Performance evaluation of microbial electrochemical systems operated with Nafion and supported ionic liquid membranes

In this work, the performance of dual-chamber microbial fuel cells (MFCs) constructed either with commonly used Nafion® proton exchange membrane or supported ionic liquid membranes (SILMs) was assessed. The behavior of MFCs was followed and analyzed by taking the polarization curves and besides, their efficiency was characterized by measuring the electricity generation using various substrates such as acetate and glucose. By using the SILMs containing either [C6mim][PF6] or [Bmim][NTf2] ionic liquids, the energy production of these MFCs from glucose was comparable to that obtained with the MFC employing polymeric Nafion® and the same substrate. Furthermore, the MFC operated with [Bmim][NTf2]-based SILM demonstrated higher energy yield in case of low acetate loading (80.1 J g−1 CODin m−2 h−1) than the one with the polymeric Nafion® N115 (59 J g−1 CODin m−2 h−1). Significant difference was observed between the two SILM-MFCs, however, the characteristics of the system was similar based on the cell polarization measurements. The results suggest that membrane-engineering applying ionic liquids can be an interesting subject field for bioelectrochemical system research

Continuous micro-current stimulation to upgrade methanolic wastewater biodegradation and biomethane recovery in an upflow anaerobic sludge blanket (UASB) reactor

The dispersion of granules in upflow anaerobic sludge blanket (UASB) reactor represents a critical technical issue in methanolic wastewater treatment. In this study, the potentials of coupling a microbial electrolysis cell (MEC) into an UASB reactor for improving methanolic wastewater biodegradation, long-term process stability and biomethane recovery were evaluated. The results indicated that coupling a MEC system was capable of improving the overall performance of UASB reactor for methanolic wastewater treatment. The combined system maintained the comparatively higher methane yield and COD removal efficiency over the single UASB process through the entire process, with the methane production at the steady-state conditions approaching 1504.7 ± 92.2 mL-CH4 L−1-reactor d−1, around 10.1% higher than the control UASB (i.e. 1366.4 ± 71.0 mL-CH4 L−1-reactor d−1). The further characterizations verified that the input of external power source could stimulate the metabolic activity of microbes and reinforced the EPS secretion. The produced EPS interacted with Fe2+/3+ liberated during anodic corrosion of iron electrode to create a gel-like three-dimensional [-Fe-EPS-]n matrix, which promoted cell-cell cohesion and maintained the structural integrity of granules. Further observations via SEM and FISH analysis demonstrated that the use of bioelectrochemical stimulation promoted the growth and proliferation of microorganisms, which diversified the degradation routes of methanol, convert the wasted CO2 into methane and accordingly increased the process stability and methane productivity

Thermophilic Solid-State Anaerobic Digestion of Corn Straw, Cattle Manure, and Vegetable Waste: Effect of Temperature, Total Solid Content, and C/N Ratio

Thermophilic solid-state anaerobic digestion (SS-AD) of agricultural wastes, i.e., corn straw, cattle manure, and vegetable waste, was carried out in this study. The effects of temperature (40-60°C), initial solid content (ISC, 17.5-32.5%), and C/N ratio (15-32 : 1) on biogas production were evaluated using a Box-Behnken experimental design (BBD) combined with response surface methodology (RSM). The results showed that optimization of process parameters is important to promote the SS-AD performance. All the factors, including interactive terms (except the ISC), were significant in the quadratic model for biogas production with SS-AD. Among the three operation parameters, the C/N ratio had the largest effect on biogas production, followed by temperature, and a maximum biogas yield of 241.4 mL gVS-1 could be achieved at 47.3°C, ISC=24.81%, and C/N=22.35. After 20 d of SS-AD, the microbial community structure under different conditions was characterized by high-throughput sequencing, showing that Firmicutes, Bacteroidetes, Chloroflexi, Synergistetes, and Proteobacteria dominated the bacterial community, and that Firmicutes had a competitive advantage over Bacteroidetes at elevated temperatures. The biogas production values and relative abundance of OPB54 and Bacteroidia after 20 d of SS-AD can be fitted well using a quadratic model, implying that OPB54 and Bacteroidia play important roles in the methanogenic metabolism for agricultural waste thermophilic SS-AD

Comparison of Biochar Materials Derived from Coconut Husks and Various Types of Livestock Manure, and Their Potential for Use in Removal of H2S from Biogas

As a potential adsorbent material, loose, porous livestock manure biochar provides a new approach to livestock manure resource utilization. In this study, coconut husks (CH) and livestock manure, i.e., cow dung (CD), pig manure (PM), and chicken manure (CM) were used as biomass precursors for preparation of biochar via high-temperature pyrolysis and CO2 activation. Characterization technologies, such as scanning electron microscopy, Fourier transform infrared spectroscopy, adsorption–desorption isotherms, and pore size distributions, were used to study the microscopic morphologies and physicochemical properties of unactivated and activated biochar materials. The results showed that CD biochar provides better adsorption performance (up to 29.81 mg H2S/g) than CM or PM biochar. After activation at 650° for 1 h, the best adsorption performance was 38.23 mg H2S/g. For comparison, the CH biochar removal performance was 30.44 mg H2S/g. Its best performance was 38.73 mg H2S/g after 1 h of activation at 750 °C. Its best removal performance is equivalent to that of CH biochar activated at a temperature that is 100 °C higher. Further material characterization indicates that the H2S removal performance of livestock-manure–derived biochar is not entirely dependent on the specific surface area, but is closely related to the pore size distribution