Measurement 44 (2011) 1801–1805

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Measurement

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Review

Volumetric gas meter for laboratory-scale anaerobic bioreactors

A. Martínez-Sibaja a,b,⇑, A. Alvarado-Lassman b, C.M. Astorga-Zaragoza a, M. Adam-Medina a,R. Posada-Gómez b, J.P. Rodríguez-Jarquin b

a Centro Nacional de Investigación y Desarrollo Tecnológico, Interior Internado, Palmira s/n, Col. Palmira, 62490, Cuernavaca, Morelos, Mexicob Instituto Tecnológico de Orizaba, Oriente 9 No. 852, Col. Emiliano Zapata, 94320, Orizaba, Veracruz, Mexico

a r t i c l e i n f o a b s t r a c t

Article history:Received 18 August 2010Received in revised form 4 July 2011Accepted 22 August 2011Available online 30 August 2011

Keywords:Laboratory-scaleVolumetric gas meterAnaerobic bioreactors

0263-2241/$ - see front matter � 2011 Elsevier Ltddoi:10.1016/j.measurement.2011.08.018

⇑ Corresponding author at: Instituto TecnológicoNo. 852, Col. Emiliano Zapata, 94320, Orizaba, Verac7773627770x213; fax: +52 7773627770x427.

E-mail address: albino@cenidet.edu.mx (A. Mart

This paper proposes a volumetric gas meter, on-line, based on the liquid displacementprinciple. The proposed measuring device is the capacity to measure volumetric gas in arange from 1 mL to 1000 mL, from a laboratory-scale biogas reactor. As application, themeter is used in order to obtain the biogas production data file of a laboratory-scale UpflowAnaerobic Sludge Blanket (UASB) reactor.

� 2011 Elsevier Ltd. All rights reserved.

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18012. Principles and implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18023. Experimental results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18044. Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1804

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1804

1. Introduction

The anaerobic digestion is a multistep biological pro-cess, in which organic matter is degraded into biogas, i.e.a gas mixture of methane and carbon dioxide [1,2]. Anaer-obic digestion processes are gaining an increasing interestin industry and government waste treatments, due to theircapacity of energy production and low sludge yield[3–5,10].

. All rights reserved.

de Orizaba, Oriente 9ruz, Mexico. Tel.: +52

ínez-Sibaja).

The typical measurement variables in order to monitorand control laboratory-scale anaerobic bioreactors are pHand biogas production. The measurement of pH is rela-tively easy, but the measurement of a low volume of gasaccurately from a laboratory-scale bioreactor is not an easytask using commercial available gas meters [3]. To solvethis practical problem some measuring devices based onthe liquid displacement principle has been developed, forthe measurement of small gas volumes [6,7]; but not allcan easily be used to obtain the volume of gas. Moreoverthese devices are unable to take measurements on-line.In order to solve these disadvantages, an automatic sam-pling device for programmed time was linked to a gas me-ter. The operation of the system was controlled by a simpleelectronic circuit [8].

Nomenclature

�C centigrade gradecm centimetred dayD dilution rate (d�1)DC direct currentg gramh hourH heightL litre

mL millilitremm H2O millimetre of waterP hydrostatic pressureq density of liquidQin influent flow rate (L/d)Sin influent substrate (g/L)

1802 A. Martínez-Sibaja et al. / Measurement 44 (2011) 1801–1805

The objective of this paper is to present a new on-linevolumetric gas meter for laboratory-scale anaerobic biore-actors. This meter is inspired in the work of [9] where asimilar meter is proposed in order to measure low gasflows from an anaerobic bioreactor. The originality of thevolumetric gas meter proposed here is that the measuringprocess is developed on-line and provide a friendly inter-face for data display. Experimentally to measure the effec-tiveness of the volumetric gas meter, this is testedexperimentally in order to measure the biogas flow ratefrom a 1.4 L UASB reactor.

2. Principles and implementation

Fig. 1 shows the block diagram of the developed on-linevolumetric gas meter. The low flow of the gas rate pro-duced for a laboratory-scale bioreactor is collected in awaterproof nylon bag to avoid a gas leak, which is con-nected to the bioreactor through a hose of 6 mm of diam-eter. The biogas collected increases the liquid level intothe gas volumetric meter and consequently the differentialpressure over the sensor is increased too. The differentialpressure sensor is a pressure to voltage converter. A dataacquisition (DAQ) board was used together with a personalcomputer (PC) for DAQ and data processing of the biogasproduced for the bioreactor.

The dimensions of the waterproof nylon bag are 20 cmlong, 10 cm wide and 5 cm high, with a volume of 1 L, whatis appropriate to contain the production of biogas gener-ated during a period about 12 h.

Fig. 1. Block diagram of the on-line volumetric gas meter.

Fig. 2 shows the structure and dimensions of the devel-oped measurement system. The prototype consists of acontainer of acrylic of 20 cm long, 10 cm wide and 20 cmhigh (equivalent to 4 L), with an internal perforated plateof acrylic to trap the waterproof nylon bag and keep thissubmerged, because the biogas that will be collected inthe bag is less dense than water. The perforated plate isplaced inside the container, 5 cm in height; all the volumeunder the plate (equivalent to 1 L) is filled with water. Thewaterproof nylon bag is placed in the bottom of the con-tainer. When the gas flow from the bioreactor enters inthe waterproof nylon bag, the volume of the bag is in-creased due to the pressure of biogas and this causes thedisplacement if the water through the holes of the perfo-rated plate to the top of the container. The displaced watercauses a hydrostatic pressure which is measured by meansof a differential pressure sensor placed exactly at the sameheight at which the perforated plate is placed.

Assuming that the volume of the displaced water isequal to the volume of biogas inside the bag, then the vol-ume of the produced biogas can be measured indirectlythrough the hydrostatic pressure. The measurement ofhydrostatic pressure on the surface of the plate is donewith a differential pressure sensor because the containeris shaped like a tank opened. In this type of tanks hydro-static pressure at any point can be known by

P ¼ qH ð1Þ

where P is the hydrostatic pressure, q is the density of li-quid, and H is the height of the liquid column.

Because of the density of water is 0.001 kg/cm3, themaximum hydrostatic pressure that will be achieved byreaching a height of 5 cm of water, is:

P ¼ ð0:001 kg=cm3Þð5 cmÞ ¼ 0:005 kg=cm2

¼ 50 mm H2O ð2Þ

The placement of the differential pressure sensor is per-formed as shown in Fig. 3. According to the result obtainedwith Eq. (2) for the selection of differential pressure sensor,it must have a minimum measuring range from 0 to 50 mmH2O.

For the implementation of the volumetric gas meter, itwas used a MPXV5004G piezoresistive transducer, whichhas a measuring range of 0–400 mm H2O, with output volt-age range of 1.0–4.9 DC Volts. This differential pressuresensor is appropriate, because the maximum pressure

Fig. 2. Structure and dimensions of the developed measurement system.

Fig. 3. Placement of the differential pressure sensor.

A. Martínez-Sibaja et al. / Measurement 44 (2011) 1801–1805 1803

measured by the system is 50 mm H2O and this value iswithin the measuring range of this sensor. Even the sensoris not limited to future enlargements of the measurementsystem biogas.

Fig. 4. Relationship between the output voltage and the differentialpressure for the MPXV5004G sensor.

The MPXV5004G piezoresistive transducer is a state-of-the-art monolithic silicon pressure sensor designed for awide range of applications. This sensor combines a highlysensitive implanted strain gauge with advanced microma-chining techniques, thin-film metallization, and bipolarprocessing to provide an accurate, high level analog outputsignal that is proportional to the applied pressure. The out-put signal of the sensor is a DC voltage that is proportional

Fig. 5. The developed volumetric gas meter.

Fig. 6. Biogas flow rate produced for the UASB reactor.

Fig. 7. Comparison between the measure of the biogas produced for theUASB reactor: (a) real time volumetric gas meter (solid line) and (b)MilliGascounter™ (dotted line).

1804 A. Martínez-Sibaja et al. / Measurement 44 (2011) 1801–1805

to the variation of pressure over the sensor in the gas me-ter; this feature is shown in Fig. 4. The sensor providesadditional features, such as compensation for effects oftemperature from 10 to 60 �C. The sensor occupies lessspace for its surface mount packaging of durable thermo-plastic, and the diaphragm stainless steel that is resistantto certain levels of acidity. The developed laboratory-scalegas flow meter is shown in Fig. 5.

In this project, the National Instruments USB-6008 mul-tifunction data acquisition (DAQ) module that has a 12bitADC resolution was used as an interface between the out-put of the differential pressure sensor and the personalcomputer, to provide reliable data acquisition at a lowprice. With plug-and-play USB connectivity, this moduleis simple enough for quick measurements but versatile en-ough for more complex measurement applications, and itdoes not need to use a data filter.

A graphical user interface (GUI) was developed with Na-tional Instruments LabVIEW™. This graphical interfaceshows the dynamics of the produced biogas in real timeand besides, it creates a data file of the produced biogas witha sampling period of 1 min. The GUI for the developed volu-metric gas meter, is shown in Fig. 6. If the START bottom isthe system is automatically adjusted to zero and the biogasflow rate is plotted in real time. When the STOP bottom isactivated, it is generated a data file of the measured biogasflow rate is generated with a sampling period of 1 min.

3. Experimental results

The 1.4 L UASB reactor was used to test the perfor-mance of the developed volumetric gas meter throughthe measuring of biogas production. Fig. 6 shows the bio-gas flow rate produced for the UASB reactor, at fixed tem-perature of 35 �C, influent substrate Sin = 3 g/L, and influentflow rate Qin = 0.7 L/d. The volume of biogas was increasedfrom 0 mL (at time 0 min) to 65 mL (at time 100 min). Atthe same conditions, Fig. 7 shows a comparison betweenthe signal plotted with the data file obtained during720 min (12 h), using the developed GUI (solid line), andthe graph obtained by means of the patented MilliGas-counter™ [11] (dotted line), which is designed for the mea-surement of small amounts of gas but does not have a GUIand is far more expensive than the developed prototype.The linear correlation coefficient between both signals is0.9817.

4. Conclusions

In this paper, a volumetric gas meter for laboratory-scale anaerobic bioreactors was developed. The proposedmeasuring device was used to measure the biogas produc-tion of an UASB reactor. One of the main advantages of thismeter is that the biogas measured is collected in a remov-able nylon bag, in order to allow that the biogas producedfor the UASB reactor must been evaluated to obtain theconcentrations of methane and carbon dioxide.

The cost of the proposed device is low compared tocommercial devices used for this porpoise, it cost at less20 time less than commercial ones.

The good performance of the developed volumetric gasmeter makes it possible. The application of this device infuture in future research projects in monitoring and con-trol of bioreactors.

References

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[3] J. Liu, G. Olsson, B. Mattiasson, Control of an anaerobic reactortowards maximum biogas production, Water Science Technology 50(2004) 189–198.

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[8] M. Macias, M. Perez, I. Caro, D. Cantero, Automatic gas meter forlaboratory fermenters, Biotechnology Techniques 9 (9) (1995) 655–658.

[9] J. Liu, G. Olsson, B. Mattiasson, A volumetric meter for monitoring oflow gas flow rate from laboratory-scale biogas reactor, Sensors andActuators B 97 (2–3) (2004) 369–372.

[10] A. Alvarado-Lassman, E. Rustrián, M.A. García-Alvarado, G.C.Rodríguez-Jiménes, E. Houbron, Brewery wastewater treatmentusing anaerobic inverse fluidized bed reactors, BioresourceTechnology 99 (2008) 3009–3015.

[11] Dr. Ritter Apparatebau GmbH & Co., Milli gas Counter, Bochum,Germany.