экология/6. Экологический мониторинг

Zaytseva A.S., Yudina N.Yu., Arlyapov V.A.

Tula State University

BOD-biosensor based on yeast strain Debaryomyces hansenii immobilized on polyvinyl alcohol matrix modified by N-vinylpyrrolidone

Water-quality monitoring is an important aspect of water management because it assists in identifying the areas in need of restoration, the extent of pollution control required, and the efficacy of pollution control efforts. Biochemical oxygen demand (BOD) is one of the common indices of pollution in wastewater. In the conventional method the BOD value in water samples takes 5 days and requires complicated procedures and skilled analysts. Therefore, the method is unsuitable for short-term water-quality control.

A rapid method of BOD estimation bases on employing microbial sensors. The sensor consists of a combination of an oxygen electrode as a transducer and a bio-film. When organic compounds present in the samples are degraded by the microorganisms immobilized in the bio-film, dissolved oxygen is consumed and determined and this is designated as a BOD₅ value.

In this project a biochemical oxygen demand (BOD) sensor has been designed using immobilized yeast strain Debaryomyces hansenii. The immobilization was carried out by dropping a cell suspension onto the polyvinyl alcohol matrix modified by N-vinylpyrrolidone and then the bio-film was fixed to the oxygen electrode. It has improved characteristics of biosensor such, as reproducibility of the sensor responses, long-term stability and linear rage of calibration curve.

In these experiments, the glucose-glutamic solution (GGS) was employed as a standard solution for the calibration curve. Fig. 1 shows a calibration curve obtained using this sensor and the GGS.

Fig. 1. Calibration curve observed using the GGS. Error bar show the standard deviation of seven measurements.

A linear relationship (r² = 0,985) was observed between the sensor responses and the BOD₅ values from 0.2 to 180 mg l^-1. The reproducibility of the sensor responses was 4.2 % (average of relative standard deviations (RSDs)) in the calibration curve obtained by using the GGS. A slope of calibration curve of 0.0067±0.0003 min^-1 was obtained.

The receptor element metabolized various organic substances, which is advantageous for BOD measurements.

Fig. 2. Long-term stability of the BOD sensor. Error bar show the standard deviation of three measurements.

Fig. 2 shows the responses obtained be the BOD sensor after storage for 20 days. The sensor tip was stored at 25°C and 6.8 pH. The responses after 20 days decreased approximately half their original values. Thus biosensor works for 20 days well.

Table 1 shows the examination of real samples using the sensor and the conventional 5-day BOD method. Wastewater samples were taken from “Industry Service” ltd., untreated wastewater from supermarket “Stroydepo” and treated wastewater from “Vodokanal” ltd. In these measurements, the sensor response of different batches was calibrated using the GGS.

Table 1. Examination of real samples.

wastewater	The BOD value measured using designed biosensor / mg l^-1	The BOD value measured using 5-day BOD method / mg l^-1
“Industry Service” ltd.	11,1 ± 0,1	11 ± 2
Supermarket “Stroydepo”	61,6 ± 0,4	60 ± 10
“Vodokanal” ltd.	4,0 ± 0,2	3,5 ± 0,5

BOD values measured using the conventional 5-day method and the biosensor, were the same taking into account confidential interval.

Time of the analysis using mentioned equipment does not exceed 10 minutes. There is no need to attract skilled analysts for measurement. The designed BOD-sensor can be used for short-term water-quality control.

Finally, we have designed the BOD-biosensor, which can used at sanitary and epidemiological service, Department for Emergency Preparedness and Response, different ecological structures.

The work was supported by the Federal Goal-oriented Program “Scientific and Scientific-Pedagogical Cadres of Innovative Russia” for 2009–2013, State Contract No 16.740.11.0766 and a grant of the President of the Russian Federation for state support of young Russian PhD scientists, Agreement No 16.120.11.4341-MK.