p 28 gutierrez - monitoring of waste

8/9/2019 P 28 Gutierrez - Monitoring of Waste

http://slidepdf.com/reader/full/p-28-gutierrez-monitoring-of-waste 1/6

MONITORING OF WASTE WATERS QUALITY USING A

MULTISENSOR SYSTEM

C. Jiménez-Jorquera; J. Orozco

*

; M. Gutiérrez

Instituto de Microelectrónica de Barcelona (IMB-CNM), CSIC. Campus UAB, 08193-Bellaterra, Spain.

E-mail: [email protected]

* Present adress: Observatoire Oceanologique, Laboratoire Arago, Avenue du Fontaulé, BP 44,

66651 Banyuls Sur Mer, France. E-mail: [email protected].

ABSTRACT

Access to potable water and the assessment of its quality, normally through physicochemicaland biological monitoring, are neuralgic issues worldwide. An important aspect in the

monitoring of water quality is the identification of pollution events to determine the

appropriate treatment and to preserve public health and ecosystems. This work investigates

the use of a multisensor system for monitoring the quality of wastewaters. The proposed

system is comprised of an array of electrochemical sensors fabricated with microelectronic

technology which offers advantages like reproducible fabrication, miniaturized size, massive

production and high benefit/cost ratio. Here we present the application of these sensors to

measure some parameters-pH, conductivity, ORP and electrochemical oxygen demand

(EOD)- of waste waters from a winemaking process.

RESUMEN

El acceso al agua potable y la evaluación de su calidad, realizada normalmente a través de

controles biológicos y físico-químicos, son temas de gran transcendencia para todo el mundo.

Un aspecto importante en el control de la calidad del agua es la identificación de casos de

contaminación para poder así determinar el tratamiento adecuado y preservar la salud pública

y los ecosistemas. Este trabajo indaga sobre el uso de un sistema multisensor para monitorizar

la calidad de aguas residuales. El sistema propuesto se compone de un conjunto de sensores

electroquímicos fabricados con tecnología microelectrónica que ofrece ventajas, tales como la

fabricación reproducible, el tamaño miniaturizado, la producción masiva y una elevada

relación beneficio / coste. Aquí presentamos la aplicación de estos sensores para medir

algunos parámetros como el pH, la conductividad, el potencial redox y la demanda

electroquímica de oxígeno (DEO) en aguas residuales provenientes de un proceso de

elaboración de vino.

RESUM

L’accés a l’aigua potable i la avaluació de la seva qualitat, realitzada normalment mitjançant

controls biològics i fisicoquímics, són aspectes de gran transcendència per a tot el món. Un

aspecte important en el control de la qualitat de l’aigua és la identificació de casos de

contaminació per a poder determinar el tractament adequat en cada cas y preservar la salut

pública i els ecosistemes. Aquest treball investiga sobre l’ús d’un sistema multisensor per al

1



monitoratge de la qualitat d’aigües residuals. El sistema proposat està format per un conjunt

de sensors electroquímics fabricats amb tecnologia microelectrònica, la qual ofereix una sèrie

d’avantatges, com la fabricació reproduïble, la mida miniaturitzada, la producció massiva y

una elevada relació benefici / cost. Aquí presentem l’aplicació d’aquests sensors per a

mesurar alguns paràmetres com el pH, la conductivitat, el potencial redox i la demanda

electroquímica d’oxigen (DEO) en aigües residuals provinents d’un procés d’elaboració de vi.

INTRODUCTION

Water is fundamental for all the Earth’s life forms and a key issue in social and economical

development. Nowadays, due to the increase of demand of potable water and pollution,

natural water sources have became insufficient to supply all the necessities. Access to potable

water and the assessment of its quality, normally through physicochemical and biological

monitoring, are neuralgic issues worldwide. The directives concerning to water quality for

human consumption and wastewater quality are very strict. To accomplish internationalnormative, analytical systems are being placed with more extent in water treatment plants or

industrial waste water collectors to evaluate and control water quality parameters. Currently,

there are a few probes in the market for in-field analysis -mainly for pH, ORP, conductivity

and temperature- based on conventional electrodes (Naim et al., 1994; Spagnl et al., 2001) but

the majority of pollutants are measured in the laboratory with standard analytical techniques

The use of solid-state sensor arrays and microsensors for in-field monitoring of environmental

parameters is gaining interest due to their advantages over conventional sensors. Specifically,

microelectrodes fabricated with semiconductor technology are small, robust, able to

integration, have low output impedance and rapid response. They are potentially useful for

environmental applications since they can be mounted in small and compact probes designedfor in-field measurements (Artigas et al., 2001; Orozco et al., 2006; Orozco et al., 2007) or

integrated in flow systems for on-line monitoring (Jiménez et al., 1996; Artigas et al., 2003).

These systems permits automatic sampling and calibration, sample treatment and sensor

conditioning, they can be installed near the sampling place (i.e. rivers, lakes, industrial

wastes) and can also accomplish some of the requirements for in-field monitoring like low

power consumption, high autonomy and robustness. In that way it is possible to obtain

information in real time and minimize variations in the sample composition due to

transportation or storage.

The measurement of Chemical Oxygen Demand (COD) is usually performed in an effluent as

indicator of its degree of contamination by organic matter. The COD of a sample is defined asthe amount of oxidizing agent, expressed as the equivalent amount of oxygen, which is

necessary for the chemical oxidation of the sample. Usually, it is determined by means of

strong oxidizing agents such as dichromate and permanganate (Greenberg, 1999). However,

these procedures are not automatic, are time-consuming and require acid digestion, which is

highly pollutant and dangerous. The electrochemical oxygen demand (EOD) is an alternative

parameter defined as the oxygen amount equivalent to the charge consumed during

electrochemical oxidation of the sample. As such, the EOD value usually differs from the

COD data. However, measurement of the EOD can be a suitable method when a simple and

fast estimation of the contamination grade by organic matter is required.

Having in mind the lack of robust and feasible sensors for in-field analysis, we have

developed microsensors for the detection of electrochemical oxygen demand (EOD),

2



conductivity and pH, together with a temperature probe. These sensors have been applied for

analyse waste water samples from a winemaking process line.

EXPERIMENTAL

Devices

ISFETs with a pH-sensitive Si3N4 gate were fabricated in the IMB with a modified aluminium

gate NMOS technology (Jiménez et al., 2005). Pt and Au microelectrodes were fabricated

using standard microelectronic technology. The silicon wafer was oxidized (1000 nm of SiO2)

and titanium or chrome (20 nm) and platinum or gold (100 nm) layers were deposited and

patterned by lift-off to form the electrodes and contact pads. For the conductivity and ORP

sensor, the design was based on a 4-electrode geometry, consisting of two external electrodes

of 2000 µm x 700 µm and two internal electrodes of 2000 µm x 240 µm spaced 240 µm. This

4-electrodes configuration was used for the conductivity sensor. For ORP measurements the

potential of only one of these 4 electrodes was measured against an Ag/AgCl (3.0 M KCl)double junction reference electrode (Orion 92-02-00). The amperometric electrode for the

EOD sensor fabrication was based on a Pt electrode of 2x2 mm2.

Once fabricated the chips (ISFETs and microelectrodes) they were glued and wire-bonded to

a standard printed circuit board (PCB) strips. Finally, they were encapsulated with a

photocurable polymer.

EOD sensors were fabricated by depositing on top of the amperometric electrodes a

composite. Composites were prepared with polystyrene, graphite as conductive material and a

mixture of AgO-CuO as catalysts. The preparation and deposition of the composite is

explained in ref. (Orozco et al., 2008).

Samples

Samples were obtained from the Torres S.A. wine cellar. In that cellar they have a wastewater

treatment plant (WWTP). The analytical data for pH, conductivity and COD obtained with

standard methods of six samples collected from the influent and six collected from the

effluent of the plant are presented in Table 1.

Samples were measured directly with pH, ORP and conductivity sensors. To measure EOD

samples were diluted 1:1 in 0.1 M NaOH before analysis in order to get the suitable pH

conditions (pH 12.8 ± 0.5).

RESULTS AND DISCUSSION

The samples were analysed with the microsensors after their calibration to assure their good

performance (Orozco, J. et al 2007). The signal obtained was interpolated in the calibration

curve and analytical data was compared with that obtained from the laboratory of the wine

cellar.

Measurement of pH and conductivity presented errors up to 10 %. For pH the average error

was 10.6% for influent samples and 1.4 % for effluent samples. As shown in Figure 1a pH

values measured with the ISFET were in general higher than with the glass electrode, and for

the influent samples the difference was greater, maybe due to the presence of suspension

matter in the samples. For conductivity values average errors were 2.5% for the influent and

4.8 % for the effluent samples. Here the dispersion of values is greater for the effluent

3

http://en.wikipedia.org/wiki/Sewage_treatment






samples but acceptable for conductivity measurements, highly dependent on the temperature

and the instrumentation.

Table 1. Analytical data from the influent and effluent of the wastewater plant.

pH Cond, mS/cm COD, ppm O2

Influent E07 7.3 3.9 870

E08 6.8 4.8 1290

E09 6.6 5.3 1573

E14 7.4 3.3 686

E15 7.2 4.5 1137

E16 7.6 5.5 1376

E21 6.7 4.0 568

E22 6.6 5.0

E23 6.4 5.9 563

Effluent S07 7.9 4.4

S08 7.7 4.3

S09 7.9 4.7

S14 8.2 5.1

S15 7.7 4.9

S16 8.3 5.0

S21 7.7 5.2

S23 8.1 5.1

Conductivity

2

3

3

4

4

5

5

6

6

E07 E08 E09 E14 E15 E16 E21 E22 E23

C o n d u c t i v i t y , m S / c m

influent m icrosensorinfluent probeeffluent microsensoreffluent probe

pH

4.0

4.5

5.0

5.5

6.0

6.5

7.0

7.5

8.0

8.5

9.0

E07 E08 E09 E14 E15 E16 E21 E22 E23

ISFET influent

pH influent

ISFET effluent

pH effluent

a) b)

Figure 1. Values of pH (a) and conductivity (b) for the microsensors and standard

electrodes from WWTP samples.

Regarding to ORP values, no data was provided from the laboratory. However, the values

obtained with our microsensors show the difference between the samples before the treatment

and after, assessing the clear the effect of stabilization achieved with this treatment (Figure 2).

4



as Figure 3 shows.

Values of EOD were not in accordance with COD values measured with the standard method.

Figure 3. DQO/EOD values of standard method and microsensors from the

influent samples of WWTP.

CONCLUSIO

e a good alternative for measurement of environmental parameters. These

are small, thus can be integrated in the same platform or in a compact flow system to get

a flow system to obtain a multisensor system that combined multivariante data

Figure 2. Microsensors ORP values from the WWTP.

Only the EOD of effluent samples were measured with our microsensors,

This fact is due to that the oxidative capacity of the catalysts in the composite electrode is

limited to not complex organic material. However, the results demonstrated that a constant

ratio is maintained between both values (factor DQO/EOD=10). Then, the microsensors could

be used for rapid determinations in order to make preliminary decisions.

NS

Microsensors can b

automatic calibration and sample treatment; are reproducible, have fast response, low power

consumption, which is quite valuable for autonomous systems placed in field, etc. Results

shown here demonstrate that the accuracy of microsensors compared with standard probes is

good.

Further work is addressed to implement all the sensors in the same platform and integrate

them in

DQO influent

0

200

400

600

800

1000

1200

14001600

1800

E07 E08 E09 E14 E15 E16 E21 E22 E23

p p m O

2

EOD sensors

DQO standard

ORP influent

-250

-200

-150

-100

-50

0

50

100

150

E07 E08 E09 E14 E15 E16 E21 E22 E23

Sample

O R P , m V

ORP effluent

0

50

100

150

200

250

S07 S08 S09 S14 S15 S16 S21 S23

Sample

O R P , m V

5



treatment will provide more automatic and autonomous systems with high accuracy. These

systems can be applied to get the global quality of waters.

ACKNOWLEDGEMENTS

The supplying of samples and analytical data from Miguel Torres S.A. is kindlyacknowledged.

nez, C.; Domínguez, C.; Mínguez, S.; Gonzalo, A.; Alonso, J. 2003.

Development of a multiparametric analyser based on ISFET sensors applied to process

water

Water, Air, and Soil

be based on solid-state microsensors. Anal. Chim. Acta 579: 95-101.

Composite planar electrode for sensing electrochemical oxygen demand. Anal.

nductivity and dissolved oxygen in nitrogen and phosphorus

REFERENCES

Artigas, J.; Jimé

control in the wine industry. Sens. Actuators B 89: 199-204.

Greenberg, A. 1999. Standard Methods for the Examination of Water and Wastewater.

Jiménez, C.; Marqués, I.; Bartrolí, J. 1996. Continuous-flow system for on-line

monitoring using back-side contact ISFET-based sensors. Anal. Chem. 68: 3801- 07.

Jiménez, C.; Baldi, A.; Abramova, N.; Bratov, A. 2005. In: Grimes, C. A.; Dickey, E. C.;

Pishko, M.V. Encyclopedia of Sensors. American Scientific Publishers.

Naim, M. A.; Shaker, N.; Salem, E. M.; El-Gamal, A.; El-Raey, M. 1994. Tritium

radioactivity in the aquatic environment over Alexandria region, Egypt.

Pollut. 73: 275-284.

Orozco, J.; Baldi, A.; Martín, P. L.; Bratov, A.; Jiménez, C. 2006. Monitoring of bentonite

pore water with a pro

Orozco, J.; Baldi, A.; Baena, R.; Cadarso, A.; Bratov, A.; Jimenez, C. 2007. Portable system

based on microsensors for environmental monitoring applications. Meas. Sci. Technol. 18:935-940.

Orozco, J.; Fernández-Sánchez, C.; Mendoza, E.; Baeza, M.; Cespedes, F.; Jiménez-Jorquera,

C. 2008.

Chim. Acta 607: 176-182.

Spagni, A.; Buday, J.; Ratini, P.; Bortone, G. 2001. Experimental considerations on

monitoring ORP, pH, co

biological removal processes. Water Sci. Technol. 43(11): 197-204.

6

p 28 gutierrez - monitoring of waste

Documents