Adsorption Of Nitrate And Phosphate By Modiifed Biochar

The accumulation of nitrogen and phosphorus in rivers, lakes and coastal areas generally leads toeutrophication. Nitrogen and phosphorus leaching loss in soil causes the agricultural resources wasteand brings the threat to the agricultural environment. Therefore, nitrate nitrogen （NO3--N） andphosphate （P） removing has an important role in purifying wastewater; Reducing nitrate nitrogen andavailable phosphorous leaching can increase the utilization rate of fertilizers and improve theagricultural environment.In this study, wheat straw biochar was made into the modified biochar by FeCl₃and was turnedinto the efficiently adsorption nitrate nitrogen and phosphorus material. Nitrate nitrogen and phosphorusremoval from aqueous solutions via adsorption by modified biochar and soil nitrate nitrogen andphosphorus leaching reduce by modified biochar were investigated, and then finds a new way to usecrops straw efficiently. The main research results are as follows:（1） Determination of the best modified method, found that:The Fe³⁺to biochar mass ratio of0.7was tested to be the best modified condition which wouldincrease the absorption of nitrate nitrogen and phosphorus greatly.（2） In nitrate and phosphate solution, the characteristic of the adsorption of nitrate nitrogen andphosphorus by best modified biochar were studied, found that:The experimental data of the adsorption process of nitrate nitrogen and phosphorus fits the fourisotherm equations, namely, Langmuir, Freundlich,Temkin and Dubinin-Radushkevich.ThroughLangmuir, the theoretical monolayer saturation capacity for N and P is2.47mg·g^-1and16.58mg·g^-1respective.Increase in adsorbent dosage increased the removal of nitrate nitrogen and phosphorus and theremoval efficiency increases up to optimum dosage beyond which the removal efficiency is negligible.In nitrate solution, the optimum dosage of best modified biochar is44g·L^-1and the best removal rate is75%; In phosphate solution, the optimum dosage of best modified biochar is8g·L^-1and the best removalrate is above99%.Increase the pH in nitrate and phosphate solution decreased the amount adsorbed of nitrate nitrogenand phosphorus.The experimental data of the adsorption process of nitrate nitrogen and phosphorus fits the pseudosecond-order kinetics model and the correlation coefficient R2is0.999and0.994respectively. Theintra-particle diffusion is not the only rate limiting step, but also other kinetic models may control therate of adsorption, all of which may be operating simultaneously, the second portion is the gradualadsorption stage, where the intra-particle diffusion is rate controlled.The adsorption process of nitrate nitrogen and phosphorus by best modified biochar may involvenot only physical but also chemical sorption processes. However, the chemical adsorption doesn’t play aleading role in the process of adsorption nitrate nitrogen while a leading role in the process of adsorption phosphorus.（3）In soil, best modified biochar was studied as a soil additive to increase the utilization rate of soilnitrate nitrogen and available phosphorous in soil profile by soil column simulation test, concluded that:In soil column simulation test, there’s no significant effect in leaking of nitrate nitrogen andavailable phosphorus in treatmeants added2.5%,5%and10%of the common biochar, while the sameratio best modified biochar was added in soil, the nitrate nitrogen leakage was significantly reduced, by20%,43%and59%respectively compared to the control with no biochar addition; Availablephosphorus leakage was also significantly decreased, by45%,59%and75%respectively.