Higher Oxygen Uptake Rate Research Articles

The role of iron in peroxidation of PUFA: Effect of pH and chelators

The aim of this work was to understand the effect of pH and chelators on free iron (Fe2+/Fe3+)‐mediated oxidation in liposome dispersions made of marine phospholipids. Consumption of dissolved oxygen was used to follow lipid oxidation. The highest oxygen uptake rates were found at pH 4–5. The increase in pH (>5.7) enhanced autoxidation rate of Fe2+ to Fe3+ and lowered solubility of Fe3+ causing decrease in oxygen uptake rates. Simultaneously, the negative charge on the liposome vesicles increased with increasing pH improving the attraction between iron and liposomes. The retention of Fe3+ ions by phospholipids is suggested to prevent complete precipitation of Fe3+ at pH > 5, which facilitates a pro‐oxidative activity of iron even at higher pH. The tested chelators reduced Fe2+ (10 μM) mediated oxidation at pH 5.5 and at 2:1 chelator‐to‐iron ratio in the following order: EDTA ∼ casein > citric acid > oxalic acid. However, when pH was reduced below the pKa of the EDTA carboxylic groups, EDTA lost its chelating abilities. The stability constants for complexes between the chelators and iron followed the same sequence as efficacy of the chelators at pH 5.5, making it an additional factor determining the efficacy of chelators. This study shows that the final oxidation rate is dependent on the overall dissolved iron in the system and the degree of attraction between iron and the surface of liposome vesicles at a given pH.Practical applicationsFor successful addition of marine polyunsaturated lipids into emulsified food, it is important to understand how physicochemical conditions affect the pro‐oxidative activity of iron and the antioxidant activity of metal chelators. This work addresses the role of pH in oxidation of marine liposomes, and the knowledge may help to characterise effective hurdles for lipid oxidation. This study shows that pH has an impact on iron solubility and attraction between iron and the liposome surface and also affects the efficacy of EDTA. This study also shows that by quantification of the dissolved oxygen consumption, it is possible to screen and evaluate the impact of surrounding conditions (pH, chelators) on iron‐mediated oxidation in a water‐based system.The study shows that oxidation rate is dependent on the overall dissolved iron in the system and the degree of attraction between iron and the surface of liposome vesicles at a given pH.

Oxygen budgets in subtidal arctic (Kongsfjorden, Svalbard) and temperate (Helgoland, North Sea) microphytobenthic communities

We compared primary production and respiration of temperate (Helgoland, North Sea) and subtidal Arctic (Kongsfjorden, Svalbard) microphytobenthic communities during sum- mer. The diatom communities were generally characterized as cosmopolitan, displayed no site specificity, and had similar chl a and fucoxanthin concentrations. Their net and gross photosynthe- sis rates and light adaptation intensities, derived from laboratory microsensor measurements, were also similar, despite differences in water temperature. Daily oxygen fluxes across the sedi- mentwater interface were estimated by combining laboratory microprofile and planar optode measurements with in situ data on oxygen penetration and light dynamics. During the study period, the Svalbard sediments were on average net heterotrophic, while the Helgoland sediments were net autotrophic (�22.4 vs. 9.2 mmol O2 m �2 d �1 ). This was due to high infaunal abundance in the Svalbard sediments that caused high oxygen uptake rates in the sediments and consumption below the sediment euphotic zone. Additionally, bioirrigation of the sediment due to infaunal burrow ventilation was reduced by light; thus, the sedimentary oxygen inventory was reduced with increasing light. Conversely, light-enhanced the oxygen inventory in the Helgoland sedi- ments. Oxygen dynamics in the Svalbard sediments were therefore dominated by bioirrigation, whereas in the Helgoland sediments they were dominated by photosynthetic oxygen production.

Recycling of Dry-Batch Digestate as Amendment: Soil C and N Dynamics and Ryegrass Nitrogen Utilization Efficiency

In this work a residue of dry-batch anaerobic digestion (DB) from the organic fraction of municipal solid waste, its composted homologous (CDB), and a municipal solid waste compost (MSWC) were characterized for their main physico-chemical traits and biological stability [oxygen uptake rate (OUR)]. These were then compared in soil incubations at 200 mg N kg−1, to assess carbon (C) and nitrogen (N) mineralization. The products’ nitrogen apparent recovery fraction (ARF) was assessed in a pot trial on Italian ryegrass. DB showed the highest OUR, followed by CDB and the more stable MSWC: 161.7; 20.7 and 5.7 mmol O2 kg−1 VS h−1, partially in agreement with the potentially mineralizable C pools in soil: 58.4; 16.6 and 19.5 % and their kinetics (k, 0.1906; 0.1405 and 0.1377 day−1). Composting greatly reduced the total carbon dioxide (CO2) emissions from 7,950 to 3,449 mg kg−1 in DB and CDB, even higher than MSWC (1,936 mg kg−1). After intense N-immobilization in soil (−22.3 %), DB finally reduced the gap (−6.9 %), also having a positive ARF (5.0 %), while CDB had greater N-immobilization (−12.9 %) and a negative ARF (−3.4 %). MSWC showed 3.8 % N-mineralization, and an intermediate ARF (2.7 %). The management of DB for plant nutrition therefore seems difficult since DB can furnish nitrogen not easily synchronizable with plant growth due to its release pattern characterized by initial immobilization. Composting increased stability but amplified N-immobilization due to the high C:N ratio of the bulking agent. A prolonged and more balanced composting process can reduce this restriction, aligning CDB with MSWC.

A new dynamic model for highly efficient mass transfer in aerated bioreactors and consequences for kLa identification

Gas-liquid mass transfer is often rate-limiting in laboratory and industrial cultures of aerobic or autotrophic organisms. The volumetric mass transfer coefficient k(L) a is a crucial characteristic for comparing, optimizing, and upscaling mass transfer efficiency of bioreactors. Reliable dynamic models and resulting methods for parameter identification are needed for quantitative modeling of microbial growth dynamics. We describe a laboratory-scale stirred tank reactor (STR) with a highly efficient aeration system (k(L) a ≈ 570 h(-1)). The reactor can sustain yeast culture with high cell density and high oxygen uptake rate, leading to a significant drop in gas concentration from inflow to outflow (by 21%). Standard models fail to predict the observed mass transfer dynamics and to identify k(L) a correctly. In order to capture the concentration gradient in the gas phase, we refine a standard ordinary differential equation (ODE) model and obtain a system of partial integro-differential equations (PIDE), for which we derive an approximate analytical solution. Specific reactor configurations, in particular a relatively short bubble residence time, allow a quasi steady-state approximation of the PIDE system by a simpler ODE model which still accounts for the concentration gradient. Moreover, we perform an appropriate scaling of all variables and parameters. In particular, we introduce the dimensionless overall efficiency κ, which is more informative than k(L) a since it combines the effects of gas inflow, exchange, and solution. Current standard models of mass transfer in laboratory-scale aerated STRs neglect the gradient in the gas concentration, which arises from highly efficient bubbling systems and high cellular exchange rates. The resulting error in the identification of κ (and hence k(L) a) increases dramatically with increasing mass transfer efficiency. Notably, the error differs between cell-free and culture-based methods of parameter identification, potentially confounding the determination of the "biological enhancement" of mass transfer. Our new model provides an improved theoretical framework that can be readily applied to aerated bioreactors in research and biotechnology.

Metabolic flux analysis of the central carbon metabolism of the industrial vitamin B12 producing strain Pseudomonas denitrificans using 13C-labeled glucose

The network topology and metabolic fluxes of central carbon metabolism in the industrial vitamin B12 producing strain Pseudomonas denitrificans were characterized under oxygen limiting levels. Cultivations were carried out with 100% [1-13C] or 20% [U-13C] glucose as substrates under different oxygen supply conditions. The labeling patterns of the proteinogenic amino acids of exponentially growing cells were used to accurately estimate the fluxes in the central carbon metabolism of P. denitrificans. Metabolic flux analysis showed that glucose was mostly catabolized by the Entner–Doudoroff and pentose phosphate pathways. Up to 33% of glucose was consumed via the PP pathway under high specific oxygen uptake rate (SOUR) conditions. This amount was 77.9% higher than that under low oxygen uptake conditions. Quantitative evidence was also found for reversible serine hydroxymethyl transferase and threonine aldolase activities. Metabolic flux and cofactor analyses further showed that higher SOUR accelerated the supply of precursors and methyl groups. SOUR also provided more NADPH for higher vitamin B12 production under the same glucose consumption.

Real-time fluid dynamics investigation and physiological response for erythromycin fermentation scale-up from 50 L to 132 m3 fermenter

The physiological response of erythromycin fermentation scale-up from 50 L to 132 m(3) scale was investigated. A relatively high oxygen uptake rate (OUR) in early phase of fermentation was beneficial for erythromycin biosynthesis. Correspondingly, the maximal consistency coefficient (K) reflecting non-Newtonian fluid characteristics in 50 L and 132 m(3) fermenter also appeared in same phase. Fluid dynamics in different scale bioreactor was further investigated by real-time computational fluid dynamics modeling. The results of simulation showed that the impeller combination in 50 L fermenter could provide more modest flow field environment compared with that in 132 m(3) fermenter. The decrease of oxygen transfer rate (OTR) in 132 m(3) fermenter was the main cause for impairing cell physiological metabolism and erythromycin biosynthesis. These results were helpful for understanding the relationship between hydrodynamic environment and physiological response of cells in bioreactor during the scale-up of fermentation process.

Intracellular co-expression of Vitreoscilla hemoglobin enhances cell performance and β-galactosidase production in Pichia pastoris

Pichia pastoris has been used to produce various recombinant proteins under high oxygen demand conditions. To improve the heterologous production of β-galactosidase, the vgb gene encoding Vitreoscilla hemoglobin (VHb) was co-expressed in the P. pastoris cytoplasm under the control of the methanol-inducible promoter. Co-expression of VHb under different aeration conditions improved cell performance in terms of growth, viability, respiratory rate, and β-galactosidase production. Under limiting aeration conditions, the VHb(+) strain produced 28.2% more biomass but 31.2% less total β-galactosidase activity than the VHb(-) strain. Under non-limiting aeration conditions, the VHb(+) strain showed 20.3% higher cell growth and 9.9% more total β-galactosidase activity than the VHb(-) strain. Moreover, under these conditions, the VHb(+) strain was 7.7% more viable and had a 28.2% higher oxygen uptake rate (OUR) than the VHb(-) strain. Evidently, VHb can enhance the OUR and promote methanol metabolism, thereby improving cell performance and β-galactosidase production.

Drum composting of municipal solid waste

The high initial C/N ratio (>30) found in Indian municipal solid waste (MSW) leads to more time required for composting (>3 months), with poor-quality compost production. Therefore, the effects of MSW amended with cattle manure (trial 1) and tree leaves (trial 2) were compared with unamended MSW (control) in a rotary drum composter. The initial C/N ratios of trial 1 and trial 2 were kept at 22, as compared to 32 for the MSW control sample. It was observed that trial 1 produced high-quality and stable compost within 20 days. It showed higher final total nitrogen (2.2%), final total phosphorus (3.2 g/kg) and low electrical conductivity (2.7 dS/m). At the end of 20 days, higher degradation caused lower final oxygen uptake rate (OUR) (1.8 mg/g volatile solids (VS)/day), final CO2 evolution (1.0 mg/g VS/day) and final C/N ratio (7.8). Trial 2 produced good-quality and stable compost resulting in 1.9% of total nitrogen, 2.7% of total phosphorus and low OUR (2.0 mg/g VS/day), CO2 evolution (1.5 mg/g VS/day) and C/N ratio (10.1) after 20 days of composting. However, the control sample with an initial C/N ratio of 32 showed higher OUR (3.6 mg/g VS/day) and CO2 evolution (2.6 mg/g VS/day) comprising a lower concentration of total nitrogen (1.6%) and total phosphorus (2.3 g/kg), which indicated an unstable and low-quality product as compared to trials 1 and 2. Therefore, results showed that the characteristics of MSW amended with cattle manure and tree leaves significantly influence the compost quality and process dynamics in a rotary drum composter.

Biodegradation potential of bulking agents used in sludge bio-drying and their contribution to bio-generated heat

Straw and sawdust are commonly used bulking agents in sludge composting or bio-drying. It is important to determine if they contribute to the biodegradable volatile solids pool. A sludge bio-drying process was performed in this study using straw, sawdust and their combination as the bulking agents. The results revealed that straw has substantial biodegradation potential in the aerobic process and sawdust has poor capacity to be degraded. The temperature profile and bio-drying efficiency were highest in the trial that straw was added, as indicated by a moisture removal ratio and VS loss ratio of 62.3 and 31.0%, respectively. In separate aerobic incubation tests, straw obtained the highest oxygen uptake rate (OUR) of 2.14 and 4.75 mg O 2 g −1VS h −1 at 35 °C and 50 °C, respectively, while the highest OUR values of sludge were 12.1 and 5.68 mg O 2 g −1VS h −1 at 35 °C and 50 °C and those of sawdust were 0.286 and 0.332 mg O 2 g −1VS h −1, respectively. The distribution of biochemical fractions revealed that soluble fractions in hot water and hot neutral detergent were the main substrates directly attacked by microorganisms, which accounted for the initial OUR peak. The cellulose-like fraction in straw was transformed to soluble fractions, resulting in an increased duration of aerobic respiration. Based on the potential VS degradation rate, no bio-generated heat was contributed by sawdust, while that contribution by straw was about 41.7% and the ratio of sludge/straw was 5:1 (w/w, wet basis).

Evaluation of an integrated sponge – Granular activated carbon fluidized bed bioreactor for treating primary treated sewage effluent

An integrated fluidized bed bioreactor (iFBBR) was designed to incorporate an aerobic sponge FBBR (ASB-FBBR) into an anoxic granular activated carbon FBBR (GAC-FBBR). This iFBBR was operated with and without adding a new starch based flocculant (NSBF) to treat synthetic primary treated sewage effluent (PTSE). The NSBF contains starch based cationic flocculants and trace nutrients. The results indicate that the iFBBR with NSBF addition could remove more than 93% dissolved organic carbon (DOC), 61% total nitrogen (T-N) and 60% total phosphorus (T-P) at just a very short hydraulic retention time of 50 min. The optimum frequency of adding NSBF to the iFFBR is four times per day. As a pretreatment to microfiltration, the iFFBR could increase 5 L/m 2 h of critical flux thus reducing the membrane fouling. In addition, better microbial activity was also observed with high DO consumption (>66%) and specific oxygen uptake rate (>35 mg O 2/g VSS h).

Semicontinuous bioreactor production of a recombinant human therapeutic protein using a chemically inducible viral amplicon expression system in transgenic plant cell suspension cultures

Plant cell culture is an alternative for the production of recombinant human therapeutic proteins because of improved product safety, lower production cost, and capability for eukaryotic post-translational modification. In this study, bioreactor production of recombinant human alpha-1-antitrypsin (rAAT) glycoprotein using a chemically inducible Cucumber mosaic virus (CMV) viral amplicon expression system in transgenic Nicotiana benthamiana cell culture is presented. Optimization of a chemically inducible plant cell culture requires evaluation of effects of timing of induction (TOI) and concentration of inducer (COI) on protein productivity and protein quality (biological functionality). To determine the optimal TOI, the oxygen uptake rate (OUR) of the plant cell culture was chosen as a physiological indicator for inducing maximum rAAT expression. Effects of COI on rAAT production were investigated using a semicontinuous culture, which enables the distinction between effects of growth rate and effects of inducer concentration. An optimized semicontinuous bioreactor operation was further proposed to maximize the recombinant protein production. The results demonstrated that the transgenic plant cells, transformed with the inducible viral amplicon expression system, maintain higher OUR and exhibit lower extracellular protease activity and lower total phenolics concentration in the optimized semicontinuous bioreactor process than in a traditional batch bioreactor operation, resulting in a 25-fold increase in extracellular functional rAAT (603 microg/L) and a higher ratio of functional rAAT to total rAAT (85-90%). Surprisingly, sustained rAAT production and steady state, long-term bioreactor operation is possible following chemical induction and establishment of the viral amplicons.

Effective and stable porcine interferon-α production by Pichia pastoris fed-batch cultivation with multi-variables clustering and analysis

Efficient porcine interferon-alpha (pIFN-alpha) expression in high density recombinant Pichia pastoris cultivation was achieved in a 5 l bench-scaled bioreactor. The results indicated that a high and stable oxygen uptake rate (OUR) during induction phase was closely related with pIFN-alpha production efficiency. The multi-variables clustering and analysis results showed that the achievement of a high and stable OUR relied on a higher glycerol consumption rate during fed-batch culture phase and a moderate methanol level (around 10 g/l) during induction phase. In the high and stable OUR environments (200-300 mmol/l/h), the highest pIFN-alpha antiviral activity could reach a level of 6.7 x 10(6) IU/ml, which was more than 10-300-folds higher than those obtained at lower OUR (80-200 mmol/l/h) using the same bioreactor and those obtained in shaking flasks. Clustering and analysis of the specific growth and glycerol consumption rates data during culture phase could detect the ill fermentation state at early stage, potentially provided a simple and effective fault alarming/diagnosis method for the achievement of stable pIFN-alpha production.

Online monitoring of OUR, KLa and OTE indicators: practical implementation in full-scale industrial WWTPs

Based on on/off aeration strategies, this paper describes all the steps involved in the development and implementation of three identification algorithms aimed at monitoring the oxygen uptake rate (OUR), the oxygen mass-transfer coefficient (K(L)a), and oxygen transfer efficiency (OTE) in aerated biological reactors. Firstly, a detailed explanation of the theoretical background behind every algorithm is given. In addition, practical issues have also been taken into account in order to guarantee the quality of estimations. Finally, the three algorithms have been implemented and validated in a full-scale industrial wastewater treatment plant with satisfactory results. Although short-term noise has been observed in the estimated data (especially at high OURs), the medium and long-term data trajectories have been correctly reproduced.

Membrane fouling control and enhanced phosphorus removal in an aerated submerged membrane bioreactor using modified green bioflocculant

This study aims at developing a modified green bioflocculant (GBF) for membrane fouling control and enhanced phosphorus removal in a conventional aerated submerged membrane bioreactor (SMBR) to treat a high strength domestic wastewater (primary sewage treated effluent) for reuse. The GBF was evaluated based on long-term operation of a lab-scale SMBR. These results showed that SMBR system could achieve nearly zero membrane fouling at a very low dose of GBF addition (500 mg/day) with less backwash frequency (2 times/day with 2-min duration). The transmembrane pressure only increased by 2.5 kPa after 70 days of operation. The SMBR could also remove more than 95% and 99.5% dissolved organic carbon and total phosphorus, respectively. From the respiration tests, it was evident that GBF not only had no negative impact on biomass but also led to high oxygen uptake rate (OUR) (>30 mg O 2/L h) and stable specific oxygen uptake rate (SOUR). These results also indicated that GBF had no effect on nitrogen removal and nitrification process.

Comparison of in vitro and in situ plankton production determinations

Plankton production was measured using 8 techniques at 4 stations in the Celtic Sea, North Atlantic Ocean, in April 2002. Primary production (PP) was derived from 14 C incorporation into particulate carbon after 24 h simulated in situ, PP( 14 CSIS), and 2 h photosynthesis-irradiance incuba- tions, PP( 14 CPUR), and from 2 published satellite algorithms, PP(VGPM) and PP(M91). Gross production (GP) was calculated from O2 evolution, GP(O2), and 18 O enrichment of dissolved O2, GP( 18 O), after 24 h simulated in situ incubations, and from in situ active fluorescence measured by fast repetition rate fluorometry (FRRF). Net community production (NCP) was determined from changes in in situ dissolved oxygen, NCP(ΔO2), and from changes in oxygen during 24 h simulated in situ incubations, NCP(O2). Dark community respiration (DCR) was derived from changes in oxygen during a 24 h dark incubation, DCR(O2), and daily oxygen uptake, DOU( 18 O, O2), was calculated from the difference between GP( 18 O) and NCP(O2). Three stations were dominated by picoautotrophs and the fourth station was dominated by diatoms. While most of the comparisons between techniques fell within previously published ranges, 2 anomalies occurred only at the diatom-dominated station. Rates of PP( 14 CPUR) were oxygen uptake in the dark. The low rates of PP( 14 CPUR) in relation to PP( 14 CSIS) may have resulted from the heterogeneous nature of the bloom and differences in sampling time. However, it is also possible that dissolved organic material (DOM) released by the stressed diatom population restricted the diffusion of 14 C into the cells, thereby causing a greater underestimate of PP by techniques using short incuba- tions. The significantly higher rates of oxygen uptake in the light are difficult to reconcile, and we do not know whether the light enhanced oxygen uptake was directly linked to carbon fixation. How- ever, the release of DOM may also have provided substrate for enhanced respiration in the light. These anomalies were only revealed through the concurrent measurement of plankton production by this wide range of techniques. Further investigation of DOM excretion and light-enhanced respira- tion during diatom blooms is warranted.

Benthic remineralization at the land–ocean interface: A case study of the Rhône River (NW Mediterranean Sea)

Biogeochemical processes in sediments under the influence of the Rhône River plume were studied using both in situ microelectrodes and ex situ sediment core incubations. Organic carbon (OC) and total nitrogen (TN) content as well as stable carbon isotopic composition of OC ( δ 13C OC) were analysed in 19 surface sediments to determine the distribution and sources of organic matter in the Rhône delta system. Large spatial variations were observed in both the total O 2 uptake (5.2 to 29.3 mmol m −2 d −1) and NH 4 + release (−0.1 to −3.5 mmol m −2 d −1) rates at the sediment–water interface. The highest fluxes were measured near the Rhône River mouth where sedimentary OC and TN contents reached 1.81% and 0.23% respectively. Values of δ 13C OC ranged from −26.83‰ to −23.88‰ with a significant seawards enrichment tracing the dispersal of terrestrial organic matter on the continental shelf. The amount of terrestrial-derived OC reaches 85% in sediments close to the Rhône mouth decreasing down to 25% in continental shelf sediments. On the prodelta, high terrestrial OC accumulation rates support high oxygen uptake rates and thus indicating that a significant fraction of terrestrial OC is remineralized. A particulate organic carbon (POC) mass balance indicates that only 3% of the deposited POC is remineralized in prodelta sediments while 96% is recycled on the continental shelf. It was calculated that a large proportion of the Rhône POC input is either buried (∼52%) or remineralized (∼8%), mostly on the prodelta area. The remaining fraction (∼40%) is either mineralized in the water or exported outside the Rhône delta system in dissolved or particulate forms.

Glucose isomerase production on a xylan-based medium by Bacillus thermoantarcticus

Abstract Effects of medium components on intracellular glucose isomerase (GI) production were investigated by Bacillus thermoantarcticus. The highest GI activity was obtained as 1630 U dm−3 in the medium containing (g dm−3): 10.6, birchwood-xylan; 5.6, yeast extract; 5.9 (NH4)2SO4 at T = 55 °C in 33 cm−3 shake-flasks. When birchwood-xylan was replaced with oat spelt- or beechwood-xylan, GI activity decreased to 1372 and 1308 U dm−3, respectively. Effects of pH at uncontrolled-pH (pHUC = 6.0) and controlled-pH (pHC = 6.0) operations, and oxygen transfer at the air inlet rate of 0.5 vvm and agitation rates of 300, 500 and 700 min−1, were investigated in 3.0 dm3 bioreactor system with 1.65 dm3 working volume in the designed medium. The highest GI activity was attained at 500 min−1, 0.5 vvm, pHUC = 6 as 1840 U dm−3 where cell concentration was 2.3 g dm−3. The use of agricultural waste xylan, as the carbon source resulted in concomitant production of xylanase and GI. The highest xylanase activity was attained as 9300 U dm−3 at 500 min−1 and 0.5 vvm. KLa varied between 0.008–0.033 s−1 whereas the highest oxygen uptake rate was 0.002 mmol dm−3 s−1. Initially biochemical reaction limitations were effective; thereafter, mass transfer resistances became more effective.

In situ oxygen uptake rates by coastal sediments under the influence of the Rhône River (NW Mediterranean Sea)

The influence of riverine inputs on biogeochemical cycling and organic matter recycling in sediments on the continental shelf off the Rhône River mouth (NW Mediterranean Sea) was investigated by measuring sediment oxygen uptake rates using a combination of in situ and laboratory techniques. Four stations were investigated during two cruises in June 2001 and June 2002, with depths ranging from 9 to 192 m and over a distance to the Rhône River mouth ranging from 4 to 36 km. Diffusive oxygen uptake (DOU) rates were determined using an in situ sediment microprofiler and total oxygen uptake (TOU) rates were measured using sediment core incubations. There was good agreement between these two techniques which indicates that the non-diffusive fraction of the oxygen flux was minimal at the investigated stations. DOU rates ranged from 3.7±0.4 mmol O 2 m −2 d −1 at the continental shelf break to 19.3±0.5 mmol O 2 m −2 d −1 in front of the Rhône River mouth. Sediment oxygen uptake rates mostly decreased with increasing depth and with distance from the Rhône mouth. The highest oxygen uptake rate was observed at 63 m on the Rhône prodelta, corresponding to intense remineralization of organic matter. This oxygen uptake rate was much larger than expected for the increasing bathymetry, which indicates that biogeochemical cycles and benthic deposition are largely influenced by the Rhône River inputs. This functioning was also supported by the detailed spatial distribution of total organic carbon (TOC), total nitrogen (TN) and C/N atomic ratio in surficial sediments. Sediments of the Rhône prodelta are enriched in organic carbon (2–2.2%) relative to the continental shelf sediments (<1%) and showed C/N ratios exceeding Redfield stoichiometry for fresh marine organic matter. A positive exponential correlation was found between DOU and TOC contents ( r 2=0.98, n=4). South-westward of the Rhône River mouth, sediments contained highly degraded organic matter of both terrestrial and marine origin, due to direct inputs from the Rhône River, sedimentation of marine organic matter and organic material redeposition after resuspension events.

Lack of metabolic thermal compensation during the early life stages of ocean pout Zoarces americanus (Bloch &amp; Schneider) : a benthic, cold‐water marine species

The present study investigated the metabolic response of young ocean pout Zoarces americanus to temperature acclimation (3 v. 11° C), and to acute changes in water temperature from 3 to 17° C. The Q10 value for standard metabolic rate between acclimation temperatures was 5·3, warm‐acclimated fish displayed higher rates of oxygen uptake at all temperatures during the acute thermal challenge, and changes in whole‐body citrate synthase activity were qualitatively similar to those seen for metabolism. These results indicate that, in contrast to temperate species, young ocean pout from Newfoundland do not show thermal compensation in response to long‐term temperature changes.

Elimination of Odor and Hydrogen Sulfide Gas by Superoxygenation of the Bluebird Force Main in Laguna Beach, California

Like many cities, the City of Laguna Beach has a transmission main that was sized twenty years ago for a projected level of development that was never realized. Consequently, the transmission main is oversized with daily service velocities running less than optimum. The mountainous terrain of the City requires a complex system of twenty-eight lift stations to serve approximately 18,000 users. The wastewater collection travel time is lengthened due to the lift station trips necessary to reach the transmission pipeline. Travel time is further exacerbated at night when flows are essentially stopped until enough flow is collected to trigger a pumping cycle in some of the smaller residential lift stations. Collectively this typical diurnal cycle is the cause for significant anaerobic conditions to develop in the collection system. The generation of malodorous hydrogen sulfide gas has plagued the City for many years. Over the last ten years, the City has tried many methods and spent a great deal of money to reduce the odor production. Three years ago the City conducted a test to determine the level of hydrogen sulfides released at blow-off vaults. Some of the vaults were located near heavily traveled pedestrian crosswalks in the City. The odorous gas levels were extraordinary and proved that antiquated conventional methods to treat odors were not effective. Costly chemical treatment was discontinued. The City sought new methods for preventative, non-chemical in pipe treatment. The root cause of most odor problems associated with wastewater collection and treatment is the presence of naturally created malodorous gases. The gases are formed by Sulfate Reducing Bacterial, (SRB’s) under anaerobic conditions resulting from the imbalance of high BOD loading and the limited solubility of oxygen into wastewater. This problem is exacerbated in long force mains and slow-cycled residential lift stations due to high microbial oxygen uptake rates, long detention times, and low dissolved oxygen (D.O.) levels. These anaerobic conditions produce significant amounts of hydrogen sulfide (H2S) which is both odorous and highly corrosive. Since anaerobic conditions are precursors to H2S formation, a logical solution to H2S control is to induce aerobic or oxic conditions. SuperOxygenation is a process to sustain aerobic conditions by using an ECO2 “Speece” Cone (Downflow Bubble Contactor) to dissolve pure oxygen into wastewater to prevent the formation of H2S.