Study On Key Measures To Improve The Performances Of Microbial Fuel Cell-based BOD Sensor

Biochemical oxygen demand (BOD) is a comprehensive index to evaluate organic matters in wastewater. The traditional standard 5-d method is the standard method for detection of BOD concentration, which has defects such as time-consuming and poor results reproducibility. Microbial fuel cell-based BOD sensor is a new method for the fast detection of BOD5, which has advantages of strong stability, wide detection range and others.In this research, further exploration was taken on the method to improve the detection performance of the mediator-less double-chamber microbial fuel cell-based BOD sensor, by modifying the anode material, replacing the types of electrode materials, optimizing the concentration of the cathode electron acceptor. In addition, by simulating actual wastewater, the feasibility of MFC-based BOD sensor in detecting the actual wastewater was investigated during the stable operation of MFC. Besides, the anodic microbial community structure was analyzed by PCR-DGGE technology.The nitric acid acidification was used for modification of graphite felt, the contact angle of graphite felt decreased significantly after nitric acid treatment for 4 h. When using acid-treated graphite felt as the electrode material and dissolved oxygen as electron acceptor graphite felt to construct MFC, and the appropriate test conditions were investigated. The results showed that optimal detecting conditions were: the cathode flow was set as 30 mL/min, the content of buffer solution and L-cysteine in waste water were 50 mL/L and 20 mg/L respectively. The detection range of BOD sensor range was from 2 to 100mg/L, with good data repeatability, and response time was all less than 10 h. The BOD concentration can be detected based on the linear correlation between BOD concentration and maximum current within a range from 2 to 50 mg/L, and the BOD concentration ranged from 2 to 100 mg/L could be tested based on the linear correlation between BOD concentration and charge generation.A MFC-based BOD sensor was constructed with carbon brush as the electrode material, dissolved oxygen as the cathode electron acceptor. With the optimized testing conditions, BOD concentration was detected. The detection range of BOD sensor was 2-100 mg/L, with good data reproducibility. The sensor could be used to determine BOD concentration of 2-60 mg/L, which supported by the good linear between peak current and BOD concentration, and the response time was all less than 2 h. The BOD concentration could be detected based on the linear correlation between BOD concentration and charge generation with a range of 2～100 mg/L, response time was all less than 12 h.Using acid-treated graphite felt as the electrode material, H2O2 solution as cathode electron acceptor, test conditions of BOD sensor were also optimized:The dosage of L-cysteine in the artificial wastewater as oxygen absorbent was optimized for 20 mg/L; The optimal dosage of phosphate buffer used to maintain pH of the anode compartment in the artificial wastewater was set at 50 mL/L. H2O2 concentration of 0.5 mmol/L was used for cathode electron acceptor, the BOD test range was 2-200 mg/L; When H2O2 concentration was 1.0 mmol/L and 1.5 mmol/L, BOD test range was 2～300 mg/L and 2～500 mg/L respectively. Within the scope of their respective BOD detection, response time was less than 4 h. By dosing tertiary butyl alcohol into catholyte of hydrogen peroxide indirectly, it was proved that hydrogen peroxide generated hydroxyl radical species which has a high oxidation potential during operation of MFC and the hydroxyl radical species participated in the cathodic reaction.In order to achieve the purpose of rapid detection accurately, selecting the acid-treated graphite felt as electrode materials, H2O2 as the cathode electron acceptor. Flour was added into the wastewater as a representative of the suspended biodegradable organic matter, and glucose as the soluble biodegradable organic matter which could be degraded by microbial flora on the anode, thus increased the electric current and the response time. The microbial community structure on the anode was studied by PCR-DGGE technology, which was composed of 8 kinds of electricity production bacteria and 8 kinds of others. Two strains were in mutual symbiosis relationship.