Composting Process Control Based on Interaction Between Microbial Heat Output and Temperature

Rational composting process control involves the interrelated factors of heat output, temperature, ventilation, and water removal. The heat is released microbially at the expense of organic material; temperature is an effect and, because it is a determinant of microbial activity, it is also a cause of heat output; ventilation supplies oxygen and removes heat, mainly through the vaporization of water; water removal results from heat removal. These relationships were implemented in a field-scale process of static-pile configuration, using a mixture of sewage sludge and wood chips. Heat removal was matched to heat output through a temperature feedback control system, thereby maintaining biologically favorable temperatures. The observations indicate that fundamentally there are two kinds of composting systems: those that are and those that are not temperature self-limiting. The self-limiting system reaches inhibitive temperatures (>60°C) which debilitate the microbial community, suppressing decomposition, heat output, and water removal. In contrast, non-self-limiting temperatures (<60°C) support a robust community, promoting decomposition, heat output, and water removal.     

Physical constraints on temperature difference in some thermogenic aroid inflorescences

* BACKGROUNDS AND AIMS: Thermogenesis in reproductive organs is known from several plant families, including the Araceae. A study was made of the relationship between temperature increase and spadix size in the subfamily Aroideae in order to determine whether the quantitative variation of heat production among species and inflorescences of different sizes follows a physical law of heat transfer. * METHODS: Spadix temperature was measured in 18 species from eight genera of tropical Araceae from the basal clade of Aroideae, both in French Guiana and in the glasshouses of the Montreal Botanical Garden. * KEY RESULTS: A significant logarithmic relationship was found between the volume of the thermogenic spadix zone and the maximum temperature difference between the spadix and ambient air. Four heat transfer models were applied to the data (conductive heat transfer alone, convective heat transfer alone, radiative heat transfer alone, and convective and radiative heat transfers) to test if physical (geometric and thermic) constraints apply. Which heat transfer model was the most probable was determined by using the criterion of a classical minimization process represented by the least-squares method. Two heat transfer models appeared to fit the data well and were equivalent: conductive heat transfer alone, and convective plus radiative heat transfers. * CONCLUSIONS: The increase in the temperature difference between the spadix and ambient air appears to be physically constrained and corresponds to the value of a thermal model of heat conduction in an insulated cylinder with an internal heat source. In the models, a heat metabolic rate of 29.5 mW g(-1) was used, which was an acceptable value for an overall metabolic heat rate in aroid inflorescences.     

Bioremediation by Composting of Heavy Oil Refinery Sludge in Semiarid Conditions

The present work attempts to ascertain the efficacy of low cost technology (in our case, composting) as a bioremediation technique for reducing the hydrocarbon content of oil refinery sludge with a large total hydrocarbon content (250–300 g kg⁻¹), in semiarid conditions. The oil sludge was produced in a refinery sited in SE Spain The composting system designed, which involved open air piles turned periodically over a period of 3 months, proved to be inexpensive and reliable. The influence on hydrocarbon biodegradation of adding a bulking agent (wood shavings) and inoculation of the composting piles with pig slurry (a liquid organic fertiliser which adds nutrients and microbial biomass to the pile) was also studied. The most difficult part during the composting process was maintaining a suitable level of humidity in the piles. The most effective treatment was the one in which the bulking agent was added, where the initial hydrocarbon content was reduced by 60% in 3 months, compared with the 32% reduction achieved without the bulking agent. The introduction of the organic fertiliser did not significantly improve the degree of hydrocarbon degradation (56% hydrocarbon degraded). The composting process undoubtedly led to the biodegradation of toxic compounds, as was demonstrated by ecotoxicity tests using luminescent bacteria and tests on plants in Petri dishes.     

Variation in microbial population during composting of agro-industrial waste

Two compost piles were prepared, using two ventilation systems: forced ventilation and ventilation through mechanical turning. The material to compost was a mixture of orange waste, olive pomace, and grass clippings (2:1:1 v/v). During the composting period (375 days), samples were periodically taken from both piles, and the enumeration of fungi, actinomycetes, and heterotrophic bacteria was carried out. All studied microorganisms were incubated at 25 and 55 °C after inoculation in appropriate growth media. Fungi were dominant in the early stages of both composting processes; heterotrophic bacteria proliferated mainly during the thermophilic stage, and actinomycetes were more abundant in the final stage of the composting process. Our results showed that the physical and chemical parameters: temperature, pH, moisture, and aeration influenced the variation of the microbial population along the composting process. This study demonstrated that composting of these types of wastes, despite the prolonged mesophilic stage, provided an expected microbial variation.     

Patterns and quantities of NH(3), N(2)O and CH(4) emissions during swine manure composting without forced aeration--effect of compost pile scale

To evaluate the NH(3), N(2)O, and CH(4) emissions from composting of livestock waste without forced aeration in turned piles, and to investigate the possible relationship between the scale of the compost pile and gas emission rates, we conducted swine manure composting experiments in parallel on small- and large-scale compost piles. Continuous measurements of gas emissions during composting were carried out using a chamber system, and detailed gas emission patterns were obtained. The total amount of each gas emission was computed from the amount of ventilation and gas concentration. NH(3) emission was observed in the early period of composting when the material was at a high temperature. Sharp peaks in CH(4) emission occurred immediately after swine manure was piled up, although a high emissions level continued after the first turning only in the large-scale pile. N(2)O emissions started around the middle stage of the composting period when NH(3) emissions and the temperature of the compost material began to decline. The emission rates of each gas in the small and large piles were 112.8 and 127.4 g NH(3)-N/kg T-N, 37.2 and 46.5 g N(2)O-N/kg T-N, and 1.0 and 1.9 g CH(4)/kg OM, respectively. It was found that changing the piling scale of the compost material was a major factor in gas emission rates.     

Simulation of an aerobic composting of activated sludge using a statistical procedure

Summary The time courses for the important factors in the composting process for activated sludge, that is the amount of CO₂ generated, the temperature, weight change and water content of the composting materials, were simulated by means of regression analysis. Furthermore, we could accurately estimate the temperature change of the composting materials in the early phase of composting from the heat balance including microbial heat generation estimated by regression analysis. Combining this simulation method with the Simplex method, we determined the optimum aeration regimen that minimized the time required for the temperature to increase to 65°C, at which most pathogens in compost materials are killed, to be 16.7 h.

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Résumé L'évolution chronologique au cours du compostage des facteurs importants (quantité de CO₂ produite, température, poids, et teneur en eau) a été simulée par une analyse de regression linéaire. D'autre part, la variation de température pendant la première phase du compostage a pu être éstimée de façon précise d'après le bilan thermique de la production microbienne de chaleur, déterminé par analyse de regression linéaire. En combinant cette simulation avec la méthode Simplex, on a déterminé un taux optimum d'aération réduisant à 16,7 h le temps nécessaire pour que la température s'élève à 65°C, c'est à dire au niveau où la plupart des bactéries pathogènes du compost sont tuées.

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Nomenclature A Area of heat transfer (m²) - C _pg Specific heat capacity of humid inlet air (kcal/°C kg dry air) - C _ps Specific heat capacity of solid material in the compost (kcal/kg °C) - E Euclid distance - F Aeration rate (kg dry air/h) - H Humidity of inlet air (kg H₂O/kg dry air) - H ^* Humidity at saturation at the inside temperature of the rotating drum (kg H₂O/kg dry air) - CO₂ evolution rate (l/h) - M Total weight of composting material (kg) - M ₀ Initial total weight of composting materials (kg) - P Number of independent variables - Q _W Latent heat of water vaporization (kcal/kg) - q _a Rate of heat loss carried away in the aerating gas (kcal/h) - q _l Rate of heat loss by conduction through the wall of the rotating drum (kcal/h) - q _r Rate of heat generation by microorganisms in the composting process (kcal/h) - q _w Rate of heat loss through evaporation of water (kcal/h) - R Evaporation rate of water (kg/h) - t Composting time (h) - T _c Temperature of composting material (°C) - T _d Temperature in condenser (°C) - t _f Final time of composting (h) - t _g,in Temperature of inlet gas (°C) - t _g,out Temperature of outlet gas (°C) - t _out Temperature outside of the rotating drum (°C) - U Overall heat transfer coefficient for the heat loss through the wall of the rotating drum (kcal/m² °C h) - w _c Water content (%) - W _c Amount of water in the composting materials (kg) - x _i Independent variable - a ₀,a ₁, ...,e ₃,e ₄ Regression coefficient - a ₀,a ₁...,e ₃,e ₄ Standard deviation     

The Pathogenic Amoeboflagellate Naegleria fowleri: Environmental Isolations,Competitors, Ecologic Interactions,and the Flagellate-Empty Habitat Hypothesis1

From several surveys of environmental sites, the virulent human pathogen, Naegleria fowleri, was isolated from a pond in Georgia, a sewage treatment plant in Missouri, and from the Potomac and Anacostia rivers near and in Washington, D.C. Widely scattered, sparse populations seemed only a potential threat to human health at the time of sampling. The data support an estimate that the sites sampled contain 10,000 typical, low temperature, bactivorous amoebae for each heat tolerant amoeba able to grow at 45° C. Heat tolerant competitors were much more common than N. fowleri. Naegleria lovaniensis, which is heat tolerant but nonpathogenic, was isolated from and downstream from an open air thermal pollution temperature gradient. Hot piles of composting sewage sludge yielded no amoeboflagellates, many heat tolerant (45–49° C) amoebae, and one thermophilic (52° C) Acanthamoeba. Features of the methods used include two-stage incubation to increase isolation of sparse organisms and distinction of N. fowleri from almost all other amoebae on agar plates. The flagellate-empty habitat hypothesis postulates a general model in which human intervention and/ or natural events remove usual competitors and the ability to transform to a motile flagellate confers an advantage in recolonizing.     

Effects of feedstock, airflow rate, and recirculation ratio on performance of composting systems with air recirculation

The thermodynamics, kinetics, and energy use of composting systems with air recirculation were determined for feedstocks comprising paper mill sludge and biosolids. Results were developed by simulating the composting system using a two-dimensional finite difference numerical model. Incorporated into the simulation model was independent regulation of temperature and oxygen using a closed loop feedback control system with a two-stage fan setting. Results showed that at low airflows and high recirculation ratios, heat removal by the exhaust gas was insufficient to maintain set point temperatures with the result that process temperatures increased and eventually limited the reaction rate. Types of feedstock, magnitude of airflow and recirculation ratio all affected the energy use of the system. Although recirculation leads to high energy use, it can produce high quality compost by having a temperature gradient of less than 2 degrees C across the bed.     

Chemical,Thermal and Spectroscopic Methods to Assess Biodegradation of Winery-Distillery Wastes during Composting

The objective of this work was to study the co-composting process of wastes from the winery and distillery industry with animal manures, using the classical chemical methods traditionally used in composting studies together with advanced instrumental methods (thermal analysis, FT-IR and CPMAS ¹³C NMR techniques), to evaluate the development of the process and the quality of the end-products obtained. For this, three piles were elaborated by the turning composting system, using as raw materials winery-distillery wastes (grape marc and exhausted grape marc) and animal manures (cattle manure and poultry manure). The classical analytical methods showed a suitable development of the process in all the piles, but these techniques were ineffective to study the humification process during the composting of this type of materials. However, their combination with the advanced instrumental techniques clearly provided more information regarding the turnover of the organic matter pools during the composting process of these materials. Thermal analysis allowed to estimate the degradability of the remaining material and to assess qualitatively the rate of OM stabilization and recalcitrant C in the compost samples, based on the energy required to achieve the same mass losses. FT-IR spectra mainly showed variations between piles and time of sampling in the bands associated to complex organic compounds (mainly at 1420 and 1540 cm^-1) and to nitrate and inorganic components (at 875 and 1384 cm^-1, respectively), indicating composted material stability and maturity; while CPMAS ¹³C NMR provided semi-quantitatively partition of C compounds and structures during the process, being especially interesting their variation to evaluate the biotransformation of each C pool, especially in the comparison of recalcitrant C vs labile C pools, such as Alkyl /O-Alkyl ratio.     

Composting of poultry manure and wheat straw in a closed reactor: optimum mixture ratio and evolution of parameters

The main objectives of this work were to investigate the evolution of some principal physico-chemical properties (temperature, carbon dioxide, oxygen, ammonia, pH, electrical conductivity, organic matter) and microbial population (mesophilic and thermophilic bacteria and fungi) during composting poultry manure with wheat straw in a reactor system, and to evaluate the optimum mixture ratio for organic substrate production. The experiments were carried out in four small laboratory reactors (1 l) and one large reactor (32 l) under adiabatic conditions over 14 days. During the process the highest temperature was 64.6°C, pH varied between 7.40 and 8.85, electrical conductivity varied between 3.50 and 4.31 dS m⁻¹ and the highest value of organic matter (dry weight) degradation was 47.6%. Mesophilic bacteria and fungi predominated in the beginning, and started the degradation with generation of metabolic heat. By increasing the temperature in reactors, the number of thermophilic microorganisms also increased, which resulted in faster degradation of substrate. The application of a closed reactor showed a rapid degradation of manure/straw mixture as well as a good control of the emissions of air polluting gases into atmosphere. The results showed that the ratio of manure to straw 5.25:1 (dry weight) was better for composting process than the other mixture ratios.     

An optimized differential heat conduction solution microcalorimeter for thermal kinetic measurements

Heat conduction calorimeters are widely used in biological sciences, but baseline instability, low resolution, electrical noise and motion artifacts have limited their utility. Two main sources of noise, baseline fluctuation or drift and a motion artifact, were traced to amplifier drift, a small (0.015°C) gradient within the constant temperature cylinder, and the method of installing the thermopiles. The addition of heaters to the top and bottom of the cylinder reduced the gradient to approximately 0.003°C and greatly reduced the slow component of the motion artifact. The drift error was reduced by proper mounting of the amplifier and its external components and the enclosure of the calorimeter in a temperature-controlled box.An R-C model of the heat flow in the calorimeter was developed which was employed to discover several means of increasing sensitivity without increasing the rise-time of the calorimeter. Analysis, also based on the model, showed that variations in the air gap between the cell holder can be a major source of error when the calorimeter is used to investigate the kinetics of a chemical reaction. This analysis also showed that the time for the heat to flow through the solution through the solution in the cell can be the dominant factor in determining the rise-time of the instrument.The heat conduction calorimeter described here has improved characterics: a baseline stability of 200 nJ · s^?1 (peak-to-peak) over a 48 h period; a resolution of 200 nJ · s^?1; a sensitivity of 6.504 ± 0.045 J · V^?1 · s^?1 referred to the sensor output; and a rise-time of 122 s for the 10–90% response.     

Open-flow respirometry under field conditions: How does the airflow through the nest influence our results?

Open-flow respirometry is a common method to measure oxygen-uptake as a proxy of energy expenditure of organisms in real-time. Although most often used in the laboratory it has seen increasing application under field conditions. Air is drawn or pushed through a metabolic chamber or the nest with the animal, and the O₂ depletion and/or CO₂ accumulation in the air is analysed to calculate metabolic rate and energy expenditure. Under field conditions, animals are often measured within the microclimate of their nest and in contrast to laboratory work, the temperature of the air entering the nest cannot be controlled. Thus, the aim of our study was to determine the explanatory power of respirometry in a set-up mimicking field conditions. We measured O₂ consumption of 14 laboratory mice (Mus musculus) using three different flow rates [50 L*h⁻¹ (834 mL*min⁻¹), 60 L*h⁻¹ (1000 mL*min⁻¹) and 70 L*h⁻¹ (1167 mL*min⁻¹)] and two different temperatures of the inflowing air; either the same as the temperature inside the metabolic chamber (no temperature differential; 20 °C), or cooler (temperature differential of 10 °C). Our results show that the energy expenditure of the mice did not change significantly in relation to a cooler airflow, nor was it affected by different flow rates, despite a slight, but significant decrease of about 1.5 °C in chamber temperature with the cooler airflow. Our study emphasises the validity of the results obtained by open-flow respirometry when investigating energy budgets and physiological responses of animals to ambient conditions. Nevertheless, subtle changes in chamber temperature in response to changes in the temperature and flow rate of the air pulled or pushed through the system were detectable. Thus, constant airflow during open-flow respirometry and consequent changes in nest/chamber temperature should be measured.     

Methods to improve the composting process of the solid fraction of dairy cattle slurry

Cattle slurry solid fraction (SF) with different dry matter (DM) contents was collected from two dairy farms and composted in static and turned piles, with different sizes and cover types, to investigate the effects of pile conditions on the physical and chemical changes in SF during composting and to identify approaches to improve final compost quality. Thermophilic temperatures were attained soon after separation of SF, but the temperature of piles covered with polyethylene did not increase above 60 degrees C. The rate of organic matter (OM) mineralisation increased for turned piles in comparison to static piles, but the maximum amount of mineralisable OM (630-675gkg(-1)) was similar for all pile treatments. The C/N ratio declined from over 36 to a value of 14 towards the end of composting, indicating an advanced degree of OM stabilisation. Mature compost was obtained from raw SF feedstock as indicated by the low compost temperature, low C/N ratio, and low content of NH(4)(+) combined with increased concentrations of NO(3)(-). The efficiency of the composting process was improved and NH(3)-N losses were minimized by increasing DM content of the SF, reducing the frequency of pile turning and managing compost piles without an impermeable cover.     

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.     

Physical characteristics of olive stone wooden residues: possible bulking material for composting process

The present work focuses on the study of the physical characteristics of olive stone wooden residues at the prospect of its use as a bulking material in compost process. The physical characteristics that were studied according to particle mesh classification, were the apparent density, porosity, water holding capacity, air free space and air pressure drop. From the experimental results, it was proved that only the fraction of 6.8–12.5 mesh, which is 29.40% of the substrate, could maintain the moisture in the optimum range 40–60%. The fraction of the particles of 2.6–23.6 mesh, which was 74.68% of the substrate, had appropriate porosity for composting. It was also proved that for dried substrate and air velocity 300 m h⁻¹, acceptable pressure drop (10 cm H₂O m⁻¹) was observed for the fraction of the particles of 2.6–27.5 mesh, which was 80.08% of the substrate, while for dried substrate and air velocity 150 m h⁻¹, the respective fraction was particles of 2.6–37.9 mesh which accounted for the 89.48% of the substrate. Conclusively, olive oil processing solid residues have the physical characteristics, so as to be used for composting or as a substrate for co-composting with high strength wastewater.     

Influence of free air space on microbial kinetics in passively aerated compost

The influence of free air space (FAS) on passively aerated composting has been reported, but the quantitative relationship between FAS and the microbial kinetics in passively aerated compost has not been investigated. This relationship was studied by composting dairy manure and straw in an enclosed, passively aerated, cylindrical vessel. Based on this experimental system, conceptual and numerical models were developed in which the compost bed was considered to consist of layered elements, each being physically and chemically homogeneous. The microbial activity in each layer was represented in order to predict oxygen and substrate consumption and the release of water and heat. Convective transport of air, moisture, and heat through the layers was represented. Microbial growth and substrate consumption rates were described using modified first-order kinetics for each of the mesophilic and thermophilic temperature regimes. The values of the microbial kinetic parameters were adjusted for each layer based on an innovative, non-linear, statistical analysis of temperature histories recorded at different layers in the compost bed during three treatments (i.e., FAS values of 0.45, 0.52, and 0.65). Microbial kinetic rate constants were found to follow a sigmoid relationship with FAS, with correlation coefficients (R(2)) of 0.97 for the mesophilic stage and 0.96 for the thermophilic stage. Temperature histories and airflow measurements from a fourth treatment (FAS value of 0.57) were used as an independent check of the model's performance. Simulation results indicate that the model could predict the general trend of temperature development. A plot of the residuals shows that the model is biased, however, possibly because many parameters in the model were not measured directly but instead were estimated from literature. The result from this study demonstrates a new method for describing the relationship between microbial kinetics (k(max)) and substrate FAS, which could be used to improve the design, optimization, and management of passively aerated composting facilities.     

The pathogenic amoeboflagellate Naegleria fowleri: environmental isolations, competitors, ecologic interactions, and the flagellate-empty habitat hypothesis

From several surveys of environmental sites, the virulent human pathogen, Naegleria fowleri, was isolated from a pond in Georgia, a sewage treatment plant in Missouri, and from the Potomac and Anacostia rivers near and in Washington, D.C. Widely scattered, sparse populations seemed only a potential threat to human health at the time of sampling. The data support an estimate that the sites sampled contain 10,000 typical, low temperature, bactivorous amoebae for each heat tolerant amoeba able to grow at 45 degrees C. Heat tolerant competitors were much more common than N. fowleri. Naegleria lovaniensis, which is heat tolerant but nonpathogenic, was isolated from and downstream from an open air thermal pollution temperature gradient. Hot piles of composting sewage sludge yielded no amoeboflagellates, many heat tolerant (45-49 degrees C) amoebae, and one thermophilic (52 degrees C) Acanthamoeba. Features of the methods used include two-stage incubation to increase isolation of sparse organisms and distinction of N. fowleri from almost all other amoebae on agar plates. The flagellate-empty habitat hypothesis postulates a general model in which human intervention and/or natural events remove usual competitors and the ability to transform to a motile flagellate confers an advantage in recolonizing.     

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     

A system for measuring leaf gas exchange based on regulating vapour pressure difference

A system for measurement of leaf gas exchange while regulating leaf to air vapour pressure difference has been developed; it comprises an assimilation chamber, leaf temperature controller, mass flow controller, dew point controller and personal computer. A relative humidity sensor and air and leaf temperature sensors, which are all used for regulating the vapour pressure difference, are mounted into the chamber. During the experiments, the computer continuously monitored the photosynthetic parameters and measurement conditions, so that accurate and intenstive measurements could be made.When measuring the light-response curve of CO₂ assimilation for single leaves, in order to regulate the vapour pressure difference, the leaf temperature and relative humidity in the chamber were separately and simultaneously controlled by changing the air temperature around the leaf and varying the air flow rate through the chamber, respectively. When the vapour pressure difference was regulated, net CO₂ assimilation, transpiration and leaf conductance for leaves of rice plant increased at high quantum flux density as compared with those values obtained when it was not regulated.When measuring the temperature-response curve of CO₂ assimilation, the regulation of vapour pressure difference was manipulated by the feed-forward control of the dew point temperature in the inlet air stream. As the vapour pressure difference was regulated at 12 mbar, the maximum rate of and the optimum temperature for CO₂ assimilation in rice leaves increased 5 molCO₂ m^–2 s^–1 and 5°C, respectively, as compared with those values obtained when the vapour pressure difference took its own course. This was reasoned to be due to the increase in leaf conductance and the decrease in transpiration rate. In addition, these results confirmed that stomatal conductance essentially increases with increasing leaf temperature under constant vapour pressure difference conditions, in other words, when the influence of the vapour pressure difference is removed.This system may be used successfully to measure inter- and intra-specific differences and characteristics of leaf gas exchange in plants with a high degree of accuracy.Abbreviations A CO₂ assimilation rate - A_max Maximum rate of CO₂ assimilation - A_opt Optimum teperature for CO₂ assimilation - CTWB Controlled-temperature water bath - DPC Dew point controller - E Transpiration rate; gl, leaf conductance - HCC Humidity control circuit - IRGA Infrared gas analyzer - LT Leaf temperature - LTC Leaf temperature controller - MFC Mass flow controller - QFD Quantum flux density - RH Relative humidity - RHC Relative humidity controller - VPD Vapour pressure difference - CO₂ Difference of CO₂ concentration between inlet and outlet air     

Multichannel automated chamber system for continuous monitoring of CO2 exchange between the agro-ecosystem or soil and the atmosphere

A multichannel automated chamber system was developed for continuous monitoring of CO₂ exchange at multiple points between agro-ecosystem or soil and atmosphere. This system consisted of an automated chamber subsystem with a CO₂ concentration analyzer and a data logging subsystem. Both subsystems were under the control of a programmable logic controller (PLC). The automated chamber subsystem contained 18 chambers (50 cm × 50 cm × 50 cm) and a compressor. The chamber lids were closed and can be automatically opened. During measurement, one of the 18 chambers was kept closed for three minutes for measuring and the other chambers were kept open to maintain the natural soil conditions to the maximum extent. Environmental variables were simultaneously measured using sensors and recorded by the data logger. The reliability of the multichannel automated chamber system was tested and the results showed that the turbulence of the fans had no significant effect on the CO₂ exchange. The changes in the air and the temperature of soil and soil moisture inside the chambers, caused by the enclosure of the chambers, were not significant. The net ecosystem CO₂ exchange for the wheat ecosystem was ?2.35 μmol·m^?2·s^>?1 and the soil respiration was 3.87 μmol·m^?2·s^>?1 in the wheat field, and 6.61 μmol·m^?2·s^>?1 in the apple orchard.