Simultaneous Treatment Of Salt Ammonia Wastewater And Electricity Generation Using A Bio-cathode Microbial Fuel Cell

The bio-cathode microbial fuel cell (BCMFC) using microorganisms as catalysts, is one of researches hotpot of microbial fuel cell in recent years, which can remove multiple contaminants simultaneously. In this study, BCMFC was utilized which anode chamber effluent was directed into intermittent aeration cathode. The nitrification-denitrification reaction occurred in the cathode. BCMFC can degrade pollution and generate energy at the same time. Taking salt with ammonia wastewater as target pollutant, at the first stage, BCMFC performance was optimized:influence of external resistance, salinity, dissolved oxygen (DO), hydraulic retention time (HRT) and carbon nitrogen ratio were discussed on the removal of carbon and nitrogen and the electricity generation in the BCMFC. At the second stage, the kinetic equations of COD degradation in the anode and ammonia removal in the cathode were fitted, and the influence of different operating conditions on the performance of BCMFC system was analyzed. At the third stage, the effect of salinity and DO on the nitrifying denitrifying enzyme was investigated. With the experiments, conclusions are given as follows.(1)The best operation condition was that seawater proportion was 10%, external resistance was 500 Ω, DO was 4.0-5.0 mg/L, HRT was 20 h,and carbon and nitrogen ratio was 25:1. When the influent ammonia concentration was 70 mg/L, the concentration of COD was about 1600 mg/L, the removal rate of ammonia nitrogen was about 95.76%, the removal rate of COD was 99%, total nitrogen removal rate was 80.11%, the maximum output power was 1536 mW/m3, the maximum current density was 3200 mA/m3, and the resistance was 224 Ω.The salinity and DO were the major factors which affected the performance of BCMFC.The performance was not obviously affected at 50% seawater proportion, while the effects of COD and ammonia removal were deteriorated at the 70% seawater proportion:the COD, ammonia and total nitrogen removal rates were 85%、 66.67% and 52.55%, respectively. And electricity generation of BCMFC was declined: the maximum output power density was 175mW/m3,the maximum current density was 1363 mA/m3, and the resistance was 1354 Ω. As the DO increased from 0.2 mg/L to 7.0 mg/L, the electricity generation of BCMFC was increased at 10% seawater proportion. The maximum output power density increased from 57 to 2500 mW/m3, the internal resistance was reduced from 2380 to 165Ω.(2) The results of dynamic optimal operating conditions were as follows: degradation of COD and ammonia were conformed to the first-order reaction kinetics. The anode degradation of COD equation was y=-0.123x+0.0771 and the regression coefficient R2 was 0.983. The ammonia nitrogen removal equation was y=-0.00625x+0.0728, the regression coefficient R2 was 0.968.Under the influence of salinity, anodic COD degradation was fitted first-order kinetics, and the corresponding reaction rate constants at 10% seawater proportion (0.123) was the highest, which was 2.41 times higher than of 70% seawater proportion (0.051). Cathodic ammonia removal reaction order was changed from the first-order to the second-order when the salinity was increased to 30% seawater proportion. The second-order reaction rate constant was declined from 9.92×10-5 (30% seawater proportion) to 1.20×10-5 (70% seawater proportion).It indicated that salinity had little effect on the anodic COD degradation and had a greater impact on the cathodic ammonia removal.With the increase of DO, anodic COD degradation was basically in accordance with the first-order kinetic equation, and the rate constant of COD for 7mg/L was 4.6 times of DO for 0.2 mg/L. It investigated that the effect of DO on the anodic COD degradation was greatly affected. The reaction rate constant of DO for 4.6mg/L was close to DO for 7mg/L. Cathode ammonia removal basically conformed to the first-order kinetics, reaction rate constant increased with the increase of DO. The first-order reaction rate constant of DO for 7mg/L was 10.5 times of DO for 2mg/L.Compared dynamic power function model with Monod model, the Monod model had poor fitting correlation, which was not suitable for fitting the COD and ammonia degradation process.(3)The nitrification and denitrification process was obviously affected by salinity.High salinity would cause nitrite accumulation, and affected the activity of ammonia monooxygenase (AMO). High salinity influenced denitrification process, which made nitrate reductase (NR) and nitrite reductase (NIR) activity in different at the case of high salinity. The effect of dissolved oxygen on the AMO was little, but the effects on nitrite oxidoreductase (NOR), NR and NIR activity were obvious.