Can sediment microbial fuel cells prevent the accumulation of porewater sulfide beneath aquaculture cages?

Aquaculture is one of the fastest-growing food sectors in the world and is expected to expand rapidly in the coming years as yields of wild capture fisheries decline. While aquaculture could relieve pressure on these fisheries it comes with its own environmental problems. In particular, the accumulation of organic waste on the seafloor beneath grow out facilities. The associated stimulation of microbial respiration results in a depletion of oxygen at depth, possibly to hypoxic or anoxic levels. The resulting shift from aerobic to anaerobic forms of metabolism, such as sulfate reduction, causes a corresponding release of hydrogen sulfide, which is toxic to multicellular organisms.

Here we wish to test the idea that sediment microbial fuel cells (SMFCs) may be an effective technique to guard against this fish-farm derived organic matter loading. In an SMFC a conductive material is placed in an anaerobic sediment and connected, via an electric circuit, to a cathode in the overlying oxygenated water column. Microbes catalyzing the anode carry out respiration by passing electrons to the anode, generating an electric current that transports these electrons to the cathode where the reduction half-reaction with oxygen occurs. This process essentially “short-circuits” the diffusion limitation that gives rise to anaerobic metabolism. Here we present a series of laboratory experiments that tests the effectiveness of sediment microbial fuel cells to prevent the accumulations of hydrogen sulfide in organic rich sediments and discuss its potential to improve the sustainability of the aquaculture industry.