Adsorption Characteristics Of Low Concentration Nitrate By Modified Biochar And Its Application In Water Treatment From Lake Taihu

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 in water remediation for scientists 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 kinds of biochar were modified to enhance the adsorption of low concentration nitrate.Furthermore,the effect of environmental conditions and underlying adsorption mechanism were elucidated.In addition,the practical applications of modified biochar were also investigated in water from Lake Taihu.The main results of this thesis are as follows:1.The adsorption capacity of low concentration nitrate on biochar was significantly improved by modifying with ferric chloride.Considering the cost and adsorption capacity together,the optimum modifying condition of iron/carbon mass ratio was 0.6.And the particle size had no effect on the adsorption capacity of nitrate for the biochar which particle size was less than 1 mm.2.Some aquatic plants were used to remove N and P from wastewater in constructed wetlands.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.Nitrate adsorption by selected biochar derived from three phytoremediation plants and two different bamboo charcoal was investigated.All modified biochars were efficient materials for nitrate removal.Laboratory adsorption experiments were conducted to assess the nitrate removal ability of modified biochars at different time,solution pH,and adsorbent dose.The adsoption isotherms were all well fitted by Langmuir model while the adsorption kinetics could be described by second order equation.3.Through the characterization of biochar before and after modification,the iron content in biochar after modification was increased to 0.92%?1.75.And a large amount of Fe3+ was adsorbed onto the surface of biochar,forming Fe-O group after modification,which increased the specific surface area and adsorption sites of biochar,thus improving its adsorption properties to nitrate.4.Two modified biochar were selected applying to the field experiment in Taihu Lake.It was found that the modified biochar could obviously adsorb various nitrogen forms in the water body.The removal rate of nitrate reached 48.9%;as for ammonia was 50.9%and the total nitrogen removal rate was 33.9%.In addition,the modified biochar can significantly inhibit the growth of planktonic algae in water.Therefore,modified biochar has great potential for application in natural water restoration.