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Jarpa, M., Rozas, O., Salazar, C., Baeza, C., Campos, J. L., Mansilla, H. D., et al. (2016). Comparison of the chemical precipitation, UV/H2O2 and Fenton processes to optimize removal of chronic toxicity from kraft mill effluents. Desalin. Water Treat., 57(30), 13887–13896.
Abstract: Secondary Treatment Effluents (STE) from Kraft mill effluents are discharged into aquatic ecosystems with high color and chronic toxicity contents owing to the recalcitrance of compounds in the effluents. The goal of the study was to evaluate the chemical precipitation, UV/H2O2, and the Fenton processes (H2O2/Fe2+) for chemical oxygen demand (COD) and for removing chronic toxicity from STE. A circumscribed central composite model and a response surface methodology were used to evaluate the effects of variables such as Al-2(SO4)(3), Fe(II), and H2O2 concentration and pH range for each treatment. The optimal conditions were 984.2mg Al-2(SO4)(3)/L and pH 5.2 for chemical precipitation; 51.4mM H2O2 and pH 5.1 for UV/H2O2; and 5.5mM Fe(II): 25mM H2O2 concentration and pH 2.8 for H2O2/Fe2+. Under such optimal conditions, COD removal was 84.7, 80.0, and 93.6%, with reaction times of 57, 75, and 10min for the chemical precipitation, UV/H2O2, and H2O2/Fe2+ methods, respectively. This study recorded chronic toxicity in STE and sludge formed during chemical precipitation with maximum reductions in percentages of Allometric Growth Rate (AGR) of 11.5 for STE without dilution (100%, p<0.05). For chemical precipitation sludge, the maximum reduction of AGR was 3.4% for a dilution of 75%. We concluded that all the assessed treatments effectively removed chronic toxicity in the treated effluents.
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Santore, R. C., Ryan, A. C., Kroglund, F., Rodriguez, P. H., Stubblefield, W. A., Cardwell, A. S., et al. (2018). Development and Application of a Biotic Ligand Model for Predicting the Chronic Toxicity of Dissolved and Precipitated Aluminum to Aquatic Organisms. Environ. Toxicol. Chem., 37(1), 70–79.
Abstract: Aluminum (Al) toxicity to aquatic organisms is strongly affected by water chemistry. Toxicity-modifying factors such as pH, dissolved organic carbon (DOC), hardness, and temperature have a large impact on the bioavailability and toxicity of Al to aquatic organisms. The importance of water chemistry on the bioavailability and toxicity of Al suggests that interactions between Al and chemical constituents in exposures to aquatic organisms can affect the form and reactivity of Al, thereby altering the extent to which it interacts with biological membranes. These types of interactions have previously been observed in the toxicity data for other metals, which have been well described by the biotic ligand model (BLM) framework. In BLM applications to other metals (including cadmium, cobalt, copper, lead, nickel, silver, and zinc), these interactions have focused on dissolved metal. A review of Al toxicity data shows that concentrations of Al that cause toxicity are frequently in excess of solubility limitations. Aluminum solubility is strongly pH dependent, with a solubility minimum near pH 6 and increasing at both lower and higher pH values. For the Al BLM, the mechanistic framework has been extended to consider toxicity resulting from a combination of dissolved and precipitated Al to recognize the solubility limitation. The resulting model can effectively predict toxicity to fish, invertebrates, and algae over a wide range of conditions. (C) 2017 SETAC
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