what kind of equipment do you have available? Multimeter? potentiostat? Under which conditions do ypou hget the low currents - do you work at short circuit or at relatively large external resistance? 

Often it already helps to decrease the external resistance to achieve larger currents. 

HI,,,...

Potentiostat  is ok..

but, Still you need to menction the operational conditions .... as suggested by Dr Uwe Schröder

i work with multimeter. cultural conditions are similar to bacterial cultural coditions, room temperature. under these favourable conditions, i measure current by shortcircuit using multimeter. 

I assume that your MFC doesn't work properly. What do you use as substrate? Real wastewater? Acetate? In case of acetate, on should expect a current density of up to 1 mA/cm2 electrode surface area. In case of more complex substrates, the current density is lower. The total current should then be current density times electrode surface area.

Do you work with electrochemically active biofilms? Or what is your biocatalyst? How long do you wait that the biofilm is established? What is the cathode material? Do you use an open air cahtode or a submersed one? What is the electrode size? What is the distance between anode and cathode? Do you use a separator?.. There are many points that could be responsible for the very low system performance.

You can also send me information about all that to my email [email protected], then I can help finding the bottleneck in your system. 

Probably add the redox mediator to increase performance.