Formalin is used at many fish farms and is typically discharged untreated from these facilities as part of normal hatchery effluents. The majority of aquaculture facilities that are regulated for formalin discharge are regulated on a concentration basis. These facilities most commonly use dilution methods to manage formalin concentrations in effluents. Dilution is not feasible at all farms, however, due to the unavailability of dilution water and the necessity of complex management practices to achieve adequate dilution. As hatchery discharge regulations become stricter, larger amounts of dilution water are required, which are not always available; therefore, practical methods of treating formalin in hatchery effluents are needed. This paper reviews the physical, chemical, and biological methods of aqueous formaldehyde neutralization and detoxification that have been tested to date and identifies those methods that may be practical for use at fish farms, including the application of sodium sulfite, commercially available neutralizers, or a combination of hydrogen peroxide and ferric ions. More research on the use of these treatment methods at aquaculture facilities is recommended to determine overall treatment effectiveness, cost, and practicality.
Erosion from construction sites significantly affects water quality in receiving streams. A rainfall simulator was used to evaluate the effectiveness of different methods for controlling erosion from construction sites. Erosion control methods investigated included dry and liquid applications of polyacrylamide (PAM), hydroseed, and straw mulch. Fertilizer was also applied to each plot to examine the effectiveness of the methods in reducing nutrient losses in runoff. Runoff samples were analyzed for total suspended solids (TSS), nitrate, total Kjeldahl nitrogen (TKN), ammonium, total phosphorus (TP), and orthophosphate. Among all treatments investigated, straw mulch was the most effective treatment for controlling TSS and nutrient losses during short term and long term simulations. The low liquid PAM (half the recommended PAM) treatment resulted in the highest reduction in runoff, TSS bound nitrogen, and total nitrogen (TN) concentrations and loadings. The study results indicate that a high application rate (twice the recommended rate) of PAM could actually increase runoff and TSS losses. At a low application rate, both liquid and dry PAM were effective in reducing TSS and nutrient losses in runoff. However, application of the liquid form of PAM to construction sites is more practical and perhaps more economical than applying the PAM in the dry form.
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.
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