Compost convective airflow under passive aeration

For composting, passive aeration can save energy costs while being just as efficient as forced or active aeration. Passive aeration requires the proper design of aeration ducts, and thus, the proper prediction of the convective airflow rates created by the temperature differential between the compost and the ambient air. To establish such relationship, the temperature and convective air flow regimes of composts were investigated using three bulking agents (wood shavings, hay and straw), each at three moisture contents (MC-60%, 65% and 70%) spanning the normal values. All bulking agent and aeration treatments were aerated in duplicate under passive and active regimes. Laboratory vessels of 105 L were used for all treatments. Passive aeration treatments produced temperatures above 57 degrees C, as did the treatments actively aerated at 4 mg of air s(-1) kg(-1) of initial dry compost material. Compost MC had an effect only on the peak compost temperature, occurring between day 2 and 6. After 6 days of composting, MC no longer had any effect on temperature regime because of the loss of moisture by each mixture. A relationship was established between the Grasholf number (Gr-ratio of buoyancy to viscous forces) and the convective airflow rates, to size the aeration ducts for passive aeration. In general, convective airflow rates ranged from 1.5 to 0.7 mg of dry air s(-1) kg(-1) of initial compost dry matter, from day 0 to day 20, respectively, and for all compost treatments. This airflow rate sizes the aeration ducts installed under compost piles for passive aeration. As compared to straw where airflow rate dropped over a given level of Gr, wood shavings and hay were found to be more effective as bulking agents, as their airflow rate increased constantly with Gr.     

Respirometric screening of several types of manure and mixtures intended for composting

The viability of mixtures from manure and agricultural wastes as composting sources were systematically studied using a physicochemical and biological characterization. The combination of different parameters such as C:N ratio, free air space (FAS) and moisture content can help in the formulation of the mixtures. Nevertheless, the composting process may be challenging, particularly at industrial scales. The results of this study suggest that if the respirometric potential is known, it is possible to predict the behaviour of a full scale composting process. Respiration indices can be used as a tool for determining the suitability of composting as applied to manure and complementary wastes. Accordingly, manure and agricultural wastes with a high potential for composting and some proposed mixtures have been characterized in terms of respiration activity. Specifically, the potential of samples to be composted has been determined by means of the oxygen uptake rate (OUR) and the dynamic respirometric index (DRI). During this study, four of these mixtures were composted at full scale in a system consisting of a confined pile with forced aeration. The biological activity was monitored by means of the oxygen uptake rate inside the material (OURinsitu). This new parameter represents the real activity of the process. The comparison between the potential respirometric activities at laboratory scale with the in situ respirometric activity observed at full scale may be a useful tool in the design and optimization of composting systems for manure and other organic agricultural wastes.     

Immunohistochemical localization of senescence marker protein-30 (SMP30) in the submandibular gland and ultrastructural changes of the granular duct cells in SMP30 knockout mice

Senescence Marker Protein-30 (SMP30) is a calcium-regulating protein that decreases in an androgen-independent manner as aging occurs. An enzyme-labeled antibody technique has demonstrated that SMP30 localized to the ducts (granular, intercalated, and striated ducts) of mouse submandibular glands. Immunoelectronmicroscopy demonstrated that the granular duct cells were strongly positive for SMP30, but that pillar cells in the granular duct were negative for the protein. In SMP30-knockout (KO) mice, the granular ducts were smaller in diameter. Swelling of mitochondria in the granular duct cells was observed; however, this phenomenon was not observed in the pillar cells. After administration of alpha-isoproterenol, a beta-adrenergic stimulant, a large numbers of small secretory granules were present in the granular duct cells and an expansion of the rough endoplasmic reticulum in SMP30-wild type (WT) mice; in contrast, little change was observed in SMP30-KO mice. These results suggest that SMP30 may be closely related to a signal transduction pathway in the granular duct cells of submandibular glands.     

Observation on the air-borne bacteria and ammonia (NS3) gas in laboratory animal facility with rotary heat exchanger]

The number of air-borne bacteria in air ducts and barrierred laboratory animal rooms with the so-called econovent rotary heat exchanger, were checked monthly during a year by the pin-hole sumpler method for air ducts and Koch method for animal rooms. Also, concentration of ammonia was checked with the same samples by gas impinger. No significantly difference in number of air-borne bacteria was seen between before and after passing the econovent. Those passing through HEPA filter was not detected. There were more air-borne bacteria in animal rooms, outside locker room and shower room than in the corridor, utensil storage, inside locker room and pass box. No ammonia were detected in the outdoor, but exhaust air duct after passing the econovent contained very small amount of ammonia. On the other hand, high concentration of ammonia were preserved in the supplying air duct, exhaust air duct and mice and rats rooms, about 86% of ammonia in exhaust air duct returned back into the supplying air duct. No influences on reproduction in mice and rats were recognized.     

The modelling of combined strategies to achieve thermophilic composting of sludge in cold region

Low ambient temperature presents a significant technical challenge for efficient operation of the composting facility located in cold region. In this study, mathematical model was used as a tool to develop the operational strategy to accomplish thermophilic composting of sewage sludge in the cold-climate environment. The correlations between composting temperature, water volatilization, heat loss rate, organics degradation and ambient temperature, feedstock temperature, sludge moisture and aeration rate were predicted and evaluated by using the numerical simulation method. The feasibility of optimizing air supply, adjusting feedstock moisture and elevating starting temperature in the low temperature surroundings was investigated. The results obtained from both mathematical modelling and pilot-scale composting experiments demonstrated that the combined strategies of the three approaches could preliminarily achieve material drying, pathogen inactivation and organics stabilization within 20 days at the ambient temperature as low as −24 °C. However, it seems difficult for anyone of these approaches to meet the requirement of thermophilic composting, independently.     

Characteristics of dairy manure composting with rice straw

The aim of this work was to investigate the effects of aeration rate, aeration method, moisture content, and manure age on the characteristics of dairy manure composting with rice straw in terms of composting temperature, oxygen consumption rate, emission of odorous gases, and final compost property. It was found that the aeration rate of 0.25 L/min-kg VS was capable of achieving the highest composting temperature, longest retention time of high temperature, and less emission of odor gases. Except for the composting temperature reached, there was no significant difference between bottom-forced and top-diffusion aerations in terms of final compost property. The higher initial moisture content (65%) was more favorable for its higher temperature, longer retention time of high temperature, and more stable end compost obtained. Fresh manure showed better composting performance than the aged manure for its higher temperature reached in less time and less ammonia emission. Oxygen consumption rates were basically similar to those of temperatures. Most emissions of the odorous gases occurred during the first week of composting, therefore, special attention should be paid to this period of time for effective odor control.     

Temporary vs. Permanent Sub-slab Ports: A Comparative Performance Study

Vapor intrusion (VI) is the migration of subsurface vapors, including radon and volatile organic compounds (VOCs), from the subsurface to indoor air. The VI exposure pathway extends from the contaminant source, which can be impacted soil or groundwater, to indoor air-exposure points. VOC contaminants of concern typically include halogenated solvents as well as petroleum hydrocarbons. Radon, a colorless radioactive gas that is released by radioactive decay of radionuclides in rock and soil, migrates into homes through VI in a similar fashion to VOCs. This project focused on the performance of permanent versus temporary sub-slab sampling ports for the determination of VI of halogenated VOCs and radon into an unoccupied house. VOC and radon concentrations measured simultaneously in soil gas using collocated temporary and permanent ports appeared to be independent of the type of port. The variability between collocated temporary and permanent ports was much less than the spatial variability between different locations within a single residential duplex. Post sampling leak test results suggested that the temporary SSP desiccation and cracking of the clay portion of the seal were not as detrimental to the port seal performance as would have been expected, this suggests that the Teflon tape portion of the seals served an important function. Pre and post sampling leak tests are advisable when temporary ports are used to collect a time-integrated sample. These results suggest that temporary sub-slab sampling ports can provide data equivalent to that collected from a permanent sub-slab sampling port.     

Bioremediation of PAH-contaminated soil by composting: A case study

Composting technique was used for bioremediation of industrial soil originating from a former tar-contaminated site. The composting process was regulated by aeration to keep optimal temperature gradient and concentrations of O₂ and CO₂ inside the composting pile. The efficiency of bioremediation was evaluated by performing analysis of 11 individual three- to six-ring unsubstituted aromatic hydrocarbons (PAH) and estimating of changes in ecotoxicity of the contaminated soil. After 42 d of composting, PAH with 3–4 rings were removed from 42 to 68%, other higher-molar mass PAH from 35 to 57%. Additional 100 d of compost maturation in open-air field did not result in a further decrease of PAH. Ecotoxicity tests performed with bioluminescent bacteriaVibrio fischerii showed a decrease in toxicity both after composting and maturation phases. However, toxicity tests on mustard-seed germination did not reveal any significant changes during composting and maturation phases.     

Low-dissolved-oxygen nitrifying systems exploit ammonia-oxidizing bacteria with unusually high yields

In wastewater treatment plants, nitrifying systems are usually operated with elevated levels of aeration to avoid nitrification failures. This approach contributes significantly to operational costs and the carbon footprint of nitrifying wastewater treatment processes. In this study, we tested the effect of aeration rate on nitrification by correlating ammonia oxidation rates with the structure of the ammonia-oxidizing bacterial (AOB) community and AOB abundance in four parallel continuous-flow reactors operated for 43 days. Two of the reactors were supplied with a constant airflow rate of 0.1 liter/min, while in the other two units the airflow rate was fixed at 4 liters/min. Complete nitrification was achieved in all configurations, though the dissolved oxygen (DO) concentration was only 0.5 ± 0.3 mg/liter in the low-aeration units. The data suggest that efficient performance in the low-DO units resulted from elevated AOB levels in the reactors and/or putative development of a mixotrophic AOB community. Denaturing gel electrophoresis and cloning of AOB 16S rRNA gene fragments followed by sequencing revealed that the AOB community in the low-DO systems was a subset of the community in the high-DO systems. However, in both configurations the dominant species belonged to the Nitrosomonas oligotropha lineage. Overall, the results demonstrated that complete nitrification can be achieved at low aeration in lab-scale reactors. If these findings could be extended to full-scale plants, it would be possible to minimize the operational costs and greenhouse gas emissions without risk of nitrification failure.     

湿度对堆肥理化性质的影响

水分是堆肥微生物生命活动的基础 ,也是堆肥中重要的工艺控制参数。弄清湿度对堆肥微生物及理化性质的影响 ,对于优化堆肥工艺参数、提高堆肥效率、降低投资和运行成本具有重要意义。综述了堆肥湿度研究的动态 ,指出了当前研究中存在的问题 ,并提出了未来的研究方向。大量的研究表明 ,湿度低于 4 5 %或高于 6 5 %都不利于堆肥处理。湿度太高会导致堆料的压实度增加、FAS减少、透气性能降低 ,从而导致堆体内氧气供应不足、堆肥升温困难、有机物降解速率降低、堆肥周期延长。湿度过低 ,水分会限制堆肥微生物的新陈代谢 ,导致微生物活性下降、堆肥腐熟困难。由于鼓风、散热、水蒸发等会使堆体内存在湿度的空间变异 ,也会降低堆肥效率和堆肥产品的质量。另外 ,堆肥湿度还影响堆肥的保肥能力。由各文献得出结论 ,堆肥的最佳湿度范围一般为 5 0 %～ 6 0 %左右     

Spatial distribution of dynamics characteristic in the intermittent aeration static composting of sewage sludge

Spatial differences and temporal changes in biological activity characteristics were investigated in a static reactor using intermittent aeration during the sewage sludge composting process. Pumice was proposed as a bulking agent in the composting of sewage sludge. Variations in temperature, moisture, oxygen level, volatile solids, specific oxygen uptake rate (SOUR) and dehydrogenase activity (DHA) were determined during 28 days of composting. The peak temperature in the upper region of the reactor was 10 °C higher than that at the bottom. The moisture level in the middle region was significantly higher than that of other positions. Analysis of SOUR and DHA indicated that the lowest level of sludge stability was at the bottom region. These spatial and temporal differences in biochemical dynamics in the static system could extend the composting period and affect product uniformity.     

Determination of aeration rate and kinetics of composting some agricultural wastes

This study aimed to determine the aeration rate and its kinetics in aerobic composting of agricultural wastes. For this aim compost materials were prepared by mixing grass trimmings, tomato, pepper, and eggplant wastes. Four vertical forced aeration type reactors and one vertical natural convection type reactor were manufactured to apply four different aeration rates. CO2 rate and temperature changes were recorded in three different places in the reactors. Moisture content, pH and organic material rate were recorded each day. While process-monitoring parameters (CO2, temperature, pH, moisture content) were used for interpretation of the process, organic material degradation was used for interpretation of the process success. The seven different kinetic models were applied for modeling decomposition rate to the experimental values. According to the results, four of these models were found applicable to this study. These models were analyzed with some statistical methods as root mean square error (RMSE), chi-square (chi2), and modeling efficiency (EF). According to the statistical results of these models, the best model was found as: [Formula: see text] where kT is the rate of decomposition (g VS/g VS day); T the process temperature (degrees C); Mc the daily moisture content (%wb); C the daily CO2 rate in composting reactor (%) and a, b, c, d are constants. According to the results, the highest organic matter degradation and temperature value were obtained at the aeration rate of 0.4 l air min(-1)kg(om)(-1). Thus, it could be applied to this mixed materials composting process.     

Population dynamics of clock-controlled biological species: models and why circadian rhythms are circadian

The endolymph flow inside the semicircular ducts is analytically investigated by considering a system of two hydrodynamically interconnected ducts. Rotation of this system adds an amount of motion (momentum) to parts of it. This results in an endolymph flow in generally all vestibular parts. The "external impulses" are the impulses which emerge by rotation of exclusively a particular vestibular part. The real impulses can be calculated from a set of equations which contain the external impulses. Analytical expressions are derived for the initial velocities in the ducts and for the maximum endolymph displacements. These formulae contain the external impulses and the ratios of: (1) the radii of crus commune and ducts (gamma), (2) the lengths of crus commune and ducts (lambda). It was proven that an interconnected system composed of two ducts, and also a system composed of two such semicircular duct systems, behaves as a pure rotation transducer (like a single duct does), also when it is rotated excentrically. Duct systems with polygonal and circular geometries were used to evaluate whether an optimal value of lambda would exist (gamma was already considered elsewhere). Optimum values of lambda in a range of about 0.10-0.52 were found. This rather wide range of values agrees with values from measurements. Optimization of an interconnected duct system appeared to be equal to optimization of a system composed of separate ducts.     

Reaerosolization of fluidized spores in ventilation systems

This project examined dry, fluidized spore reaerosolization in a heating, ventilating, and air conditioning duct system. Experiments using spores of Bacillus atrophaeus, a nonpathogenic surrogate for Bacillus anthracis, were conducted to delineate the extent of spore reaerosolization behavior under normal indoor airflow conditions. Short-term (five air-volume exchanges), long-term (up to 21,000 air-volume exchanges), and cycled (on-off) reaerosolization tests were conducted using two common duct materials. Spores were released into the test apparatus in turbulent airflow (Reynolds number, 26,000). After the initial pulse of spores (approximately 10(10) to 10(11) viable spores) was released, high-efficiency particulate air filters were added to the air intake. Airflow was again used to perturb the spores that had previously deposited onto the duct. Resuspension rates on both steel and plastic duct materials were between 10(-3) and 10(-5) per second, which decreased to 10 times less than initial rates within 30 min. Pulsed flow caused an initial spike in spore resuspension concentration that rapidly decreased. The resuspension rates were greater than those predicted by resuspension models for contamination in the environment, a result attributed to surface roughness differences. There was no difference between spore reaerosolization from metal and that from plastic duct surfaces over 5 hours of constant airflow. The spores that deposited onto the duct remained a persistent source of contamination over a period of several hours.     

Size distributions of total airborne particles and bioaerosols in a municipal composting facility

Size distributions of total airborne particles and bioaerosols were measured in a full-scale composting facility, using an optical particle counter and an agar-inserted six-stage impactor, respectively. Higher concentrations of total airborne particles and bioaerosols were detected at a sampling location near the screening process preceded by the composting process than at sampling locations in the composting process. At the sampling location near the screening process, the concentrations of total airborne particles were approximately 10(8)particles/m3 at the size of 0.3 microm and 10(5)particles/m3 at 6.2 microm. The concentration of bioaerosols was about 10(4)CFU/m3 in each stage of 7.0 microm (1st stage), 7.0-4.7 microm (2nd), 4.7-3.3 microm (3rd), 3.3-2.1 microm (4th), 2.1-1.1 microm (5th) and 1.1-0.65 microm (6th). Most of submicron particles smaller than 1 microm among the total airborne particles were believed to originate from the ambient air.     

Comparison of the Rotorod to other air samplers for the determination of Ambrosia artemisiifolia pollen concentrations conducted in the Environmental Exposure Unit

The Environmental Exposure Unit (EEU) is a 924 m³ facility (Kingston General Hospital, Ontario) in which uniform concentrations of various pollens in HEPA-filtered air at known rates of laminar airflow can be maintained. This facility provided a unique opportunity to compare several air samplers without the environmental variation inherent in outdoor comparisons. The purpose of this study was to conduct a quantitative comparison of pollen measurements using the Rotorod, Burkard™ Personal Volumetric Air Sampler, Air-O-Cell™ and a 37 mm open-faced filter cassette with a microporous filter in the EEU. Pollen samples were taken during clinical trials being conducted in the Unit. Raw pollen counts/m³ obtained using the different methods were corrected using published particle collection efficiencies for the particle size (∼ ∼20 μm) and airflow. Data were analyzed by ANOVA/Tukey HSD. No statistically significant differences were found between pollen concentrations determined by Rotorod, Air-O-Cell and filter cassette. Pollen levels determined by the Burkard were up to 2 times higher than the other sampling methods. Relative standard deviations were similar for the Rotorod, Burkard, and filter cassette and higher for the Air-O-Cell. This study demonstrated that, under our conditions, the Rotorod sampler provides consistent and reliable measurements of ragweed pollen concentrations.     

Oxygenation of intensive cell-culture system

The abilities of various methods of oxygenation to meet the demands of high-cell-density culture were investigated using a spin filter perfusion system in a bench-top bioreactor. Oxygen demand at high cell density could not be met by sparging with air inside a spin filter (oxygen transfer values in this condition were comparable with those for surface aeration). Sparging with air outside a spin filter gave adequate oxygen transfer for the support of cell concentrations above 10⁷ ml^–1 in fully aerobic conditions but the addition of antifoam to control foaming caused blockage of the spinfilter mesh. Bubble-free aeration through immersed silicone tubing with pure oxygen gave similar oxygen transfer rates to that of sparging with air but without the problems of bubble damage and fouling of the spin filter. A supra-optimal level of dissolved oxygen (478% air saturation) inhibited cell growth. However, cells could recover from this stress and reach high density after reduction of the dissolved oxygen level to 50% air saturation.     

Reaerosolization of Fluidized Spores in Ventilation Systems

This project examined dry, fluidized spore reaerosolization in a heating, ventilating, and air conditioning duct system. Experiments using spores of Bacillus atrophaeus, a nonpathogenic surrogate for Bacillus anthracis, were conducted to delineate the extent of spore reaerosolization behavior under normal indoor airflow conditions. Short-term (five air-volume exchanges), long-term (up to 21,000 air-volume exchanges), and cycled (on-off) reaerosolization tests were conducted using two common duct materials. Spores were released into the test apparatus in turbulent airflow (Reynolds number, 26,000). After the initial pulse of spores (approximately 10¹⁰ to 10¹¹ viable spores) was released, high-efficiency particulate air filters were added to the air intake. Airflow was again used to perturb the spores that had previously deposited onto the duct. Resuspension rates on both steel and plastic duct materials were between 10⁻³ and 10⁻⁵ per second, which decreased to 10 times less than initial rates within 30 min. Pulsed flow caused an initial spike in spore resuspension concentration that rapidly decreased. The resuspension rates were greater than those predicted by resuspension models for contamination in the environment, a result attributed to surface roughness differences. There was no difference between spore reaerosolization from metal and that from plastic duct surfaces over 5 hours of constant airflow. The spores that deposited onto the duct remained a persistent source of contamination over a period of several hours.     

Air-filled porosity and permeability relationships during solid-state fermentation

An experimental apparatus was constructed to measure the structural parameters of organic porous media, i.,e. mechanical strength, air-filled porosity, air permeability, and the Ergun particle size. These parameters are critical to the engineering of aerobic bioconversion systems and were measured for a straw--manure mixture before and after 13 days of in-vessel composting. Porosity was measured using air pycnometry at four (day 0) and five (day 13) moisture levels, with each moisture level tested at a range of different densities. Tested wet bulk densities varied with moisture level, but dry bulk densities generally ranged from 100 to 200 kg m(-3). At each moisture/density combination, pressure drop was measured at airflow rates ranging from 0.001 to 0.05 m sec(-1), representing the range of airflow rates found in both intensive and extensive composting. Measured air-filled porosities were accurately predicted from measurements of bulk density, moisture, and organic matter content. Reductions in air-filled porosity at increasing moisture content were accompanied by an increase in permeability, apparently due to aggregations of fines. This aggregation was quantified by calculating an effective particle size from the Ergun permeability relationship, which increased from 0.0002 m at 50% moisture to 0.0021 m at 79% moisture. The range of airflow velocities reported in composting systems requires consideration of the second-order drag force term, particularly at velocities approaching 0.05 m s(-1) for the higher moisture treatments tested. Calculated permeabilities for the matrix ranged from 10(-10) to 10(-7) m2, varying with both air-filled porosity and moisture. Mechanical strength characterization provided a means to predict the effects of compaction on air-filled porosity and permeability of porous media beds. The results of this investigation extend porous media theory to the organic matrices common in solid-state fermentations and help build a framework for quantitative and mechanistic engineering design.     

Quantitative modeling identifies critical cell mechanics driving bile duct lumen formation

Biliary ducts collect bile from liver lobules, the smallest functional and anatomical units of liver, and carry it to the gallbladder. Disruptions in this process caused by defective embryonic development, or through ductal reaction in liver disease have a major impact on life quality and survival of patients. A deep understanding of the processes underlying bile duct lumen formation is crucial to identify intervention points to avoid or treat the appearance of defective bile ducts. Several hypotheses have been proposed to characterize the biophysical mechanisms driving initial bile duct lumen formation during embryogenesis. Here, guided by the quantification of morphological features and expression of genes in bile ducts from embryonic mouse liver, we sharpened these hypotheses and collected data to develop a high resolution individual cell-based computational model that enables to test alternative hypotheses in silico. This model permits realistic simulations of tissue and cell mechanics at sub-cellular scale. Our simulations suggest that successful bile duct lumen formation requires a simultaneous contribution of directed cell division of cholangiocytes, local osmotic effects generated by salt excretion in the lumen, and temporally-controlled differentiation of hepatoblasts to cholangiocytes, with apical constriction of cholangiocytes only moderately affecting luminal size.