| Usually, phosphorus (P) is limiting nutrient for the growth of organisms in most ecosystems and also a major cause of eutrophication. P is present almost solely as phosphates. In the past several decades, the removal of phosphate ions in natural water systems has received great attention. Among them, adsorption is regarded as a cost-effective, highly efficient approach. In China, about 60 percent of them is waste and gets burnt.In this paper, the rice straw derived activated carbon (ARC) was activated by CaCl2 for phosphorous removal. The effects of variables (CaCl2/AC mass ratio and activation temperature) have been studied by the single-factor method. The individual and collective effects of the main independent parameters (adsorption time, pH valued of solution and ARC dosage) was employed to assess on the phosphate removal efficiency and the possible adsorption mechanism; the N and P retention capability of this ARC under leaching condition in 3 different kind of soil column (clay soil, silty loam and sandy soil) was also studied; at last, the effect of different application mangement of RC (including ARC and NRC; broadcast and packed-cast; 1 and 2 t hm"2) on rice paddy field was studied, including the change of suface water, the soil and the rice.The results suggested that:1) The rice-straw carbon without activation had very low efficiency of P adsorption (with dosage of 4 g L-1, efficiency rate<5%), whereas when the ARC was prepared at of 700℃ of carbonizing temperature,0.5 (WcaCl2/ Wrice straw) of immersion rate, the P removal efficiency of CaCl2-activated rice straw carbon (ARC) was more than 95%(dosage:4 g L-1; initial concentration:10 mg P L-1). The adsorption equilibrium well fits in with the Langmuir isotherm (R2=0.947), The change of pH values (from 6.87 to 9.62) and the adsorption process suggested that the probable mechanism of phosphate ions onto ARC was not only ion exchange and coulomb interaction, but also a result of Lewis acid-base interaction due to Ca ion coordination bonding. Thus, ARC has great phosphate removal efficiency in solution and could be used as an adorable P adsorbent;2) When the ARC was applied on leaching soil column, with the 24 h leaching condition, compared with the Blank column, the N and P retention rates of 3 different kind of soil column (clay soil, silty loam and sandy soil) had significant difference. In the clay soil column, the retention rate was much better (the accumulating retaining rate of TP, TN were 70% and 20%) than in the silty loam and sandy soil column (the accumulating retaining rate of TP, TN were 10～18% and 0～10%). The ARC had a certain capability of P and N retention in soil, while the efficiency was effected by the properties of soil;3) Rice straw carbon (RC) with the dosage of 1 and 2t hm-2 applied on the paddy field could significantly reduced the risk of N and P loss through suface runoff.3 h after fertilization, with the broadcast of ARC (2 t hm-2), the concentration of TP and TN could reduce by 60～85% and 50%, respectively; With the application of RC (1 and 2 t hm"2), the pH of paddy soil increased about 0-0.1, the Organic P and NH4+-N contents also increased a little,0.04～0.16 g P kg-1 and 0.04～0.16 g P kg-1, respectively, while the STC, STN and STP of soil with all the RC treatment didn’t have significant change; With the broadcast of RC, the plant heigh increased 1-7 cm, while the effective parnicles, gross weight and grain yield didn’t have significant increase, indeed, the RC with packed-cast way could slightly decrease the grain yield, that might because the carbon solely adsorpted the N and P, and reduced the adsorption of plant. In conclusion, the RAC broadcasting on rice peddy could significantly reduce the risk of P and N loss in the runoff, while had not considerable effect on soil and grain yield. |
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