# An Approach to Predicting Sediment Microbial Fuel Cell Performance in Shallow and Deep Water
## 3 Results  
### Shallow Water Predictions (<100 m)  
Figures 1 and 2 (previously published in [13]) show a general approach to estimating MFC continuous power output in San Diego Bay. Output in response to variable TOC as percent weight in the sediment and water temperatures can be applied to sediment TOC maps and seasonal temperature distributions to derive seasonal estimates of MFC power employing a 1 m\({}^{2}\) anode. These estimates can be used as an engineering constraint when designing sensor and communications gear for marine deployment. Herein we illustrate this approach to predict MFC power output in two shallow water environments (the Gulf of Mexico and the Yellow Sea) during the summer and winter, and in the deep sea where seasonal temperature changes are not considered important. Figure 1: General approach used to predict in situ sediment MFC power potential. Empirical data with varying anode sizes, water temperature, and sediment percent TOC were normalized to consider the performance of a 1 m\({}^{2}\) anode with variable temperature and TOC. Figure 2: Predicted MFC power potential in San Diego Bay from a 1 m\({}^{2}\) anode and \(\sim\)700 known sediment TOC concentrations (black dots) and seasonal water temperatures. Power density from shallow sediments was calculated by applying three equations sequentially:  
\[\text{Power density}=4.62\,\text{ln(TOC)}+13.8\,\text{(mW/m^{2}}\text{ at 20 }^{\circ}\text{C)} \tag{1}\]  
\[\text{Power density}=0.65\,\text{*}\,\text{(}^{\circ}\text{C)}-6.5\,\text{(mW/ m^{2})}\text{ (independent of TOC)} \tag{2}\]  
\[\text{Power density}=-0.89\,\text{*}\,\text{ln(cm^{2})}+15\text{ (field probe was 2.6 cm^{2} graphite)} \tag{3}\]  
The Equation (1) first relate power density output to TOC as measured with a small graphite anode at 20 \({}^{\circ}\text{C}\) in the field, then (2) relate power density to in situ bottom temperatures, and (3) scale expected power density to a 1 m\({}^{2}\) anode. We illustrate this approach to predicting MFC performance in the Gulf of Mexico based on our measured performance curves and environmental data (Figures 3-6). Figure 3 shows sediment TOC sample locations overlain on bathymetry off the south Texas coast. The bathymetry is from a high-resolution coastal relief model [16]. Locations of sediment samples are from the South Texas Outer Continental Shelf Project (STOCS) conducted by the University of Texas and the USGS with funding from BLM/NOAA. The USGS analyzed the geochemistry of sediment and suspended sediment, clay mineralogy, and physical properties from 264 samples collected from 26 October 1974 to 21 December 1974. The data are available online [17]. Figure 4 shows the interpolated TOC in surficial sediment as percent weight. Data were interpolated using Golden Graphics Surfer TM software using a kriging algorithm. Figure 5 shows bottom water temperatures taken from numerous XBT and CTD casts whose locations are shown as black dots. Bottom temperatures rise approximately 10 \({}^{\circ}\text{C}\) from February to August. Figure 6 shows the calculated power density with a 1 m\({}^{2}\) anode. The power density varies spatially from approximately 1 to 10 mW/m\({}^{2}\), and increases by about 1 to 2 mW/m\({}^{2}\) from February to August, due to seasonal increases in water temperature. Figure 3: Sediment TOC collection sites off the Texas coast. Figure 4: Interpolated sediment TOC concentrations off the Texas coast. Figure 5: Bottom water temperatures in February (**left**) and August (**right**) off the Texas coast. We similarly predicted MFC performance in the Yellow Sea between China and South Korea (Figures 7-10). Figure 7 shows the bathymetry in the Yellow Sea. Bottom depths were taken from \(-\)10,000 CTD and XBT casts where bottom depth was noted. Data are available online from NOAA [18]. Figure 8 shows sediment TOC sample locations and their interpolated values. The TOC data are from the Naval Oceanographic Office (NAVOCEANO) unclassified collection and available upon request.