Microbial fuel cells (MFC's) have been operated with manifold substances. Experiments with municipal wastewater, swine wastewater and even brewery wastewater had been successfully conducted. In previous studies the application of separated urine, with its comparable high energy content, showed breakdown of electricity generation. Studies with MFCs showed inhibition e ects due to salinity, ammonium concentration or pH. Which of these factors in urine is limiting, was to determine in this study.
For these experiments a two chamber MFC with graphite electrodes was used. At the cathode a ferricyanide solution was used as nal electron acceptor. In the startup ammonium concentration was low in the anode solution and pH was set to 7 with the help of a phosphate bu er. Ionic strength was from the beginning as high as in urine. Acetate was used as substrate and electron donor. After a certain power output was reached ammonium was continuously increased until the maximal concentration of 6.35 gN/l. In the next experiment pH was stepwise increased from pH 7 to pH 9.
Current generation showed a strong temperature dependence. It could be modeled well by the arrhenius approach. Power output was therefore doubled by an increase of temperature from 15 °C to 25 °C. Maximal power density of the cell was 180 mW/m². An increase of ammonium concentration to 6.35 gN/l did not lead to a breakdown in power output as in earlier studies. Though a slight decrease in power output was observed, it is not clear if that was caused by the ammonium concentration. The increase of pH from 7 to 9 lead to an increase of power output from 1.3 to 8.2 mW/m². An ammonia concentration up to 3.4 gN/l did apparently not have an e ect on exoelectrogenic bacteria.
All the tested parameters did not inhibit power output substantially. Therefore urine treatment with microbial fuel cells still seems to be a practicable solution even tough other possible inhibitory factors must be checked and stored urine has to be applied as well.