| On the basis of consulting the literature materials and summarizing the investigation and preliminary experiment, the five kinds adsorbents and the three kinds of aquatic plants were selected at first. Then, the optimum adsorbent and the optimum aquatic plant were selected. Finally, the combination system consisting of the optimum adsorbent and the optimum hydroponic plant were constructed to treat the Cr(?)-containing wastewater. And the removal efficiency of Cr(?) was investigated by the combination system.The main research results are as follows:In the selection of vermiculite, polyurethane foam, fly ash, zeolite and activated carbon, under the condition of appropriate p H and suitable addition amounts, the equilibrium adsorption amounts adsorbed by the vermiculite and polyurethane foam were better than that of others when the concentration of Cr(?) was 5mg·L-1. Then,the vermiculite and polyurethane foam were used for the activated sludge interception test, the result shown that the dry weight of activated sludge fixed by vermiculite and polyurethane foam were 0.031 g and 0.042 g, respectively. Because the polyurethane foam can intercept more activated sludge and was difficult to flow with the water, it was selected as the adsorbent for the next research.In the discussion of the adsorption mechanism of polyurethane foam, the result shown that this process of adsorption were both endothermic and spontaneous, and this adsorption process was mainly depend on physical adsorption, while accompany with chemical adsorption. Four types of desorption agent were used to desorpt the polyurethane foam, the result shown that the Na OH with the concentration of0.1mol·L-1 was of the best desorption effect.In the screening of the three kinds of aquatic plants, the different plants had different tolerance concentration for Cr(?), and the tolerance concentration for Cr(?)from high to low was Water hyacinth,Cress and Alternanthera philoxeroides in turn.After Water hyacinth,Cress and Alternanthera philoxeroides were cultivated for 16 d in their tolerance concentration for Cr(?), the enrichment amounts of Cr(?) in Water hyacinth,Cress and Alternanthera philoxeroides were 57.01mg·kg-1, 14.97mg·kg-1 and26.76mg·kg-1, respectively. In view of water hyacinth had better tolerance concentration and enrichment amount for Cr(?), it was selected as hydroponic plant for the next research.In the study of polyurethane foam-water hyacinth combined system, when the initial concentration of Cr(?) was 5mg·L-1, the effluent concentration of Cr(?) less than 0.05 mg·L-1 was required. At first, two kinds of systems were founded, namely the system 1(which was consisting of polyurethane foam and water hyacinth) and the system 2(which was just consisting of water hyacinth). The result shown that when the effluent concentration of Cr(?) was less than 0.05 mg·L-1, the system 1 took lesstime than system 2.Then, the system 1 was used for the multicycle run, the result shown that when the effluent concentration of Cr(?) was less than 0.05 mg·L-1,the?,?,? and ?cycles took 16 d, 21 d, 18 d and 17.5d, respectively. The remove amounts of Cr(?) by the activated sludge was gradually increase at the end of each cycle, and the remove rate of Cr(?) reached 43.9% in tube 1 at the end of the?cycle. In the test of the tolerance concentration for Cr(?), the results indicated the tolerance concentration for Cr(?) of the combination system was 8 mg·L-1 or so.The whole research shown that the polyurethane foam-water hyacinth combined system can remove Cr(?) when the initial concentration of Cr(?) was not more than8mg·L-1, and the system had a higher removal efficiency when the initial concentration of Cr(?) was not more than 5mg·L-1.The polyurethane foam not only can be used as biological carrier but also can be recycled, and water hyacinth is cheap,the system has certain practical value for the treatment of low Cr(?)-containing wastewater. |
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