Method for measuring biodegradable soluble organic nitrogen of drinking water
Technical Field
The invention relates to the technical field of water treatment, in particular to a method for measuring biodegradable soluble organic nitrogen of drinking water.
Background
The soluble total nitrogen of the drinking water comprises three inorganic nitrogen of ammonia nitrogen, nitrate nitrogen and nitrite nitrogen and soluble organic nitrogen (DON). Most of the inorganic nitrogen in the drinking water treatment plant can be removed by nitrification-denitrification, but DON is hardly removed completely, while Biodegradable Dissolved Organic Nitrogen (BDON) refers to the portion of DON in the water body that can be metabolized and utilized by heterotrophic bacteria, and is more difficult to remove by chemical oxidation. The BDON not only can be used as a nitrogen source for the growth of microorganisms in a water distribution system to bring about potential safety hazards of the microorganisms, but also is an important precursor of nitrogen-containing disinfection byproducts with cytotoxicity and genetic toxicity.
At present, no direct and perfect BDON measuring method exists at home and abroad. Generally, most researchers at home and abroad compare differences of DONs before and after culture to calculate BDON mainly through a static culture method. The method has simple operation, cheap and easily obtained inoculation liquid, and can simultaneously carry out batch determination. In general, the analysis of BDON values is susceptible to microbial inoculation and inoculation cycles. Higher inoculum size increases the error in final BDON value due to the increase in DON values resulting from release of endogenous species from the bacteria, and lower inoculum size underestimates BDON values due to insufficient degradation of organic matter by the microorganisms. Khan et al (Water environ. Res.,2009,81(8),779-787) invented a method for measuring factory Water BDON of a sewage plant by using a static culture method, taking bacteria in sewage to be measured as inoculation liquid, and accurately reflecting the outlet Water BDON of the sewage plant when the sludge concentration (MLSS) of the added inoculation liquid is determined to be 240mg/L through a preliminary experiment. The Chinese patent with the patent number CN107655842A determines a sewage sample BDON through a similar experiment, and shows that when the concentration of DOC in the sewage sample is less than or equal to 30mg/L, the concentration of inoculating liquid sludge is 240mg/L, when the concentration of DOC in the sewage sample is more than 30mg/L and less than or equal to 70mg/L, the concentration of inoculating liquid sludge is 350mg/L, when the concentration of DOC in the sewage sample is more than 70mg/L, the concentration of inoculating liquid sludge is 420mg/L, and the BDON can accurately reflect the effluent BDON of a sewage plant. However, for raw water of drinking water and drinking water in the treatment process, because the organic matter content of the raw water is very low (the DOC concentration is less than 10mg/L), the method for measuring the sewage sample has the problem of lack of accuracy and precision in measuring the water sample of the drinking water.
The previous method for measuring the biodegradable soluble organic nitrogen of the sewage comprises the following steps: the concentration of DON in the sewage is high (mg/L level), the concentration of the inoculation liquid sludge required for measuring BDON is high, and the required culture period is long. The concentration of DON in a drinking water sample is low (mu g/L level), and the accuracy and the precision of measuring the BDON of the drinking water by using a method for measuring the BDON of the sewage are lacked. And various DON's (e.g., unstable DON in fresh water and sea water) may not be degraded with the inoculum from river water. Based on this, the applicant proposed a method for determining the biodegradable solubility of drinking water with eggs.
Disclosure of Invention
The present invention is directed to solving the above problems and providing a method for measuring biodegradable soluble organic nitrogen in drinking water, and a preferred embodiment of the present invention includes: the method can be used for measuring the organic nitrogen content in drinking water and surface water, and has the technical effects of simple operation, low operation cost and the like, and the details are explained below.
In order to achieve the purpose, the invention provides the following technical scheme:
the invention provides a method for measuring biodegradable soluble organic nitrogen of drinking water, which comprises the following steps:
s110, pretreating a sample to be detected, filtering the sample to be detected by using a filter membrane, and determining the DON concentration of the filtered sample, and recording the DON concentration as DONi;
S120, preparing an inoculation mother liquor, and preparing a culture inoculation mother liquor MLSS with inoculation activated sludge concentration of 100-200 mg/L;
s130, performing mixed culture, namely taking the water sample to be detected processed in the step S110 and the culture inoculation mother liquor prepared in the step S120 according to the material taking ratio of 50-150:1, fully shaking and uniformly mixing the water sample and the culture inoculation mother liquor in the step S120, placing the mixture in a reagent bottle, performing light-tight culture for 7-20 days, and measuring the DON concentration in the mixture after the culture is finished, wherein the DON concentration is marked as DONf;
S140, according to the formula BDON DONi-DONfAnd calculating the BDON value of the water sample to be detected.
Preferably, in step S110, the filter membrane is an acetate membrane, and the pore size of the filter membrane is 0.22 μm.
Preferably, the step S120 includes the following operations:
s121, taking activated sludge in an aerobic section of a water plant;
s122, measuring the MLSS concentration of the activated sludge by using quantitative filter paper filtration, and marking as MLSS0;
S123, diluting the activated sludge to 100-200 mg/L to obtain a culture inoculation mother liquor.
Preferably, in operation S123, the sludge concentration of the mother liquor for culture and inoculation is 150 g/L.
Preferably, in step S130, the ratio of the water sample to be tested to the culture inoculation mother liquor is 100: 1.
Preferably, in step S130, the reagent bottle is a brown glass reagent bottle.
Preferably, in step S130, the temperature in the incubator is 25 ± 0.5 ℃.
Preferably, in step S130, the culture time is 14 days.
In conclusion, the beneficial effects of the invention are as follows: 1. by adopting the method, the content of biodegradable soluble organic nitrogen in water samples with low nitrogen level, such as drinking water, surface water and the like, can be measured, and the measurement precision is high;
2. the method has the advantages of simple operation, cheap and easily obtained inoculation liquid, low operation cost and capability of carrying out batch determination;
3. the method can be applied to the determination of biodegradable soluble organic nitrogen in actual water bodies such as drinking water, surface water and the like.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 shows BDON concentrations of 1 to 5 in water samples to be tested in examples 1 to 5 of the present invention.
Fig. 2 is an operational schematic of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be described in detail below. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the examples given herein without any inventive step, are within the scope of the present invention.
The invention provides a method for measuring biodegradable soluble organic nitrogen of drinking water, which comprises the following steps as shown in figure 2:
s110, pretreating a sample to be detected, filtering the water sample to be detected by using a filter membrane, wherein the filter membrane is an acetate fiber membrane, the aperture of the filter membrane is 0.22 mu m, and determining the DON concentration of the filtered water sample and marking as DONi;
S120, preparing an inoculation mother liquor, and preparing a culture inoculation mother liquor MLSS with inoculation activated sludge concentration of 100-200 mg/L, wherein the method specifically comprises the following operations:
s121, taking activated sludge in an aerobic section of a water plant;
s122, measuring the MLSS concentration of the activated sludge by using quantitative filter paper filtration, and marking as MLSS0;
S123, diluting the activated sludge to 100-200 mg/L to obtain a culture inoculation mother liquor, wherein the preferable concentration is 150 g/L;
s130, performing mixed culture, namely taking the water sample to be detected processed in the step S110 and the culture inoculation mother liquor prepared in the step S120 according to the material taking ratio of 50-150:1, preferably 100:1, taking 200ml of the water sample to be detected, culturing 2ml of the inoculation mother liquor, sufficiently shaking, uniformly mixing in a 250ml brown glass reagent bottle, placing in a thermostat at the temperature of 25 +/-0.5 ℃ for 7-20 days, preferably 14 days in a dark place, and measuring the DON concentration after the culture is finished, wherein the DON concentration is recorded as DONf;
S140, according to the formula BDON DONi-DONfAnd calculating the BDON value of the water sample to be detected.
Concentration of DON (DON) in the drinking water sample described in step S110 and step S130iAnd DONf) The ammonia nitrogen-containing nitrite nitrogen is calculated by the difference value of total soluble organic nitrogen (TDN) and ammonia nitrogen (NH3-N), nitrate nitrogen (NO3-N) and nitrite nitrogen (NO2-N), namely DON (mu g/L, counted by N) is TDN- (NH3-N + NO3-N + NO 2-N); the concentration of the total soluble organic nitrogen is measured by adopting a Hash total nitrogen reagent package (persulfate oxidation-ultraviolet spectrophotometry); the concentration of the ammonia nitrogen is measured by adopting a nano reagent-spectrophotometry method; the concentration of the nitrate nitrogen is measured by adopting a Hash nitrate reagent powder pillow bag (cadmium reduction method); the concentration of the nitrite nitrogen is measured by adopting a pillow bag (diazotization method) of a Hash nitrite reagent powder
The specific embodiment is as follows:
example 1:
taking raw water from a certain drinking water treatment plant, marking as a sample 1, immediately filtering the raw water by using a filter membrane with the diameter of 0.22 mu m, and measuring total soluble organic nitrogen (TDN) and ammonia Nitrogen (NH) in the filtered sample3-N), nitrate Nitrogen (NO)3-N) and nitrous Nitrogen (NO)2-N) according to the formula DON (μ g/L, in N) ═ TDN- (NH)3-N+NO2-N+NO3-N) calculating the concentration of DONi(ii) a Then 2mL of the inoculation mother liquor MLSS with the initial concentration of 150mg/L and 200mL of the sample 1 are taken in a 250mL brown reagent bottle, mixed fully and shaken uniformly, and cultured for 14 days in a dark place at the constant temperature of 25 ℃. Under the same conditions, the blank test was supplemented with sterile water culture as a control group. Determining TDN, NH of the water sample after the culture3-N,NO3-N and NO2The value of N and the DON concentration calculated and recorded as DONfFinally, the BDON value is calculated, and the result is shown in figure 1.
Example 2:
taking reservoir water from a certain reservoir, marking as a sample 2, immediately filtering with a 0.22 μm filter membrane, and measuring total soluble organic nitrogen (TDN) and ammonia Nitrogen (NH) in the filtered sample3-N), nitrate Nitrogen (NO)3-N) and nitrous Nitrogen (NO)2-N) according to the formula DON (μ g/L, in N) ═ TDN- (NH)3-N+NO2-N+NO3-N) calculating the concentration of DONi(ii) a Then 2mL of the inoculation mother liquor MLSS with the initial concentration of 150mg/L and 200mL of the sample 1 are taken in a 250mL brown reagent bottle, mixed fully and shaken uniformly, and cultured for 14 days in a dark place at the constant temperature of 25 ℃. Under the same conditions, the blank test was supplemented with sterile water culture as a control group. Determining TDN, NH of the water sample after the culture3-N,NO3-N and NO2The value of N and the DON concentration calculated and recorded as DONfFinally, the BDON value is calculated, and the result is shown in figure 1.
Example 3;
a glycine solution with an initial mass concentration of 1mg/L (in terms of N) was prepared and recorded as sample 3, 2mL of an inoculum stock MLSS with an initial concentration of 150mg/L was added to 200mL of the glycine solution, and the mixture was incubated at a constant temperature of 25 ℃ for 14 days in the absence of light. Under the same conditions, the blank test was supplemented with sterile water culture as a control group. Determining total soluble organic nitrogen (TDN) and ammonia Nitrogen (NH) in the water sample after the culture3-N), nitrate Nitrogen (NO)3-N) and nitrous Nitrogen (NO)2-N) according to the formula DON (μ g/L, in N) ═ TDN- (NH)3-N+NO2-N+NO3-N) calculating the DONfAnd BDON, the results are shown in FIG. 1.
Example 4:
preparing a tyrosine solution with the initial mass concentration of 1mg/L (counted by N), recording as a sample 4, adding 2mL of inoculation mother liquor MLSS with the initial concentration of 150mg/L into 200mL of the tyrosine solution, and carrying out light-shielding culture for 14 days at the constant temperature of 25 ℃. Under the same conditions, the blank test was supplemented with sterile water culture as a control group. Determining total soluble organic nitrogen (TDN) and ammonia Nitrogen (NH) in the water sample after the culture3-N), nitrate Nitrogen (NO)3-N) and nitrous Nitrogen (NO)2-N) according to the formula DON (μ g/L, in N) ═ TDN- (NH)3-N+NO2-N+NO3-N) calculating the DONfAnd BDON, the results are shown in FIG. 1.
Example 5:
preparing 1mg/L (calculated by N) glutamic acid solution2mL of the inoculation mother liquor MLSS with the initial concentration of 150mg/L was added to 200mL of glutamic acid solution, and the mixture was incubated at a constant temperature of 25 ℃ for 14 days in the dark. Under the same conditions, the blank test was supplemented with sterile water culture as a control group. Determining total soluble organic nitrogen (TDN) and ammonia Nitrogen (NH) in the water sample after the culture3-N), nitrate Nitrogen (NO)3-N) and nitrous Nitrogen (NO)2-N) according to the formula DON (μ g/L, in N) ═ TDN- (NH)3-N+NO2-N+NO3-N) calculating the DONfAnd BDON, the results are shown in FIG. 1.
As can be seen from fig. 1, in the actual water sample, the BDON values of the sample 1 and the sample 2 are lower, and the BDON value of the water sample prepared from the amino acid solution is higher, so that actually, the amino acid standard is more easily biodegraded. Therefore, the determination method provided by the invention can also be used for determining the BDON value in a drinking water source.
The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and all the changes or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the appended claims.