Study On The Pretreatment Of Different Forms Of Nitrogen In Sewage Detecting By A Nitrogen Stable Isotope

Nitrogen is one of the essential elements for microbial growth.Since Since Kohl first used natural δ^<sup>15N to identify the source of nitrate pollution in water,the stable nitrogen isotope technology has been widely used in the studyof nitrogen source 、migration and transformation in the environment.This technique provides a strong technical support for us to glimpse the process of conversion of nitrogen sources in biogeochemical cycles.The application of stable nitrogen isotope technology in the study of nitrogen transport and transformation in domestic sewage is limited because of the higher nitrogen concentration 、 the complex composition 、 the coexistence of different forms of nitrogen in domestic sewage,and the complicated process of isotope pretreatment.In this paper,aimied at the problems existing in the stable nitrogen isotope pretreatment of domestic sewage,a stable isotope pretreatment experiment of mixed nitrogen source was established.we optimized the digestion conditions of organic matter,discussed the best experimental conditions for NH₄⁺-N distillation,selected the best adsorbent and drying method,and clarified the transformation and distillation methodofNO₃^--N.And finally a stable isotope pretreatment method for different forms of nitrogen in domestic sewage was obtained.Which provides a systematic detection technique for the stable isotope determination of different forms of nitrogen in domestic sewage.In this study,a pretreatment method was proposed based on the distillation method :The inorganic NH₄⁺-N was distilled off first,and collected the distillation residue,and then the conversion and separation of organic nitrogen and NO₃^--N were carried out respectively.Finally,different forms of nitrogen were distilled in form of NH₄⁺-N,and the effective separation and enrichment of different forms of nitrogen in wastewater were realized.The experimental results show that:KTN and DON could beconverted into NH₄⁺-N stably and efficiently under digestion conditions such as 3mL 5%（m/v）CuSO₄and 10mL concentrated H₂SO₄ and 6g K₂SO₄ for 30 min.The optimum distillation time of ammonia nitrogen was 50 min and the optimum alkali dosage was 5mL 40%（m/v）NaOH solution.When the concentration was 0 80 mg ·L^-1,the nitrogen recovery rate up to 95%.By comparing the two different absorption modes of zeolite adsorption and acid uptake,we found that acid uptake was highly efficient and stable.The dilute sulfuric acid(0.04 mol·L^-1)was chosen as the best absorption liquid.and the nitrogen isotope fractionation effect was less（<0.04 ‰）when dried at pH = 3.0 ± 0.3,50 ℃.The optimum pretreatment conditions of stable isotope of nitrate nitrogen were as follows: the distillation time was 25 min,the optimum dosage of reducing agent nitrogen alloy was 5g,the recovery rate ofNO₃^--N in the range of 0²0mg·L-1more than 95%.Based on the established δ¹5N stable isotope analysis technique,the change of different forms of nitrogen in the pipe network was explored.The study shows that with the increase of the distance along the pipe network,the relative depleted¹5N library is formed in NH₄⁺-N,and DON forms a relatively enriched ¹5N library,which shows the tendency of organic nitrogen to inorganic nitrogen in the sewage pipe network.