ammonia is a residual product of the digestion of the fishes, but at the same time represents a poison for the fishes. Non-ionized ammonia (NH.sub.3) inhibits the growth already at a concentration of 0.025 mg/ml. This implies that with a pH of 8.3 the concentration of NH.sub.3 +NH.sub.4.sup.+ of 0.25 mg/l inhibits the growth, and with a pH of 7.3 the growth inhibition concentration of NH.sub.3 +NH.sub.4.sup.+ is 2.5 mg/l. This is evident from the following equation:
With the application of hitherto known methods for mechanical-biological purification the oxygen demand (BOD.sub.5) is reduced by about 90 percent, when the purification plant is correctly dimensioned. Furthermore the ammonia/ammonium ought possibly to be nitrified to nitrate, which the fish can endure in concentrations of 100-200 mg N/l.
The inconvenience of using known mechanical-biological purification methods for fish-breeding in closed water systems, in which the water is only slightly polluted, are that the purification becomes too expensive as the water quantities are very large and because it is difficult to obtain the necessary efficiency, as the water to be purified remains for almost the same period of time in the purification plant as in community plants, in which the pollution is
REFERENCES:
patent: 3723308 (1973-03-01), Breck
patent: 3985648 (1976-10-01), Casolo
patent: 4198326 (1980-04-01), Lishevskaya et al.
patent: 4344851 (1982-08-01), Sherman et al.
Cintins Ivars
SRS Water Research Corporation AB
LandOfFree
Method to purify water does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method to purify water, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method to purify water will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-983417