WO2024115589A1 - Système et procédé d'optimisation de méthanotrophie bactérienne dans des réservoirs à fumier - Google Patents

Système et procédé d'optimisation de méthanotrophie bactérienne dans des réservoirs à fumier Download PDF

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WO2024115589A1
WO2024115589A1 PCT/EP2023/083591 EP2023083591W WO2024115589A1 WO 2024115589 A1 WO2024115589 A1 WO 2024115589A1 EP 2023083591 W EP2023083591 W EP 2023083591W WO 2024115589 A1 WO2024115589 A1 WO 2024115589A1
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methane
concentration
headspace
ppm
flow
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PCT/EP2023/083591
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English (en)
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Søren O. PETERSEN
Lise BONNE GULDBERG
Anders FEILBERG
Chun Ma
Frederik DALBY
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Aarhus Universitet
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Publication of WO2024115589A1 publication Critical patent/WO2024115589A1/fr

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    • A—HUMAN NECESSITIES
    • A01—AGRICULTURE; FORESTRY; ANIMAL HUSBANDRY; HUNTING; TRAPPING; FISHING
    • A01C—PLANTING; SOWING; FERTILISING
    • A01C3/00—Treating manure; Manuring
    • A01C3/02—Storage places for manure, e.g. cisterns for liquid manure; Installations for fermenting manure
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F11/00—Treatment of sludge; Devices therefor
    • C02F11/02—Biological treatment
    • C02F11/04—Anaerobic treatment; Production of methane by such processes
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F3/00—Biological treatment of water, waste water, or sewage
    • C02F3/006—Regulation methods for biological treatment
    • A—HUMAN NECESSITIES
    • A01—AGRICULTURE; FORESTRY; ANIMAL HUSBANDRY; HUNTING; TRAPPING; FISHING
    • A01C—PLANTING; SOWING; FERTILISING
    • A01C3/00—Treating manure; Manuring
    • A01C3/02—Storage places for manure, e.g. cisterns for liquid manure; Installations for fermenting manure
    • A01C3/028—Covers, roofs or other structures for covering manure storage places
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/72—Treatment of water, waste water, or sewage by oxidation
    • C02F1/74—Treatment of water, waste water, or sewage by oxidation with air
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
    • C02F2103/20—Nature of the water, waste water, sewage or sludge to be treated from animal husbandry
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2209/00—Controlling or monitoring parameters in water treatment
    • C02F2209/001—Upstream control, i.e. monitoring for predictive control
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2209/00—Controlling or monitoring parameters in water treatment
    • C02F2209/003—Downstream control, i.e. outlet monitoring, e.g. to check the treating agents, such as halogens or ozone, leaving the process
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2209/00—Controlling or monitoring parameters in water treatment
    • C02F2209/22—O2
    • C02F2209/225—O2 in the gas phase
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2209/00—Controlling or monitoring parameters in water treatment
    • C02F2209/28—CH4
    • C02F2209/285—CH4 in the gas phase

Definitions

  • the invention relates to a system and a method for optimizing the bacterial methanotrophy conditions inside covered manure tanks.
  • Anthropogenic methane emissions to the atmosphere are known to be a factor contributing to global warming. Its greenhouse power is 84 times higher than the one of carbon dioxide (over a 20-year time horizon) and there are several industrial processes generating and emitting it to the atmosphere, such as oil and gas, coal mining, agriculture and farming. Overall, methane has contributed to roughly a 30% of all the observed global warming since the start of the industrialization and its emissions are growing at the fastest rate among the greenhouse gases.
  • methane emissions originating from livestock farming are estimated to comprise between 15 and 30% of all the world methane emissions.
  • This type of methane emission is estimated to grown towards 70% in the coming decades due to the world population growth, the economic development and the urban migration, all contributing to a higher demand for animal protein.
  • Methane emissions during manure storage is a main source of greenhouse gases from livestock farms with liquid manure management.
  • the bacterial methane oxidation activity at the manure-air interface is limited by the fact that methane primarily escapes through cracks or by ebullition.
  • the dilution of methane in the atmosphere dramatically reduces the potential for methane oxidation before it is emitted.
  • liquid manure may form a natural organic surface crust during storage, the curst comprising undigested volatile solids and bedding material or a crust can be formed by admixing of e.g. chopped straw.
  • Previous studies have shown the presence of methanotrophic bacteria in the formed upper crust, giving the opportunity to oxidize part of the emitted methane and preventing its emission to the atmosphere, i.e. the crust has been identified as a potential microbial filter for CH4 oxidation.
  • a survey shows that around 20% of all slurry storage tanks in Denmark already today have a permanent cover, typically a tent structure, but for most of the tanks the cover is a solid crust that forms at the manureair interface during manure storage.
  • the method comprises the step of continuously measuring a concentration of methane, e.g. representing a concentration of methane in the headspace of the livestock manure tank.
  • a concentration of methane e.g. representing a concentration of methane in the headspace of the livestock manure tank.
  • a change in the concentration of methane in the headspace of the livestock manure tank can then be monitored, temporarily, but preferably continuously.
  • a flow of ventilating air to the manure tank can then be adjusted, preferably automatically, based on said monitored change, preferably the rate of change. I.e. the adjustment of the flow is preferably determined relative to the rate of in the concentration of methane.
  • said flow of ventilating air fluidly connects the headspace of the livestock manure tank with outside atmospheric conditions, thereby optimizing conditions for aerobic microbial methanotrophy in the upper crust to reduce emission of methane from the manure storage tank.
  • Methanotrophs are expected to grow in the presence of methane and oxygen, and non- inhibitory levels of mineral N (in the form of ammonia, and nitrite or nitrate), but the distribution of active methane oxidizing bacteria (MOB) is unknown and shift in response to environmental conditions and substrate availability in microenvironments. It is also unknown which absolute concentrations of methane and oxygen are needed to saturate methanotrophic activity as this will also change dynamically with diurnal and seasonal variations in methane production and oxidation activity.
  • MOB active methane oxidizing bacteria
  • the ventilation regulation is merely based on the absolute methane concentration, as seen in the prior art where ventilation regulation is based on a predefined window of absolute methane concentrations, the aerobic microbial methanotrophy cannot be regulated efficiently leading to less filtering effect of the crust and higher emission of methane.
  • the rate of change refers to how quickly the methane concentration changes over time, i.e. the acceleration or deceleration of change in methane concentration, and not the magnitude of individual changes themselves.
  • the present inventors have thus realized that if the regulation of ventilation is based on the change over time, i.e.
  • ventilation regulation can be optimized and automated to ensure that there is always sufficient methane to saturate the current methanotrophic activity.
  • monitoring the change in methane concentration over a predefined time period corresponds to monitoring the rate of change of the methane concentration.
  • the presently disclosed approach can lead to an optimization of the aerobic microbial methanotrophy in the upper crust of the manure tank, and hence a reduction in the overall methane emissions compared with uncovered tanks.
  • the ventilation of liquid manure storage can be regulated, preferably automatically, via a ventilation system on the storage tanks, by locating a physical hard cover on top of the tank, thereby isolating it from the outer atmosphere and by locating or generating a manure surface crust.
  • the hard cover helps to provide a controlled and optimized methane and oxygen concentration inside the tank.
  • the crust provides a medium for methanotrophic bacteria to grow and allows the bacteria to stay in contact with surrounding gaseous methane and oxygen due to its porosity.
  • the change in methane concentration is then analysed in a predefined time interval to provide the rate of change, and, depending on the magnitude and direction of the change (increasing or decreasing), the ventilation rate is adjusted for the subsequent time interval.
  • the key variable is the product of ventilation rate and methane concentration, i.e. methane emission, and the purpose is to minimise this variable in a quasi-continuous way.
  • One advantage of the presently disclosed approach is that it is self-optimizing, because it is possible to continuously and automatically adjust to diurnal and seasonal variations in methane production and oxidation activity.
  • the present disclosure further relates to a control system, preferably self-regulating, for controlling aerobic microbial activity in an upper crust of a livestock manure tank, preferably having an (airtight) cover located over the crust.
  • the control system preferably comprises one or more sensors one or more sensors for measuring methane concentration in the headspace.
  • a ventilation unit can be provided for providing controllable atmospheric communication between an outer atmosphere and the headspace of the manure tank.
  • a feedback control unit is advantageously provided and preferably configured to continuously monitor a change in methane concentration in the headspace and adjust, preferably automatically, the ventilation unit based on said monitored change, preferably the rate of change, in methane concentration in the headspace. I.e.
  • the feedback control unit may be configured to change the ventilation flow between the outer atmosphere and the tank atmosphere in response to a measured change in methane concentration.
  • the feedback control unit is preferably configured to provide for the optimal properties for the methanotrophic activity of microbes located in the manure uppermost crust inside the tank, in particular by continuously monitoring the rate of change in methane concentration, because it is the change in methane concentration that provides the crucial information about the methanotrophic activity.
  • the feedback control unit is preferably configured to automatically apply changes to the ventilation unit to maintain the optimal properties to reduce methane emission.
  • the presently disclosed control system is preferably configured to execute the presently disclosed control method.
  • Fig. 1 shows a flow chart of a method for controlling the atmosphere inside a livestock manure tank.
  • Figs. 2-5 show plots showing the response of a dynamic ventilation system to diurnal changes in storage conditions (mainly air temperature), with methane accumulating during night-time.
  • Fig. 2 shows the air flow rate
  • Fig. 3 shows the CH4 concentration (ppm);
  • fig. 4 shows the air temperature (°C) outside, and
  • fig. 5 shows relative CH4 emission rate.
  • Figs. 6-8 are plots showing response of dynamic ventilation control to the change from forced ventilation (methane cone, below the limit of detection) to auto-control during one day.
  • Fig. 6 shows air flow rate (m3/h);
  • fig. 7 shows headspace CH4 concentration (ppm); and
  • fig. 8 shows the calculated relative CH4 emission rate.
  • Fig. 9 shows a picture of one of the pilot storage tanks.
  • Fig. 10 shows the fraction of the methane that has been oxidized in the headspace of the two pilot storage tanks, both operated with the presently disclosed auto-control method during two periods in Denmark in July and August. Detailed description
  • a key aspect of the presently disclosed approach is to optimise conditions for microbial methane oxidation in organic surface crusts.
  • the crust hosts methanotrophic bacteria with a capacity for the reduction of the methane emissions from the tank towards the outer atmosphere.
  • the solid “natural” crust is an essential part of the present approach, however it is also a naturally formed element of the liquid manure tank. I.e. the crust itself is not part of the presently claimed invention, because the present approach merely relates to a method and a system for optimizing the methane filtering conditions inside the crust by regulating the flow of gas to and/or from the headspace above the crust.
  • the crust formation might be facilitated by a treatment of the manure, such as the addition of hay, the modification of the diet of the livestock animals or the direct transfer from other manure tank, or it could potentially be a synthetic porous material.
  • the crust When partly dried, the crust is a mosaic of partly air-filled pores where a diverse microbial community can develop in biofilms on solid surfaces.
  • Populations of aerobic methanotrophs can be expected to develop in microenvironments with the required availability of methane and oxygen, and non-inhibitory levels of mineral N.
  • the challenge is that the physical location of active methane oxidising bacteria (methanotrophs) is unknown and may shift in response to environmental conditions and substrate availabilities and successional changes in community composition. For example the temperature change of the manure during night or the different seasons throughout the year cause a different methanotrophic activity.
  • one embodiment of the presently disclosed approach comprises the step of continuously measuring a concentration of methane, and optionally oxygen, representing a concentration of methane (oxygen)in the headspace of the livestock manure tank.
  • a gas sensor for measuring the concentration of the methane (oxygen) in the headspace, or at least the change thereof, preferably the rate of change thereof does not have to be located in the headspace, but can for example be located in a corresponding ventilation channel.
  • the relevant gas concentration can be continuously measured, but in terms of methane it is the change in concentration over a time period that is important. If this time period is too short, the changes might be too small to be observable and might be buried in noise.
  • the adjustment of the flow of ventilating air to the manure tank is, at least partly, based on the monitored change in methane concentration, preferably the rate of change in methane concentration, such as the change in methane concentration over a time period.
  • the overall ventilation regulation principle can for example be based on the following assumptions: a) In case there is no or little change in the methane concentration of ventilation air during a time interval AT, the inventors have realized that methane oxidation activity most likely is not significant, or there is a balance between methane production in the liquid phase and methane oxidation in the crust. The response can then be to reduce or maintain the ventilation flow in order to increase the headspace methane concentration and hence substrate availability for methanotrophs to stimulate their activity.
  • methane concentration is already increasing, methane is not the limiting factor, and hence other factors, such as oxygen availability, mineral N and/or temperature, must be limiting.
  • the response can then be to increase the ventilation rate in order to improve oxygen availability in the crust. It is also assumed that methane production in the liquid phase is unaffected by ventilation rate, whereas methane oxidation is a first order process (i.e. concentration dependent) with respect to methane availability.
  • the flow ventilation air is reduced (or maintained), for example by a percentage, such as for example by between 1-5%, preferably 2%, if the gas concentration inside the livestock manure tank is constant or with absolute change in gas concentration over a time period below a predefined threshold.
  • the flow of ventilation air is reduced, for example by a percentage, such as for example by between 1-5%, preferably 2%, if the relative change in gas concentration inside the livestock manure tank declines below a predefined threshold.
  • the flow of ventilating air is increased, for example by a percentage, such as for example by between 1-5%, preferably 2%, if the relative change in gas concentration inside the livestock manure tank increases above a predefined threshold.
  • a further embodiment comprises the steps of continuously measuring a concentration of oxygen representing a concentration of oxygen in the headspace of the livestock manure tank.
  • the automatic adjustment of the flow of ventilating air to the manure tank may take account of said oxygen concentration comparison.
  • the required minimum concentration of oxygen may be a predefined percentage, for example between 70% and 90%, such as 80%, of the atmospheric oxygen concentration (of approx. 21%).
  • the flow of ventilating air to the manure tank is increased if the concentration of oxygen in the headspace decreases below a predefined threshold.
  • This threshold may be defined to be similar to the required minimum concentration of oxygen in the headspace, but it can also be somewhat higher to avoid that the required minimum concentration of oxygen is reached, for example between 1 and 10 percentage points higher, preferably between 1 and 5 percentage points higher. E.g. if the required minimum concentration is 80% of the atmospheric concentration, then the threshold may be between 81% and 90%, or between 81% and 85%, of the atmospheric concentration of oxygen.
  • the flow of ventilating air is reduced, if the change in the concentration of methane in the headspace of the livestock manure tank during a predefined time period is below a predefined threshold, i.e. the rate of change.
  • the predefined threshold may be between 1 and 1000 ppm, preferably between 1 and 100 ppm, more preferably between 1 and 10 ppm, such as 5 ppm. But it can also be defined as a percentage, e.g. of the headspace methane concentration or a relative change during the time period.
  • the flow of ventilating air is reduced if a reduction in concentration of methane in the headspace of the livestock manure tank declines below a predefined threshold during a predefined time period.
  • the predefined threshold preferably may be between -1000 and -1 ppm, preferably between -100 and -1 ppm, more preferably between -10 and -1 ppm, such as -5 ppm. But it can also be defined as a percentage, e.g. of the headspace methane concentration or a relative change during the time period.
  • the flow of ventilating air is increased if an increase in concentration of methane in the headspace of the livestock manure tank increases above a predefined threshold during a predefined time period.
  • the predefined threshold may be between 1 and 1000 ppm, preferably between 1 and 100 ppm, more preferably between 1 and 10 ppm, such as 5 ppm. But it can also be defined as a percentage, e.g. of the headspace methane concentration or a relative change during the time period.
  • the flow of ventilating air is reduced, if change in the concentration of methane in the headspace of the livestock manure tank during a predefined time period is below a predefined threshold, and wherein the flow of ventilating air is reduced if a reduction in the concentration of methane in the headspace of the livestock manure tank declines below the predefined threshold during a predefined time period, and wherein the flow of ventilating air is increased if an increase in the concentration of methane in the headspace of the livestock manure tank increases above a predefined threshold during the predefined time period.
  • the ventilation flow is adjusted by a predefined percentage, and wherein said percentage preferably is between 0.1 and 10%, preferably between 0.5 and 5%, more preferably between 1 and 3%, such as around 2%.
  • This ventilation regulation principle is typically carried out over a predefined time period and normally repeated for the subsequent time period and so one, a time period typically in the order of minutes, for example a predefined time period of between 1 and 30 minutes, less than 30 minutes, less than 15 minutes, or between 1 and 30 minutes, preferably between 5 and 15 minutes, such as 5 or 10 minutes.
  • a challenge that can be observed with the ventilation control described above is that sometimes the ventilation converges toward zero, because if the measured change is concentration is low, the ventilation rate may be repeatedly reduced.
  • This updated, and sometimes more dynamic, ventilation regulation principle can for example be based on the function which in each time step recalculates the new ventilation rate F t 2 at time point t2 based on old ventilation rate Fti at old time point t1 with reference to a predefined threshold value Cmax of the methane concentration, where Cti is the methane concentration at old time point t1 and Ct2 is the methane concentration at new time point t2.
  • the threshold value Cmax is set at between 10000-30000 ppm methane, for example 20000 ppm methane, which is way below the risk of explosion, which only occurs above 40000-50000 ppm methane, however the explosion limit is also depending on the oxygen content.
  • This updated regulation principle has the advantage that the methane production does not come out of control and that the regulation is applicable to both positive and negative changes in methane concentration.
  • the new methane concentration Ct2 at new time t2 is not necessarily compared in each recalculation with the concentration at the start of this interval, Cti , but can advantageously instead be compared with an external reference value, C re f, which is the methane concentration that was measured last time there was a shift in the ventilation rate. This can be expressed as
  • the updated ventilation regulation principle is typically also carried out over a predefined time period and normally repeated for the subsequent time period and so one, a time period typically in the order of minutes, for example a predefined time period of between 1 and 30 minutes, less than 30 minutes, less than 15 minutes, or between 1 and 30 minutes, preferably between 5 and 15 minutes, such as 5 or 10 minutes.
  • the predefined time period may preferably be less than 10 minutes, preferably less than 5 minutes, more preferably less than 3, most preferably less than 2 minutes or maybe even on order of 1 minute.
  • any measuring device such as gas concentration sensors, are preferably located in the ventilation conduct of the ventilation system to avoid a direct exposure to the corrosive elements. Locating the measuring devices anywhere in the tank is expected to give comparable measurements. The measurement of the conditions inside the tank can be performed at a desired frequency.
  • the measuring frequency of the measuring devices might be once per second, once every minute, or once an hour.
  • a currently preferred data acquisition frequency is around 0.1-1 Hz for measuring the methane concentration and every 10 minutes for inducing changes in the ventilation system based on the measured values and the optimal calculated values.
  • modifications in the measuring frequency may be performed with no substantial change in control of the tank conditions, as far as the results reflect a realistic concentration evolution of the gases inside the tank.
  • the measured gas concentrations measured inside and/or outside the tank are the gases needed to detect variations in bacterial methanotrophy inside the tank, and conditions for the process. Monitoring of methane is essential, while monitoring of oxygen can be used to ensure sufficient oxygen for methanotrophy as part of the ventilation control.
  • the detectors needed to measure said gas concentrations are preferably located at least one of the following locations comprising the manure tank cover: in the flow system of ventilating air, or inside the manure tank, such as the headspace between the upper part of the crust and the internal lower tank cover.
  • detectable gas concentration changes are needed, for example depending on the detection limit of the methane sensor used, as well as the length of the predefined time interval. For example during cold periods with low microbial activity in manure environments, the time intervals needed to reach a measurable methane concentration change is likely to be longer, if for example a low cost sensor is used. But with advanced analytical equipment a concentration change can be detected much earlier than with a low-cost sensor with a much higher detection limit, and hence the actually selected implementation is based on an analysis of cost-effectiveness.
  • the ventilation control system maintains headspace oxygen concentration at above 15% to ensure that a niche for aerobic methane oxidation always exists.
  • temperature sensors may be placed inside the manure tank, such as the headspace, outside the manure tank, in the duct of the ventilating air system, inside the solid crust or inside the liquid part of the manure.
  • Gas sensors may be located in the atmosphere outside the tank, in the atmosphere inside the tank and/or in the ventilation conduct comprised in the ventilation system.
  • the ventilation system preferably comprises one or more fans, adjustable air inlets and outlets, ventilation conducts connecting the inside and the outside atmospheres and flow sensors.
  • the different parts of the ventilation system are preferably connected to and controlled by the feedback control unit.
  • the airtight cover configured for covering the crust may be part of the control system.
  • the present disclosure further relates to a system for automatically controlling aerobic microbial methanotrophy in an upper crust of a ventilated manure storage tank, comprising a non-transitive, computer-readable storage device for storing instructions that, when executed by a processor, performs the presently disclosed control method.
  • the system may comprise a mobile device comprising a processor and a memory and being adapted to perform the method but it can also by a stationary system or a system operating from a centralized location, and/or a remote system, involving e.g. cloud computing.
  • the invention further relates to a computer program having instructions which when executed by a computing device or system cause the computing device or system to automatically and dynamically stimulate aerobic microbial methanotrophy in an upper crust of a ventilated livestock manure storage tank, according to the described method.
  • Computer program in this context shall be construed broadly and include e.g. programs to be run on a PC or software designed to run on smartphones, tablet computers or other mobile devices.
  • the settings for AT and AC have been defined manually in the preliminary tests with a prototype control, but the presently disclosed approach may preferably include automated adjustment of AT and AC on the basis of detection limit and rate of change. It can also be necessary to define the nominal change in ventilation rate. This may be defined as a relative change or, alternatively, the change needed to change methane concentration by a predefined percentage or an absolute value based on observations in the previous time interval.
  • the presently disclosed approach has been evaluated in two pilot-scale storage tanks to obtain proof of concept.
  • a prototype control system was implemented in two 6.5 m 3 storage tanks at an existing pilot-scale storage facility.
  • a full-scale storage may be 4000 m 3 but the same regulation principle as disclosed herein apply.
  • Individual fans were used for each of these storage units in order to be able to operate them separately.
  • One of the 6.5 m 3 storage tanks is shown in fig. 9, with a formerly used ventilation duct to a centralised fan still visible in the back.
  • the storage tank A with 0.7 m above-ground has an airtight cover with a central outlet (100 mm diam.) and eight air inlets around the perimeter. All parts of the ventilation system except the fan are standard components from Lindab.
  • the ventilation duct B which is connected to a radial fan C, includes an FTCU flow-controller D with ultrasound-based measurement of air-flow and Bluetooth interface for data transmission.
  • the radial fan of polypropylene (HF R 75-16 D; Ejnar A. Wilson) has a wide dynamic range, but not sufficient to support very low air flows ( ⁇ 1m 3 IT 1 ), and therefore this pilot-scale system includes an extra air inlet E with an electronically controlled damper for intake of ambient air to reduce to amount drawn from the storage tank.
  • two sensors for measurement of methane and oxygen are installed around 400 mm downstream from the 90° bend of the ventilation duct.
  • the pilot-scale system includes temperature sensors for outside temperature, headspace temperature and exhaust temperature, as well as slurry temperature at 5 and 30 cm below the crust surface. Also, sensors recording outside and exhaust humidity are included.
  • the system is prepared for monitoring of outside methane concentration, which must be subtracted from methane in the exhaust (ventilation) air in order to calculate emissions from the slurry inside the tank. For the initial tests, however, this sensor was not included due to lack of a suitable instrument for long-term deployment, and instead gas samples were collected in a quasi-continuous way in 3-liter alufoil gas sampling bags and analysed by gas chromatography.
  • Ventilation control in the absence of methane. If there is no detectable methane in the ventilation air, as will be the case if at high ventilation rates, the dilution brings methane concentrations in the storage headspace below the detection limit of the sensor employed (or during winter storage where in fact there is little or no methane production). The potential for methane oxidation will in this situation be enhanced by increasing the headspace concentration.
  • variable threshold C re f As also disclosed herein there is a risk that the ventilation rate will decrease towards zero.
  • One option is to introduce the variable threshold C re f as discussed above.
  • Methane consists of two isotopocules, 13 CH 4 and 12 CH 4 , which are both substrates for microbial methane oxidation.
  • methanotrophs have a preference for the lighter molecule, and in the presence of methane oxidation this discrimination against 13 CH 4 will result in enrichment of the residual methane released to the atmosphere. This phenomenon is well described in the scientific literature and is the basis of a method to quantify methane oxidation in the soil cover at landfill sites.
  • isotope ratio measurements of methane in ventilation air can provide independent confirmation of methane oxidation activity in surface crusts. This was confirmed by analysing the isotopic composition of methane during a period of several weeks. First, a campaign was conducted with small dynamic chambers installed directly on top of the crust or near the edge where the crust had been removed in order to collect methane directly from the liquid phase. It was confirmed that the isotope ratio of methane shifted towards higher (less negative) values as evidence that methane was oxidised in the crust. The methane removal in this test was 40-60% as derived from isotopic composition of methane.
  • the removal of methane from ventilation air during auto-control operation was estimated from air flow and methane concentration.
  • the methane removal was estimated to be 95%, while a campaign 16-17 Sept 2021 with opposite setups (i.e. the other pilot tank in auto-control and the first as reference) showed a methane removal of 72%.
  • Methane oxidation is not governed by methane concentration alone, but also by oxygen availability and several other environmental factors.
  • the ventilation control can be further improved, in particular for long term dynamics, if the ventilation rate is adjusted relative to a predefined threshold methane concentration Cmax.
  • gas samples were collected from ventilation air over two months, two periods where a first of the two tanks was operated with the presently disclosed regulation approach, and the second of the two tanks with fixed ventilation rate, and four periods with the presently disclosed regulation approach for the second tank and fixed ventilation rate for the first tank.
  • methane emission rates ranged from 0.5 to 2.3 g CH4 m 3 h' 1 , whereas with the presently disclosed regulation approach it ranged from 0.1 to 0.8 g CH4 m 3 h’ 1 .
  • methane emission rates ranged from 0.5 to 2.3 g CH4 m 3 h' 1
  • methane regulation approach ranged from 0.1 to 0.8 g CH4 m 3 h’ 1 .

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  • Treatment Of Sludge (AREA)

Abstract

La divulgation se rapporte à un système et un procédé d'optimisation des conditions de méthanotrophie bactérienne à l'intérieur de réservoirs à fumier recouverts. Un mode de réalisation concerne un procédé de régulation automatique de la méthanotrophie microbienne aérobie dans une croûte supérieure d'un réservoir de stockage de fumier de bétail ventilé (A) ayant un couvercle étanche à l'air au-dessus de la croûte supérieure définissant un espace libre entre la croûte supérieure et le couvercle étanche à l'air, le procédé comprenant les étapes consistant à mesurer en continu une concentration de méthane représentant une concentration de méthane dans l'espace libre du réservoir à fumier de bétail, surveiller en continu un taux de variation de la concentration de méthane dans l'espace libre du réservoir à fumier de bétail, et régler automatiquement un débit d'air de ventilation vers le réservoir à fumier sur la base dudit taux de variation surveillé, ledit débit d'air de ventilation reliant de manière fluidique l'espace vide du réservoir à fumier à bétail à des conditions atmosphériques extérieures, optimisant ainsi les conditions de méthanotrophie microbienne aérobie dans la croûte supérieure afin de réduire l'émission de méthane à partir du réservoir de stockage de fumier.
PCT/EP2023/083591 2022-11-29 2023-11-29 Système et procédé d'optimisation de méthanotrophie bactérienne dans des réservoirs à fumier WO2024115589A1 (fr)

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