GB2531331A - Method for measuring biological oxygen demand - Google Patents
Method for measuring biological oxygen demand Download PDFInfo
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- GB2531331A GB2531331A GB1418412.1A GB201418412A GB2531331A GB 2531331 A GB2531331 A GB 2531331A GB 201418412 A GB201418412 A GB 201418412A GB 2531331 A GB2531331 A GB 2531331A
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- release valve
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- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 title claims abstract description 50
- 239000001301 oxygen Substances 0.000 title claims abstract description 50
- 229910052760 oxygen Inorganic materials 0.000 title claims abstract description 50
- 238000000034 method Methods 0.000 title claims description 50
- 239000007789 gas Substances 0.000 claims abstract description 159
- 239000007788 liquid Substances 0.000 claims abstract description 40
- 238000010521 absorption reaction Methods 0.000 claims abstract description 16
- 230000007423 decrease Effects 0.000 claims abstract description 12
- 230000009467 reduction Effects 0.000 claims abstract description 11
- 230000004044 response Effects 0.000 claims abstract description 7
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims description 8
- 238000012360 testing method Methods 0.000 claims description 4
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 claims description 2
- 229910001882 dioxygen Inorganic materials 0.000 claims description 2
- SGPGESCZOCHFCL-UHFFFAOYSA-N Tilisolol hydrochloride Chemical compound [Cl-].C1=CC=C2C(=O)N(C)C=C(OCC(O)C[NH2+]C(C)(C)C)C2=C1 SGPGESCZOCHFCL-UHFFFAOYSA-N 0.000 claims 3
- 241001481828 Glyptocephalus cynoglossus Species 0.000 claims 1
- 240000008042 Zea mays Species 0.000 claims 1
- 235000005824 Zea mays ssp. parviglumis Nutrition 0.000 claims 1
- 235000002017 Zea mays subsp mays Nutrition 0.000 claims 1
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- 230000029087 digestion Effects 0.000 abstract description 7
- 239000000523 sample Substances 0.000 description 37
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 21
- 238000005259 measurement Methods 0.000 description 12
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- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 6
- 239000002028 Biomass Substances 0.000 description 5
- 244000005700 microbiome Species 0.000 description 5
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- WQZGKKKJIJFFOK-GASJEMHNSA-N Glucose Natural products OC[C@H]1OC(O)[C@H](O)[C@@H](O)[C@@H]1O WQZGKKKJIJFFOK-GASJEMHNSA-N 0.000 description 3
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- 241000894006 Bacteria Species 0.000 description 2
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- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 1
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- 108090000790 Enzymes Proteins 0.000 description 1
- -1 NaOH or KOH Chemical class 0.000 description 1
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
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- 229910001385 heavy metal Inorganic materials 0.000 description 1
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Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
- G01N33/18—Water
- G01N33/1806—Biological oxygen demand [BOD] or chemical oxygen demand [COD]
Landscapes
- Life Sciences & Earth Sciences (AREA)
- Health & Medical Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Food Science & Technology (AREA)
- Analytical Chemistry (AREA)
- Molecular Biology (AREA)
- Biomedical Technology (AREA)
- Biodiversity & Conservation Biology (AREA)
- Medicinal Chemistry (AREA)
- Physics & Mathematics (AREA)
- Emergency Medicine (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Apparatus Associated With Microorganisms And Enzymes (AREA)
Abstract
An apparatus for the determination of Biological oxygen demand (BOD) of a sample, comprises: (a) a digester, for receiving the sample 8; (b) a CO2 absorption unit 10, for removing CO2 produced during digestion; (c) a gas release valve arranged to release an oxygen containing gas through a liquid into the digester in response to a reduction in pressure in the digester; and (d) a gas flow measuring device 5, for measuring the flow of oxygen through the gas release valve. Absorption of CO2 by the CO2 absorption unit decreases the pressure within the digester, causing inflow of gas through the gas release valve which is measured by the gas flow measuring device to determine the BOD of the sample. A device for use with a gas flow measuring system having a gas release valve arranged to open and thereby release biogas into a liquid reservoir, comprises a housing defining a chamber and having an inlet and an outlet. The housing is submergible in the liquid reservoir, and the inlet is configured to receive the gas release valve and the outlet is arranged above the inlet and is configured for connection to a digester.
Description
Method for Measuring Biological Oxygen Demand
Field of the Invention
The invention is in the area of environmental chemistry and biotechnology and in particular S relates to determination of biochemical oxygen demand through gas displacement. More particularly, the invention relates to measurement of volume of air displacing oxygen consumed in the complex environmental or industrial sample.
Background to the invention
Biochemical oxygen demand (BOD) is the most widely used parameter for determining levels of organic pollution of wastewater and surface water (Metcalf et al., 2004). During the process of aerobic degradation of organic matter various groups of microorganisms compete for oxygen and food. In the process of aerobic microbial degradation organic matter is converted into microbial biomass (Jouanneau et al., 2014), H20, 002, and other trace gases whereas oxygen is consumed; dynamics of oxygen consumption in solid and liquid samples by bacteria and other microorganisms reflect the level of organic pollution (Kumar & Kumar, 2005). Several approaches to determining BOD have been developed, ranging from manometric and photometric to online measurements with sensors or probes, and commercially available semi-automated versions. Most widely used method for BUD measurements in industry is the manometric method using OxiTop®, OxyDirect®, or similar equipment due to the simplicity of their use (Jouanneau et al., 2014). However, the number of samples that can be processed simultaneously with the manometric method is limited; consequently, additional measuring units need to be purchased for larger numbers of samples (n>30) included in routine monitoring or complex research settings (Kumar & Kumar, 2005).
Handling of samples may affect the accuracy of the determination of BUD. In the respirometric approaches, observed BUD reaction rate coefficients are significantly affected by particle size of biomass and substrates (Metcalf et al., 2004); blending of large particulate material during processing may thus in some cases lead to higher BUD estimates (Kumar & Kumar, 2005). In the manometric approaches excess modifications, such as dilution of samples, are not needed (CaIdwell & Langelier, 1948); however, the decrease in oxygen concentration during the breakdown of organic components may affect further microbial activity. In addition, when complex organic matter such as leachates is analyzed by different methods, values of BUD differ significantly, showcasing the systematic bias introduced by analytical approaches (Fulazzaky, 2013). Furthermore, variations in recorded BOD values stem from procedures in which particle size distributions are modified through various types of mechanical pretreatment in order to fit small-volume analytical vessels (Vhq < 100 mL) (Metcalf et al., 2004).
Summary of the Invention
S In order to solve some of the issues related to BOO measurements relevant for industry, a pressure equalization method for BOD analysis was developed. The method may make use of the commercially available Automatic Methane Potential Test System II unit or similar device (AMPTS II; Bioprocess Control Sweden AB) (US20120064565A1; Badshah et al. 2012) with the approach based on pressure equalization where no manometer or membrane is needed.
In this way, the use of AMPTS-type devices is expanded from conventional analysis of methane and/or biogas production to measurement of the aerobic BOO and other similar / related parameters (e.g. toxicity/inhibition in case of presence of heavy metals, industrial wastes, antibiotics, sanitizers, commercial disinfectants), allowing for the possibility of determining two process parameters (biogas and BOO) using the same apparatus within the same laboratory. Using this approach, samples with high concentrations of agricultural, industrial, and wastewater anaerobic digestion effluents, may be analyzed. BOD measurement in the invention resembles in its essence the standardized manometric method where BOO is estimated by a pressure drop (measured with a manometer) as a consequence of consumption of oxygen during aerobic digestion. Instead of a manometric measurement, experiments conducted in this assay use an AMPTS II unit (Figure 1) for monitoring oxygen uptake, enabling determination of dynamics of oxygen consumption in solid (e.g. soil) and liquid (e.g. waste-water) samples by bacteria and other microorganisms independently on a pilot scale (0,5 L to 10 L of liquid volume (or even greater)). This allows for use of more realistic sample volumes compared to 50-250-mL volumes normally used, and alleviates the need for intensive sample homogenization including particle size decrease
known in the prior art.
The present invention provides a method, apparatus and device useful in the determination of biological oxygen demand.
In an embodiment, the invention provides an apparatus for determining the Biobgical Oxygen Demand (BOD) of a sample, the apparatus comprising: a digester, for receiving the samp'e to he digested; a CO2 absorption unit, for removing 002 produced during digestion of the sampe; a gas release valve arranged to release an oxygen containing gas through a liquid into the digester in response to a reduction in pressure in the digester and a gas flow measuring device, for measuring the flow of oxygen gas through the gas release valve; wherein absorption of C02 by the CO2 absorption unit decreases the pressure within the digester, causing inflow of gas through the gas release valve which is measured by the gas flow measuring device to determine the BOD of the sample.
The apparatus may comprise an additional inlet valve through which gas, such as air, may be introduced to equalize pressure within the apparatus. The gas flow measuring device may comprise means for determining the length of time that the gas release valve is open, and/or for determining the number of times that the gas release valve is open.
In another embodiment, the invention provides a method for determining the Biological Oxygen Demand (BOD) of a sample, the method comprising: introducing the sample to be tested into a digester providing a CO2 fixation unit for absorbing C02 produced in the digester, thereby reducing pressure in the digester providing a gas release valve submerged in a liquid reservoir, the gas release valve arranged to release oxygen containing gas into the digester in response to the reduction in pressure; and providing a gas flow measuring device for measuring flow of the oxygen containing gas into the digester measuring the flow of oxygen containing gas into the digester to determine Biological Oxygen Demand.
Release of oxygen containing gas into the digester results in equalization of pressure within the digester. In some cases, the oxygen containing gas is air. The air may be sucked through the valve from outside of the gas flow measuring device.
The gas flow measuring device may be a liquid displacement gas flow measuring device.
The method may also involve introducing a control sample that has a known BOD into another digester.
The method may involve the step of equalizing the pressure in the system. Equalization of the system may occur after the sample has been introduced into the digester, and before the flow of oxygen containing gas into the digester is measured. Equalization may involve the introduction of oxygen containing gas, such as air, into the dgester. Equalization may involve the introduction nto the gas 190w measuring device.
The flow of oxygen containing gas into the digester may be measured by measuring the number of times and duration of time that a valve within the gas flow measuring device is in the open state.
The nvention further provides a device for use with a gas flow measuring system. having a gas release valve arranged to open and thereby r&ease biogas into a Uquid reservoir, the device comprising: a housing defining a chamber and having an inlet and an outiet: the housing being submergible in the liquid reservoir; the inlet being configured to receive the gas release valve such that when the gas release valve is open gas is released into the chamber; and the outlet being arranged above the inlet when the gas release valve is received within the inlet; wherein the outlet is configured for connection to a digester.
Such a device may he used in an apparatus for measuring Biological Oxygen Demand according to the invention. The device may be used to connect a gas flow measuring system upstream of a digester.
The 002 absorption unit is arranged within the digester, or otherwise connected to the digester. A further CO2 absorption unit may additionally be provided. The CO2 absorption unit may comprise metal hydroxide, preferably NaOH or KOH.
In some embodiments disclosed herein, the apparatus, method or device may utilise a Automated Methane Potential Test System 1TIV (Bioprocess Control) The invention also provides an apparatus, device or method substantially as described herein with reference to the accompanying drawings.
Detailed Description
The invention includes the combination of the aspects and preferred features described except where such a combination is clearly impermissible or expressly avoided.
As described herein, we have developed a pressure equalization method for BOD analysis.
We compared the values obtained by this approach to values obtained through the use of OxiTop® bottles and determined the dynamics of oxygen consumption in 30 samples with varying concentrations of different biomasses and substrates using a single unit, confirming S the suitability of this apparatus and the procedure for a wide range of organic loadings.
Biological Oxygen Demand (BOD) is the amount of oxygen needed by aerobic biological organisms to break down organic material present in a given sample at certain temperature over a specific time period. BOD5, for example, refers to the biological oxygen demand of a sample over five days. In the methods described herein, BOD may be measured over one day, two days, three days, four days, five days, six days, seven days, eight days, nine days, ten days, or more. BOD may be measured over one week, two weeks or more. In preferred methods described herein, biological oxygen demand is measured over five days.
The invention utilizes a gas fixing unit. Gas-fixing units (also known as gas-stripping units) remove one or more components from the gas mixture. In some cases, the gas-fixing unit removes CO2 from the gas passed therethrough, resulting in a gas mixture substantially free from 002. The resulting gas mixture may therefore comprise exclusively, or consist substantially of, oxygen (02), nitrogen (N2) and other trace gases. The 002 gas-stripper may be NaOH or KOH. Fixation of 002 may be irreversible. That is, fixed 002 is not released back into the system. Fixation of 002 may result in a decrease in pressure in the system.
In some cases, the gas fixing unit is provided within the digester. For example, it may be provided within the chamber of the digester, or within an outlet tube that is in fluid communication with the digester. In some cases, the gas fixing unit is external to the digester. The external gas-fixing unit may provide additional gas-fixing capacity, if a sample has high 002 production. For example, an external gas-fixing unit may be useful where a prolonged incubation time is to be used, or where agents that are inhibitory to respiration are removed from the sample, or where a sample has a high biomass or high microorganism content. The external gas-fixing unit may be provided in addition to, or instead of, the gas fixing unit within the digester. The gas fixing unit may comprise a vessel containing a source of a metal hydroxide, such as NaOH or KOH, for example NaOH or KOH pellets, that is connectable to the digester. For example, the external gas fixing unit may comprise a 250mL incubation flask containing lOg NaOH pellets which is connected to the digester through a port. In some embodiments, the external gas-fixing unit and/or digester are adapted such that the external gas-stripping unit may be added or replaced during a digestion, without needing to restart the determination. For example, the external gas-fixing unit may be connected to the digester via a switch, such that the gas-fixing unit may be introduced without significantly reducing pressure within the digester.
The methods and apparatus described herein use a gas flow measuring system to measure S the volume of gas entering the system. Suitable gas flow measuring systems include those with a submerged valve that is biased closed when the system is equilibrated, and which opens in response to a reduction in pressure within the system, thereby allowing gas to enter the system. For example, a liquid displacement gas flow measuring device as disclosed in US2012/0064565, incorporated by reference herein. Such devices employ a pivoting valve located within a reservoir. The valve may be biased closed by the weight of liquid in the reservoir. That is, the liquid in which the valve is submerged. The valve is biased closed by the water pressure exerting a downward force on the valve, and opens in response to a reduction in that downward force, or a reduction in that downward force relative to upward force from gas behind the valve. A reduction in the amount of gas in the system may reduce the pressure exerted on the valve by the liquid, thereby allowing the valve to open. Opening of the valve may result in gas release into the reservoir, and thereby into the system. This results in an increase in pressure, returning the valve to the closed position. In some cases, the gas is air. The air may be "sucked" into the reservoir through the valve, from outside of the system.
Thus, absorption of CO2 by the gas fixation unit may result in a decrease in gas pressure in the system, theleby reducing pressure on the liquid, thereby resulting in opening of the valve, and release of gas. The valve may comprise a buoyant material, thereby enabling it to float in the liquid in which it is submerged. A suitable gas flow measuring system is shown in the apparatus of Figure 1. In some cases, the gas flow measuring system is an AMPTSII system. The liquid contained within, or introduced into, the reservoir, may be any inert liquid.
That is, a liquid that does not absorb a component of the gas entering the reservoir through the valve. In some cases, the liquid is water.
In the methods and apparatus of the invention, the gas flow measuring system is provided upstream of the digester. Thus, gas flowing into the digester flows through the gas flow measuring system in order to enter the digester. This is different to, for example, biogas production analysis, in which the gas flow measuring system is provided downstream of the digester in order to determine the amount of gas flowing from the digester.
The apparatus of, and used in the methods of, the present invention, utilizes a closed system. That is to say that in use the system is substantially sealed to the external environment, such that when the apparatus is used to determine the BOO of a sample, the only inlet for fluid or gas into the system is through the gas release valve, and therefore through the gas flow measuring device. The apparatus may be airtight, or substantially airtight. The apparatus or system may be equilibrated or equalized prior to use. That is, S pressure in the apparatus or system is equalized. The pressure may be equalized prior to use such that the pressure within the system is equal to atmospheric pressure. That is, the system or apparatus is not under elevated pressure such that a moderate or minor decrease in pressure is not sufficient to allow the gas release valve to open. Conversely, the system or apparatus is not under vacuum, or negative pressure, such that the gas release valve is in the open state to release gas into the system during the initial stages of the method.
Equalizing, or equilibrating, the system allows the total amount and flow rate of supplied air to be determined, and the amount of oxygen consumed to be determined. The apparatus may optionally comprise an additional air inlet to enable equilibration or equalization of pressure in the system. The additional inlet may be in the gas flow measuring device. In some cases the additional inlet is in the digester.
Gas entering the system preferably contains oxygen. The gas may be air, or a mixture of gases that is broadly similar to air in composition. Thus, the input gas may comprise approximately 78% N2, 21% 02, and traces of other gases. Preferably, the gas is air. The methods disclosed herein may additionally involve obtaining a sample of air and determining the composition of that sample. In particular, determining the amount of oxygen in the sample.
The invention may use a gas capture device to transfer gas entering the system to the digester. The device may be suitable for use with a gas flow measuring device that utilizes a gas flow valve submerged in a liquid reservoir or bath, such as an AMPTSII unit. In such devices the valve is submerged in the liquid reservoir. The gas capture may comprise a housing that is submergible in the liquid reservoir. It is not necessary for the housing to be entirely submerged within the reservoir, although it may be. However, the housing is submerged such that the interface between the housing of the device and the reservoir of the biogas volume-measuring device is bathed in liquid. In this way, gas released from the biogas flow valve flows towards the outlet of the device and does not escape the device through the inlet. The interface between the gas capture device and the liquid reservoir thus contributes to the closed nature of the system described herein. The gas capture device may be adapted for connection of an AMPTSII unit upstream of a digester, enabling flow of gas therebetween.
The methods of the invention involve maintenance of a substantially constant gas pressure in the system or apparatus. In this way, CO2 absorbed by the gas fixation unit results in a decrease in pressure exerted by gas in the system. This reduction in pressure results in the opening of a valve at the air inlet, allowing an oxygen containing gas such as air to be S introduced into the system, thereby restoring the pressure. Method of the invention may therefore involve a step of equilibrating the pressure within the system. The equilibration step may occur following introduction of the sample to the digester and before beginning the determination of BOD.
The methods and apparatus of the invention utilize a digester. The digester has a chamber for receiving the sample to be tested. The digester may be connected to a temperature controller to regulate temperature within the digester. In some cases, the digester includes means for heating the digester. The temperature within the digester may be controlled within predetermined levels. For example, between 10°C and 45°C, between 15°C and 30°C, or around 20°C. For example, the digester may include a heating element, or may be connectable to an external heat source. The digester may include agitation means, such as a stirrer, such that a sample contained within the digester may be constantly or temporarily agitated. Agitation may facilitate dissolution of oxygen in the chamber of the digester into the sample.
In the present invention, less manual labor is required compared to other BOD determination procedures as no pretreatment of samples, such as pre-filtration, centrifugation, or homogenization of particle sizes, is required; the procedure allows for working on an industrial scale (i. e. large volume samples, realistic particle size distribution) and gives results more comparable to those obtained in industrial environments. The procedure is robust since it does not contain the fine and sensitive components such as membranes and manometers, which often deteriorate and require regular servicing; therefore, the procedure reduces the extent of necessary maintenance of the analytical device. The invention is suitable for both laboratory research and industrial use. Majority of the materials needed for construction of the device are available from the classical laboratory production line and do not represent an expensive solution linked to exclusive suppliers. This way high purchasing costs are avoided and fast and easy servicing of appliances is enabled.
The gas flow measuring device may contain one or more cells located under the liquid level of a reservoir, each comprising a pressure responsive valve. The valve is biased to be closed, at least partly due to downward pressure exerted on the valve by the liquid in the reservoir. Gas flowing into the device collects behind the valve and is released into the
S
reservoir when the pressure exerted by the liquid is reduced relative to the upward pressure exerted by the collecting gas. As described herein, the system for determining BOD is equilibrated to a predetermined pressure. As digestion of the sample proceeds in the digester, and CO2 is absorbed by the gas-fixing unit, the pressure in the digester decreases.
S The digester is in fluid communication with the gas flow measuring device, and thus the decrease in pressure in the digester is transferred to the liquid reservoir. Thus, as digestion proceeds, the pressure exerted on the liquid in the reservoir is reduced, thereby reducing the pressure exerted by the liquid on the valve relative to the upward pressure exerted by the gas. The valve opens to release gas into the reservoir, thereby increasing the amount of gas, and therefore the amount of pressure in the gas flow measuring device. The increase in pressure in the system is transferred to the digester due to the fluid communication between the digester and the gas flow measuring device, thereby transferring the newly introduced gas to the digester.
As explained above, the gas flow measuring device may contain one or more cells, each comprising a pressure responsive valve. In this way, the biological oxygen demand of one or more samples may be run simultaneously, or in parallel. In some embodiments, the apparatus and methods of the invention enable the calculation of the BOD of up to 15 samples, or up to 30 samples simultaneously, through utilization of a 15 or 30 channel gas flow measuring device. However, a gas flow measuring device with any number of channels may be utilized, depending on the number of samples to be analyzed.
Opening of the valve provides a signal about the volume of gas passing into the reservoir, and therefore also provides a signal about the reduction of pressure in the digester. One or both of these signals may be used to determine the CO2 produced, and the BOD of the sample in the digester. This system can be used in batch or semi-continuous mode in experiments using real-scale substrates and inocula.
Certain embodiments of the invention use a gas capture device to direct gas from the gas flow measuring device into the digester. A suitable device for use with gas flow measuring system comprises a housing which defines a chamber and has an inlet and an outlet; the housing being submergible in the liquid reservoir; the inlet being configured to receive the gas flow valve such that when the gas flow valve is open gas is released into the chamber; and the outlet being arranged above the inlet when the gas flow valve is received within the inlet. This device enables gas exiting the gas flow measuring device to be directed into the digester. The device may be connected to the digester by means of a tube, such as a silicon tube.
The device may consist of multiple hollow sections, each connected to airtight gas lines made of silicone tubing. In order to prevent floating or overturning, the device must be securely fixed in position, by either weighing with a load, or clamping to the bottom of the S reservoir with custom made plastic clips, depending on the type of the apparatus. The device may be a 15-channel device, but the number of channels may be custom tailored as desired.
In particularly preferred embodiments, a 15-channel or 30-channel device is used.
Submerging the housing of gas capture device at least partially into the reservoir creates a substantially airtight seal between the device and the gas flow measuring device and contributes to the closed nature of the apparatus of the invention.
In some apparatus and methods disclosed herein, a control is used. Thus, one or more samples for which BOD is to be determined are analyzed alongside a sample with known BOD. The sample or samples and control may be run in parallel, that is substantially simultaneously, and/or using an alternative channel in the same apparatus.
Aspects and embodiments of the present invention will now be illustrated, by way of example, with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art. All documents mentioned in this text are incorporated herein by reference.
Throughout this specification, including the claims which follow, unless the context requires otherwise, the word "comprise," and variations such as "comprises" and "comprising," will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.
It must be noted that, as used in the specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from "about" one particular value, and/or to "about" another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent "about," it will be understood that the particular value forms another embodiment.
Brief Description of the Figures
Embodiments and experiments illustrating the principles of the invention will now be discussed with reference to the accompanying figures in which: Figure 1 is a schematic representation of the main embodiment of the invention (single channel version) wherein an air inlet 1 is passed into an AMPTS unit 4 filled with liquid 2 (water) and covered with a gas capturing element 3 (hollow plastic cover). The element 3 is S connected via silicone tubing 6 to a sample vessel 7 containing the sample (i. e. the biomass and the microorganisms) 8. The sample is mixed used a magnetic stirrer 9. As the aerobic microbial degradation proceeds, oxygen is consumed and 002 produced. The 002 is captured by a gas stripping unit (the internal 002 trap) 10, resulting in a pressure drop, which is transferred through the tube 6 to the gas capturing device 3, causing the AMPTS unit 4 to intake air through the inlet 1. The amount of taken air is measured with the gas flow sensor 5 and used as measure of BOD. For the purpose of taking subsamples during the experiment, and amendments to the sample in long-term experiments, port 11 may be used, reaching from above the sample vessel through the vessel cover (a rubber stopper) and into the sample. The additional stripping unit (002 trap) 14 was designed to extend the working range of the internal 002 stripping unit as an external accessory, to prevent the need for intervention during prolonged incubations, and may be connected to the vessel inlet 6 and outlet 11 by tubes 13 and 12, respectively.
Figure 2 is a schematic representation of a gas capture device useful in the apparatus according to the invention. The device 1 is a hollow plastic cover and as such may be placed over the gas inlet so that an oxygen containing gas flowing into the reservoir is captured and passed through the outlet 2. The outlet 2 may be connected to a two-way splitter 3. The first tube 4 from the splitter may be connected to a valve 5 whereas the second tube 6 is connected to the digestor.
Figure 3. BOD5 values obtained for wastewater treatment plant effluent, and a variant supplemented with 10 g glucose. Five replicates were used.
Figure 4. The relationship between BOO daily measurements from unmodified-realistic waste water (BOD-C-5L) as control and sonicated aliquots (BOD-S-5L) as determined using either the 5-L pressure equalization approach, or the OxiTop® bottles.
Figure 5. BOO measurements determined at days 5, 10, 15, 21, and 30, using waste-water treatment plant effluent in 5-L scale without modifications.
Examples
Example 1
Initially, fifteen 5-L flasks (Schott, Germany) were used and filled up to 2 L with liquid samples containing biomass and organic matter in solid or liquid state, and incubated at 20°C in an in-house built thermostatic water bath made of watertight styrofoam (KolbI et al., 2014). A CO2 fixation unit containing NaOH pellets was developed and securely placed within the 5-L flasks. Removal of 002 in the fixation units created a drop in pressure that was transferred to an AMPTS II unit. To enable pressure equalization an additional air inlet was connected to the AMPTS II unit. The volume of the air (21 % 02, 78% N2, traces of other gases) was recorded in the AMPTS II unit. Thus the total amount and flow rate of supplied air were determined and the amount of oxygen consumed established in analogy to the current approaches to BOD measurements. During the experiments, access to the samples in the sample vessels was made through a special port extending to the liquid level, enabling retrieval of 3-5-mL subsamples with a 10-mL syringe for additional chemical-biological tS analyses of nutrient status, as well as supplementing the sample with nutrients, enzymes or other additives for extended testing. Device is thus not limited by the fixed volume in the gas chamber as in the case of OxiTop®, extending the working range (e.g. extended time, organic loading) and limiting the extent of manual preparation (dilution preparation not required).
Validation of the method -reøroducibility of results For validation of the pressure equalization method for BOD analysis 10 g of glucose (Sigma Aldrich, USA) was transferred to a 5-L vessel with 2 L of inoculum from the Saleska Valley wastewater treatment plant effluent. No glucose was added to control vessels. Pentuplicate vessels were closed with rubber stoppers. Mixing in the vessels was monitored via a computer and in-house built water baths (KolbI et al., 2014) were used to maintain the temperature at 2000 (but could also be set to vary incubation temperatures from 4°C to 38°C). Vessels were connected with airtight silicone tubing to airtight bottles (external traps) containing NaOH pellets for fixation of CO2 and from there to the gas analysis device (Stres et al., [UK IPO patent application number 1417141.7]) that was placed over the AMPTS unit filled with distilled water. The results showed acceptable reproducibility using large sample volumes, as RDS was below 10% (Figure 2).
Example 2
Determination of the effect of particle size manipulation The experiments, using the same samples as in Example 1, were performed, using either the pressure equalization method or the OxiTop® bottles, comparing non-homogenized and t2 homogenized (ultrasonicated) samples in order to determine the effect of particle size reduction, which is achieved by homogenization. Particle size analysis showed a significant decrease in particle size. BOD values of non-modified samples were significantly lower from those obtained from pretreated samples using either the pressure equalization method or the OxiTop® bottles. Results obtained with the pressure equalization approach were comparable to those obtained with the OxiTop® bottles (Figure 3).
Example 3
Determination of BOD in long-term experiments The experiments, using the same samples as in Example 1, were performed, using the pods in the cover of the sample vessel to resupplement the sample with key nutrients.
Experiments were carried out for 30 days (Figure 4).
Literature Each of the following documents is incorporated by reference herein in its entirety.
CaIdwell, D.H., Langelier, W.F. 1948. Manometric Measurement of the Biochemical Oxygen Demand of Sewage. Sewage Works Journal, 20(2), 202-218.
Fulazzaky, M.A. 2013. Measurement of biochemical oxygen demand of the leachates.
Environmental Monitoring and Assessment, 185(6), 4721-4734.
Jouanneau, S., Recoules, L., Durand, M.J., Boukabache, A., Picot, V., Primault, Y., Lakel, A., Sengelin, M., Barillon, B., Thouand, G. 2014. Methods for assessing biochemical oxygen demand (BOD): A review. Water Research, 49(0), 62-82.
KolbI, S., Paloczi, A., Panjan, J., Stres, B. 2014. Addressing case specific biogas plant tasks: Industry oriented methane yields derived from 5L Automatic Methane Potential Test Systems in batch or semi-continuous tests using realistic inocula, substrate particle sizes and organic loading. Bioresource Technology, 153(0), 180-188.
Kumar, R., Kumar, A. 2005. WATER ANALYSIS I Biochemical Oxygen Demand. in: Encyclopedia of Analytical Science (Second Edition), (Eds.) P. Worsfold, A. Townshend, C. Poole, Elsevier. Oxford, pp. 315-324.
Metcalf, L., Eddy, H.P., Tchobanoglous, G. 2004. Wastewater engineehng treatment, disposal, and reuse. McGraw-Hill, New York [etc.].
Badshah, M., Lam, D.M., Liu, J., Mattiasson, B. 2012. Use of an Automatic Methane Potential Test System for evaluating the biomethane potential of sugarcane bagasse after different treatments. Bioresource Technology, 114, 262-269.
US20120064565A1
Claims (5)
- Claims 1. An apparatus for determinin.g the Biological Oxygen Demand (BOO) of a sample, the apparatus comprising: S a. a thgester, for receiving the sample to be digested; h. a 002 absorption unit, for removing CO2 produced during dgestion of the sample; c. a gas release valve arranged to release an oxygen containing gas through a liquid into the digester in response to a reduction in pressure in the digester; ID and d. a gas flo'N measuring device, for measuring the flow of oxygen gas through the gas release valve; wherein absorption of 002 by the 002 absorption unit decreases the pressure within the digester, causing inflow of gas through the gas release valve witch is measured by the gas flow measuhng device to determine the BOD of the sample.
- 2. An method for determining the Biological Oxygen Demand (BOD) of a sample, the method comprising: a. introducing the sample to be tested into a digester; h. providing a CC)2 lixation unit for absorbing 002 produced in the digester; thereby reducing pressure in th.e digester; c. providing a gas release valve submerged in a liquid reservoir, the gas release valve arranged to release oxygen containing gas into the digester in response to the reduction in pressure; and d. providing a gas flow measuring device for measuring flow of an oxygen containing gas into the digester; e. measuring flow of gas into the digester to determine Biological Oxygen Demand.
- 3 A device for use with a gas 110w measuring system having a gas release valve arranged to open and thereby release biogas into a liquid reservoir, the device corn prising: a housing defining a chamber and having an inlet and an outlet; the housing being submergible in the liquid reservoir; the inlet being configured to receive the gas release valve such that when the gas release valve is open gas is released into the chamber; and the ouflet being arranged above the inet when the gas release va've is received within the in!et; wherein the ouflet is configured for connection to a digesLer.
- 4. Use of the device of daim 3 in an apparatus for measuring Bioogica Oxygen Demand according to daim 1
- 5. A method according to daim 2 further comprising a step of equflibrating pressure in the system after step a and before step a. I06. The apparatus or method according to claim 1 or claim 2 wherein the CO2 absorption unit is arranged within the digester.7. The apparatus or method according to claim 1 or claim 2 wherein the 002 absorption unit is connected to the digester.8. The apparatus or method according to claim 1, 2 or 6 further comprising a supplementary 002 absorption unit.9. The apparatus, method or device according to any one of the preceding claims wherein the gas release valve is provided by an Automated Methane Potential Test System II.10. An apparatus, device or method substantially as described herein with reference to the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB1418412.1A GB2531331A (en) | 2014-10-17 | 2014-10-17 | Method for measuring biological oxygen demand |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB1418412.1A GB2531331A (en) | 2014-10-17 | 2014-10-17 | Method for measuring biological oxygen demand |
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| GB2531331A true GB2531331A (en) | 2016-04-20 |
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Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1354344A (en) * | 1971-09-15 | 1974-06-05 | Comp Nat Amenagement | Apparatus for measuring the oxygen consumption of a reducing organic medium |
| US4016065A (en) * | 1975-10-16 | 1977-04-05 | Idaho Research Foundation, Inc. | Electrolytic field respirometer |
| WO2010120229A1 (en) * | 2009-04-14 | 2010-10-21 | Bioprocess Control Sweden Ab | Device for measuring an ultra low gas flow |
-
2014
- 2014-10-17 GB GB1418412.1A patent/GB2531331A/en not_active Withdrawn
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1354344A (en) * | 1971-09-15 | 1974-06-05 | Comp Nat Amenagement | Apparatus for measuring the oxygen consumption of a reducing organic medium |
| US4016065A (en) * | 1975-10-16 | 1977-04-05 | Idaho Research Foundation, Inc. | Electrolytic field respirometer |
| WO2010120229A1 (en) * | 2009-04-14 | 2010-10-21 | Bioprocess Control Sweden Ab | Device for measuring an ultra low gas flow |
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| Publication number | Publication date |
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| GB201418412D0 (en) | 2014-12-03 |
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