Study On The Optimization Of SMFC Operation Conditions In Natural Water

Microbial fuel cell (MFC) is a new bio-electrochemical technology, having the capacity ofdegrading organic substrates in the waste and generating electricity at the same time because ofwhich it has received great attention in recent years. MFC employs the electrogenesis bacteriaas catalyzer to degrade the substrates and release extracellular electronics converting thechemical energy directly into the electricity. Compared with the traditional MFC, sedimentmicrobial fuel cell (SMFC) is a device with its anode buried in the sediment and cathodesuspended in the aquatic environment. This unique structure make SMFC have greatapplication potential in the situ-bioremediation of polluted lakes and rivers. However, theapplication of SMFC is confined by its low output power density. In this paper, aiming atoptimizing the operation conditions and enhancing the performance of SMFC, the effect ofexternal resistance, environment conditions and additional conductive graphite fibers wereinvestigated systematically. The main research results are as follows:(1) Four scale-up SMFCs were buried in the natural water (31o29.160N,120o15.736E).The investigations of natural water quality and sediment character indicated that the DO, T andpH in the water fluctuated daily. The water conductivity and COD changed slowly and theorganic substrates in the sediment were well-distributed.(2) Effect of the different external resistances on the electricity generation and organicsremoval efficiency of the SMFC were studied. The results showed as follows: the outputvoltages of SMFC were increased with the increase of the external resistance. The SMFC-100exhibited the uppermost maximum power density,8.9mW/m2. The SMFC-100provided thehighest organics removal efficiency(LOI),38±4.7%.(3) Effect of the environment variations on the electricity generation and sedimentcharacters of the SMFC in natural water were studied. The results showed as follows: Thetemperatures of anodic sediments and DO concentrations of water around the cathodesremarkably affected the electrogenesis and organics removal efficiency of SMFC. Runing innatural waters, the restrictive temperature and DO for SMFC were6.4oC and4.7mg/L,respectively. Furthermore, after long-term running, the pH and LOI of sediments on the surfacesof the anodes obviously decreased whereas the electrogenesis bacteria could only utilize theorganics in the sediment contacting and near the anode surfaces.(4) Effect of graphite fibers on the electricity generationand substrate degradation of theSMFC were studied. The results showed as follows: the performance of SMFC can be improvedby simply mixed the anode sediment with graphite fibers which are low cost and chemicalstabilization. The SMFC mixed with5g fibers showed the output voltage and COD removalefficiency, which were154mV and44.6%, respectively.