Application of Methods for the Detoxification and Neutralization of Formalin in Fish Hatchery Effluents

Abstract

Sodium sulfite, Neutralex, hydrogen peroxide, and hydrogen peroxide with a ferric iron catalyst were studied for potential application in reducing formalin in effluents from aquaculture facilities. The neutralization capacity of each method was examined at formalin concentrations that are typically found in effluents from fish hatcheries that utilize formalin to control ectoparasite infestations on fish. The toxicities of the products were also evaluated. A 75% reduction in formalin concentration was observed within the first 10 min after the addition of sodium sulfite at a 3:1 (sodium sulfite : formalin) mass treatment ratio. The addition of Neutralex to test solutions at a 6:1 (Neutralex : formalin) mass treatment ratio reduced the formalin concentration by approximately 90% of initial values within 10 min and completely eliminated formalin within 20 min. Degradation of formalin was not successful under the test conditions using hydrogen peroxide alone or in combination with a ferric iron catalyst. Both of the sodium sulfite-formalin and Neutralexformalin reaction products were more toxic to Ceriodaphnia dubia test animals than formalin alone. Although regulatory limits for formalin discharge from aquaculture facilities could most likely be achieved with sodium sulfite or Neutralex, the direct discharge of their neutralizer-formalin reaction products would probably be harmful to some aquatic species.

Use of formalin in intensive aquaculture: properties, application and effects on fish and water quality

“…In addition to these processes, other methods for the detoxification and neutralization of formalin have been proposed (Masters ; Gearheart et al . ). Masters () proposes the neutralization (chemical degradation) of the formalin in water, using commercial products.…”

“…On the other hand, the maximum reduction of 75% of the initial formalin concentration was achieved using sodium sulphite – Na 2 SO 3 (reaction 14), while the commercial product Neutralex completely eliminated the formalin in the test solutions (Gearheart et al . ). Neutralex is indicated to reduce formaldehyde concentrations to less than 10 mg L −1 within 24 h in 10% neutral‐buffered formalin wastes (Masters ; Gearheart et al .…”

“…Neutralex is indicated to reduce formaldehyde concentrations to less than 10 mg L −1 within 24 h in 10% neutral‐buffered formalin wastes (Masters ; Gearheart et al . ). The sodium meta‐bisulphite (Na 2 S 2 O 5 ) is the main ingredient of Neutralex and when it is dissolved in water originates sodium bisulphite – NaHSO 3 (reaction 15) (Irwin ).…”

“…Gearheart et al . () evaluated the potential of sodium sulphite, Neutralex , hydrogen peroxide without and with a ferric iron catalyst to reduce the concentration of formalin in effluents from aquaculture facilities and obtained different results for each case. On the one hand, the reactions with the hydrogen peroxide without or with a ferric iron catalyst did not cause substantial reductions in formalin concentrations.…”

“…In addition to the necessary pH adjustments following the treatment, the products resulting from these reactions affected the survival and reproduction of an indicator organism, the water flea ( Ceriodaphnia dubia ) in chronic toxicity tests (Gearheart et al . ) …”