Feasibility of Generating Renewable Energy from Wastewater Treatment Process Using Microbial Fuel Cells: The West Bank as Case Study

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An-Najah National University
Microbial fuel cells (MFCs) technology, is an innovative and relatively new technology by which organic matter can be simultaneously biodegraded anaerobically and generate electrical energy directly. MFCs can be used in various applications such as: water desalination, biosensors as well as water and wastewater treatment. Through this study, MFCs as a wastewater treatment system was investigated for the first time in Palestine. Palestine is a developing country that suffers from improper wastewater collection and treatment systems in addition to water supply shortage that can cause increasing organics concentrations in the discharged wastewater. MFC model used in this research was double chambered-MFC (DS-MFC), it was operated by primary effluent wastewater as substrate, salt bridge was used as proton exchange media and water saturated of dissolved oxygen was used as cathodic solution. This research consists of two main parts: First, investigation of many parameters that may affect MFCs efficiency, such as: electrode material type, electrode size, salt bridge diameter, type of salt solution that used in salt bridge and concentration of salt solution used in the salt bridge. This part was conducted by constructing and operating different MFCs to investigate each parameter (variable) individually. All conditions, except the concerned parameter, were fixed for each parameter experiment. Three duplicates-MFCs for each variable value were used to obtain reliable results. Output open circuit voltage (OCV) was measured one time per day and for one week for each variable and then the obtained output voltage data were analyzed as a trial to find the most suitable conditions. The second part is aimed to understand and model the relationship between COD of substrate in MFC at any time and output voltage from the MFC at the same time in addition to define the kinetic reaction order of COD removal process. Four different COD-MFCs were constructed, three duplicates for each. Initial COD value was approximately fixed for each 3 duplicates, and other parameters were set and fixed as found from the first part of this research. After 15 days-startup period the MFCs were operated for 30 days. COD was measured for the twelve MFCs each two days and output voltage was measured each 24 hours. Analysis of the obtained data from performed experiments, showed that MFCs with copper electrode produce output voltage significantly higher than MFCs with carbon brushes electrodes which, in turn, achieved output voltage significantly higher than both that achieved by MFCs with zinc electrodes and MFCs with manufactured carbon electrodes. It was found that diameter of salt bridge affects the output voltage of MFCs; MFCs with 10 mm salt bridge shown significantly higher output voltage than MFCs with both 16 and 24 mm salt bridges. This behavior could be interpreted by increasing the electrical resistance when the diameter is increased. It was found that KCl salt bridge is significantly more efficient than NaCl salt bridges when they were used in MFCs for wastewater treatment. It was found also that MFCs with 1M KCl salt bridges can produce output voltage significantly higher than that produced by MFCs with 3M KCl salt bridges. Results revealed that the COD of the substrate used in MFC at any time is related proportionally to output voltage from that MFC at the same time, this relationship can be fitted as natural logarithmic model as following: COD (mg/L) = 229.85 Ln (V)-1039.6; where V is output voltage (mV), and this model can be used with large number of limitations to indicate COD for a wastewater sample by measuring output voltage of MFC operated by that sample. Maximum COD removal percentage achieved in this study was 87.1 % which is comparable to published achievements. It was found that COD removal behavior in this study was ranged between 1st and 2nd order kinetic reactions. A maximum output power achieved was 0.585 W/m3 with an average output power of 0.251 W W/m3.