The influence of sludge retention time on mixed culture microbial fuel cell start-ups

A review of the operating parameters on the microbial fuel cell for wastewater treatment and electricity generation

Environmental and economic considerations suggest a more efficient and comprehensive use of biomass for bioenergy production. One of the most attractive technologies is the microbial fuel cell using the catabolic activity of microorganisms to generate electricity from organic matter. The microbial fuel cell (MFC) has operational benefits and higher performance than current technologies for producing energy from organic materials because it converts electricity from the substrate directly (at ambient temperature). However, MFCs are still not suitable for high energy demand due to practical limitations. The overall performance of an MFC depends on the electrode material, the reactor design, the operating parameters, substrates, and microorganisms. Furthermore, the optimization of the parameters will lead to the commercial development of this technology in the near future. The simultaneous effect of the parameters on each other (intensifier or attenuator) has also been investigated. The investigated parameters in this study include temperature, pH, flow rate and hydraulic retention time, mode, external resistance, and initial concentration.

The Influent Effects of Flow Rate Profile on the Performance of Microbial Fuel Cells Model

The energy contained in wastewaters has been identified as a promising sustainable energy resource that could be harvested by using microbial fuel cells (MFC). When dealing with real wastewaters, the MFCs should be able to manage high flow rates and flow rates fluctuations. In this work, the short-term effects of the influent flow rate variations on the performance of a microbial fuel cell has been studied. With this aim, the influent flow rate was stepwise increased from 0.72 to 7.2 L/d and then stepwise decreased. The obtained results indicate that, on the one hand, an increase in the influent flow rate leads to higher chemical oxygen demand removal rates up to 396 g/(L/d) and higher electric power generation almost 18 mW/m2, but to lower coulombic efficiencies. On the other hand, the reduction of the flow rate increases the coulombic efficiencies, as well as the percentage of chemical oxygen demand removed, but decreases electric power generation. In the short-term, the exposition to higher influent flow rates causes the growth of the microbial population of the MFC, the growth of the non-electrogenic microorganisms being higher than that of the electrogenic ones. The higher growth of non-electrogenic microorganisms may lead to lower coulombic efficiencies.

Driving force behind electrochemical performance of microbial fuel cells fed with different substrates

The performance of miniaturized microbial fuel cells operating with five different substrates (acetate, lactate, glucose and octanoate) were studied with the aim to identify the reason for its different performance. In all cases, the COD removal rate was about 650 mg COD L^-1 d^-1. However, the bio-electrochemical performance of the MFC was very different, showing the MFC fed with acetate the best performance: 20 A m^-2 as maximum current density, 2 W m^-2 of maximum power density, 0.376 V of OCV and 12.6% of CE. In addition, the acetate showed the best bio-electrochemical performance in the polarization curves and cyclic voltammetries. These polarization curves were modelled and the key to explain the better electrical performance of acetate was its lower ohmic losses. When working with acetate, its ohmic losses were one log-unit below those attained by the other substrates. These lower ohmic losses were not associated to the electrolyte conductivity of the fuel but to the lower ohmic loses of the biofilm generated.