Microbial Sensor Determination of BOD Experiment

Summary

Environmental protection, the evaluation of water quality organic pollution and sewage treatment efficiency of the important indicators BOD (biochemical oxygen demand), that is, biochemical oxygen demand, the standard dilution method (BOD5) to determine the 5 d, time-consuming and inconvenient, with microbial sensors to determine the 15 min will be able to complete, fast, simple. Source: Microbiology Laboratory (Third Edition)

Operation method

basic program

Principle

Microbial sensor equipment consists of an immobilized microbial cell membrane, electrodes, amplifiers and recorders. The basic principle of the microbial sensor for BOD measurement is that when the bio-oxidizable organic matter exists in the measured water, the microorganisms within the immobilized membrane switch from endogenous respiration to exogenous respiration, which decreases the partial pressure of oxygen around the immobilized membrane due to oxygen depletion and thus alters the strength of the output current of the oxygen electrode, which varies with the concentration of BOD and shows a linear relationship within a certain range. Schematic diagram of a microbial sensor for BOD measurement 1. Figure 1 Schematic diagram of a microbial sensor for BOD measurement

Materials and Instruments

Wastewater Samples
BOD Standard Solution Phosphate Buffer
Microbiological Sensors MS-1 BOD Analyzer Microsampler Liquid Dosing Bottle Thermal Sink Magnetic Stirrer

Move

1. Instrument adjustment

1.1 Operate according to the instruction manual of the instrument, after turning on the power, preheat for 20 min, keep constant speed stirring, and control the temperature of water bath at 29±0.5 ℃.

1.2 Calibrate the oximeter to the mechanical zero point.

1.3 Turn the sensitivity knob of the oximeter and fine-tune the sensitivity adjustment so that the sensor input signal reaches the fullness, i.e., the instrument pointer points to 200 mmHg (1 mmHg = 133.22 Pa) or 21%.

1.4 Observe for 2 min, and when there is no drift of the pointer or the baseline drawn by the recorder is flat, the micro-sampler can be used to add samples for measurement.

2. Plotting the standard curve

2.1 Add 2.5, 25, 51 and 78 ul of BOD standard solution into a measuring cup containing 5 ml of phosphate buffer with a micro-sampler, and the final concentration of BOD is 1, 10, 20 and 30 mg/L, respectively.

2.2 Note down the number of readings (mmHg) and the time (min) from the beginning of the addition of the sample until the pointer re-stabilizes, the stabilization is judged by the pointer no longer oscillates or the line plotted by the recorder re-straightens within 2 min.

2.3 Plot the standard curve on the coordinate paper, the vertical coordinate is the value of the decline in readings, and the horizontal coordinate is the _BODG, i.e., the BOD value of the GGA solution measured by the microbial sensor.

3. Determination of wastewater samples

3.1 Preheat the sample in a small glass at 282℃ for 5 min.

3.2 Take 100 ul of wastewater sample with a micro-sampler and add it to the measuring cup containing 5 ml of phosphate buffer; if the concentration of wastewater is too high (BOD>2000 mg/L), it should be diluted appropriately before measurement; if the concentration of wastewater is too low (BOD<100 mg/L), the volume of the sample can be increased, but it should not be more than 500 ul (i.e., not more than 10% of the overall Hovenia of the measuring solution).

3.3 After the instrument pointer is stabilized again, write down the reading. Then check the corresponding _BODG value from the standard curve, and then calculate the _BODM value of the sample according to the following formula.

_BODM (mg/L) = _BODG/ [ Volume of sample × (volume of buffer + volume of sample)

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