Patent Publication Number: US-2019178803-A1

Title: Method of measuring concentration of dissolved organic nitrogen in sewage

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of International Patent Application No. PCT/CN2017/095851 with an international filing date of Aug. 3, 2017, designating the United States, now pending, and further claims foreign priority benefits to Chinese Patent Application No. 201710048270.3 filed Jan. 20, 2017. The contents of all of the aforementioned applications, including any intervening amendments thereto, are incorporated herein by reference. Inquiries from the public to applicants or assignees concerning this document or the related applications should be directed to: Matthias Scholl P. C., Attn.: Dr. Matthias Scholl Esq., 245 First Street, 18th Floor, Cambridge, Mass. 02142. 
    
    
     BACKGROUND 
     This disclosure relates to a method of measuring concentration of dissolved organic nitrogen in sewage. 
     Total dissolved nitrogen (TDN) in sewage includes dissolved inorganic nitrogen (DIN) and dissolved organic nitrogen (DON). 
     Conventionally, to measure the concentration of DON, the concentrations of TDN and DIN (including ammonia nitrogen, nitrate nitrogen and nitrite nitrogen) are measured, respectively, and then the difference between them is calculated. The entire measurement processes are complex and inefficient, and the results are generally inaccurate. 
     SUMMARY 
     Disclosed is a method of measuring concentration of dissolved organic nitrogen in sewage. 
     The disclosure provides a method of measuring concentration of dissolved organic nitrogen in sewage, the method comprising:
         (1) filtering a sewage sample using a filter membrane;   (2) measuring concentrations of total dissolved nitrogen (TDN), ammonia nitrogen (NH 4   + ), and nitric nitrogen (NO 3   − ) in the sewage sample, respectively designated as C TDN(I) , C NH4   +   (I)  and C NO3   −   (I) ;   (3) calculating ratios of (C NH4   +   (I) +C NO3   −   (I) )/C TDN(I)  and C NO3   −   (I) /C NH4   +   (I) , and according to the ratios, performing one of the following to measure concentrations of nitrogen-containing groups in the sewage sample;
           (3.1) when (C NH4   +   (I) +C NO3   −   (I) )/C TDN(I) &lt;0.7, measuring a concentration of nitrite nitrogen (NO 2   − ) in the sewage sample, designated as C NO2   −   (I) , and calculating a concentration of dissolved organic nitrogen (DON) in the sewage sample as follows: DON=C TDN(I) −C NH4   +   (I) −C NO3   −   (I) −C NO2   − (I);   (3.2) when (C NH4   +   (I) +C NO3   −   (I) )/C TDN(I) ≥0.7 and C NO3   −   (I) /C NH4   +   (I) ≥1, dialyzing the sewage sample in a suspended dialysis bag for between 22 and 26 hours, and measuring concentrations of total dissolved nitrogen (TDN), ammonia nitrogen (NH 4   + ), nitric nitrogen (NO 3   − ) and nitrite nitrogen (NO 2   − ) in the sewage sample, respectively designated as C TDN(II) , C NH4   +   (II) , C NO3   −   (II) , and C NO2   −   (II) , and calculating a concentration of dissolved organic nitrogen (DON) in the sewage sample as follows: DON=C TDN(II) −C NH4   +   (II) −C NO3   −   (II) −C NO2−(II) ; and   (3.3) when (C NH4   +   (I) +C NO3   −   (I) )/C TDN(I) ≥0.7 and C NO3   −   (I) /C NH4   +   (I) &lt;1, dialyzing the sewage sample in a suspended dialysis bag for between 34 and 38 hours, and measuring concentrations of total dissolved nitrogen (TDN), ammonia nitrogen (NH 4   + ), nitric nitrogen (NO 3   − ) and nitrite nitrogen (NO 2   − ) in the sewage sample, respectively designated as C TDN(III) , C NH4   +   (III) , C NO3   −   (III) , and C NO2   −   (III) , and calculating a concentration of dissolved organic nitrogen (DON) in the sewage sample as follows: DON=C TDN(III) −C NH4   +   (III) −C NO3   −   (III) −C NO2   −   (III) .   
               

     The filter membrane can have a pore size of 0.45 μm. 
     The suspended dialysis bag in (3.2) and (3.3) can be a cellulose ester membrane, hydrophilic, and can have a molecular weight cut-off (MWCO) of 100-500 Da; and the hydraulic retention time of the dialysate in the sewage sample can be 4 h. 
     The concentrations of the total dissolved nitrogen (TDN), ammonia nitrogen (NH 4   + ), nitric nitrogen (NO 3   − ) and nitrite nitrogen (NO 2   − ) can be measured using potassium persulfate oxidation-ion chromatography, salicylic acid-hypochlorite spectrophotometry, ion chromatography and N-(1-naphthyl)-ethylenediamine spectrophotometry, respectively. 
     Advantages of the method of measuring concentration of dissolved organic nitrogen in sewage in the disclosure are summarized as below. 
     1. The method is efficient, and energy-saving; 
     2. The measurement method is accurate; and 
     3. The method is easy to operate, and is cost-effective. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a flow chart of a method of measuring concentration of dissolved organic nitrogen in sewage as described in the disclosure; and 
         FIG. 2  is a comparison diagram of concentrations of dissolved organic nitrogen measured by conventional methods and the method as described in the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     To further illustrate, examples detailing a method of measuring concentration of dissolved organic nitrogen in sewage are described below. It should be noted that the following examples are intended to describe and not to limit the description. 
     Example 1 
     1. 100 mL of municipal sewage (labeled as sample 1) was filtered using a filter membrane having a pore size of 0.45 μm. 
     2. The concentrations of the total dissolved nitrogen (TDN), NH 4   +  and NO 3   −  of the sewage were measured using potassium persulfate oxidation-ion chromatography, salicylic acid-hypochlorite spectrophotometry, and ion chromatography, respectively, and were recorded as C TDN(I) , C NH4   +   (I)  and C NO3   −   (I) ; 
     3. The results showed that (C NH4   +   (I) +C NO3   −   (I) )/C TDN(I) =0.92&gt;0.7 and C NO3   −   (I) /C NH4   +   (I) &gt;1. The sewage was dialyzed in a suspended dialysis bag for 24 hours. The suspended dialysis bag was a cellulose ester membrane, hydrophilic, and had a molecular weight cut-off (MWCO) of 100 Da; and the hydraulic retention time of the dialysate in the sewage sample was 4 h. Thereafter, the concentrations of the total dissolved nitrogen (TDN), ammonia nitrogen (NH 4   + ), nitric nitrogen (NO 3   − ) and nitrite nitrogen (NO 2   − ) were measured using potassium persulfate oxidation-ion chromatography, salicylic acid-hypochlorite spectrophotometry, ion chromatography and N-(1-naphthyl)-ethylenediamine spectrophotometry, respectively, and recorded as C TDN(II) , C NH4   +   (II) , C NO3   −   (II) , and C NO2   −   (II) , respectively. 
     4. The concentration of the dissolved organic nitrogen (DON) in the sewage sample was calculated as follows: DON=C TDN(II) −C NH4   +   (II) −C NO3   −   (II) −C NO2−(II) . The DON in the sample 1 was 0.80 mg/L. To ensure the accuracy and reliability of the measurement, the measurement was performed three times and the measured values were averaged. The results are shown in  FIG. 2 . 
     Example 2 
     1. 100 mL of municipal anaerobic sewage (labeled as sample 2) was filtered using a filter membrane having a pore size of 0.45 μm. 
     2. The concentrations of the total dissolved nitrogen (TDN), NH 4   +  and NO 3   −  of the sewage were measured using potassium persulfate oxidation-ion chromatography, salicylic acid-hypochlorite spectrophotometry, and ion chromatography, respectively, and were recorded as C TDN(I) , C NH4   +   (I)  and C NO3   −   (I) ; 
     3. The results showed that (C NH4   +   (I) +C NO3   −   (I) )/C TDN(I) =0.73&gt;0.7 and C NO3   −   (I) /C NH4   +   (I) &lt;1. The sewage was dialyzed in a suspended dialysis bag for 34 hours. The suspended dialysis bag was a cellulose ester membrane, hydrophilic, and had a molecular weight cut-off (MWCO) of 100 Da; and the hydraulic retention time of the dialysate in the sewage sample was 4 h. Thereafter, the concentrations of the total dissolved nitrogen (TDN), ammonia nitrogen (NH 4   + ), nitric nitrogen (NO 3   − ) and nitrite nitrogen (NO 2   − ) were measured using potassium persulfate oxidation-ion chromatography, salicylic acid-hypochlorite spectrophotometry, ion chromatography and N-(1-naphthyl)-ethylenediamine spectrophotometry, respectively, and recorded as C TDN(III) , C NH4   +   (III) , C NO3   −   (III) , and C NO2   −   (III) , respectively. 
     4. The concentration of the dissolved organic nitrogen (DON) in the sewage sample was calculated as follows: DON=C TDN(III) −C NH4   +   (III) −C NO3   −   (III) −C NO2   −   (III) . The DON in the sample 2 was 2.43 mg/L. To ensure the accuracy and reliability of the measurement, the measurement was performed three times and the measured values were averaged. The results are shown in  FIG. 2 . 
     Example 3 
     1. 100 mL of municipal aerobic sewage (labeled as sample 3) was filtered using a filter membrane having a pore size of 0.45 μm. 
     2. The concentrations of the total dissolved nitrogen (TDN), NH 4   +  and NO 3   −  of the sewage were measured using potassium persulfate oxidation-ion chromatography, salicylic acid-hypochlorite spectrophotometry, and ion chromatography, respectively, and were recorded as C TDN(I) , C NH4   +   (I)  and C NO3   −   (I) ; 
     3. The results showed that (C NH4   +   (I) +C NO3   −   (I) )/C TDN(I) =0.75&gt;0.7 and C NO3   −   (I) /C NH4   +   (I) &gt;1. The sewage was dialyzed in a suspended dialysis bag for 24 hours. The suspended dialysis bag was a cellulose ester membrane, hydrophilic, and had a molecular weight cut-off (MWCO) of 100 Da; and the hydraulic retention time of the dialysate in the sewage sample was 4 h. Thereafter, the concentrations of the total dissolved nitrogen (TDN), ammonia nitrogen (NH 4   + ), nitric nitrogen (NO 3   − ) and nitrite nitrogen (NO 2   − ) were measured using potassium persulfate oxidation-ion chromatography, salicylic acid-hypochlorite spectrophotometry, ion chromatography and N-(1-naphthyl)-ethylenediamine spectrophotometry, respectively, and recorded as C TDN(II) , C NH4   +   (II) , C NO3   −   (II) , and C NO2   −   (II) , respectively. 
     4. The concentration of the dissolved organic nitrogen (DON) in the sewage sample was calculated as follows: DON=C TDN(II) −C NH4   +   (II) −C NO3   −   (II) −C NO2−(II) . The DON in the sample 3 was 1.89 mg/L. To ensure the accuracy and reliability of the measurement, the measurement was performed three times and the measured values were averaged. The results are shown in  FIG. 2 . 
     Example 4 
     1. 100 mL of municipal sewage (labeled as sample 4) was filtered using a filter membrane having a pore size of 0.45 μm. 
     2. The concentrations of the total dissolved nitrogen (TDN), NH 4   +  and NO 3   −  of the sewage were measured using potassium persulfate oxidation-ion chromatography, salicylic acid-hypochlorite spectrophotometry, and ion chromatography, respectively, and were recorded as C TDN(I) , C NH4   +   (I)  and C NO3   −   (I) ; 
     3. The results showed that (C NH4   +   (I) +C NO3   −   (I) )/C TDN(I) =0.95&gt;0.7 and C NO3   −   (I) /C NH4   +   (I) &gt;1. The sewage was dialyzed in a suspended dialysis bag for 25 hours. The suspended dialysis bag was a cellulose ester membrane, hydrophilic, and had a molecular weight cut-off (MWCO) of 100 Da; and the hydraulic retention time of the dialysate in the sewage sample was 4 h. Thereafter, the concentrations of the total dissolved nitrogen (TDN), ammonia nitrogen (NH 4   + ), nitric nitrogen (NO 3   − ) and nitrite nitrogen (NO 2   − ) were measured using potassium persulfate oxidation-ion chromatography, salicylic acid-hypochlorite spectrophotometry, ion chromatography and N-(1-naphthyl)-ethylenediamine spectrophotometry, respectively, and recorded as C TDN(II) , C NH4   +   (II) , C NO3   −   (II) , and C NO2   −   (II) , respectively. 
     4. The concentration of the dissolved organic nitrogen (DON) in the sewage sample was calculated as follows: DON=C TDN(II) −C NH4   +   (II) −C NO3   −   (II) −C NO2−(II) . The DON in the sample 4 was 0.51 mg/L. To ensure the accuracy and reliability of the measurement, the measurement was performed three times and the measured values were averaged. The results are shown in  FIG. 2 . 
     Example 5 
     1. 100 mL of 0.99 mg/L standard glutamate solution was mixed with 10 mL of 40.09 mg/L potassium nitrate solution. The mixture (labeled as sample 5) was filtered using a filter membrane having a pore size of 0.45 μm. 
     2. The concentrations of the total dissolved nitrogen (TDN), NH 4   +  and NO 3   −  of the mixture were measured using potassium persulfate oxidation-ion chromatography, salicylic acid-hypochlorite spectrophotometry, and ion chromatography, respectively, and were recorded as C TDN(I) , C NH4   +   (I)  and C NO3   −   (I) ; 
     3. The results showed that (C NH4   +   (I) +C NO3   −   (I) )/C TDN(I) =0.81&gt;0.7 and C NO3   −   (I) /C NH4   +   (I) &gt;1. The sewage was dialyzed in a suspended dialysis bag for 24 hours. The suspended dialysis bag was a cellulose ester membrane, hydrophilic, and had a molecular weight cut-off (MWCO) of 100 Da; and the hydraulic retention time of the dialysate in the sewage sample was 4 h. Thereafter, the concentrations of the total dissolved nitrogen (TDN), ammonia nitrogen (NH 4   + ), nitric nitrogen (NO 3   − ) and nitrite nitrogen (NO 2   − ) were measured using potassium persulfate oxidation-ion chromatography, salicylic acid-hypochlorite spectrophotometry, ion chromatography and N-(1-naphthyl)-ethylenediamine spectrophotometry, respectively, and recorded as C TDN(II) , C NH4   +   (II) , C NO3   −   (II) , and C NO2   −   (II) , respectively. 
     4. The concentration of the dissolved organic nitrogen (DON) in the sewage sample was calculated as follows: DON=C TDN(II) −C NH4   +   (II) −C NO3   −   (II) −C NO2−(II) . The DON in the sample 5 was 1.05 mg/L. To ensure the accuracy and reliability of the measurement, the measurement was performed three times and the measured values were averaged. The results are shown in  FIG. 2 . 
     As shown in  FIG. 2 , when the sewage samples 1-4 were not pretreated using the method described in the disclosure, the standard deviation of the measured values was large, and thus the concentration of the DON in the sewage cannot be concluded, or even a negative value was obtained. According to the measurement method as described in the disclosure, the measured value of the DON concentration of the sample 5 was 1.03±0.03 mg/L, and the standard error between the measured value and the truth value (0.99 mg/L) is 4.04%. The standard error between the DON concentration measured using conventional methods and the truth value in the sample 5 is 33.33%. Therefore, the method of measurement of the concentration of DON is accurate. The standard deviation of the repeated tests is within 10%. 
     It will be obvious to those skilled in the art that changes and modifications may be made, and therefore, the aim in the appended claims is to cover all such changes and modifications.