Nitrogen removal from slaughterhouse wastewater in a sequencing batch reactor under controlled low DO conditions

The aim of this study was to examine nitrogen removal from slaughterhouse wastewater in a laboratory-scale sequencing batch reactor (SBR) operated at low dissolved oxygen (DO) levels under two aeration strategies: intermittent aeration (IA) and continuous aeration (CA). Under the IA strategy, during the aeration periods, the maximum DO was controlled at 10% saturation; under the CA strategy, in the first hour of the react phase, the DO was maintained at 10% saturation, and then it was kept at 2–3% saturation in the remaining react phase. Total nitrogen removals of up to 95 and 91% were achieved under the IA and CA aeration strategies, respectively. It is proposed that in situ measurement of oxygen utilization rates can be used to control the operation of SBRs for nitrogen removal.     

The effect of dissolved oxygen (DO) concentration on the glycosylation of recombinant protein produced by the insect cell-baculovirus expression system.

The effect of dissolved oxygen concentration on human secreted alkaline phosphatase (SEAP) glycosylation by the insect cell-baculovirus expression system was investigated in a well-controlled bioreactor. Oligomannose-type N-linked glycans (i.e., Man2 to Man6 and Man3F) were present in SEAP produced by Spodoptera frusiperda Sf-9 (Sf-9) and Trichoplusia ni BTI-Tn-5B1-4 (Tn-5B1-4) insect cell lines. The relative amounts of the most highly processed glycans (i.e., Man3F and Man2 in the SEAP from Sf-9 and Tn-5B1-4 cells, respectively) were significantly higher at 50% of air saturation than at either 10% or 190% of air saturation. That is, glycan processing was inhibited at both low and high dissolved oxygen concentrations.     

The trade-offs and effect of carrier size and oxygen-loading on gaseous toluene removal performance of a three-phase circulating-bed biofilm reactor

We conducted a series of steady-state and short-term experiments on a three-phase circulating-bed biofilm reactor (CBBR) for removing toluene from gas streams. The goal was to investigate the effect of macroporous-carrier size (1-mm cubes versus 4-mm cubes) on CBBR performance over a wide range of oxygen loading. We hypothesized that the smaller biomass accumulation with 1-mm carriers would minimize dissolved-oxygen (DO) limitation and improve toluene removal, particularly when the DO loading is constrained. The CBBR with 1-mm carriers overcame the performance limitation observed with the CBBR with 4-mm carriers: i.e., oxygen depletion inside the biofilm. The 1-mm carriers consistently gave superior removal of toluene and chemical oxygen-demand, and the advantage was greatest for the lowest oxygen loading and the greatest toluene loading. The 1-mm carriers achieved superior performance because they minimized the negative effects of oxygen depletion, while continuing to provide protection from excess biomass detachment and inhibition from toluene.     

Nutrient and waste product concentration differences in upper and lower body arteries of fetal sheep

Well oxygenated blood returning from the placenta is preferentially shunted into the left side of the fetal heart and the ascending aorta. This results in higher oxygen saturation in arterial blood supplying the fetal upper body than in blood supplying the lower body. Since the placenta is also the site of nutrient and waste exchange, we evaluated differences in arterial concentrations of nutrients and waste products in fetal upper and lower body. Studies were carried out on ten, chronically catheterized, third trimester, fetal sheep. Blood samples, drawn simultaneously from the carotid and femoral arteries, were analyzed for glucose, oxygen saturation, oxygen content, total amino acids, lactate, urea nitrogen, and hydrogen ion concentration. Carotid arterial blood had higher levels of glucose (1.4 +/- 0.1 mg/dl (SEM); P less than 0.001), of alpha-amino nitrogen (0.4 +/- 0.1 mg/dl, equivalent to amino acid concentration difference of 2.5 mg/dl, P less than 0.025), of oxygen saturation (9.9 +/- 0.5%, P less than 0.001), and of oxygen content (1.0 +/- 0.1 ml/dl; P less than 0.001). Carotid values exceeded femoral by an average of 10% for glucose, 4% for amino nitrogen, 29% for oxygen saturation and 23% for oxygen content. Carotid arterial blood had lower urea nitrogen, (-0.5 +/- 0.2 mg/dl; P less than 0.05) and hydrogen ion (-1.1 +/- 0.1 nM/L; P less than 0.001) concentrations, but these differences averaged only 2% between vessels. Lactate concentration in the carotid and femoral arteries was the same. Fetal glucose and oxygen levels were closely related.(ABSTRACT TRUNCATED AT 250 WORDS)     

Nitrogen Retention, Removal, and Saturation in Lotic Ecosystems

Increased nitrogen (N) loading to lotic ecosystems may cause fundamental changes in the ability of streams and rivers to retain or remove N due to the potential for N saturation. Lotic ecosystems will saturate with sustained increases in the N load, but it is unclear at what point saturation will occur. Rates of N transformation in lotic ecosystems will vary depending on the total N load and whether it is an acute or chronic N load. Nitrogen saturation may not occur with only pulsed or short-term increases in N. Overall, saturation of microbial uptake will occur prior to saturation of denitrification of N and denitrification will become saturated prior to nitrification, exacerbating increases in nitrate concentrations and in N export downstream. The rate of N export to downstream ecosystems will increase proportionally to the N load once saturation occurs. Long term data sets showed that smaller lotic ecosystems have a greater capacity to remove in-stream N loads, relative to larger systems. Thus, denitrification is likely to become less important as a N loss mechanism as the stream size increases. There is a great need for long-term studies of N additions in lotic ecosystems and clear distinctions need to be made between ecosystem responses to short-term or periodic increases in N loading and alterations in ecosystem functions due to chronic N loading.     

A study on optimum load for physical work.

Five healthy men were chosen as experimental subjects and were divided into groups at random. The subjects walked with a load in a shoulder-waist-back manner on the treadmill at the speed of 5, 7 and 9 km h-1. The parameters measured were as follows: oxygen expenditure, energy consumption, heart rate and self appraisal. Based on the experimental results and analysis of multiple regression, the authors suggested that physical loading should not exceed 25 kg (i.e. roughly equal to 39% of average body weight of male Chinese), when the walking speed was at 5 km h-1. The suitable loading at physical work would be 20 kg (i.e. equal to 31% of the average body weight of male Chinese).     

The effects of hypoxia on load compensation during sustained incremental resistive loading in patients with obstructive sleep apnea.

Inspiratory load compensation is impaired in patients with obstructive sleep apnea (OSA), a condition characterized by hypoxia during sleep. We sought to compare the effects of sustained hypoxia on ventilation during inspiratory resistive loading in OSA patients and matched controls. Ten OSA patients and 10 controls received 30 min of isocapnic hypoxia (arterial oxygen saturation 80%) and normoxia in random order. Following the gas period, subjects were administered six incremental 2-min inspiratory resistive loads while breathing room air. Ventilation was measured throughout the loading period. In both patients and controls, there was a significant increase in inspiratory time with increasing load (P = 0.006 and 0.003, respectively), accompanied by a significant fall in peak inspiratory flow (P = 0.006 and P < 0.001, respectively). The result was a significant fall in minute ventilation in both groups with increasing load (P = 0.003 and P < 0.001, respectively). There was no difference between the two groups for these parameters. The only difference between the two groups was a transient increase in tidal volume in controls (P = 0.02) but not in OSA patients (P = 0.57) during loading. Following hypoxia, there was a significant increase in minute ventilation during loading in both groups (P < 0.001). These results suggest that ventilation during incremental resistive loading is preserved in OSA patients and that it appears relatively impervious to the effects of hypoxia.     

Energy metabolism of Chironomus anthracinus (Diptera: Chironomidae) from the profundal zone of Lake Esrom,Denmark, as a function of body size,temperature and oxygen concentration

The profundal zone of Lake Esrom, Denmark has a dense population of Chironomus anthracinus, which survives 2–4 months of oxygen depletion each summer during stratification. The metabolism of 3rd and 4th instar larvae was examined in regard to variation in biomass and temperature. Respiration at air saturation was described by a curvilinear multiple regression relating oxygen consumption to individual AFDW and temperature. At 10 °C and varying oxygen regimes the O₂ consumption and CO₂ production of 4th instar larvae were almost unaltered from saturation to about 3 mg O₂ l^–1, but decreased steeply below this level. The respiratory quotient increased from 0.82 at saturation to about 3.4 at oxygen concentrations near 0.5 mg O₂ l^–1. This implied a shift from aerobic to partially anaerobic metabolism. At 0.5 mg O₂ l^–1 the total energy production equalled 20% of the rate at saturation of which more than one third was accounted for by anaerobic degradation of glycogen. This corresponded to a daily loss of 12 µg mg AFDW^–1 or approximately 5% of the body reserves. At unchanged metabolic rate the glycogen store would last three weeks, but long term oxygen deficiency causes a further suppression of the energy metabolism in C. anthracinus.     

Biological activity in the composting reactor of the bio-toilet system

The bio-toilet is becoming commercially available and it is actually used in Japan in public parks, sightseeing areas, and households; however, the biological activity in the system during degradation of toilet wastes, particularly faeces, is unknown. Thus, in this study activity of microorganisms in the bio-toilet system during degradation of faeces was assessed through the quantification of reductions in total solids (TS), volatile solids (VS), and chemical oxygen demand (COD) during batch tests in laboratory-scale composting reactors. Additionally, the fate of nitrogen and its transformation processes in such reactors were evaluated. TS, VS, and COD reductions were on the order of 56%, 70%, and 75%, respectively, irrespective of the organic loading regarded. Total nitrogen (T-N) reductions quantified 94%, regardless of the organic loading. Furthermore, all T-N reductions observed during composting were equivalent to the NH(3)-N released from the reactor, i.e., 94% of ammonia was lost.     

Lung collapse in the diving sea lion: hold the nitrogen and save the oxygen

Lung collapse is considered the primary mechanism that limits nitrogen absorption and decreases the risk of decompression sickness in deep-diving marine mammals. Continuous arterial partial pressure of oxygen profiles in a free-diving female California sea lion (Zalophus californianus) revealed that (i) depth of lung collapse was near 225 m as evidenced by abrupt changes in during descent and ascent, (ii) depth of lung collapse was positively related to maximum dive depth, suggesting that the sea lion increased inhaled air volume in deeper dives and (iii) lung collapse at depth preserved a pulmonary oxygen reservoir that supplemented blood oxygen during ascent so that mean end-of-dive arterial was 74 ± 17 mmHg (greater than 85% haemoglobin saturation). Such information is critical to the understanding and the modelling of both nitrogen and oxygen transport in diving marine mammals.     

The vertical distribution of macrobenthos within the substratum of the Brazos river,Texas

Vertical stratification samplers were developed for sampling the grave-sand substrate of a Brazos River, Texas riffle. Fifteen of 25 species recovered, occurred below 10 cm. Mean percentages of total organisms recovered were 66.4%, 20%, 6.1% and 7.5% per 10 cm level, respectively, from the surface down. Dominant insects were Neochoroterpes mexicanas naiads and chironomid, Simulium, Cheumatopsyche and Stenelmis larvae. Seasonal population peaks of these five groups in the top 10 cm correspond with observed emergence peaks. The smaller size classes were generally predominant in the 0–10 cm level. Larvae of Stenelmis were the most evenly distributed among the various 10 cm levels in all size classes. A movement of Cheumatopsyche and Neochoroterpes to lower levels was observed following a large flood, suggesting an escape response to increased silt load and scouring.Dissolved oxygen ranged from saturation at the surface down to 0.4–0.7 ppm at 30–40 cm, indicating that it was possibly limiting at lower levels. Maximum temperature difference between to cm levels was only 3 C. Flow was negligible below to cm.The vertical stratification sampler recovered significantly greater populations in the surface 20 cm, but not in the total 40 cm, than a modified Hess sq. ft. sampler.Study supported in part by the Faculty Research Fund and Institute for Environmental Studies of North Texas State University.     

Interactions of Physical,Chemical and Biological Processes in Depth and Time within a Productive English Lake during Summer Stratification

A survey is given of physical, chemical and biological events in the water-mass of a productive lake (Esthwaite Water, N. England) during summer stratification. They are interrelated in terms of i) responses to meteorological changes (ii) susceptibility to density stratification (iii) participation in acid-base and redox systems, with interactions of these (iv) modification due to the generation of particulate material from soluble precursors (v) limiting factors in such bio-generation (vi) mechanisms of internal nutrient loading, and (vii) control by the characteristics of individual plankters. The significance is demonstrated of differential inputs of meteorological variables, and especially of biological production and degradation, for determining the overall structure and metabolism of the lake.     

Effect of dissolved oxygen and carbon–nitrogen loads on denitrification by an aerobic consortium

Four samples of natural ecosystems and one sample from an activated sludge treatment plant were mixed together and progressively adapted to alternating aerobic/anoxic phases in the presence of nitrate in order to enrich the microflora in aerobic denitrifiers. Aerobic denitrifying performances of this mixed ecosystem at various dissolved oxygen concentrations and various carbon–nitrogen loads were evaluated and compared to those obtained with the aerobic denitrifier Microvirgula aerodenitrificans. The consortium and the pure strain exhibited an aerobic denitrifying activity at air saturation conditions (7 mg dissolved oxygen l^–1), i.e. there was co-respiration of the two electron acceptors with significant specific nitrate reduction rates. Dissolved oxygen concentrations had no influence on denitrifying performances above a defined threshold: 0.35 mg l^–1 for the consortium and 4.5 mg l^–1 for M. aerodenitrificans respectively. Under these thresholds, decreasing the dissolved oxygen concentrations enhanced the denitrifying activity of each culture. The higher the carbon and nitrogen loads, the higher the performance of the aerobic denitrifying ecosystem. However, for M. aerodenitrificans, the nitrate reduction percentage was affected more by variations in nitrogen load than in carbon load. Received: 6 December 1999 / Received revision: 8 March 2000 / Accepted: 10 March 2000     

The depletion of starch from the sapwood of the ash (Fraxinus excelsior) and its relation to attack by powder-post beetles (Lyctus spp.)

The depletion of starch in the living sapwood of ash was examined as a possible means of rendering converted timber immune from attack by Lyctus (powder-post beetle).
Observations on disks of timber kept under controlled conditions showed that depletion is conditioned by access of oxygen; thus although in the standing tree depletion proceeds from without inwards, it can be induced in any part of the sapwood, and in any direction, by permitting access of oxygen, i.e. there is no polarity in depletion. The optimum temperature range for depletion in ash is from 31 to 36 C.: above 45 C. death of the cells may interrupt depletion.
The presence of β-indoly acetic acid does not influence rate of depletion. Reformation of the starch in the depleted wood in the presence of cane sugar could not be induced. The enzyme concerned in mobilization of the starch appears to be a labile one with an optimum in the neighbourhood of 40 C. and to be produced during the active respiration of the cells, starch depletion ceasing when oxygen is withdrawn.
In transversely cut disks the rate of respiration at 33 C. ceases to be proportional to the volume of tissue after a thickness of about 6 mm. has been attained. At 20 C. disks 10 mm. thick may be evenly depleted. Infestation experiments upon timber undergoing depletion showed that the attack by Lyctus is circumscribed by starch-level and not by total nitrogen or soluble sugars.
Under correct conditions of kilning, 1 in. sapwood plank can be rendered starch-free in about 20 days: with larger sizes depletion is uncertain and probably uneconomic.
The methods of starch and sugar analysis used in the work are appended.     

Nutrient-enhanced productivity in the northern Gulf of Mexico: past,present and future

Nutrient over-enrichment in many areas around the world is having pervasive ecological effects on coastal ecosystems. These effects include reduced dissolved oxygen in aquatic systems and subsequent impacts on living resources. The largest zone of oxygen-depleted coastal waters in the United States, and the entire western Atlantic Ocean, is found in the northern Gulf of Mexico on the Louisiana/Texas continental shelf influenced by the freshwater discharge and nutrient load of the Mississippi River system. The mid-summer bottom areal extent of hypoxic waters (<2 mg l^–1 O₂) in 1985–1992 averaged 8000 to 9000 km² but increased to up to 16000 to 20700 km² in 1993–2001. The Mississippi River system is the dominant source of fresh water and nutrients to the northern Gulf of Mexico. Mississippi River nutrient concentrations and loading to the adjacent continental shelf have changed in the last half of the 20th century. The average annual nitrate concentration doubled, and the mean silicate concentration was reduced by 50%. There is no doubt that the average concentration and flux of nitrogen (per unit volume discharge) increased from the 1950s to 1980s, especially in the spring. There is considerable evidence that nutrient-enhanced primary production in the northern Gulf of Mexico is causally related to the oxygen depletion in the lower water column. Evidence from long-term data sets and the sedimentary record demonstrate that historic increases in riverine dissolved inorganic nitrogen concentration and loads over the last 50 years are highly correlated with indicators of increased productivity in the overlying water column, i.e. eutrophication of the continental shelf waters, and subsequent worsening of oxygen stress in the bottom waters. Evidence associates increased coastal ocean productivity and worsening oxygen depletion with changes in landscape use and nutrient management that resulted in nutrient enrichment of receiving waters. A steady-state model, calibrated to different observed summer conditions, was used to assess the response of the system to reductions in nutrient inputs. A reduction in surface layer chlorophyll and an increase in lower layer dissolved oxygen resulted from a reduction of either nitrogen or phosphorus loading, with the response being greater for nitrogen reductions.     

Wetlands as Sinks for Reactive Nitrogen at Continental and Global Scales: A Meta-Analysis

Wetlands support physical and ecological functions that result in valuable services to society, including removal of reactive nitrogen (Nr) from surface water and groundwater. We compiled published data from wetland studies worldwide to estimate total Nr removal and to evaluate factors that influence removal rates. Over several orders of magnitude in wetland area and Nr loading rates, there is a positive, near-linear relationship between Nr removal and Nr loading. The linear model (null hypothesis) explains the data better than either a model of declining Nr removal efficiency with increasing Nr loading, or a Michaelis–Menten (saturation) model. We estimate that total Nr removal by major classes of wetlands in the contiguous U.S. is approximately 20–21% of the total anthropogenic load of Nr to the region. Worldwide, Nr removal by wetlands is roughly 17% of anthropogenic Nr inputs. Historical loss of 50% of native wetland area suggests an equivalent loss of Nr removal capacity. Expanded protection and large-scale restoration of wetlands should be considered in strategies to re-balance the global nitrogen cycle and mitigate the negative consequences of excess Nr loading.     

Optimal oxygen pressure and time for reduced bubble formation in the N2-saturated decompressed prawn.

Bubbles that grow during decompression are believed to originate from preexisting gas micronuclei. We showed that pretreatment of prawns with 203 kPa oxygen before nitrogen loading reduced the number of bubbles that evolved on decompression, presumably owing to the alteration or elimination of gas micronuclei (Arieli Y, Arieli R, and Marx A. J Appl Physiol 92: 2596-2599, 2002). The present study examines the optimal pretreatment for this assumed crushing of gas micronuclei. Transparent prawns were subjected to various exposure times (0, 5, 10, 15, and 20 min) at an oxygen pressure of 203 kPa and to 5 min at different oxygen pressures (PO2 values of 101, 151, 203, 405, 608, and 810 kPa), before nitrogen loading at 203 kPa followed by explosive decompression. After the decompression, bubble density and total gas volume were measured with a light microscope equipped with a video camera. Five minutes at a PO2 of 405 kPa yielded maximal reduction of bubble density and total gas volume by 52 and 71%, respectively. It has been reported that 2-3 h of hyperbaric oxygen at bottom pressure was required to protect saturation divers decompressed on oxygen against decompression sickness. If there is a shorter pretreatment that is applicable to humans, this will be of great advantage in diving and escape from submarines.     

Effects of thermal stratification and mixing on reservoir water quality

In this study, the effect of thermal stratification on water quality in a reservoir has been investigated by field observations and statistical analysis. During the summer period, when stratification is evident, field observations indicate that the observed dissolved oxygen concentrations drop well below the standard limit of 5 mg l⁻¹ at the thermocline, leading to the development of anoxia. The reasons for variations in the dissolved oxygen concentrations were investigated. Variations of air temperature and other meteorological factors and lateral flows from side arms of the lake were found to be responsible for the increase of dissolved oxygen concentrations. It was also observed that turbidity peaked mostly in the thermocline region, closely related to the location of the maximum density gradient and thus low turbulence stabilizing the sediments in the vertical water column. Relatively cold sediment-laden water flowing into the lake after rain events also resulted in increased turbidity at the bottom of the lake. Nondimensional analysis widely used in the literature was used to identify the strength of the stratification, but this analysis alone was found insufficient to describe the evolution of dissolved oxygen and turbidity in the water column. Thus correlation of these parameters was investigated by multivariate analysis. Fall (partial mixing), summer (no mixing), and winter (well mixed) models describe the correlation structures between the independent variables (meteorological parameters) and the dependent variables (water-quality parameters). Statistical analysis results indicate that air temperature, one day lagged wind speed, and low humidity affected variation of water-quality parameters.     

Summer profundal hypoxia determines the coupling of methanotrophic production and the pelagic food web in a subtropical reservoir

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Effect of seasonal hypoxia on the benthic foraminiferal community of the Louisiana inner continental shelf: The 20th century record

A species census in sediment core samples reveals significant changes in the composition of the Louisiana-shelf benthic foraminiferal community in the past century; these changes can be explained by an increase in the severity of seasonal hypoxia in bottom waters. Agglutinated and porcelaneous orders living in water depths less than 60 m suffered a noticeable decline during this time. In particular, the genus Quinqueloculina was severely affected by the progression of hypoxia, and nearly disappeared from parts of the study area. In contrast, several hyaline taxa, especially Nonionella basiloba, Buliminella morgani, and Epistominella vitrea, tolerated the progressive oxygen depletion well. Results of cluster and principal components analyses of the foraminiferal assemblage data match the observed species distribution trends and indicate that seasonal hypoxia on the Louisiana shelf, related to eutrophication and water stratification, worsened in the past century, even near the outer edge of the present-day zone of spring and summer oxygen depletion. The temporal trends in the foraminiferal record correspond to that of fertilizer use in the U.S. and nitrogen loading in the Mississippi River, suggesting that the anthropogenic factor has been particularly strong in the development of coastal hypoxia since the early 1940s.