Aeration Regimes Research Articles

Effect of carbon source on compost nitrogen and carbon losses

The effect of C source on N losses by volatilization during composting was measured using four bulking agents, each at three humidity levels and composted in duplicate under passive and active aeration. The bulking agents were pine shavings alone and corrected with soybean, chopped grass hay alone and corrected with urea, long (unchopped) wheat straw and chopped oat straw. The readily available C of each bulking agent was determined by analyzing for BOD 5. In 105 l laboratory vessels, the bulking agents were mixed with liquid swine manure and tap water for a C/N of 20 and three humidity levels of 60%, 65% and 70%. While being aerated actively or passively, the mixtures were composted for 21 days. Their initial and final C and N contents were measured to conduct a mass balance analysis and calculate C and N losses. C and N losses were compared to bulking agent BOD 5. N losses were compared to C losses. The humidity level and aeration regime had no effect on C and N losses but the N losses were correlated to C losses and only the C losses could be correlated to the BOD 5 of the bulking agent. Thus, the N losses are related not only to the availability of C but also to the extent of composting. A relationship established between N and C losses indicated that 85% of the initial total N of the compost was available for microbial degradation and that 70% of the available C was lost as CO 2 during the immobilization process.

Financial risk analysis of three aeration regimes in catfish cage culture

This study analysed the benefits and costs of three airlift aeration regimes — continuous (24 hr), partial (9 hr/night plus emergencies), and no aeration — for channel catfish in cages. Data from four field studies included four dependent variables based on size at harvest, and six independent variables. Four regression models were fit with a modified Cobb‐Douglas production function in a Seemingly Unrelated Regression system. Yield projections from the production function were then used in a stochastic economic model with prices and variable costs expressed as triangular distributions. Results indicated that none of the aeration methods was preferred to the others by either first‐ or second‐degree stochastic dominance criteria, although partial aeration was the risk‐neutral choice. A power analysis was used to demonstrate that an impractical number of replicates would be needed to detect a difference between partial and continuous aeration that was both economically and statistically significant.

Nitrification potential of attached biofilms in dairy farm waste stabilisation ponds

Dairy farm waste stabilisation ponds are a major source of ammoniacal-N to surface waters in New Zealand. Ammoniacal-N is of particular concern in New Zealand where native aquatic invertebrates appear to be very sensitive to ammonia toxicity. This paper investigates improvement of ammoniacal-N nitrification in dairy farm facultative ponds with mechanical aeration and provision of biofilm attachment surfaces. Biofilm was grown on surfaces at different depths (0.1 m, 0.2 m and 0.6 m) under three mechanical aeration regimes (no aeration, night-only aeration and continuous aeration). Nitrification potential of biofilm was determined as the rate of ammoniacal-N removal in bioassays with ammoniacal-N spiked pond water or culture medium under controlled conditions (20°C, pH 7.0, constant stirring, DO 2–3 g m−3, dark). The nitrification potentials (0.30 g N m−2 biofilm d−1 to 2.17 g N m−2 biofilm d−1) of biofilm-coated surfaces were largely controlled by oxygen availability and consistency of supply in the pond. Nitrification potentials were high where oxygen availability was high, such as close to the pond surface where atmospheric re-aeration and algal photosynthesis were prevalent. Nitrification potentials of biofilms incubated at depth were enhanced by mechanical aeration, with higher values achieved under the continuous aeration regime and at more turbulent sites closer to the aerator.

Influence of tray hydraulics on tray column dynamics

To column control, in contrast to column design, tray hold-up and dependencies of tray hold-up on the operating conditions play an important role. The essence of this article is the development of an improved model of tray hydraulics over a broad operating range and its experimental validation by means of batch distillation. First, the column dynamics are related to tray column design parameters and operating conditions. The model parameters are fitted by column residence time measurements. Two tray load regimes are distinguished: an aeration regime and an obstruction regime. At low column load a vapour increase will decrease the tray mass since the liquid is driven out by larger aeration. At high load the opposite is the case, since the liquid is driven up by stowage. The resulting dynamic behaviour is studied by linearising the rigorous tray model in an operating point. Especially the influence of the vapour flow on the column dynamics is investigated. For the influence of the tray composition change on the molar mass, a new composition-shift parameter κ is defined. The influence appeared to be small.

Effect of carbon substrate and aeration on nitrate reduction and expression of the periplasmic and membrane-bound nitrate reductases in carbon-limited continuous cultures of Paracoccus denitrificans Pd1222.

The expression and in situ activity of the membrane-bound and periplasmic nitrate reductases have been assayed in Paracoccus denitrificans Pd1222 grown under a range of aeration regimes in malate-limited or butyrate-limited chemostat cultures. In butyrate-limited cultures the expression of periplasmic nitrate reductase and the rate of in situ nitrate reduction were high at all oxygen concentrations measured between 0% and 100% air saturation. By contrast, in malate-limited cultures expression of the periplasmic nitrate reductase was low at 80-100% air saturation but increased to a maximum between 20% and 50% air saturation. Aerobic nitrate reduction was much higher in butyrate-limited than in malate-limited cultures, demonstrating a significant role for this process during butyrate metabolism. The rate of nitrate respiration increased in both the malate- and butyrate-limited cultures as aerobic metabolism switched completely to anaerobic metabolism. Expression of the membrane-bound nitrate reductase could be detected in butyrate-limited chemostat cultures maintained at an oxygen level of 100% air saturation. No membrane-bound nitrate reductase was detectable under similar conditions in malate-limited cultures but expression was detected at oxygen concentrations of 50% air saturation and below. Taken together, the results show that the nature of the carbon substrate and oxygen concentration can both influence expression of the periplasmic and membrane-bound nitrate reductases. The conditions under which expression of the periplasmic nitrate reductase and aerobic nitrate respiration are maximal can be rationalized in terms of a role for the periplasmic nitrate reductase in dissipating excess reductant generated during oxidative metabolism of reduced carbon substrates.

Classification of moisture and aeration regimes in sub-boreal forest soils

One hundred and two white spruce (Picea glauca (Moench) Voss) stands were studied in the Sub-boreal Spruce zone of British Columbia and were quantitatively classified into seven soil moisture regimes (moderately dry, slightly dry, fresh, moist, very moist, wet, and very wet) according to actual/potential evapotranspiration ratio, depth to gleyed layer or prominent mottling, and depth to groundwater table. The delineated soil moisture regimes demonstrated strong relationships with the composition of understory vegetation and white spruce foliar nutrients and site index. These relationships implied that the three differentiating characteristics used in the classification provided a good estimation of growing-season soil water supply. In addition to soil moisture regimes, three soil aeration regimes (adequate, restricted, and deficient) were delineated according to presence or absence of gleyed horizons and groundwater table, slope gradient, and soil texture. These soil aeration regimes helped in explaining the variation in white spruce site index, especially on water-surplus sites. Thus, an integrated classification of soil moisture-aeration regimes was proposed to explain the effect of soil moisture and aeration on white spruce productivity.The results of this study gave further evidence that soil moisture and aeration regimes, differentiated on the basis of climatic data and soil morphological properties, are useful measures of soil moisture and aeration conditions in sub-boreal forest soils.

Use of synoptic variables in predicting white spruce site index

Based on data from 102 white spruce-dominated stands in the sub-boreal spruce zone of British Columbia, forest site quality was evaluated using both species-specific and ecological approaches. White spruce site index, determined from stem analysis data, was used as a species-specific measure of site quality. Climate regimes and soil moisture, aeration and nutrient regimes were used as ecological measures of site quality. Subzones and variants, differentiated by zonal vegetation, were used as synoptic measures of climate. Soil moisture regimes, differentiated by actual/potential evapotranspiration ratio, depth to a gleyed layer or prominent mottles, and depth to a groundwater table, were used as synoptic measures of soil moisture. Soil aeration regimes, differentiated by soil water saturation, slope, drainage, and soil texture, were used as synoptic measures of soil aeration. Soil nutrient regimes, differentiated by mineralizable nitrogen (kg ha-1) and carbon/nitrogen ratio, was used as synoptic measures of available soil nutrients. These measures were related to white spruce site index through regression analysis and limiting factor analysis. The results showed that soil moisture, aeration, and nutrients were growth-limiting factors while climatic variations within the sub-boreal spruce zone were not important. The best regression model explained about 90% of the total variance in site index, with standard error of estimates of 1.2 m. This strong relationship suggests that ecological site classifications can be used to evaluate both ecological site quality and forest productivity.

Response to higher sediment loads by Pocillopora damicornis planulae

Planulae collected from the reef coral Pocillopora damicornis were exposed to four different levels of sediment (0, 10, 100, 1000 mg l-1) for 14 days under two contrasting water agitation levels (aerated vs. non-aerated). There was no significant difference in larval settlement among the varius sediment treatments and between agitation levels used in this study. However, a significant number of settled planulae underwent reversed metamorphosis (“polyp bail-out”) in the 100 and 1000 mg l-1 treatments of both water aeration regimes indicating conditions were not appropriate for continued development and growth. Data suggested that successful recruitment may be limited in areas with greater than normal sediment loads.

Soil compaction and water table effects on soil aeration and corn growth in a greenhouse study

A greenhouse experiment was conducted to study the effects of aeration on growth of corn seedlings. Variable aeration regimes were created by a combination of 3 levels of soil compaction (1.20, 1.37 and 1.56 Mg m −3) and 3 water table depths (10-cm, 20-cm and 30-cm). Soil aeration was assessed by measuring the oxygen diffusion rate (ODR) and the gaseous composition of soil air. Samples of soil air were analyzed for concentrations of oxygen, carbon dioxide, ethylene and nitrous oxide. The ODR decreased with increasing soil compaction. The average ODR for the 30 cm water table was 193.5, 89.2 and 15.4 μg O 2 m −2 s −1 for the three compaction treatments of 1.2, 1.37 and 1.56 Mg m −3, respectively. At 40 days after planting, concentration of carbon dioxide in soil air was as high as 0.5% by volume. High concentrations of ethylene and nitrous oxide were also measured in those samples that contained high levels of carbon dioxide. The range of concentration was 2–19 ppm for ethylene and 2–20 ppm for nitrous oxide. The vegetative growth of corn seedlings, as measured by root and shoot weights and plant height, was not significantly affected by the treatments imposed. However, stomatal conductance and photosynthesis significantly differed among treatments.

Macroalgal-sediment nutrient interactions and their importance to macroalgal nutrition in a eutrophic estuary

The potential for algal banks to influence water quality and sediment nutrient flux was examined through laboratory experiments and in situ monitoring of algal banks. Loose macroalgal banks displayed seasonal changes in tissue nutrient concentrations suggesting a strong dependence on water column nutrients. These banks fail to generate conditions suitable to sediment nutrient release. Dense banks generated low oxygen conditions in the inter-algal water (0–1 mg l −1), corresponding to zones of high, and relatively stable, phosphate and ammonium concentrations (up to 96 μg l −1 PO 4P and 166 μg l −1 NH 4N). Laboratory experiments confirmed that macroalgal banks can generate reducing conditions at the sediment surface, regardless of the aeration regime, through the decomposition of macroalgal tissue. Platinum electrode potentials as low as −200 mV were recorded in the inter-algal water. In such banks, redox-dependent sediment nutrient release and anaerobic accumulation of nitrogen accounted for inter-algal nutrient concentrations of over 60 μg l −1 phosphate and 800 μg l −1 ammonium. The generation of reducing conditions in inter-algal water required 7 days of still conditions and so this mechanism of nutrient generation is unlikely to be important in winter, when strong winds frequently shift the algal banks. It is suggested that in summer this mechanism may provide a source of nutrients to dense algal banks, supplementing reserves stored in winter.

Submerged production of pectolytic enzymes by Aspergillus niger: effect of different aeration/agitation regimes

The production of a pectolytic enzyme complex in a 10-l strirred tank bioreactor was studied using the Aspergillus niger mutant A 138. A time course of the fermentation showed that the enzyme synthesis is not associated with growth. Maximal activity was reached after 95 h and from that time on it remained constant. Redox potential and pH values proved to be valuable indicators of the initiation and end of enzyme synthesis. The specific morphology of the fungus, growing in distinct pellets with long peripheral hyphae, resulted in a very dense and viscous broth. It represented a special problem for heat and mass transfer. An attempt was made to overcome this problem by different agitation and aeration regimes. These parameters did not change the morphology but had a marked influence on enzyme synthesis. When, at the time of maximal growth rate, aeration was increased from 0.5 vvm to 1.2 vvm, and agitation from 300 rpm to 500 rpm, the depectinizing activity was doubled in comparison with the results obtained when 0.5 vvm and 300 rpm were used throughout fermentation. When more intensive agitation was employed from the beginning of the process, the depectinizing activity was lowered from 60 to 45 units/ml, together with the viscosity and polygalacturonase activity. However, at the same time, the pectin esterase and pectinlyase yields increased. The required fermentation time was reduced from 95 to 65 h.

Effect of irrigation from a point source (trickling) on oxygen flux and on root extension in the soil

A two-dimensional trickle-irrigated soil model was examined in order to determine its aeration regime. Oxygen diffusion rate (O.D.R.) was used as an index of the soil aeration regime, and its influence on the development of root systems was determined. Volumetric soil air content was calculated from soil water tension data, using a retention curve. The root system was markedly concentrated at the periphery of the trickle-irrigated soil volume, while in the center there were few roots. An exponential correlation was found between root distribution and O.D.R., in which 20×10−8g O2×cm−2×min−1 was the critical value for root growth. There was a linear correlation between O.D.R. and volumetric air content which was affected by diffusion distance.

Alcoholic Fermentation and Malate Metabolism in Rice Germinating at Low Oxygen Concentrations

Germinating rice was exposed, in the dark, to low or zero O2 concentrations for 4-5 days by: (1) submergence under 4-5 cm of stagnant solution (3 ppm O2); (2) exposure to a N2 atmosphere; or (3) submergence under solutions flushed with N2. These treatments completely inhibited root growth. Elongation of coleoptiles was stimulated in the stagnant solutions, but not in the N2 treatments. In most experiments, low O2 concentrations resulted in twofold to eightfold increases of malate concentrations in the shoots. Absence of O2 during exposure to H14CO3-, for 30-60 min, inhibited CO2 dark fixation. This inhibition was considerably smaller when seedlings had been raised in N2 rather than in air. Under aerobic conditions during fixation, excised shoots from seedlings raised in N2 fixed more CO2 than shoots from seedlings raised in air. Malate always contained 70% or more of the total fixed 14C, irrespective of the O2 regime during germination and during 14CO2 fixation. Ethanol in stagnant solutions was shown to be formed by the rice seedlings, rather than by bacteria. Ethanol formation during one single day was 20-30-fold greater than the highest recorded amounts of malate in the seedlings. Alcoholic fermentation also responded quickly to changes in aeration regimes, indicating it was an important adaptive factor. Another likely adaptive feature was the high K+ concentration in shoots, even of seedlings grown in the complete absence of O2. It is suggested that these high K+ concentrations have a function in maintaining turgor required for the rapid extension growth of the coleoptiles under low O2 concentrations.

Relative Influence of Moisture–Aeration and Nutrients on Vegetation and Black Spruce Growth in Northern Ontario

Results from a principal component analysis suggest that nutrient regime is more important to vegetational variation than the moisture–aeration regime. Correlations between site index and habitat measures suggest that the moisture–aeration regime influences tree growth more than the nutrient regime. For particular components of vegetational variation and for segments of the total data, the proportional influence of the two gradients varies. Moisture–aeration and nutrient regimes explain a large proportion of the variation in minor vegetation and tree growth on black spruce peatlands.

The Growth and Chemical Composition of Four Grass Species in Relation to Soil Moisture and Aeration Factors

This experiment was harvested over a period of 2 years and occupied eight sites situated on the Hill Farming Research Organisation's Research Station at Sourhope, which is in the Cheviot Hills at the head of the Bowmont Valley. The climate of the area is characteristic of south-east Scotland, being relatively dry and sunny compared with other similar hill areas, most of which are farther to the west. The average annual rainfall, recorded at 270 m O.D., is 973 3 mm. The sites were at an altitude of 300 m and surrounded by hills rising to 490 m O.D. and included as wide a range of soil moisture and aeration regimes and as small a range of nutrient levels as possible. The soils, all of which are in the Sourhope Association, are developed on drift material derived from the Old Red Sandstone Cheviot Andesite (Muir 1956; Ragg 1960) and include poorly drained gleys of the Atton series, and well-drained brown earths of the Sourhope series. The vegetation on these sites ranged from Festuca-Agrostis grassland in the drier sites to Carex spp. and Juncus acutiflorus-rich communities in the wetter ones. There were three sites on gleys (Atton series), two on well-drained soils (one a Sourhope series brown earth, and one an alluvial complex soil, the well-drained characteristics of which were due largely to a coarse gritty B horizon), and three sites on soils intermediate in character between the Sourhope and Atton series. The selected sites were checked for uniformity

Effects of aeration and mineral supply on growth and mineral content of shoots and roots of apple trees (var. 'Golden Delicious' on M.IX).

One- or 2-year-old Golden Delicious apple trees on M.IX were grown either in a clay loam (in 60-1 containers) or in nutrient solution and the effects were studied of several aeration regimes. With the soil-grown trees these comprised flooding to various soil depths and for different times. With the trees grown in nutrient solution the aeration regimes compared were nutrient solution without aeration, tap water with or without aeration, and aerated nutrient solution (control). Shoot growth was depressed by high water tables, and that of trees receiving non-aerated nutrient solution or tap water (whether aerated or not) ceased after about 2 weeks. The root growth of trees receiving non-aerated nutrient solution or tap water was similarly depressed, but, by contrast, aerated tap water enhanced root growth. Details are given of treatment effects on the Ca, K, N and soluble sugar contents of the young and old leaves and of the young roots. The uptake of all mineral elements was similarly affected by lack of aeration, suggesting that the relationship between low Ca content and increased bitter pit incidence is not associated with differential absorption but rather with differential Ca distribution. (Abstract retrieved from CAB Abstracts by CABI’s permission)