Jaecheul Yu

Microalgae cultivation for bioenergy production using wastewaters from a municipal WWTP as nutritional sources

In order to reduce input cost for microalgal cultivation, we investigated the feasibility of wastewater taken from a municipal WWTP in Busan, Korea as wastewater nutrients. The wastewaters used in this study were the effluent from a primary settling tank (PS), the effluent from an anaerobic digestion tank (AD), the conflux of wastewaters rejected from sludge-concentrate tanks and dewatering facilities (CR), and two combined wastewaters of AD:PS (10:90, v/v) and AD:CR (10:90, v/v). Chlorella sp. ADE5, which was isolated from the AD, was selected for the feasibility test. The highest biomass production (3.01 g-dry cell weight per liter) of the isolate was obtained with the combined wastewater ADCR, and it was 1.72 times higher than that with BG 11 medium. Interestingly, the cells cultivated with wastewater containing PS wastewater were easily separated from the culture and improved lipid content, especially oleic acid content, in their cells.

Electricity generation and microbial community in a submerged-exchangeable microbial fuel cell system for low-strength domestic wastewater treatment

A submerged type microbial fuel cell (MFC) system, which consisted of six readily exchangeable air-cathode MFCs, was evaluated for continuous treatment of low-strength domestic wastewater. When supplied with synthetic wastewater (COD 100 mg/L), the system showed increasing maximum power densities from 191 to 754 mW/m2 as COD loading rates increased (0.20-0.40 kg/m3/day). COD removal efficiencies decreased with increased COD loading rates but the effluent COD concentrations met the relevant effluent quality standard (CODMn 20 mg/L) at all conditions. The system was then operated with domestic wastewater (c.a. 100 mg COD/L) at 0.32 and 0.43 kg/m3/day. The system showed much lower power densities (116-149 mW/m2) at both loading rates, compared to synthetic wastewater. Anodic microbial communities were completely different when the wastewater type was changed. These results suggest that the newly developed MFC system could be applied to treat low-strength domestic wastewater without requiring any additional organic removal stage.

Microbial community structure and dynamics in a mixotrophic nitrogen removal process using recycled spent caustic under different loading conditions.

A laboratory-scale Bardenpho process was established to investigate the proper nitrogen loading rate (NLR) when modified spent caustic (MSC) is applied as electron donor and alkalinity source for denitrification. MSC injection induced autotrophic nitrogen removal with sulfur as electron donor and heterotrophic denitrification. The nitrogen removal rate (NRR) did not increase proportionally to NLR. Based on the total nitrogen concentration in the effluent observed in the trials with MSC, the NLR in the influent should not exceed 0.15 kg N/m(3)d in order to satisfy water quality regulations. Microbial communities in the anoxic reactors were characterized by pyrosequencing of 16S rRNA gene sequences amplified by the polymerase chain reaction of DNA extracted from sludge samples. Microbial diversity was lower as MSC dosage was increased, and the injection of MSC caused an increase in SOB belonging to the genus Thiobacillus which is responsible for denitrification using sulfur.

Comparison of Exoelectrogenic Bacteria Detected Using Two Different Methods: U-tube Microbial Fuel Cell and Plating Method

In a microbial fuel cell (MFC), exoelectrogens, which transfer electrons to the electrode, have been regarded as a key factor for electricity generation. In this study, U-tube MFC and plating methods were used to isolate exoelectrogens from the anode of an MFC. Disparate microorganisms were identified depending on isolation methods, despite the use of an identical source. Denaturing gel gradient electrophoresis (DGGE) analysis showed that certain microorganisms became dominant in the U-tube MFC. The predominant bacterium was similar to Ochrobactrum sp., belonging to the Alphaproteobacteria, which was shown to be able to function as an exoelectrogen in a previous study. Three isolates, one affiliated with Bacillus sp. and two with Paenibacillus sp., were identified using the plating method, which belonged to the Gram-positive bacteria, the Firmicutes. The U-tube MFCs were inoculated with the three isolates using the plating method, operated in the batch mode and the current was monitored. All of the U-tube MFCs inoculated with each isolate after isolation from plates produced lower current (peak current density: 3.6–16.3 mA/m2) than those in U-tube MFCs with mixed culture (48.3–62.6 mA/m2). Although the isolates produced low currents, various bacterial groups were found to be involved in current production.

Variations of electron flux and microbial community in air-cathode microbial fuel cells fed with different substrates

Microbial fuel cells (MFCs) can convert chemical energy to electricity using microbes as catalysts and a variety of organic wastewaters as substrates. However, electron loss occurs when fermentable substrates are used because fermentation bacteria and methanogens are involved in electron flow from the substrates to electricity. In this study, MFCs using glucose (G-MFC), propionate (P-MFC), butyrate (B-MFC), acetate (A-MFC), and a mix (M-MFC, glucose:propionate:butyrate:acetate = 1:1:1:1) were operated in batch mode. The metabolites and microbial communities were analyzed. The current was the largest electron sink in M-, G-, B-, and A-MFCs; the initial chemical oxygen demands (COD(ini)) involved in current production were 60.1% for M-MFC, 52.7% for G-MFC, 56.1% for B-MFC, and 68.3% for A-MFC. Most of the glucose was converted to propionate (40.6% of COD(ini)) and acetate (21.4% of COD(ini)) through lactate (80.3% of COD(ini)) and butyrate (6.1% of COD(ini)). However, an unknown source (62.0% of COD(ini)) and the current (34.5% of COD(ini)) were the largest and second-largest electron sinks in P-MFC. Methane gas was only detected at levels of more than 10% in G- and M-MFCs, meaning that electrochemically active bacteria (EAB) could out-compete acetoclastic methanogens. The microbial communities were different for fermentable and non-fermentable substrate-fed MFCs. Probably, bacteria related to Lactococcus spp. found in G-MFCs with fermentable substrates would be involved in both fermentation and electricity generation. Acinetobacter-like species, and Rhodobacter-like species detected in all the MFCs would be involved in oxidation of organic compounds and electricity generation.

Microbial selenite reduction with organic carbon and electrode as sole electron donor by a bacterium isolated from domestic wastewater.

Selenium is said to be multifaceted element because it is essential at a low concentration but very toxic at an elevated level. For the purpose of screening a potential microorganism for selenite bioremediation, we isolated a bacterium, named strain THL1, which could perform both heterotrophic selenite reduction, using organic carbons such as acetate, lactate, propionate, and butyrate as electron donors under microaerobic condition, and electrotrophic selenite reduction, using an electrode polarized at -0.3V (vs. standard hydrogen electrode) as the sole electron donor under anaerobic condition. This bacterium determined to be a new strain of the genus Cronobacter, could remove selenite with an efficiency of up to 100%. This study is the first demonstration on a pure culture could take up electrons from an electrode to perform selenite reduction. The selenium nanoparticles produced by microbial selenite reduction might be considered for recovery and use in the nanotechnology industry.

Power generation response to readily biodegradable COD in single-chamber microbial fuel cells

Single-chamber microbial fuel cells (MFCs) using domestic wastewater (DWW) and milk processing wastewater (MWW) were operated at different organic loading rates (OLRs). The maximum power density (PDmax) and OLR (readily biodegradable COD [RBCOD] and soluble COD [SCOD]) followed the Lineweaver-Burk equation in all influents. The coefficients of determination were 0.9209 and 0.9975 for SCOD and RBCOD, respectively. OLR based on RBCOD showed better power generation function than that based on SCOD. PDmax (2.9-12.2 W/m(3)) in DWW was lower than that (6.9-24.9 W/m(3)) in MWW but the net energy recovery (kWh/kg-SCOD(removed)) in DWW (0.542-1.108) was larger than that in MWW (0.322-0.602). This was attributed to the higher ratio of RBCOD/SCOD (0.44) and the lower values of RBCOD (40 mg/L) in DWW, compared to RBOCD/SCOD (0.11) and RBCOD (110 mg/L) in MWW. Therefore, RBCOD is an important indicator for estimating power generation.

Electricity generation and microbial community in microbial fuel cell using low-pH distillery wastewater at different external resistances.

Single chamber MFC (SMFC) consisted of two separator-electrode assemblies (SEA) using low-pH distillery wastewater (DW) was operated under continuous mode. The electricity generation and microbial community were analyzed according to the external resistance (Rext; 0.1, 0.5, 1, and 5 kΩ). The two SEAs exhibited different electricity generations, despite sharing the same anodic chamber. The SMFC showed the largest maximum power density (PDmax) of 3.7 W/m(3) (SEA 1) and 12.9 W/m(3) (SEA 2) at 5 kΩ. These results demonstrated that low-pH wastewater could be sufficiently used as fuels for electricity generation. Pyrosequencing analysis showed that microbial communities at the phylum level were significantly different according to the Rext. The communities of SEA 1 were slightly different from those of SEA 2. In both SEAs, Firmicutes (>45%) were the most dominant at 0.1 kΩ, while Firmicutes (>34%) and Caldiserica (>34%) were dominant at 5 kΩ. Caldiserica sp. might significantly contribute to electricity generation under low-pH and high-Rext.

Simultaneous arsenite oxidation and nitrate reduction at the electrodes of bioelectrochemical systems

Arsenic and nitrate contaminations in the soil and groundwater have urged the scientific community to explore suitable technologies for treatment of both contaminants. This study reports, for the first time, a novel application of bioelectrochemical systems for coupling As detoxification at the anode and denitrification at the cathode. A similar As(III) oxidation efficiency was achieved when anode potential was controlled by a potentiostat or a direct current (DC) power supply. However, a slightly lower nitrate reduction rate was obtained in reactors using DC power supply during simultaneous operation of nitrate reduction and As(III) oxidation. Microbial community analysis by denaturing gradient gel electrophoresis indicated the presence of some autotrophic As(III)-oxidizing bacteria, including Achromobacter spp., Ensifer spp., and Sinorhizobium spp., that can flexibly switch their original metabolism of using oxygen as sole electron acceptor to a new metabolism mode of using solid-state anode as sole electron acceptor driving for As(III) oxidation under anaerobic conditions. Although further research is required for validating their applicability, bioelectrochemical systems represent a brilliant technology for remediation of groundwater contaminated with nitrate and/or arsenite.

Effect of organic loading rates and influent sources on energy production in multi-baffled single chamber microbial fuel cell

AbstractMulti-baffled single chamber microbial fuel cells (MBSC-MFCs) were operated with different wastewater sources and organic loading rates (OLRs). As the OLRs increased, the maximum power density (Pmax) in MFCs with an identical influent source also increased. In the case of using a different influent source, Pmax was different even though the MFC had been operated with the similar OLR or hydraulic retention time. Therefore, power generation would be affected concurrently by a range of factors, including the substrate type.