Joo-Youn Nam

Effects of organic loading rates on the continuous electricity generation from fermented wastewater using a single-chamber microbial fuel cell.

Novel coupling of single-chamber microbial fuel cells (MFCs) with granular activated carbon anodes were constructed, and their ability to produce electricity from fermented wastewater operating in continuous mode was investigated. MFCs treating real fermented wastewater can generate a power density of approximately 1884 mW/m(3), which is equivalent to approximately 51.5% of that obtained from the MFCs (3664 mW/m(3)) using acetate at the same organic loading rate (OLR) of 1.92 g/Ld. As the OLR was increased in a stepwise fashion, power density increased to 2981 mW/m(3) at an OLR of 3.84 g/Ld. The corresponding energy production was 268 kJ/m(3)d. The decrease in the power density was mainly due to the higher internal resistance resulted from complex substrate. Based on the electrode characteristics, it was verified that colloidal particulates and complex organics in the real fermented wastewater not only lowered power density but also played a role as rate-limiting factors in the continuous generation of electricity.

Enrichment of microbial electrolysis cell biocathodes from sediment microbial fuel cell bioanodes.

ABSTRACT Electron-accepting (electrotrophic) biocathodes were produced by first enriching graphite fiber brush electrodes as the anodes in sediment-type microbial fuel cells (sMFCs) using two different marine sediments and then electrically inverting the anodes to function as cathodes in two-chamber bioelectrochemical systems (BESs). Electron consumption occurred at set potentials of −439 mV and −539 mV (versus the potential of a standard hydrogen electrode) but not at −339 mV in minimal media lacking organic sources of energy. Results at these different potentials were consistent with separate linear sweep voltammetry (LSV) scans that indicated enhanced activity (current consumption) below only ca. −400 mV. MFC bioanodes not originally acclimated at a set potential produced electron-accepting (electrotrophic) biocathodes, but bioanodes operated at a set potential (+11 mV) did not. CO2 was removed from cathode headspace, indicating that the electrotrophic biocathodes were autotrophic. Hydrogen gas generation, followed by loss of hydrogen gas and methane production in one sample, suggested hydrogenotrophic methanogenesis. There was abundant microbial growth in the biocathode chamber, as evidenced by an increase in turbidity and the presence of microorganisms on the cathode surface. Clone library analysis of 16S rRNA genes indicated prominent sequences most similar to those of Eubacterium limosum (Butyribacterium methylotrophicum), Desulfovibrio sp. A2, Rhodococcus opacus, and Gemmata obscuriglobus. Transfer of the suspension to sterile cathodes made of graphite plates, carbon rods, or carbon brushes in new BESs resulted in enhanced current after 4 days, demonstrating growth by these microbial communities on a variety of cathode substrates. This report provides a simple and effective method for enriching autotrophic electrotrophs by the use of sMFCs without the need for set potentials, followed by the use of potentials more negative than −400 mV.

Variation of power generation at different buffer types and conductivities in single chamber microbial fuel cells

Microbial fuel cells (MFCs) are operated with solutions containing various chemical species required for the growth of electrochemically active microorganisms including nutrients and vitamins, substrates, and chemical buffers. Many different buffers are used in laboratory media, but the effects of these buffers and their inherent electrolyte conductivities have not been examined relative to current generation in MFCs. We investigated the effect of several common buffers (phosphate, MES, HEPES, and PIPES) on power production in single chambered MFCs compared to a non-buffered control. At the same concentrations the buffers produced different solution conductivities which resulted in different ohmic resistances and power densities. Increasing the solution conductivities to the same values using NaCl produced comparable power densities for all buffers. Very large increases in conductivity resulted in a rapid voltage drop at high current densities. Our results suggest that solution conductivity at a specific pH for each buffer is more important in MFC studies than the buffer itself given relatively constant pH conditions. Based on our analysis of internal resistance and a set neutral pH, phosphate and PIPES are the most useful buffers of those examined here because pH was maintained close to the pK(a) of the buffer, maximizing the ability of the buffer to contribute to increase current generation at high power densities.

A comparison study on the high-rate co-digestion of sewage sludge and food waste using a temperature-phased anaerobic sequencing batch reactor system.

Assessing contemporary anaerobic biotechnologies requires proofs on reliable performance in terms of renewable bioenergy recovery such as methane (CH(4)) production rate, CH(4) yield while removing volatile solid (VS) effectively. This study, therefore, aims to evaluate temperature-phased anaerobic sequencing batch reactor (TPASBR) system that is a promising approach for the sustainable treatment of organic fraction of municipal solid wastes (OFMSW). TPASBR system is compared with a conventional system, mesophilic two-stage anaerobic sequencing batch reactor system, which differs in operating temperature of 1st-stage. Results demonstrate that TPASBR system can obtain 44% VS removal from co-substrate of sewage sludge and food waste while producing 1.2m(3)CH(4)/m(3)(system)/d (0.2m(3)CH(4)/kgVS(added)) at organic loading rate of 6.1gVS/L/d through the synergy of sequencing-batch operation, co-digestion, and temperature-phasing. Consequently, the rapid and balanced anaerobic metabolism at thermophilic stage makes TPASBR system to afford high organic loading rate showing superior performance on OFMSW stabilization.

Hydrolytic activities of extracellular enzymes in thermophilic and mesophilic anaerobic sequencing-batch reactors treating organic fractions of municipal solid wastes.

Extracellular enzymes offer active catalysis for hydrolysis of organic solid wastes in anaerobic digestion. To evidence the quantitative significance of hydrolytic enzyme activities for major waste components, track studies of thermophilic and mesophilic anaerobic sequencing-batch reactors (TASBR and MASBR) were conducted using a co-substrate of real organic wastes. During 1day batch cycle, TASBR showed higher amylase activity for carbohydrate (46%), protease activity for proteins (270%), and lipase activity for lipids (19%) than MASBR. In particular, the track study of protease identified that thermophilic anaerobes degraded protein polymers much more rapidly. Results revealed that differences in enzyme activities eventually affected acidogenic and methanogenic performances. It was demonstrated that the superior nature of enzymatic capability at thermophilic condition led to successive high-rate acidogenesis and 32% higher CH(4) recovery. Consequently, these results evidence that the coupling thermophilic digestion with sequencing-batch operation is a viable option to promote enzymatic hydrolysis of organic particulates.

Enhancement of bioenergy production and effluent quality by integrating optimized acidification with submerged anaerobic membrane bioreactor.

To ensure effluent quality in the treatment of high-strength organic waste and enhance CH(4) production, this study investigates the applicability of process optimization and a submerged anaerobic membrane bioreactor (SAMBR) for a two-phase anaerobic digestion (TPAD) system. The use of response surface methodology (RSM) suggests that the optimum conditions for maximum volatile fatty acids (VFA) production were a hydraulic retention time (HRT) of 2.01 days and a substrate concentration of 29.30 g/L based on chemical oxygen demands (COD). A confirmation experiment showed that an empirical model could predict a VFA increase of 76% under the proposed conditions with a relative error of 4%. SAMBRs could convert the VFA in acidogenic effluent to CH(4) with an average production rate of 0.28 m(3)/m(3)/d in an HRT of 14 days. All of the SAMBRs could achieve COD removal rates of over 99% by the increased solid retention time and secondary membrane formation.

Optimization of membrane stack configuration for efficient hydrogen production in microbial reverse-electrodialysis electrolysis cells coupled with thermolytic solutions

Waste heat can be captured as electrical energy to drive hydrogen evolution in microbial reverse-electrodialysis electrolysis cells (MRECs) by using thermolytic solutions such as ammonium bicarbonate. To determine the optimal membrane stack configuration for efficient hydrogen production in MRECs using ammonium bicarbonate solutions, different numbers of cell pairs and stack arrangements were tested. The optimum number of cell pairs was determined to be five based on MREC performance and a desire to minimize capital costs. The stack arrangement was altered by placing an extra low concentration chamber adjacent to anode chamber to reduce ammonia crossover. This additional chamber decreased ammonia nitrogen losses into anolyte by 60%, increased the coulombic efficiency to 83%, and improved the hydrogen yield to a maximum of 3.5 mol H2/mol acetate, with an overall energy efficiency of 27%. These results improve the MREC process, making it a more efficient method for renewable hydrogen gas production.

Examination of protein degradation in continuous flow, microbial electrolysis cells treating fermentation wastewater.

Cellulose fermentation wastewaters (FWWs) contain short chain volatile fatty acids and alcohols, but they also have high concentrations of proteins. Hydrogen gas production from FWW was examined using continuous flow microbial electrolysis cells (MECs), with a focus on fate of the protein. H2 production rates were 0.49±0.05 m(3)/m(3)-d for the FWW, compared to 0.63±0.02 m(3)/m(3)-d using a synthetic wastewater containing only acetate (applied potential of 0.9 V). Total organic matter removal was 76±6% for the FWW, compared to 87±5% for acetate. The MEC effluent became relatively enriched in protein (69%) compared to that in the original FWW (19%). Protein was completely removed using higher applied voltages (1.0 or 1.2 V), but current generation was erratic due to more positive anode potentials (-113±38 mV, Eap=1.2V; -338±38 mV, 1.0 V; -0.426±4 mV, 0.9V). Bacteria on the anodes with FWW were primarily Deltaproteobacteria, while Archaea were predominantly Methanobacterium.

A comparative study of perchlorate degradation in acute toxicity and chronic toxicity.

Since the discovery of perchlorate in water system, the public has been concerned about its human health effect. In practice it was reported that chronic exposure to perchlorate may lead to damage in thyroid hormone activity. This study introduced a method of perchlorate reduction, using autotrophic bacteria which utilise hydrogen as an electron donor. Two experiments were conducted to compare the effects of acute and chronic perchlorate toxicity on bacterial perchlorate reduction potential. One was a batch-fed operation generating acute toxicity and another was a continuous-fed operation generating chronic toxicity. Acclimation period of the batch-fed operation was 14 days while that of the continuous-fed operation was 31 days as commensurate with double. Lots of batch tests using the mixed culture passing through acclimation were conducted to figure out kinetics of biological perchlorate reduction. The maximum perchlorate utilisation rate (q(max)) of the mixed culture acclimated by acute toxicity was 2.92 mg ClO(4)(-)/mg dry-weight (DW)/d, while that of chronic toxicity was 0.27 mg ClO(4)(-)/mg DW/d. Half-maximum rate constants (K(s)) of acute and chronic toxicity were 567.3 and 25.6 mg ClO(4)(-)/L respectively. This result showed that acute toxicity acclimated the mixed culture more rapidly and produced a higher activity for biological perchlorate reduction than chronic toxicity.

Degradation of sulfonamide antibiotics and their intermediates toxicity in an aeration-assisted non-thermal plasma while treating strong wastewater

Aeration-assisted non-thermal plasma (NTP) process is known as promising due to simultaneous generation of oxygen- and nitrogen-based reactive chemicals for non-biodegradable pollutants removal in a wastewater. Despite its effective oxidizing capability, the decomposition mechanism of antibiotics is not yet clarified well. This study verifies the NTPs removal potential of non-biodegradable sulfonamide antibiotics in the treatment of strong wastewater. The instantaneous production of hydrogen peroxide (H2O2) was quantified to prove synergistic advanced oxidation, and degradation kinetic coefficients of N, N-Dimethyl-4-nitrosoaniline (RNO) reveals rapid oxidation rate of NTP. Also, the results of an acute-toxicity test using Daphnia magna demonstrate how the toxicity of antibiotics intermediates responds to the NTP. Results indicate that the NTP has better potential than conventional oxidation processes in terms of OH-radical generation due to the interplay of reactive species. This study provides useful information that aeration-assisted NTP application to wastewater treatment can be a viable option to enhance treatment efficiency via plasma-related reactive species and that how environmental ecotoxicity responds to the by-products of sulfonamide antibiotics.