Ammonium Removal and Electricity Generation by Using Microbial Desalination Cells
Figure 13. Resistance decade box been added to the cuvette (LCK 302 cuvette ranging from 47 -130 mg/L of NH4-N, Figure 12) and been shacked; fourthly, 15 minutes was for cooling and then tested in the spectrophotometer. The value will be finally shown in the screen and NH4+ concentration can be calculated. 4.2.5. Incubator Incubator is a container that provides a constant temperature (adjustable) so as to ensure a stable growing environment for microorganism. Usually the incubator used in the laboratory is electric heating, but the old method of using hot water may also achieve the heating function. At the Hammarby SjĂśstadsverk Laboratory (as shown in Figure 11), electrical heating made by MEMMERT, Germany is used. During the experiment, incubator was used when membrane required to be soaked in DI water before 24 hours of usage. 4.2.6. Resistance decade box Resistance decade box is a device that can change external resistance and at the same time the resistance value can be displayed. By connecting it to the MFC/MDC circuit, external resistance can be adjusted to test internal resistance. In this MDC experiment, internal resistance is required to be measured not only because it is a key factor that affects electricity generation, but also reflects the advantages/drawbacks of MFC/MDC structures and membrane block effect. Generally, when the external resistance equals to the internal resistance, the value of maximum power density Pm will reach the peak.
Pm 
E2 4 Ri
where
Pm =
Maximum power density
E = Ri =
Electromotive force Internal resistance 17