Microbial desalination cells (MDCs) provide for simultaneous wastewater treatment and desalination while producing clean electricity from the organic wastes. However, one major drawback with MDCs technology is its unsustainable cathode chamber where expensive catalysts and toxic chemicals are employed for electricity generation, similar to other bioelectrochemical systems. Introducing biological cathodes may enhance the system performance in an environmentally-sustainable manner. This study describes the use of algae as sustainable biocatalyst/biocathode in photosynthetic MDCs. Since alga is a photosynthetic microorganism, the availability of light as well as the electron-donating anodic process may have significant effects on the biocathode performance. A series of experiments evaluating these effects proved that algae perform better under natural light/dark cycles and that higher COD concentrations do not necessarily improve the power density. A maximum power density of 1.1 W/m(3) NCC (0.77 W/m(3) NAC) was observed for a COD concentration of 500 mg/L while the same for 1000 mg/L of COD was 0.987 W/m(3) NCC (0.69 W/m(3) NAC). This study confirms the beneficial use of algae as a sustainable and photosynthetic biocathode in MDCs to supply electron acceptors in an environmental-friendly manner. (C) 2014 Elsevier B.V. All rights reserved.