In practice, shrimp farmers in Thailand commonly apply a chlorine dose of 30 mg Cl2 l−1 which may achieve the purpose of disinfecting organisms in pond water, but its certainly inadequate to terminate micro-organisms in the pond bottom. Although the free and total residual chlorine remaining in the water was still sufficiently high to kill aquatic organisms, it was ineffective to treat bottom dwellers. At chlorine dose of 2400 mg Cl2 l−1, 100% bacteria within 2.1-cm sediment depth was inactivated in 2-day exposure. With this dose the amount of chlorine needed to treat the sediment was 2.11 kg Cl2 m−2 with free and total residual chlorine in the overlying water at 850 and 1300 mg Cl2 l−1, respectively. If this dose was applied to the shrimp pond with the assumption of little chlorine loss from exposure to sun light, it would require an estimated amount of 2 ton ha−1 of active chlorine or 3 ton ha−1 of HTH to treat shrimp ponds effectively. This level of chlorine treatment is neither economically nor environmentally practical.
An alternative method should be investigated and found for effective disinfection of shrimp pond from pathogenic microorganisms harbored in pond bottom. We recommend a practical procedure for chlorine application in shrimp ponds. The first step is to apply high chlorine dose to pond sediment with a shallow overlying water of 2–5-cm depth for 2 days to inactivate the bacteria in the sediment; the second step is to raise the water to a depth for shrimp culture (usually 1.0–1.5 m depth) to dilute the remaining residual chlorine to a level that can inactivate bacteria in the overlying water column. With this procedure, the estimated amount of chlorine needed to disinfected sediment and water for 1 ha of shrimp pond with 2–cm overlying water is 480 kg ha−1 active chlorine or 740 kg ha−1 HTH.
In practice, shrimp farmers in Thailand commonly apply a chlorine dose of 30 mg Cl2 l−1 which may achieve the purpose of disinfecting organisms in pond water, but its certainly inadequate to terminate micro-organisms in the pond bottom. Although the free and total residual chlorine remaining in the water was still sufficiently high to kill aquatic organisms, it was ineffective to treat bottom dwellers. At chlorine dose of 2400 mg Cl2 l−1, 100% bacteria within 2.1-cm sediment depth was inactivated in 2-day exposure. With this dose the amount of chlorine needed to treat the sediment was 2.11 kg Cl2 m−2 with free and total residual chlorine in the overlying water at 850 and 1300 mg Cl2 l−1, respectively. If this dose was applied to the shrimp pond with the assumption of little chlorine loss from exposure to sun light, it would require an estimated amount of 2 ton ha−1 of active chlorine or 3 ton ha−1 of HTH to treat shrimp ponds effectively. This level of chlorine treatment is neither economically nor environmentally practical.
An alternative method should be investigated and found for effective disinfection of shrimp pond from pathogenic microorganisms harbored in pond bottom. We recommend a practical procedure for chlorine application in shrimp ponds. The first step is to apply high chlorine dose to pond sediment with a shallow overlying water of 2–5-cm depth for 2 days to inactivate the bacteria in the sediment; the second step is to raise the water to a depth for shrimp culture (usually 1.0–1.5 m depth) to dilute the remaining residual chlorine to a level that can inactivate bacteria in the overlying water column. With this procedure, the estimated amount of chlorine needed to disinfected sediment and water for 1 ha of shrimp pond with 2–cm overlying water is 480 kg ha−1 active chlorine or 740 kg ha−1 HTH.
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