PRODUCTIVITY OF PODOSTEMUM CERATOPHYLLUM IN THE NEW RIVER,VIRGINIA

Productivity of Podostemum ceratophyllum, the dominant aquatic macrophyte in the New River, was measured at four sites representing soft- and hardwater reaches of the river. Available dissolved inorganic carbon (DIC) was 4–5 times greater in the hardwater reach. The difference in available DIC was reflected in standing crop and productivity of P. ceratophyllum. Maximum standing crops of P. ceratophyllum at the two hardwater sites (Sites 1 and 2) were 244.8 ± 30.7 g ash-free dry wt (AFDW) m^−-2 and 193.8 ± 18.7 g AFDW m^−-2 compared to 128.5 ± 14.9 g AFDW m^−-2 and 101.3 ± 6.9 g AFDW m^−-2 for the softwater sites (Sites 3 and 4). Productivity, based on differences in standing crops, was: Site 1, 1.08 ± 0.12 g C m^−-2 d^−-1; Site 2, 0.86 ± 0.08 g Cm^−-2d^−-1; Site 3,0.58 ± 0.06 g C m^−-2 d^−-1; Site 4,0.45 ± 0.03 g C m^−-2 d^−-1. Corresponding values for productivity as ¹⁴C uptake were: 2.77 ± 0.44 g C m^−-2 d^−-1; 2.10 ± 0.45 g C m^−-2 d^−-1; 0.34 ± 0.04 g C m^−-2 d^−-1; 0.28 ± 0.03 g C m^−-2 d^−-1. Productivity/biomass (P/B) based on ¹⁴C uptake and standing crop revealed that P. ceratophyllum productivity was inhibited at the softwater sites perhaps due to carbon limitation. Because of its abundance and its high productivity, P. ceratophyllum is hypothesized to contribute significantly to the New River organic matter budget.     

Anaerobic pre-treatment of slaughterhouse wastewater using fixed-film reactors

The aim of this work was to study the performance of anaerobic fixed-film reactors with non-random support, for poultry slaughterhouse wastewater pre-treatment, including the influence of operating conditions. The work was carried out with two lab-scale reactors, one upflow and the other downflow, both equipped with vertical corrugated PVC tubes as support and a recirculation circuit. Both reactors were operated at 35°C.COD removal efficiencies ranging from 85% to 95% were achieved for organic loading rates of 8 kg COD m⁻³ d⁻¹, while the highest organic loading rates (35 kg COD m⁻³ d⁻¹) led to efficiencies of 55–75%. The reactors did not show destabilization after 12 h shock loads of 50 kg COD m⁻³ d⁻¹ .Reactor stability was easily achieved under intermittent operation, with weekend breaks, after which the reactors rapidly returned to their optimal performance. The influences of the hydraulic retention time, temperature, the recirculation ratio and flow direction were also studied.     

Kinetic modeling of light limitation and sulfur deprivation effects in the induction of hydrogen production with Chlamydomonas reinhardtii. Part II: Definition of model‐based protocols and experimental validation

Photosynthetic hydrogen production under light by the green microalga Chlamydomonas reinhardtii was investigated in a torus‐shaped PBR in sulfur‐deprived conditions. Culture conditions, represented by the dry biomass concentration of the inoculum, sulfate concentration, and incident photon flux density (PFD), were optimized based on a previously published model (Fouchard et al., 2009. Biotechnol Bioeng 102:232–245). This allowed a strictly autotrophic production, whereas the sulfur‐deprived protocol is usually applied in photoheterotrophic conditions. Experimental results combined with additional information from kinetic simulations emphasize effects of sulfur deprivation and light attenuation in the PBR in inducing anoxia and hydrogen production. A broad range of PFD was tested (up to 500 µmol photons m⁻² s⁻¹). Maximum hydrogen productivities were 1.0 ± 0.2 mL H₂/h/L (or 25 ± 5 mL H₂/m² h) and 3.1 mL ± 0.4 H₂/h L (or 77.5 ± 10 mL H₂/m² h), at 110 and 500 µmol photons m⁻² s⁻¹, respectively. These values approached a maximum specific productivity of approximately 1.9 mL ± 0.4 H₂/h/g of biomass dry weight, clearly indicative of a limitation in cell capacity to produce hydrogen. The efficiency of the process and further optimizations are discussed. Biotechnol. Bioeng. 2011;108: 2288–2299. © 2011 Wiley Periodicals, Inc.     

Enhancement of hydrogen production in a single chamber microbial electrolysis cell through anode arrangement optimization

Reducing the inner resistances is crucial for the enhancement of hydrogen generation in microbial electrolysis cells (MECs). This study demonstrates that the optimization of the anode arrangement is an effective strategy to reduce the system resistances. By changing the normal MEC configuration into a stacking mode, namely separately placing the contacted anodes from one side to both sides of cathode in parallel, the solution, biofilm and polarization resistances of MECs were greatly reduced, which was also confirmed with electrochemical impedance spectroscopy analysis. After the anode arrangement optimization, the current and hydrogen production rate (HPR) of MEC could be enhanced by 72% and 118%, reaching 621.3 ± 20.6 A/m³ and 5.56 m³/m³ d respectively, under 0.8 V applied voltage. A maximum current density of 1355 A/m³ with a HPR of 10.88 m³/m³ d can be achieved with 1.5 V applied voltage.     

Histological and pharmacological investigations of the two symmetrically situated giant neurons,RPeNLN and LPeNLN,identified on the anterior surface of the pedal ganglia of an african giant snail (achatina fulica férussac)

• 1.1. Morphological and pharmacological investigations were made of two giant neurons, RPeNLN (right pedal nerve large neuron) and LPeNLN (left pedal nerve large neuron), situated symmetrically on the anterior surface of the pedal ganglia of an African giant snail (Achatina fulica Férussac).
• 2.]2. The two neurons (about 250–300 μm in diameter) were the largest ones identified in the ganglia of the snail species. The axonal pathways of the two neurons were symmetrical; of their four main axonal branches, the three main branches innervated the ipsilateral pedal nerves, whereas the last main branch projected to the contralateral pedal nerves.
• 3.]3. The pharmacological features of the two neurons were very similar. Both were inhibited markedly by dopamine [minimum effective concentrations (MECs): 3 × 10⁻⁶-10⁻⁵M], dl-octopamine (MECs: 2 × 10⁻⁶-2 × 10⁻⁵M), 5-hydroxytryptamine (MEC: 3 × 10⁻⁶M), GABA (MEC: 3 × 10⁻⁵ M), l-homocysteic acid (MECs: 3 × 10⁻⁵-10-10⁻⁴M) and erythro-β-hydroxy-l-ghitanuc acid (MEC: 3× 10⁻⁵M). Acetylcholine showed varied effects, either excitatory or inhibitory, on the two neurons examined. No substances were found to have any marked excitatory effects on the neurons.

     

Two-phase partitioning bioreactors in environmental biotechnology

Operation of microbial electrolysis cells (MECs) without an ion exchange membrane could help to lower the construction costs while lowering the ohmic cell resistance and improving MEC conversion rates by minimizing the pH gradient between anode and cathode. In this research, we demonstrate that membraneless MECs with plain graphite can be operated for methane production without pH adjustment and that the ohmic cell resistance could be lowered with approximately 50% by removing the cation exchange membrane. As a result, the current production increased from 66 ± 2 to 156 ± 1 A m⁻³ MEC by removing the membrane with an applied voltage of −0.8 V. Methane was the main energetic product despite continuous operation under carbonate-limited and slightly acidified conditions (pH 6.1–6.2). Our results suggest that continuous production of hydrogen in membraneless MECs will be challenging since methane production might not be avoided easily. The electrical energy invested was not always completely recovered under the form of an energy-rich biogas; however, our results indicate that membraneless MECs might be a viable polishing step for the treatment of the effluent of anaerobic digesters as methane was produced under low organic loading conditions and at room temperature. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Coupling microbial fuel cells with a membrane photobioreactor for wastewater treatment and bioenergy production

Microbial fuel cells (MFCs) and membrane photobioreactors are two emerging technologies for simultaneous wastewater treatment and bioenergy production. In this study, those two technologies were coupled to form an integrated treatment system, whose performance was examined under different operating conditions. The coupled system could achieve 92–97 % removal of soluble chemical oxygen demand (SCOD) and nearly 100 % removal of ammonia. Extending the hydraulic retention time (HRT) of the membrane photobioreactor to 3.0 days improved the production of algal biomass from 44.4 ± 23.8 to 133.7 ± 12.9 mg L^?1 (based on the volume of the treated water). When the MFCs were operated in a loop mode, their effluent (which was the influent to the algal reactor) contained nitrate and had a high pH, leading to the decreased algal production in the membrane photobioreactor. Energy analysis showed that the energy consumption was mainly due to the recirculation of the anolyte and the catholyte in the MFCs and that decreasing the recirculation rates could significantly reduce energy consumption. The energy production was dominated by indirect electricity generation from algal biomass. The highest energy production of 0.205 kWh m^?3 was obtained with the highest algal biomass production, resulting in a theoretically positive energy balance of 0.033 kWh m^?3. Those results have demonstrated that the coupled system could be an alternative approach for energy-efficient wastewater treatment and using wastewater effluent for algal production.     

Integrated hydrogen production process from cellulose by combining dark fermentation, microbial fuel cells, and a microbial electrolysis cell

Hydrogen gas production from cellulose was investigated using an integrated hydrogen production process consisting of a dark fermentation reactor and microbial fuel cells (MFCs) as power sources for a microbial electrolysis cell (MEC). Two MFCs (each 25 mL) connected in series to an MEC (72 mL) produced a maximum of 0.43 V using fermentation effluent as a feed, achieving a hydrogen production rate from the MEC of 0.48 m³ H₂/m³/d (based on the MEC volume), and a yield of 33.2 mmol H₂/g COD removed in the MEC. The overall hydrogen production for the integrated system (fermentation, MFC and MEC) was increased by 41% compared with fermentation alone to 14.3 mmol H₂/g cellulose, with a total hydrogen production rate of 0.24 m³ H₂/m³/d and an overall energy recovery efficiency of 23% (based on cellulose removed) without the need for any external electrical energy input.     

First estimates of productivity in Lessonia trabeculata and Lessonia nigrescens (Phaeophyceae, Laminariales) from the southeast Pacific

Lessonia is the main Laminariales found along the southeast Pacific coast. Lessonia nigrescens Bory de Saint‐Vincent in the intertidal and Lessonia trabeculata Villouta et Santelices in the subtidal, are the most important habitat constructors in rocky coastal communities in northern and central Chile. In both species, the seasonal production and erosion of distal tissue were estimated in biomass units using the Area of Constant Biomass Model that combined the individual blade elongation, obtained with the traditional hole‐punching method, with the blade length and biomass distribution along the blade. In austral late spring (December 96) and autumn (May 97), blade production and erosion were transformed to the level of population from standing stock measurements (number and biomass of blades and plants per substrate area), considering that previous blade weight analysis showed the highest and lowest values at these times, as well as the population parameter extremes that were expected to occur. Both species displayed a seasonal pattern, with a production increase in later winter and spring and decrease towards the end of summer that coincided with higher distal tissue erosion. At the level of individual blades, Lessonia trabeculata showed higher mean production (0.026 g dw d⁻¹) and erosion (0.01 g dw d⁻¹) than L. nigrescens (production 0.01 g dw d⁻¹ and loss 0.002 g dw d⁻¹). The standing stocks, with respect to density and biomass, were similar in spring and autumn for both populations. Nevertheless, the net productivity (production minus erosion) of the intertidal L. nigrescens showed greater values due to the greater density of blades (2112 ± 1360 (SE) blades m⁻²) compared with the subtidal L. trabeculata (527 ± 151 (SE) blades m⁻²). Spring net productivities of 42 g dw m⁻²d⁻¹ (254 g ww m⁻²d⁻¹; 11.46 gC m⁻²d⁻¹) for L. nigrescens and 11 g dw m⁻² d⁻¹ (64 g ww m⁻² d⁻¹; 2.46 gC m⁻²d⁻¹) for L. trabeculata were estimated. A preliminary model of production and biomass fate for Lessonia populations is proposed.     

Hydrogen Production by Geobacter Species and a Mixed Consortium in a Microbial Electrolysis Cell

A hydrogen utilizing exoelectrogenic bacterium (Geobacter sulfurreducens) was compared to both a nonhydrogen oxidizer (Geobacter metallireducens) and a mixed consortium in order to compare the hydrogen production rates and hydrogen recoveries of pure and mixed cultures in microbial electrolysis cells (MECs). At an applied voltage of 0.7 V, both G. sulfurreducens and the mixed culture generated similar current densities (ca. 160 A/m³), resulting in hydrogen production rates of ca. 1.9 m³ H₂/m³/day, whereas G. metallireducens exhibited lower current densities and production rates of 110 ± 7 A/m³ and 1.3 ± 0.1 m³ H₂/m³/day, respectively. Before methane was detected in the mixed-culture MEC, the mixed consortium achieved the highest overall energy recovery (relative to both electricity and substrate energy inputs) of 82% ± 8% compared to G. sulfurreducens (77% ± 2%) and G. metallireducens (78% ± 5%), due to the higher coulombic efficiency of the mixed consortium. At an applied voltage of 0.4 V, methane production increased in the mixed-culture MEC and, as a result, the hydrogen recovery decreased and the overall energy recovery dropped to 38% ± 16% compared to 80% ± 5% for G. sulfurreducens and 76% ± 0% for G. metallireducens. Internal hydrogen recycling was confirmed since the mixed culture generated a stable current density of 31 ± 0 A/m³ when fed hydrogen gas, whereas G. sulfurreducens exhibited a steady decrease in current production. Community analysis suggested that G. sulfurreducens was predominant in the mixed-culture MEC (72% of clones) despite its relative absence in the mixed-culture inoculum obtained from a microbial fuel cell reactor (2% of clones). These results demonstrate that Geobacter species are capable of obtaining similar hydrogen production rates and energy recoveries as mixed cultures in an MEC and that high coulombic efficiencies in mixed culture MECs can be attributed in part to the recycling of hydrogen into current.Electrohydrogenesis is an efficient method for generating hydrogen gas from organic matter in reactors known as microbial electrolysis cells (MECs) (17, 18, 26). MECs differ from air-cathode microbial fuel cells (MFCs) in that the cathode remains anaerobic, and voltage is added in order to generate hydrogen at the cathode. Under the biological conditions in MECs, hydrogen evolution is not a thermodynamically favorable reaction. However, combining the hydrogen formation reaction potential of −0.41 V at the cathode (E_CAT) with the anode potential (E_AN) typically obtained in MFCs with an E_AN of −0.30 V (1 g of acetate/liter) results in a minimum required voltage of only 0.14 V. Applied voltages (E_AP) of 0.2 V (0.45 kWh/m³ H₂) or larger are needed in practice to produce measurable quantities of hydrogen, but this input is substantially less than the average of 2.3 V (5.1 kWh/m³ H₂) required for water electrolysis (13).Recent improvements in designs and materials have substantially improved hydrogen yields, production rates, and energy recoveries (3, 18, 27-29, 33). Hydrogen recoveries using typical dead-end fermentation end products such as acetate and butyrate have reached 80 to 100%, whereas other complex substrates such as glucose and cellulose have yielded recoveries of ca. 70% (5). Production rates larger than 6 m³ H₂/m³/day have been obtained using MECs (32), which are similar to an average rate of 2.5 m³ H₂/m³/day obtained for hydrogen production by biological fermentation (10). Energy recoveries relative to the electrical energy input as high as 680% have already been shown (5), and overall energy recoveries that include the energy of the substrate have reached 85% (2, 5).Hydrogen losses can occur using a mixed culture in an MEC, reducing hydrogen yields, production rates, and recoveries (3, 11, 16, 32). Hydrogen recoveries can drop significantly at lower applied voltages in membraneless MECs because of methanogenic consumption of hydrogen (2, 8, 11, 34). Using a membraneless MEC, Call and Logan (2) found that the overall hydrogen recovery of 90% at an E_AP of 0.6 V was reduced to 18% at an E_AP of 0.2 V and that methane concentrations increased from 0.9 to 28% in the product gas. Reducing solution pH can help inhibit methanogens, but a methane concentration of 22% was observed in a membrane free MEC at pH 5.8 (11). When hydrogen is the intended product of an MEC, methane production is detrimental to the process. However, biologically produced methane is a renewable energy source, and membraneless MECs can be used to generate methane instead of hydrogen, although energy recoveries are lower (8). Hydrogen can also be consumed by chemolithotrophic bacteria in mixed-culture MECs. These bacteria may transfer the associated electrons to a suitable electron acceptor, such as carbon dioxide, and in some cases, the anode. In the latter scenario, the electrons from hydrogen would be recycled internally, causing an increase in coulombic efficiency (16). Hydrogen losses reduce hydrogen and energy recoveries, and alternative methods for generating methane-free and high hydrogen content gas are needed.Pure culture MECs are one method to avoid losses to methanogens, but production rates and efficiencies with pure cultures can be low compared to those with mixed cultures. Using a pure culture of Shewanella oneidensis MR-1 and lactate, Hu et al. obtained a hydrogen production rate of 0.025 m³ H₂/m³/day at an E_AP of 0.6 V (11). However, production rates at this same applied voltage using mixed cultures have reached 1 to 2 m³ H₂/m³/day (2, 5). In MFCs, S. oneidensis has produced low coulombic efficiencies (<10%) (24, 25) and maximum current densities of ca. 50 mA/m² (15) with lactate, compared to ca. 9,900 mA/m² (9) for mixed cultures.Several Geobacter species are commonly found in mixed culture MFCs, and tests with pure cultures of Geobacter sulfurreducens have demonstrated power and current densities close to or equal to those achieved with mixed cultures. In an air cathode MFC, G. sulfurreducens produced a lower power density (461 mW/m², 1.5 A/m²) than a mixed culture (576 mW/m², 1.3 A/m²) (12). The reduced performance of G. sulfurreducens in the air cathode MFC may have been due to oxygen intrusion across the cathode. Using an MFC with a ferricyanide cathode, Nevin et al. (23) reported a power density of 1.9 W/m² (4.6 A/m²) for G. sulfurreducens compared to 1.6 W/m² (3.2 A/m²) for a mixed consortium. When the authors placed the G. sulfurreducens MFC in an anaerobic chamber, the coulombic efficiency improved from 55% to ca. 100%, confirming the importance of strictly anaerobic conditions for G. sulfurreducens. This suggests that the anaerobic environment of MECs may provide excellent conditions for obtaining current densities comparable to those of mixed cultures with pure cultures of Geobacter species, while at the same time eliminating methane gas production.In order to investigate the performance of Geobacter species in MECs, we selected two Geobacter species based on their differences in hydrogen utilization. G. sulfurreducens was selected because it is capable of producing high current densities in MFCs, and it can utilize hydrogen. G. metallireducens, which does not oxidize hydrogen, was examined to determine whether higher hydrogen recoveries were possible with a bacterium that cannot oxidize hydrogen. Both of these cultures were compared to a mixed culture under identical conditions in order to further examine the role of internal hydrogen recycling in MECs and to show that methane-free gas can be produced in MECs at rates comparable to those obtained with mixed cultures.     

Production enhancement of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) in Halogeometricum borinquense,characterization of the bioplastic and desalination of the bioreactor effluent

Polyhydroxyalkanoates (PHAs) are a replacement of conventional single-use plastics. Bioprocess conditions of the extreme halophilic archaeon Halogeometricum borinquense strain RM-G1 were selected resulting in the synthesis of 66.80 ± 1.69 % PHA (of cell dry mass) in 72 h using glycerol and tryptone as carbon and nitrogen sources respectively, yielding volumetric productivity of 0.206 ± 0.006 gL⁻¹ h⁻¹ in a repeated batch process in a small-scale bioreactor where 20 % of the production medium was used as the inoculum for the subsequent batch. The purified PHA was characterized as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with 10.21 mol% 3-hydroxyvalerate content possessing glass transition temperature -12.6 °C, degradation temperature 285 °C, number average molecular weight 156,899 Da, weight average molecular weight 288,723 Da, polydispersity index 1.8 and melting temperatures 139.1 °C and 152.5 °C. Maximum (21.7 ± 0.6 L m^-2 h⁻¹) and average (17.2 ± 0.6 L m^-2 h⁻¹) flux values were their respective highest and crystallization time was its least (3.0 ± 0.16 h) when ΔT was 90 °C and polytetrafluoroethylene membrane was applied for desalination of the bioreactor effluent by Direct Contact Membrane Distillation. While using polyvinylidene fluoride membrane, maximum 25.5 ± 0.5 L m^-2 h⁻¹ and average 18.6 ± 0.2 L m^-2 h⁻¹ fluxes were obtained and crystallization time decreased (3.25 ± 0.16 h) even when ΔT was lowered by 20 °C.     

Long-term continuous partial nitritation-anammox reactor aeration optimization at different nitrogen loading rates for the treatment of ammonium rich digestate lagoon supernatant

Dissolved oxygen (DO) is an important parameter for partial nitritation-anammox process but previously not evaluated for the treatment of digested biosolid thickening lagoon supernatant. Using intermittent aeration we investigated nitrogen removal from such supernatant in an integrated fixed film activated sludge (IFAS) process operated under a variety of hydraulic retention times (1.2–2.5 days). The overall nitrogen removal rate (NRR) was significantly increased (P < 0.01) from 0.26 ± 0.01 kg N m⁻³ d^-1 at HRT of 2.5 days to 0.50 ± 0.01 kg N m^-3 d^-1 at HRT of 1.2 day. Higher nitrogen loading rates needed higher DO concentrations in order to cope with the increased oxygen demand by ammonium-oxidizing bacteria (AOB). Enhancing the DO concentration from 0.18 mg L^-1 to 0.35 mg L^-1 improved AOB activity. However, when the bulk liquid DO was in the range of 0.28−0.35 mg L^-1, anammox activity inhibition was observed associated with a significant free nitrous acid (FNA) accumulation (21.70 ± 4.10 μg L^-1). Batch studies confirmed the inhibition of anammox activity under high DO conditions (0.28−0.35 mg L^-1). Aeration strategies, other than increasing the DO set points, should be investigated in order to be able to work at high nitrogen loading rates without compromising anammox activity.     

Solubilization,characterization and photoaffinity labeling of the mitochondrial dihydropyridine receptor from bovine adrenal medulla

• 1.1. The mitochondrial dihydropyridine receptor was solubilized with Chaps at a detergent/ protein ratio of 2.5, during 45 min at 4°C.
• 2.2. From the rate constants of association (8.10 ± 0.25 × 10⁴ M⁻¹ min⁻¹) and dissociation (0.022 ± 0.001 min⁻¹ a K_d of 275 nM was calculated, while from saturation experiments a K_d of 270 ± 30 nM and a density of receptors of 106 ± 9 pmol/mg protein was obtained.
• 3.4. The solubilized receptors are heat-resistant, sensitive to the trypsin and to the reduction of disulfide bonds.
• 4.5. In native membranes, a polypeptide of 50 kDa was specifically photolabelled with [³H]Azidopine.

     

Photochemical energy conversion using immobilized blue-green algae

A blue-green alga, Anabaena N-7363, was immobilized in 2% κ-carrageenan gel. The hydrogen productivity of the immobilized algae was 2.4 times higher than that of free algae, with a maximum rate of hydrogen production of 3.24 mmol h⁻¹ g⁻¹ dry gel, in a nitrogen free medium under illumination (6000 lux). The immobilized blue-green algae (39 kg wet gel) was employed for continuous production of hydrogen under illumination (6000 lux), producing 0.5–1.1 ml min⁻¹ for more than 8 days. The hydrogen produced was supplied to a phosphoric acid fuel cell, which generated an approximate 50 mW power output and a current of 300 mA over a period of 4 h.     

CNP budgets of a coral-dominated fringing reef at La Réunion,France: coupling of oceanic phosphate and groundwater nitrate

Productivity, nutrient input, nutrient uptake, and release rates were determined for a coral-dominated reef flat at La Réunion, France, to assess the influence of groundwater nitrogen on carbon and nutrient budgets. Water samples were collected offshore in the ocean, at the reef crest and back reef for nutrients, picoplankton, pH, and total alkalinity. Volume transport of ocean water across the reef flat was measured using both current meters and drogues. Groundwater advected onto the reef flat and mixed with incoming ocean water. Metabolic rates for the reef community were determined to be: gross primary production = 1,000 mmol C m⁻² d⁻¹, community respiration = 960 mmol C m⁻² d⁻¹, and community calcification = 210 mmol C m⁻² d⁻¹. Across the reef flat, silicate behaved conservatively, there was net uptake of phosphate (0.06 mmol P m⁻² d⁻¹) and net release of nitrate, ammonia, dissolved and particulate organic nitrogen (total 7.0 mmol N m⁻² d⁻¹). Groundwater nitrate contributed 37% of the increase in nitrate plus ammonia. The first-order mass transfer coefficient of phosphate was 3.3 m d⁻¹, and for nitrate plus ammonia, 5.9 m d⁻¹. Gross N and P uptake from estimates of mass transfer and uptake of particles were 0.37 mmol P m⁻² d⁻¹ and 7.2 mmol N m⁻² d⁻¹, respectively giving an N:P uptake ratio of 20:1. Thus, the elevation of nitrogen across the reef flat maintains a high N:P flux, enhancing algal growth downstream of the transect. We conclude that net community production (40 mmol C m⁻² d⁻¹) was sustained by net uptake of phosphate from the ocean and net uptake of new nitrogen from groundwater.

     

Effect of mixing on biogas production during mesophilic anaerobic digestion of screened dairy manure in a pilot plant

The effect of mixing on biogas production of a 1.5‐m³ pilot continuous stirred tank reactor (CSTR) processing screened dairy manure was evaluated. Mixing was carried out by recirculation of reactor content with a mono pump. The experiment was conducted at a controlled temperature of 37±1°C and hydraulic retention times (HRTs) of 20 and 10 days. The effect of continuous and intermittent operation of the recirculation pump on biogas production was studied. At 10 days of HRT, the results showed a minimal influence of recirculation rate on biogas production and that continuous recirculation did not improve reactor performance. At 20 days of HRT, the recirculation rate did not affect reactor performance. Combination of low solid content in feed animal slurry and long HRTs results in minimal mixing requirements for anaerobic digestion.     

Sulfate reduction and microbial community of autotrophic biocathode in response to acidity

Microbial electrolysis cells (MECs) with autotrophic biocathode are a promising technology for removal of pollutants in wastewater. The aim of this study was to investigate the effect of initial acidity of wastewater on performance of sulfate-reducing biocathodes. MECs with biocathodes were operated with initial pH values of catholyte ranged from 3.0 to 7.0. The optimum initial pH value was 6.0 with a maximum sulfate reductive rate and biomass of 57 mg L⁻¹ d⁻¹ and 2.1 ± 0.4 mg g⁻¹, respectively. With initial pH 7.0, the pH value of catholyte increased to 9.8 ± 0.2 after an operation cycle, which resulted in low performance of the biocathode. A considerable sulfate reductive rate of 31 ± 0.85 mg L⁻¹ d⁻¹ was achieved with initial pH 3.0. Desulfovibrio sp. grew dominantly with abundance of 46%–66% in the cathode biofilm with initial pH values from 3.0 to 6.0 and contributed to the sulfate reduction. Clostridium and Parapedobacter also had high abundance in pH 6.0 cathode, indicated that interspecies electron transfer between electrochemical active and sulfate-reducing bacteria could play an important role in sulfate removal. The results suggest that acidity of catholyte is an important factor to be considered to utilize autotrophic biocathode MECs for wastewater treatment.     

Domestic wastewater treatment using multi-electrode continuous flow MFCs with a separator electrode assembly design

Treatment of domestic wastewater using microbial fuel cells (MFCs) will require reactors with multiple electrodes, but this presents unique challenges under continuous flow conditions due to large changes in the chemical oxygen demand (COD) concentration within the reactor. Domestic wastewater treatment was examined using a single-chamber MFC (130 mL) with multiple graphite fiber brush anodes wired together and a single air cathode (cathode specific area of 27 m²/m³). In fed-batch operation, where the COD concentration was spatially uniform in the reactor but changed over time, the maximum current density was 148?±?8 mA/m² (1,000 Ω), the maximum power density was 120 mW/m², and the overall COD removal was >90 %. However, in continuous flow operation (8 h hydraulic retention time, HRT), there was a 57 % change in the COD concentration across the reactor (influent versus effluent) and the current density was only 20?±?13 mA/m². Two approaches were used to increase performance under continuous flow conditions. First, the anodes were separately wired to the cathode, which increased the current density to 55?±?15 mA/m². Second, two MFCs were hydraulically connected in series (each with half the original HRT) to avoid large changes in COD among the anodes in the same reactor. The second approach improved current density to 73?±?13 mA/m². These results show that current generation from wastewaters in MFCs with multiple anodes, under continuous flow conditions, can be improved using multiple reactors in series, as this minimizes changes in COD in each reactor.     

Coupling glucose fermentation and homoacetogenesis for elevated acetate production: Experimental and mathematical approaches

Homoacetogenesis is an important potential hydrogen sink in acetogenesis, in which hydrogen is used to reduce carbon dioxide to acetate. So far the acetate production from homoacetogenesis, especially its kinetics, has not been given sufficient attention. In this work, enhanced production of acetate from anaerobic conversion of glucose through coupling glucose fermentation and homoacetogenesis is investigated with both experimental and mathematical approaches. Experiments are conducted to explore elevated acetate production in a coupled anaerobic system. Acetate production could be achieved by homoacetogenesis with a relative high acetate yield under mixed fermentation conditions. With the experimental observations, a kinetic model is formulated to describe such a homoacetogenic process. The maximum homoacetogenic rate (k_m,homo) is estimated to be 28.5 ± 1.7 kg COD kg⁻¹ COD day⁻¹ with an uptake affinity constant of 3.7 × 10⁻⁵ ± 3.1 × 10⁻⁶ kg COD m⁻³. The improved calculation of homoacetogenic kinetics by our approach could correct the underestimation of homoacetogenesis in anaerobic fermentation processes, as it often occurs in these systems supported by literature analysis. The model predictions match the experimental results in different cases well and provide insights into the dynamics of anaerobic glucose conversion and acetate production. Furthermore, acetate production via homoacetogenesis increases by about 40% through utilizing the fed‐batch coupling system, attributed to a balance between the hydrogen production in the acetogenesis phase and the hydrogen consumption in the homoacetogenesis phase. This work provides an effective way for increased anaerobic acetate production, and gives us a better understanding about the homoacetogenic kinetics in the anaerobic fermentation process. Biotechnol. Bioeng. 2011;108: 345–353. © 2010 Wiley Periodicals, Inc.     

Digital heart rate monitor derived from the arterial pressure pulse

This monitor displays heart rate without the need for electrical contact with the experimental animal. The device uses a quartz pressure transducer connected to an arterial catheter and has a full scale accuracy of ± 3 beats min⁻¹; its range is 0–400 beats min⁻¹. There is an output voltage proportional to heart rate and internal calibration facilities are provided at 60 and 360 beats min⁻¹.