WATER TREATMENT PROCESS IN CLOSED CIRCUIT AQUACULTURE SYSTEMS

摘要

Method for treating water in closed-circuit fish-farming systems comprises passing the water through a filter bed of solid material into which an oxygen-contg. gas is injected. This eliminates nitrogenous pollutants and replaces consumed oxygen in a single stage and, if necessary, also removes solid wastes. The flow rates of gas and water are controlled so that the pH is maintained at 5-9, esp. by stripping CO2 formed during the nitrification. Adequate purificn. is achieved in a single stage and treatment is carried out outside the fish-raising pond. Little or no fresh water needs to be supplied and stock levels 3-5 times higher than those generally used can be maintained. The filter material acts as a support for the denitrifying bacteria and the system can cope with large variations in the degree of nitrogen pollution.