| The leaching of nitrogen and phosphorus caused by soil erosion in Chongqing is one of the main sources of non-point source pollution.Looking for an environmentally friendly and effective way to solve the nitrogen and phosphorus pollution is the hotspot in environmental management research.Because of the special pore structure and a large special surface area,biochar has a good adsorption characteristics and can effectively improve the soil water retention and fertility capacity.The garden waste can be used as the raw materials of biochar,which can be returned to the field in order to realize its harmless dispose.In this paper,biochar was produced from landscaped waste(Erythrina arborescens),and the differences in physicochemical properties of biochar were obtained by pyrolysis temperature of 300°C,400°C,500°C,600°C,700°C and 800°C.Besides,the absorption mechanism of biochar to the ammonia nitrogen and phosphorus in the waste water was explored.At the same time,the static adsorption experiments were carried out with different pyrolysis temperature and different addictive proportions(0%?1%?3%?5%?10%)of biochar in soil.And then the effect of different biochar additions application on soil physicochemical properties and the migration of nitrogen and phosphorus in soil were studied by the dynamic soil column leaching experiment to explore the feasibility of biochar for wastewater treatment and effectiveness of biochar fixing nitrogen and phosphorus in soil.The research could provide a new way for the treatment and resource utilization of garden greening waste,and at the same time could provide the theoretical basis for reducing the agricultural non-point source pollution.The main results and conclusion are as follows:(1)Effect of pyrolysis temperature on the basic properties and structure of biochar: With the increase of pyrolysis temperature,the color of biochar changed from brown to dark black,and the yield and cation exchange capacity of biochar decreased,while the conductivity,ash and pH increased.In addition,the contents of ammonia nitrogen,nitric nitrogen and total nitrogen in biochar also were decreased with the increase of pyrolysis temperature,while the total phosphorus content was irregular with the increase of pyrolysis temperature.Elements with biochar elevated pyrolysis temperature changes,where in the C content increased,the N,H,O content reduced.The SEM and specific surface area and pore size analysis of biochar showed that the specific surface area and pore volume of biochar increased with the increase of pyrolysis temperature.The average pore size of biochar corresponding to different pyrolysis temperatures increased first and then decreased,and the pore size was mainly distributed between 2-50 nm.(2)The adsorption results of biochar on ammonia nitrogen and phosphorus are as follows: the adsorption capacities of BC300,BC500 and BC700 to ammonia nitrogen were 3.04mg/g,3.13mg/g and 3.03mg/g,respectively,while BC500 and BC700 on the adsorption capacities of phosphorus were 3.21mg/g,3.05mg/g,respectively.Besides,the research found that it was more favorable for biochar to ammonia nitrogen adsorption with the neutral condition and more favorable for biochar to phosphorus adsorption with the alkaline condition.(3)Effects of biochar on migration of ammonia and phosphorus in soil: During the leaching process of 70 days,the volume accumulation of leaching solution was less than that of blank control group,and the pH and conductivity of leaching solution increased with the increase of biochar addition.In addition,the accumulation of ammonia in the leaching solution with 1% carbon content was the lowest,which was lower than that of the blank group(30.7%).Compared with the control group,the addition of 1%,3%,5% and 10% biochar and the accumulation of nitrate and nitrogen were reduced by 27.3%,40.2%,51.7% and 61.1% respectively,while the total nitrogen accumulation decreased by 28.4 %,25.8%,12.5%,-17.3%.For total phosphorus,the leaching rate of total phosphorus in the leaching solution was reduced by 12.9% compared with the blank group(0%)only when the ratio of biochar was 1%.(4)Impact of biochar on soil phychemical properties: the addition of biochar an significantly increased soil pH,electric conductivity,cation exchange capacity and organic matter.And they all had positively correlated with soil depth.Besides,the ammonia nitrogen,nitrate nitrogen and total phosphorus content were decreased with the increase of soil depth.But with the biochar addition,the ammonia nitrogen,nitrate nitrogen and total phosphorus content were higher than the control group(biochar/soil = 0%).And we also found the content of total nitrogen in the soil was lower than the control group. |
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