Application of microbial agents in the rapid detector for BOD in the wastewater from ships

Abstract:

Objective To develop a rapid detector for biochemical oxygen demand (BOD) in the wastewater from ships entering ports in response to the stringent mandates of the International Maritime Organization (IMO). The objective is to facilitate swift detection of domestic wastewater produced by the multitude of vessels arriving at the port.Methods When testing the BOD standard solution, Clostridium butyricum and Bacillus subtilis were used to manufacture the biosensitive elements inducing electron transfer during the consumption of dissolved oxygen (DO), which led to a change in electrical conductivity (COND). By treating dissolved oxygen as a pivotal indicator and an intermediary in the monitoring process, this study explored the correlation between changes in electrical conductivity and sample concentration. Through the development of a quadratic polynomial fitting model that correlates electrical conductivity with dissolved oxygen levels, and by establishing a connection between dissolved oxygen and sample concentration, this research delves into the correlation between variations in electrical conductivity and the concentration of the sample.Results The changes in electrical conductivity exhibited by different solutions enabled the detector to rapidly distinguish between the wastewater with a BOD concentration higher than 25 mg/L (the slope of the COND variation value is less than -0.01) and that below 25 mg/L (the slope of the COND variation value is greater than -0.01). By establishing a highly correlated fitting curve between dissolved oxygen and electrical conductivity (coefficient of determination R²=0.977 83), this study achieved precise reading of samples within the ultra-low concentration range (BOD<25 mg/L). The accuracy rate of the measurements exceeded 85% in the in-suit tests conducted in Qinhuangdao, Hebei, China.Conclusion The measurement data read by the rapid detector for BOD is highly consistent with the results obtained by the dilution inoculation method. Moreover, the detector is capable of performing rapid quantitative analysis of BOD in domestic wastewater from ships entering ports within 30 min, demonstrating high detection efficiency.