The application of fresh water algae to produce electricity in saline water media

Abstract

Currently, there is an increased need for renewable energy resources to combat the rapid depletion of fossil fuels. Bio-photovoltaic (BPV) cells represent an environmentally friendly means of electricity generation from photosynthetic organisms such as algae. However, the applicability of scaling up BPVs to fit larger operations has been a challenge. This research presents a novel, simple and cost-effective chamber-less BPV that can be easily applied on a large-scale. The research also examined the effects of electrode spacing, height of the cell and water salinity on the performance of the BPV. Chlorella Vulgaris alga was cultured using UST medium, and was allowed to form a biofilm on a stainless steel anode. The chamber-less design consisted of three parallel and transparent acrylic plates (10 cm x 20 cm) positioned one on top of the other; a base, a middle plate holding the anodic biofilm and a top plate with a 4cm x 5cm opening in which a graphite air cathode settled. Light could reach the biofilm on the middle plate through the transparent top plate. The three plates were supported together by two acrylic rods, which allowed easy adjustment of electrode spacing and cell height. Current intensity was measured under different cathode-anode spacing distances, heights and salinities. The BPV device produced maximum outputs at a spacing, height and salinity of 2 cm, 15 cm and 20000 TDS respectively. The highest power produced from the device was 0.12 W/m2. Spacing negatively correlated with power output (R=-0.556) while height and salinity correlated positively (R=0.938, R=0.793 respectively). A salinity of 40000 TDS, however, caused a reduction in electric current after 15 minutes, which indicates that Chlorella Vulgaris malfunctions at higher salinities. The low-cost, easy-maintenance, chamber-less design of this BPV qualifies it for large scale practice. Additionally, increased power outputs at greater heights and salinities highlights its potential use in brackish waters or deep ponds.