**2. Algal fuel cell configuration**

AFCs are electro biochemical devices which have anode and cathode compartments enclosed with a photosynthetic microorganism. Here photosynthesis is carried out and they act as electron donors producing organic metabolites. The main objective of configuring AFC is to increases the power density and achieving high performance in order to create a cost effective system. Major configurations of AFC are a single chamber, two chambers, three chambers, coupled and sediment types.

In single chamber AFC, bacteria and microalgae are grown together in one chamber which is membrane less wherein micro-algae forms a biofilm on the anode and some are usually configured with an air cathode [7, 8]. Carbon dioxide generated by autotrophic and heterotrophic organisms are consumed simultaneously by algae in the same chamber. In single chamber AFC, bacterial co-cultures are grown synergistically with algal co-cultures [9]. Single chambers are easy to manage in lab when compared to other configurations. Single chamber AFC are easy to operate, cost effective in scaling up and can be used commercially.

Dual or two chambered AFC consists of two separate chambers in which microalgae and bacteria are separated by a membrane [10, 11]. In two chambered configuration, cathodic compartment contains microalgae that are illuminated for photosynthesis reaction. The anodic compartment is also illuminated making the algae to cover the bacterial compartment in most of the studies. Highly relative internal resistance and crossover of the membrane are some issues are associated with this system.

Three chambered MFCs are an additional chamber containing salt water that gives stress to the production of power. The third chamber is in between the cathode and anode chambers. Partial desalination is observed in the middle chamber where cations move towards cathode and anion towards anode [7].

In sediment AFC, an anode is buried in sediment and a cathode is on the top of sediment immersed in the water having microalgae. The differences in existing electro-potentials generate energy [12, 13]. During this process the released electrons are captured by the anode and current is generated in an electrical circuit. In this configuration, cathode compartment was changed to biogenic one.
