Study On Microbial Electrochemical Technology For Water Alert System

On-line water alert system is critical to protect the ecological safety as well as the general public health.The microbial electrochemical technology?MET?based water quality early warning is a new biological early warning technology.The existence of toxic agents could inhibit the metabolism and also the extracellular electron transfer?EET?process of electrochemically active microorganism,and thus trigger a warning when the change of electrical signal output reached to a certain level.One of the most basic forms of MET sensors is the microbial fuel cell?MFC?sensor.The practical usage of MET for water quality early warning is partly restricted by the low sensitivity and the problem of false negative.Low sensitivity is reflected as the high concentration of the detection limit and also the long response time.False negative is caused by the combined shock of organic matter/toxicant.This study optimized reactor structure of microbial electrochemical sensor device and also the control mode of external circuit to improve the sensitivity.In addition,a novel MFC sensor based on the biocathode sensitive element was constructed to address false negative.Finally,the performance of the MET based water quality early warning system was evaluated during the on-site monitoring of a local wastewater treatment plants.This study applied the flow-through anode in MFC sensor to stimulate the mass transfer process.Results revealed that the sensitivity increased by 15-41times herein,compared to that with flow-by anode.A cathode-shared MFC sensor array was designed.Miniaturization could shorten the response time as suggested mass transfer stimulation,while cathode-shared configuration could improve the detection credibility by eliminating the difference of the cathodic performance.This study optimized two typical steady state control modes,i.e.,the constant external resistance?CER?and constant anode potential?CAP?.It was found that the sensitivity of MFC sensor under the CAP mode was 2-10 times higher than that under CER mode.Under the CAP mode,the optimal anode potential was approximately-0.15 V.This study further provided a new transient-state operation mode for MFC sensor for the first time,which was proved applicable for three kinds of pollution detections?organic matter,pH and heavy metal?with the sensitivity increased by 50%-247%.It was found by equivalent circuit analysis that the MFC sensor under transient-state operation mode was sensitive to the change of both activation resistance(R_ct)and capacitance of membrane(C_in),while the MFC sensor under traditional steady state operation was sensitive to the change of R_ct only.This work for the first time demonstrated the availability of the biocathode sensing element for MFC sensor based early warning device.Using the biocathode sensing element,the sensor's sensitivity increased by 1-15 times at formaldehyde concentration range of 0.0005%⁰.01%.The biocathode sensing element decreased the warning failure when challenged by a combined shock of organic matter/toxicant.In this study,a novel MFC sensor with gas diffusion?GD?-biocathode sensing element was fabricated,which could be directly used for the monitoring of both aerobic and anaerobic water bodies and could largely increased the application range of MFC sensors.The performance of the MET based water quality early warning system,was evaluated during the on-site monitoring of a local wastewater treatment plants.Wireless data transmission was realized for remote transmission of monitoring results and warning signal.For a biocathode MFC sensor,when the COD raised to 320 mg/L,an early warning signal is triggered within 40 minutes.For the bioanode MFC sensor,when the inlet was added with 0.1%of formaldehyde,the early warning signal is successfully triggered within 10 minutes.The recovery strategies for biocathode MFC sensor and bioanode MFC sensor were proposed respectively.