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Adsorption is widely used in the treatment of effluents and contaminated water. However, the removal of the pollutant alone does not ensure that the effluent can be safely discharged in the environment. Controlling effluent toxicity may become an important tool to ensure that the quality of the treated effluent is compatible with that of the receiving water body. In this sense, this study evaluated the efficiency of rice husk ash (RHA) to adsorb chromium(VI) using the Allium cepa toxicity test. Adsorption was assessed based on the variables adsorption time, initial concentration, and pH. The data obtained were fitted the pseudo-second-order and the pseudo-first-order models, and the Langmuir and Freundlich isotherms. Kinetic analysis indicated removal rates between 43 and 100%. All data were best fitted by the pseudo-second-order model. Also, pH 1 and pH 2 data were best fitted by the Freundlich and Langmuir isotherms, respectively. In the Allium cepa test, pH 2 solutions were toxic. At pH 7, the Alium cepa test confirmed the efficiency of chromium(VI) adsorption by RHA, ensuring acceptable germination index values.

The validation of adsorption treatment based on toxicity assays aims to assess the actual environmental impact caused by effluents after treatment. This study describes the use of rice husk ash as adsorbent and evaluates the efficiency of adsorption treatment to remediate groundwater contaminated with benzene, toluene, ethylbenzene, and xylene (BTEX). The synthetic effluent was prepared with standard benzene, toluene, ethylbenzene, and xylene solutions. Adsorption was assessed at treatment times 0, 60, 120, and 240 min. Compounds were quantified by gas chromatography with flame ionization detector. The treatment was validated based on ecotoxicity assays using Allium cepa as indicator organism. For the treatment times stipulated, samples containing 25, 50, and 100% of BTEX were used. The dilutions were carried out with drinking water according to Fiskesjö (1985). The relative growth index (RGI), root inhibition index (Ii), and germination index (GI) confirmed the efficiency of the treatment approach tested. The best adsorption time for an initial BTEX concentration of 3.378 mg/L was 60 min. Critical level (EC50) and critical concentration that induced phytotoxic effect on A. cepa germination was observed only for the undiluted effluent.

The validation of adsorption treatment based on toxicity assays aims to assess the actual environmental impact caused by effluents after treatment. This study describes the use of rice husk ash as adsorbent and evaluates the efficiency of adsorption treatment to remediate groundwater contaminated with benzene, toluene, ethylbenzene, and xylene (BTEX). The synthetic effluent was prepared with standard benzene, toluene, ethylbenzene, and xylene solutions. Adsorption was assessed at treatment times 0, 60, 120, and 240 min. Compounds were quantified by gas chromatography with flame ionization detector. The treatment was validated based on ecotoxicity assays using Allium cepa as indicator organism. For the treatment times stipulated, samples containing 25, 50, and 100% of BTEX were used. The dilutions were carried out with drinking water according to Fiskesjö (1985). The relative growth index (RGI), root inhibition index (Ii), and germination index (GI) confirmed the efficiency of the treatment approach tested. The best adsorption time for an initial BTEX concentration of 3.378 mg/L was 60 min. Critical level (EC50) and critical concentration that induced phytotoxic effect on A. cepa germination was observed only for the undiluted effluent. [ABSTRACT FROM AUTHOR]