Applying Electricity-driven Dialysis Pretreatment For Dissolved Organic Nitrogen Measurement

Total nitrogen is an important indicator of water quality in natural water s, and dissolved organic nitrogen(DON) is an important component of the total nitrogen(TN). DON can cause eutrophication, resulting in algae and microbial proliferation, so that drinking water can be polluted. In the water supply system, DON can promote microbial growth, which may lead to filter blocking and treatment efficiency reduction. In the disinfection process, DON can react with disinfectants, and generate nitrogenous disinfection byproducts(N-DBPs). Nitrogenous disinfection byproducts are toxins and harmful to human health. In order to prevent and control the risks caused by organic nitrogen, we firstly need to measure the concentration of DON accurately and quickly.Currently, the measurement method of DON is to use the subtractive method. DON detection is obtained by extracting dissolved inorganic nitrogen(DIN) from the total nitrogen. The extraction process is complex, and analytical errors are amplified during the process, especially when the concentrations of DON are low. Occasionally, it is possible to obtain negative DON concentration.In order to solve the abovementioned problems, this study evaluated a pretreatment method for DON measurement using electricity-driven dialysis. The challenge of this pretreatment method is DON and DIN separa tion. Through this pretreatment method, removal of DIN and retainment of DON were maximized. After the pretreatment, the concentration of TN becomes equivalent to DON. Similar to acidification process of total organic carbon(TOC) analysis. This pretreatment method can eliminate interfering of DIN, and detect DON rapidly, accurately and directly.This study evaluated the influencing factors of the pretreatment, theses influence factors including the ratio of sample volume and membrane area( V/S), voltage, concentration of the electrolyte, types of electrolyte, flow rate of electrolyte and initial concentration of sample. The study found that with decreasing V/S ratio, DIN removal efficiency significantly enhanced; as the voltage and electrolyte concentration increases, the rate of DIN removal accelerated. The flow rate of electrolyte affected DIN removal less, but the faster the flow rate, the greater removal efficiency of DIN within a certain range. Test for two kinds of e lectrolytes, sodium chloride is better than sodium sulfate for DIN removal. In this study, the experiment of pretreatment were proceed using 0.1 mol/L of sodium chloride, 10 ml/min of flow rate within 1 cm of V/S under 30 V voltage.The removal and retention effects of the representative nitrogen substance were tested under above condition. After the study, it is turn to be that the average removal of DIN can reach 98% within 90 min, nitrate and nitrite can almost completely remove. The average retention of DON(except for glutamate outside) can reach 90%. In addition, the retention of glycine, tripetide and tryptophan can reach almost 100%. During pretreatment, the p H value of sample cell and anode reservoir solution gradually decreased from 7 to 4, cathode reservoir solution increase from7 to 9. In this p H, dialysis membrane present negative, so that prevent cations go through the dialysis membrane, resulting ammonia removal efficiency was only about 94% in 90 minutes. Because of the ionization of gluta mic acid and lower molecular weight of urea, DON has little loss. When DON and DIN mixed together, the removal of DIN and the retention of DON can almost reach 100%. Comparing measurement the DON concentration after pretreatment and the true value, the slope of linear is almost 1, and R2> 0.99, no matter the value of the DIN/TDN in sample. Especially for DIN/TDN> 0.6 water sample, it is necessary to do pretreatment. Using the pretreatment methods on natural water samples, the low concentrations of DON can be detect directly. It is turn to be that this pretreatment method is applicable to natural water bodies.Compared the spectral scanning before and after pretreatment, illustrate that electricity-driven dialysis pretreatment did not change the structure of DON. The method detection limit(MDL) of pretreatment method about DON measurement is 0.033 mg-N/L. Conclusion that DON measurement using electricity-driven dialysis pretreatment can improve the accuracy and precision of DON detection significantly.