| Biochar as an environmental friendly material has been widely applied in sequestrating carbon,reducing greenhouse-gas emissions,improving soil quality and increasing corp yields.It has generated great interest for scientists and policy markers in recent years.Biochar is recognized as an important cost-effective adsorbent storing chemical contaminants including heavy metals,organic compounds,and other environmental pollutions.Most of the traditional biochar,however,have limited ability to adsorb P,N or other anionic nutrients.In this work,several biochars were modified by different methods to enhance nitrate and phosphate adsorption.Furthermore,the effect of environment conditions and underlying adsorption mechanism were elucidated.In addition,the practical application of biohar were also investigated.The main results of this thesis are as follows:(1)Adsorption characteristics of nitrate were investigated with two common biochars prepared from peanut shell and wheat straw.Laboratory adsorption experiments were conducted to assess the nitrate and phosphate removal ability of two modified biochars at different time,solution pH,adsorbent dose and coexisting anions.The maximum nitrate adsorption amount was 2674 mg N·kg-1 and 1285 mg N·kg-1 and the maxmum phosphate adsorption amount was 872 mg P·kg-1 and 927 mg P·kg-1 for peanut shell and wheat straw biochars respectively.Peanut shell biochar was better for nitrate removal and wheat straw biochar was better for phosphate removal.The adsoption isotherms were all well fitted by Langmuir model while the adsorption kinetics could be described by second order equation.Besides,acidic and neutral conditions were more favorable for the adsorption process and there was no obvious competitive adsorption between nitrate and phosphate.(2)Some aquatic plants were uesd to remove N and P from wastwater.However,wetland plants would release nutrients back into water by decomposition process if they were not harvested timely and disposed properly.Harvested plant biomass can be used as a kind of feedstock for biochar.Phosphate sorption by selected biochar derived from three phytoremediation plants(reed,cattail,and calamus)were investigated.All the modified biochars were efficient materials for phosphate removal.The sorption capacity increased with concentration of phosphate.Among these biochars,Mg modified biochar(500?)had a greater phosphate sorption capacity than the other adsorbents.The maxium P sorption amount of the Mg modified reed biochar could reach 86.21 mg·kg-1.(6)The practical application of biochar was also developed.To overcome the problem of biochar outflow,methods for immobilizied biochar were explored.The optimal preparation conditions of immobilized biochar microspheres were determined as 2%alginate and 0.1 g·mL-1 biochar.Under this condition,the immobilized biochar microspheres were well-shaped and had a strong adsorption capacity for nitrate.Immobilization would not significantly reduce the adsorption capacity of modified biochar.(3)Denitrifying phosphate-accumulating bacteria(DNPAO)were selected and acclimated.Fe modified biochar combined with the bacteria had the highest removal rate of 83.4%after 6 hours.Compared with single effect,Fe modified biochar raised the speed of denitrification and accumulated less toxic by-products(NO2--N and NH4+-N).This method had remarkable advantages.(4)Modified biochar biological aerated filter had a high removal rate of nitrate and phosphate.The result showed that under the condition of HRT of 1 hour and C/N were 6,NO3--N removal rate could reach 95%after 6 hours and PO43--P removal rate could reach 90%after 3 hours.The removal rate of original biochar biological aerated filter were lower than it.So,modified biochar biological aerated filter had a vast potential for eutrophic waters treatment with low cost and high efficiency. |
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