Ka Yu Cheng

Ammonium as a sustainable proton shuttle in bioelectrochemical systems.

This work examines a pH control method using ammonium (NH(4)(+)) as a sustainable proton shuttle in a CEM-equipped BES. Current generation was sustained by adding NH(3) or ammonium hydroxide (NH(4)OH) to the anolyte, controlling its pH at 7. Ammonium ion migration maintained the catholyte pH at approximately 9.25. Such NH(4)(+)/NH(3) migration accounted for 90±10% of the ionic flux in the BES. Reintroducing the volatilized NH(3) from the cathode into the anolyte maintained a suitable anolyte pH for sustained microbial-driven current generation. Hence, NH(4)(+)/NH(3) acted as a proton shuttle that is not consumed in the process.

Effects of pig manure compost and nonionic-surfactant Tween 80 on phenanthrene and pyrene removal from soil vegetated with Agropyron elongatum

This paper evaluates the effects of pig manure compost (PMC) and Tween 80 on the removal of phenanthrene (PHE) and pyrene (PYR) from soil cultivated with Agropyron elongatum. Soils spiked with about 300 mg kg(-1) of PHE and PYR were individually amended with 0%, 2.5%, 5% and 7.5% (dry wt) of PMC or 0, 20 and 100 mg kg(-1) of Tween 80. Unplanted and sterile microcosms were prepared as the controls. PAH concentration, total organic matter (TOM), dissolved organic carbon (DOC), total heterotrophic and PAH degrading microbial populations in soil were quantified before and after 60d period. The results indicated that A. elongatum could significantly enhance PYR removal (from 46% to 61%) but had less impact on PHE removal (from 96% to 97%). Plant uptake of the PAHs was insignificant. Biodegradation was the key mechanism of PAH removals (<3% losses in the sterile control). Increase in PMC or Tween 80 levels increased the removal of PYR but not of PHE. Maximal PYR removal of 79% and 92% were observed in vegetated soil receiving 100 mg kg(-1) Tween 80 and 7.5% PMC, respectively. Enhanced PYR removal in soil receiving PMC could be explained by the elevated levels of DOC, TOM and microbial populations as suggested by Pearson correlation test. While the positive effect of Tween 80 on PYR removal could probably due to its capacities to enhance PYR bioavailability in soil. This paper suggests that the addition of either PMC or nonionic-surfactant Tween 80 could facilitate phytoremediation of PAH contaminated soil.

Novel methanogenic rotatable bioelectrochemical system operated with polarity inversion

A novel membraneless bioelectrochemical system termed rotatable bioelectrochemical contactor (RBEC) was fabricated and evaluated for its ability to recover useful energy (here methane) from a low organic strength wastewater. We studied the operational characteristics of the RBEC by operating it as a three-electrode electrolysis cell. A stack of conductive disks (each subdivided into two half disks), similar to rotating biological contactors, were rotated with one-half disk immersed in the wastewater and the other into the gas headspace. By carrying out regular half rotations (180° rotation) the anode became the cathode and vice versa. This operation resulted in the build-up of a biofilm that could catalyze both an anodic acetate oxidation and a cathode-driven methanogenesis. Methane production rate was directly proportional to the applied electrical energy. Increase in current density (from 0.16 to 4.1 A m(-2)) resulted in a faster COD removal (from 0.2 to 1.38 kg COD m(-3) day(-1)) and methane production (from 0.04 to 0.53 L L(-1) day(-1)). Of the electrons flowing across the circuit, over 80% were recovered as methane. Such methane production was electrochemically driven by the headspace-exposed cathodic half disks, which released the methane directly to the gas-phase. Energy analysis shows that the new design requires less energy for COD removal than what is typically required for oxygen supply in activated sludge processes. Because the system could operate without wastewater recirculation against gravity; additional pH buffer chemicals; ion-exchange membranes or electrochemical catalysts, it has desirable characteristics for process up-scale. Further, the current report shows the first example of a BES with identical biofilm (due to intermittent polarity inversion) on both electrodes.

Ano-Cathodophilic Biofilm Catalyzes Both Anodic Carbon Oxidation and Cathodic Denitrification

Biocathodic denitrification using bioelectrochemical systems (BES) have shown promise for both wastewater and groundwater treatment. Typically, these systems involve anodic carbon oxidation and cathodic denitrification catalyzed by two electroactive biofilms located separately at an anode and a cathode. However, process efficiencies are often limited by pH drifts in the respective electrode-biofilms: acidification (pH <5.5) in the bioanode and basification (pH >8.5) in the biocathode. Here, we describe for the first time a single electroactive biofilm that acts as a bioanode and a biocathode, alternately catalyzing anodic acetate oxidation (Coulombic efficiency (CE) 85.3%) and cathodic denitrification (CE 87.3%) (-400 mV Ag/AgCl). Our results indicate that the ano-cathodophilic biofilm denitrified autotrophically using the electrode (-200 to -600 mV Ag/AgCl) as a direct electron donor. Further, the alkalinity produced from cathodic denitrification partially (19%) neutralized the acidity of the anodic reaction. Switching the electrode potential to temporarily favor either an anodic or cathodic reaction may represent a unique method for removing carbon and nitrate from contaminated liquors. This study offers new insights into the development of sustainable BES-based nutrient removal processes.

Effect of Synthetic Surfactants on the Solubilization and Distribution of PAHs in Water/Soil-Water Systems

The present study examined the effects of four surfactants, including three non-ionic surfactants (Tween 80, Triton X-100 and Brij 35) and an anionic surfactant SDS on the solubilization and distribution of phenanthrene (Phe) and pyrene (Pyr) in soil-water systems. All four surfactants could enhance the solubilization of Phe and Pyr in aqueous phase linearly when surfactant concentrations exceeded their respective critical micelle concentrations (CMC). Molar solubilization ratio (MSR) which indicated surfactants solubilization capacity for Phe and Pyr, was highest for Tween 80 for both PAHs, and SDS had the lowest among the four surfactants, while Triton X-100 and Brij 35 had about the same MSR for both PAHs. Moreover, all the surfactants could provide a strong micelle partitioning phase for the more hydrophobic Pyr than Phe as revealed by their high micelle - aqueous phase partition coefficient, K mc. Batch desorption studies also demonstrated that Tween 80 had the best capacity for the desorption of both Phe and Pyr in the soil-water systems, and followed by Triton X-100 and Brij 35, while SDS seems to have no positive effect on the desorption of PAHs probably due to its relatively high CMC value. Therefore, from the application standpoint, the results obtained in this study suggest that Tween 80 would be the most suitable candidate among the four surfactants in improving solubilization and desorption of PAHs in soil-water system, which are believed to be the prerequisites for successful bioremediation technology for PAH contaminated soil.

A novel post denitrification configuration for phosphorus recovery using polyphosphate accumulating organisms

Enhanced biological phosphorus removal (EBPR) has been widely used to remove phosphorus (P) from wastewater. In this study we report a novel modification to the EBPR approach, namely enhanced biological phosphorus removal and recovery (EBPR-r) that facilitates biological recovery of P from wastewater using a post denitrification configuration. The novel approach consists of two major steps. In the first step, a biofilm of phosphorus accumulating organisms (PAOs) is exposed to a wastewater stream in the absence of active aeration, during which P is taken up by the biofilm using nitrate and residual dissolved oxygen as electron acceptors. Thus, P and nitrogen (N) removal from wastewater is achieved. During the second step, the P enriched biofilm is exposed to a smaller recovery stream supplemented with an external carbon source to facilitate P release under anaerobic conditions. This allows P to be recovered as a concentrated liquid. The EBPR-r process was able to generate a P recovery stream four time more concentrated (28 mg-P/L) than the wastewater stream (7 mg-P/L), while removing nitrate (denitrification) from the wastewater stream. Repeated exposure of the biofilm (10 P-uptake and release cycles) to a recovery stream yielded up to 100 mg-P/L. Overall, EBPR-r is the first post denitrification strategy that can also facilitate P recovery during secondary wastewater treatment.

Ammonia recycling enables sustainable operation of bioelectrochemical systems.

Ammonium (NH4(+)) migration across a cation exchange membrane is commonly observed during the operation of bioelectrochemical systems (BES). This often leads to anolyte acidification (pH <5.5) and complete inactivation of biofilm electroactivity. Without using conventional pH controls (dosage of alkali or pH buffers), the present study revealed that anodic biofilm activity (current) could be sustained if recycling of ammonia (NH3) was implemented. A simple gas-exchange apparatus was designed to enable continuous recycling of NH3 (released from the catholyte at pH >10) from the cathodic headspace to the acidified anolyte. Results indicated that current (110 mA or 688 Am(-3) net anodic chamber volume) was sustained as long as the NH3 recycling path was enabled, facilitating continuous anolyte neutralization with the recycled NH3. Since the microbial current enabled NH4(+) migration against a strong concentration gradient (~10-fold), a novel way of ammonia recovery from wastewaters could be envisaged.

Influence of ionic conductivity in bioelectricity production from saline domestic sewage sludge in microbial fuel cells

This study aimed at manipulating ionic conductivity (EC) to harvest the maximum electrical energy from seawater-based domestic wastewater sewage sludge (SWS), unique to only a few cities, through microbial fuel cell (MFC). SWS has never been investigated as a MFC substrate before, and thus the influence of high in-situ EC on the energy recovery was unknown. In this study, the EC of the SWS was reduced through mixing it with fresh water-based domestic wastewater sewage sludge (FWS) or diluted 50% using deionized water while FWS and SWS were individually served as reference treatments. SWS:FWS mix (1:1) exhibited a maximum Coulombic efficiency of 28.6±0.5% at a COD removal of 59±3% while the peak power density was 20-fold higher than FWS. The improved performance was due to the lower ohmic internal resistance (36.8±4.2Ω) and optimal conductivity (12.8±0.2mScm(-1)). Therefore, dilution with FWS could enhance energy recovery from SWS.

Bioelectricity production from food waste leachate using microbial fuel cells: effect of NaCl and pH.

Microbial fuel cells are a promising technology for simultaneous treatment and energy recovery from food waste leachate. This study evaluates the effects of NaCl (0-150 mM) and pH on the treatment of food waste leachate using microbial fuel cells. The food waste leachate amended with 100mM NaCl enabled the highest maximum power density (1000 mW/m(3)) and lowest internal resistance (371Ω). Increasing the anodic pH gradually from acidic to alkaline conditions (pH 4-9) resulted in a gradual increase in maximum power density to 9956 mW/m(3) and decrease in internal cell resistance to 35.3Ω. The coulombic efficiency obtained under acidic conditions was only 17.8%, but increased significantly to 60.0% and 63.4% in the neutral and alkaline pHs MFCs, respectively. Maintaining a narrow pH window (6.3-7.6) was essential for efficient bioelectricity production and COD removal using microbial fuel cells for the treatment of food waste leachate.

Energy-efficient treatment of organic wastewater streams using a rotatable bioelectrochemical contactor (RBEC)

A membraneless bioelectrochemical system - rotatable bio-electrochemical contactor (RBEC) consists of an array of rotatable electrode disks was developed to convert the chemical energy from wastewater organics (acetate) directly into electricity. Each rotatable electrode disk had an upper-air exposing and a lower-water submerging halves. Intermittent rotation (180°) enabled each halve to alternately serve as anode and cathode. Removal of chemical oxygen demand (COD) was increased by 15% (from 0.79 to 0.91 kg COD m(-3) d(-1)) by allowing electron flow from the lower to the upper disk halves. Coupling with a potentiostat could alleviate cathodic limitation and increased COD removal to 1.32 kg COD m(-3) day(-1) (HRT 5h). About 40% of the COD removed was via current, indicating that the biofilm could use the lower half disk as electron acceptor. The RBEC removed COD more energy-efficiently than conventional activated sludge processes as active aeration is not required (0.47 vs. 0.7-2.0 kW h kg COD(-1)).