Agricultural Wasted Carbon Source Addition On Nitrogen Removal Of Low-polluted Water And Its Environmental Effect

In recent years,agricultural non-point source pollution has become one of the main influencing factors of global water environment quality,and the ditch system,as an important part of the"process"technology of non-point source pollution control,has shown great potential for interception and purification.At present,a large number of studies have been carried out on the ecological transformation of ditches by planting plants and laying substrates,but the lack of carbon sources in low-polluted water has always been the important limiting factor to nitrogen removal in ditches.Therefore,based on the investigation of the impact of straw carbon source added on water nitrogen removal and the law of greenhouse gas emission,this study explored the nitrogen removal effect of three different agricultural waste carbon sources（straw,coconut bran and sawdust）behavior of low temperature in winter and high temperature in summer,and considered the environmental factors and greenhouse gas emission at the same time;then the difference between the addition of carbon sources on the promotion of water denitrification rate was analyzed by combining ¹⁵N isotope labeling and membrane injection mass spectrometry.The main findings are summarized as follows:（1）The simulation test results under low temperature conditions in winter showed that the straw group had the best nitrogen removal effect in both two stages,with the total nitrogen removal rates of 5.4%and 84.2%,respectively.The addition of coconut bran and wood chips rose the total nitrogen in the water body in the previous stage,but showed a better removal effect in the later.At the same time,it was found that three kinds of treatments in the later stage of the experiment has reduced the combined greenhouse effect by N₂O and CH₄.（2）The simulation test results under high temperature conditions in summer show that the removal rate of nitrate nitrogen of straw group has reached 92.5%in a short time,which is much higher than other treatments,but there was also founded the accumulation of ammonium nitrogen;The nitrogen change of coconut bran and sawdust group was close to that of the control（with no obvious removal effect）.The analysis of environmental factors showed that the addition of three carbon source materials reduced the p H and dissolved oxygen in different degrees during the whole experimental period.Meanwhile,the straw group also led to the significant increase of total phenolic acid and chemical oxygen demand.The calculation of comprehensive greenhouse effect shows that compared with straw and coconut bran,the addition of experimental sawdust in summer leads to a significant increase in greenhouse gas emissions on account of the high N₂O accumulation in the early.（3）The results showed that straw addition could significantly enhance the denitrification intensity of water in a short time,the maximum denitrification rate could reach 1482.42μmol·L^-1·h^-1,while decreased significantly in the later stage.The denitrification rate of water with coconut bran and sawdust was 3.609～60.87μmol·L^-1·h^-1 during the whole test period.Straw,coconut bran and sawdust,three kinds of agricultural waste carbon sources,showed different degrees of promoting effects on denitrification both winter and summer.Although the addition of different cellulose carbon sources had better NO₃^--N removal effect（especially straw）,the high temperature in summer led the decrease of DO and gave rise to total phenol and COD in varying degrees,which had certain negative environmental effects.It can be concluded that in winter and spring when the temperature is low,the reasonable selection and collocation of different carbon sources can promote the denitrification of water and reduce the adverse environmental impact,which has a certain application potential...