Microbial fuel cells (MFCs) are a kind of bioreactor for generating electricity, facilitated by exoelectrogens while treating wastewater. The present article focuses on the performance of an air cathode plexiglass MFC in terms of chemical oxygen demand (COD) removal efficiency and power output by performing two sets of experiments. The proton exchange membrane and electrode materials were Nafion 117 and carbon felts, whereas, for stable biofilm formation on the anode surface, a pure culture of Shewanella baltica 20 was used. Firstly, sterile Luria-Bertani (LB) media containing lactate, ranging from 20 to 100 mM, was continuously fed to an MFC, and a maximum power density of 55 mW/m² was observed. Similarly, artificial wastewater with COD ranging from 3250 mg/L to 10,272 mg/L was supplied to the MFC in the second set of experiments. In this case, the maximum power density and COD removal efficiency were 12 mW/m² and 57%, respectively. In both cases, the hydraulic retention time (HRT) was 1.5 h. It was found that electricity generation depends on the characteristics of the wastewater. These initial findings confirm that the design aspects of an MFC, i.e., surface area to volume ratio, and external resistance with respect to the quality of influent need to be optimised to improve the MFC’s performance.

In this paper, the inhibitory effects of added hydrogen in reactor headspace on fermentative hydrogen production from acidogenesis of glucose by a bacterium, Clostridium acetobutylicum, was investigated experimentally in a batch reactor. It was observed that hydrogen itself became an acute inhibitor of hydrogen production if it accumulated excessively in the reactor headspace. A mathematical model to simulate and predict biological hydrogen production process was developed. The Monod model, which is a simple growth model, was modified to take inhibition kinetics on microbial growth into account. The modified model was then used to investigate the effect of hydrogen concentration on microbial growth and production rate of hydrogen. The inhibition was moderate as hydrogen concentration increased from 10% to 30% (v/v). However, a strong inhibition in microbial growth and hydrogen production rate was observed as the addition of H₂ increased from 30% to 40% (v/v). Practically, an extended lag in microbial growth and considerably low hydrogen production rate were detected when 50% (v/v) of the reactor headspace was filled with hydrogen. The maximum specific growth rate (µ_max), substrate saturation constant (ks), a critical hydrogen concentration at which microbial growth ceased (H₂*) and degree of inhibition were found to be 0.976 h⁻¹, 0.63 ± 0.01 gL, 24.74 mM, and 0.4786, respectively.

In this paper, a sensitivity analysis of a continuous stirred tank bioreactor (CSTBR) was conducted to determine a parametrically sensitive regime. The growth of a lactic acid bacterium, namely, Lactobacillus casei, in a pH-controlled CSTBR was considered as a process model. Normalized objective sensitivities of the minimum pH were determined with respect to input parameters. A generalized criterion for sensitivity was defined for determining the parametric range of three input variables, i.e., dilution rate base stream (θ), base concentration (R), and initial pH (pH₀) for maintaining optimal pH range in the reactor. The system exhibits sensitive behavior for θ, R, and pH₀, from 0.095 to 0.295, 0 to 0.865, and 4.42 to 4.77, respectively. The critical values of θ, R, and pH₀ are 0.0195, 0.48, and 4.6, respectively. The mathematical model can also be used to determine a parametrically sensitive regime for other important parameters, namely, temperature, the concentration of metabolites, and other byproducts. The mathematical tool can also be used in bioreactor design and the improvement of control strategies.

A Cost Benefit Analysis (CBA) of Bio-waste Gasification as part of a techno-economic feasibility for establishing a small scale production facility for processing bio-waste into liquid fuels is presented in this paper. It is well known that transport sector is a big consumer of fossil fuels. Different bio-fuels are potential candidates to replace to petroleum based fuels in automobiles without requiring major changes to the engine. Biofuels can also be produced from various biomass including bio-waste from domestic and industrial sectors. The size and type of the gasification plants depend on demand and available feedstock. Thus for small and sparse communities such as Narvik, setting up a plant is not considered to be economical. This paper investigates the viability of a small plant to produce fuels to meet the demand of public transport in the region. The plant was sized based on the amount of biomass produced annually from the forests and municipal bio- waste (MBW). The annually available amounts of biomass from forests and MBW for treatment to produce biodiesel were estimated. For this scenario, a downdraft gasifier of 6.0 MW was considered adequate. Current annual demand of diesel for public transport buses in Narvik was also estimated. It was found out that only 28% of the estimated biodiesel product will be sufficient for running the public transport busses in Narvik. Therefore the plant can supply fuel for other applications. Cost analysis included estimations of capital, operational and maintenance (O&M) costs for the biomass pre-treatment processes, the gasification plant and the gas to liquid (GTL) plant is fully discussed. It was concluded that the payback period can be achieved within four years. The study demonstrated that small to medium size gasification plants can fulfil energy demand locally utilising local biomass feedstock and contribute towards environmental targets.