HJ 347.2-2018Water quality - Determination of fecal coliform - Manifold zymotechnics (English PDF)

6.8 Disodium EDTA solution: rho (C10H14N2O8Na2·2H2O) = 0.15 g/ml

Weigh 15 g of disodium EDTA (6.6). Dissolve it in an appropriate amount of water.

Make its volume reach to 100 ml. This solution can be stored for 30 days.

7.3 Constant temperature incubator or water bath: The allowable temperature deviation

is 37 °C ± 0.5 °C, 44 °C ± 0.5 °C.

7.4 pH meter: Accurate to 0.1 pH unit.

7.5 Inoculation loop: 3 mm in diameter.

7.6 Test tubes: 300 ml, 50 ml, 20 ml.

7.7 Common laboratory instruments and equipment.

Note: Glassware and sampling equipment shall be wrapped, according to the requirements of aseptic operation before the test; sterilized by high pressure steam at 121 °C for 20 minutes, for later use.

8.1 Sample collection

The point layout and sampling frequency shall be implemented, in accordance with the relevant provisions of GB/T 14581, HJ/T 494, HJ/T 91.

When collecting microbial samples, the sampling bottle (7.1) shall not be washed by the sample. The sample shall be collected in a sterilized sampling bottle. The sampling volume of clean water bodies is not less than 400 ml. The sampling volume of other water bodies is not less than 100 ml.

When collecting surface water samples, such as rivers, lakes, reservoirs, it may hold the bottom of the bottle, to directly insert the stoppered sampling bottle into the water, at about 10 ~ 15 cm away from the water surface, with the bottle mouth facing the direction of water flow. Pull out the stopper, to let the sample flow into the bottle. Then cap the bottle. Remove the sampling bottle from the water. If there is no water flow, it may hold the bottle, to push it horizontally forward. The sampling volume is generally about 80% of the capacity of the sampling bottle. After the samples are collected, they are quickly wrapped with sterile wrapping paper.

When collecting samples from the faucet device, do not select a leaking faucet. Before collecting water, open the faucet to the maximum flow, to let the water run for 3 ~ 5 minutes. Then close the faucet. Use flame to burn it, for about 3 minutes, for sterilization; OR use 70% ~ 75% alcohol to sterilize the faucet. Turn on the faucet to the maximum, to let the water run for 1 min, to fully remove the retained impurities in the water pipe. When sampling, control the water flow rate to carefully let it flow into the bottle.

When collecting surface water, wastewater samples, samples at a certain depth, sterilized special sampling devices can also be used for sampling.

When stratified sampling is carried out, at the same sampling point, it shall be carried out from top to bottom, to avoid disturbance of different levels.

If a sample containing active chlorine is collected, add sodium thiosulfate solution (6.7), before sterilizing the sampling bottle, to remove the inhibitory effect of active chlorine on bacteria (add 0.1 ml of sodium thiosulfate solution per 125 ml volume). If the sample with high heavy metal ion content is collected, add disodium EDTA solution (6.8), before sterilizing the sampling bottle, to eliminate interference (add 0.3 ml of disodium

EDTA solution per 125 ml volume).

Note: 15.7 mg of sodium thiosulfate (6.5) can remove 1.5 mg of active chlorine in the sample;

the consumption of sodium thiosulfate can be adjusted, according to the actual active chlorine content of the sample.

8.2 Sample preservation

After sampling, it shall be tested within 2 hours. Otherwise, it shall be refrigerated below 10 °C but not more than 6 hours. After the laboratory receives the sample, if the test cannot be carried out immediately, the sample shall be refrigerated below 4 °C and tested within 2 hours.

9.1 Sample dilution and inoculation

9.1.1 15-pipe method

After thoroughly mixing the samples, add 10 ml of samples, to each of 5 test tubes (with an inverted tube), which contain 5 ml of sterilized triple lactose peptone medium (6.2), according to the requirements of aseptic operation. Add 1 ml of the sample, to each of

5 test tubes (with an inverted tube), which contains 10 ml of sterilized haploid peptone

9.2 Initial fermentation test

Incubate the test tube after inoculation (9.1) at 37 °C ± 0.5 °C, for 24 h ± 2 h.

When the color of the fermentation test tube turns yellow, it is acid production; when there are air bubbles in the small inverted glass tube, it is gas production. Test tubes, which produce acid and gas, indicate a positive test. If the gas production in the inverted tube is not obvious, it may gently tap the test tube. If there are small bubbles rising, it is positive.

9.3 Re-fermentation test

Gently shake the test tubes, that show positive or suspected positive (produces acid only, without gas production), in the initial fermentation test (9.2). Use an inoculation loop (7.5), which has been flame-burn sterilized and cooled, to respectively transfer the cultures into the test tube, which contains the EC medium (6.3). Incubate it at 44.5 °C

± 0.5 °C, for 24 h ± 2 h. All test tubes must be placed in a constant temperature incubator or water bath (7.3), within 30 min after transfer. Immediately observe it after the incubation. If it produces gas in the inverted tube, it is confirmed to be positive for fecal coliforms.

9.4 Control tests

9.4.1 Blank control

Perform a laboratory blank determination in accordance with steps 9.1 ~ 9.3, using sterile water (6.4), for each test.

9.4.2 Positive and negative controls

Prepare the positive strains of fecal coliform (such as Escherichia coli) and negative strains (such as Enterobacter aerogenes), into bacterial suspensions, which have a concentration of 300 ~ 3000 MPN/L. Respectively take the corresponding volumes of bacterial suspension, to inoculate it into the test tube, according to the requirements of inoculation (9.1). Then culture it, according to the requirements of the initial fermentation test (9.2) and the re-fermentation test (9.3). The positive strain shall show a positive reaction; the negative strain shall show a negative reaction. Otherwise, the measurement result of the sample is invalid. It shall find out the reason; make determination again.

10.1 Result calculation

When inoculating 12 samples, check Table A.1 in Appendix A, to get the MPN value of fecal coliforms per liter.

When inoculating 15 samples, check Table A.2 in Appendix A, to get the MPN value;

then convert the number of fecal coliform bacteria (MPN/L) in the sample, according to formula (1):

10.2 Result representation

The determination result is reserved to the integer place, with two significant figures at most. When the determination result is >= 100 MPN/L, it is expressed in scientific notation. When the determination result is lower than the detection limit, it is expressed as "undetected" or "< 3 MPN/L", for the 12-pipe method; it is expressed as "undetected" or "< 20 MPN/L", for the 15-pipe method. See Appendix B, for the recommended format of fecal coliform inspection records and reports.

11.1 Precision

6 laboratories carry out 6 repeated determinations, for the actual samples and certified standard samples of the fecal coliforms (concentration of 3670 MPN/L, acceptable range of 330 ~ 7710 MPN/L), which have 3 different concentrations: low concentration (groundwater, average concentration of 54 MPN/L), medium concentration (surface water, average concentration of 2.7 x 104 MPN/L), high concentration (domestic sewage, average concentration of 2.8 x 107 MPN/L): the relative standard deviation in the laboratory ranges from 2.3% to 3.8%, 2.0% to 11%, 1.1% to 5.4%, 5.1% to 17%, respectively; the inter-laboratory relative standard deviations are 3.4%, 11%, 1.6%,

5.4%, respectively; the inter-laboratory 95% confidence intervals are as shown in Table

2 .

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