Construction And Primary Investigation Of Nitrogen Removal And Power Generation On Photocatalysis-microbial Fuel Cells

The discharge of nitrogen contaminated wastewater is an important reason for the pollution of bodies. Based on the new concept, microbial fuel cells(MFCs) supply the possibility of nitrogen removal and electricity generation, simultaneously. Ammonia is the main form of nitrogen in the wastewater, through the literature analysis, it is found that the easiness of denitrification and difficulty of nitrification in the MFCs severely restricted the application of this technology. According to this problem, a kind of novel MFCs system called photocatalysts microbial fuel cells(Photo-MFCs) is designed by connecting photocatalysis to the traditional MFCs. P-and n-type photocatalysts are used to realize the separation and enrichment of photogenerated holes and electrons. Holes, which have strong oxidizing, can strengthen the nitrification in the anode chamber, while electrons, which have strong reducibility, can strengthen the denitrification in the cathode chamber. Thus, Photo-MFCs can solve the nitrification problem, which is the technical bottleneck of traditional MFCs. At the same time, Photo-MFCs can couple the nitrogen removal to the electricity generation, thus, improve the power output of MFCs. In this study the effect of organic matters, ammonia and nitrate concentration on nitrogen removal and electricity generation of Photo-MFCs were studied respectively under the conditions of organic matters and ammonia as the mixed substrate and ammonia as the sole substrate. The effect of photocatalysis strengthen on nitrogen removal and electricity generation of Photo-MFCs were also studied. Finally, this study analyzed the transformation and migration of nitrogen and electron transfer process. The main conclusions are as follows:â‘  With the decreasing concentration of organic matters, nitrogen removal and electricity generation of Photo-MFCs are declined when organic matters and ammonia as the mixed substrate. When the concentration of influent organic matter decreased from 122±2.8mg/L to 0, the removal rate of total nitrogen in Photo-MFCs is reduced by 2.74 times, and the current decreased from 1.06 m A to 0.16 m A during 12 hours. Low concentration of organic matters is benefit to nitrification in the anode chamber. In the anode chamber, he ammonia removal amount is increased from 6.3±2.70mg/L to 11.5±0.70mg/L, and the cumulant of nitrate is increased from-0.7±1mg/L to 6.7± 0.7mg/L in the absence of organic matters.â‘¡ Nitrogen removal and electricity generation are still realized when ammonia as the sole substrate. Ammonia concentration have significant influence of nitrogen removal and electricity generation in Photo-MFCs, and the nitrate concentration have no obvious effects. With the increasing concentration of ammonia in the anode, the nitrogen removal and electricity generation are first increased and then decreased, Photo-MFCs have the best effect of nitrogen removal and electricity generation when the ammonia concentration is 70mg/L. The maximum ammonia removal amount and nitrate cumulant are 19.3 mg/L and 15.41mg/L in the anode chamber, respectively; The removal amount of nitrate and total nitrogen are 22.3 mg/L and 17.1 mg/L during 12 hours, respectively; And the maximum electric current is 0.042 m A, the maximum power density is 3.68μW /m2.â‘¢ When ammonia as the sole substrate, nitrate is the main product in the anode, accounting for approximately 62.6% of the ammonium consumed. Nitrite accounted for 7%, and approximately 0.9% of ammonium is consumed by diffusion to the cathode. The remainder may have been consumed by volatilization or assimilation by microorganisms. In the cathode, nitrogen is the main product of the nitrate consumed, and only a little nitrite accumulated.â‘£ Illumination is contribute to promote the effect of nitrogen removal and electricity generation. During 12 hours the nitrification rate is increased from 0.58 to 1.34 mg/(L h), and the denitrification rate is increased from 0.5 to 1.2 mg/(L h) under the UV irradition. In addition, the current generation increases from 0.012 to 0.032 m A(an average current). Illumination can increase the redox potential of electrode, are benefit to nitrification and denitrification. The voltage between the two electrodes of Photo-MFCs is increase from 20 to 72 m V under the UV irradition. The electron transfer process is: ammonia â†' nitrifying bacteria â†' n-type semiconductor â†' p-type semiconductor â†' denitrifying bacteria â†' nitrate â†' nitrogen.