Water clarification system for intensive fish farming - centrifuges effluent to which oxygen and hydrated lime are added

摘要

Stale water continuously drawn off from a pond on a farm for intensive fish prodn., and replaced by clarified, esp. aerated water, is centrifuged to separate it into a concentrated sludge and clarified water. This with the addn. of a quantity of fresh water is then returned to the pond. System maintains the water in fish ponds for intensive prodn. in a condition in which the fish thrive and are free from disease, without a clarifying process which is disproportionately high in cost and requiring the input of energy to maintain the temp. of the pond uniform in summer and winter. Solid matter is removed at a rate which is higher than that at which bacteria and fungus can multiply. The sludge produced can be composted and used as fertiliser. The concentration of salts and dissolved organic matter can also be maintained at a level to keep the fish healthy. Oxygen in the form of fine bubbles in injected into the stale water as it is drawn from the tank, and before centrifuging also, hydrated lime is added. This precipitates calcium carbonate which envelopes particles of albumen etc. The ratio of clarified to fresh water returned to the tank is only as 8:1.