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Automatic Network for Surveillance of WWTP Effluents

Jordi Cros Herrero1, Antonio Gonzalez Catena

2, Ramón Prats Vilme

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1R&D Director, Adasa Sistemas. C/ José Agustín Goytisolo, 30-32, 08908 L’Hospitalet de Llobregat,

Barcelona, Spain (Email: jcros@adasasistemas.com) 2REACAR Network Project Director, Adasa Sistemas. (Email: agonzalez@adasasistemas.com)

3Adasa Sistemas, S.A.U.. C/ José Agustín Goytisolo, 30-32, 08908 L’Hospitalet de Llobregat, Barcelona,

Spain (Email: rprats@adasasistemas.com)

Abstract

As the amount of urban wastewater increases, treated effluent discharges from treatment

plants becomes one of the most important causes of contamination of public domain

freshwater. Current legislation enforces periodic checks of effluents, but such controls cannot

detect potential releases of insufficiently purified wastewater produced in the periods between

successive samples, so it is possible to have WWTPs with correct analytics working

incorrectly most of the time.

The REACAR network, promoted by the Guadiana River Basin, has demonstrated the

feasibility, both technically and economically, of a system capable of tracking the quality of

effluent to evaluate the overall operation of the WWTP.

Keywords Wastewater, monitoring, real time

INTRODUCTION

Water Framework Directive and River Basin Authorities

Since 2000, the Water Framework Directive1 requires EU states to set quality objectives for all

water bodies within its defined territory. It also requires the monitoring of the ecological quality

of each to ensure they meet the proposed objectives. In Spain, the government has delegated this

responsibility to River Basin authorities.

The current Spanish legislation related to water sector determines all discharges which can cause

any contamination at freshwater public domain must have an administrative authorization. This

authorization shall establish the conditions of the discharges (Art. 100 of TRLA2).

In rivers, the main sources of these discharges are:

- Human activities.

- Agricultural and livestock activities.

- Industrial activities.

- Wastewater Treatment Plants.

The urban WWTPs are the points of reception and treatment of urban wastewater. In Spain, the

WWTPs must also have the administrative authorization issued by the River Basin Authorities.

As a result, the fulfilment of such authorization is becoming a priority.

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Wastewater Treatment Plants

In WWTP, wastewater is subjected to appropriate treatments to reduce the pollutants load to

values with no detectable impact on the receiving environment. The proper functioning of the

WWTP can only be achieved when the limit values of the discharge characteristic parameters

are set in the corresponding authorization.

In Spain, the WWTP owners are usually the municipalities, responsible for sanitation and

sewage treatment (art. 25 of LBRL3) to be administered individually or jointly as appropriate. In

addition to internal controls performed in WWTPs to verify equipment operation and

performance, periodic checks are carried out in the final effluent to comply with current

legislation, based on sampling and subsequent laboratory analysis, usually on a monthly

frequency (91/271/EEC4). However, such controls cannot detect releases of insufficiently

purified wastewater produced in the periods between successive samples. Therefore, it is

possible to have the paradox of WWTPs with correct analytics working incorrectly most of the

time.

THE REACAR NETWORK

In order to protect the environment and fill the conditions of discharges set in the corresponding

authorization, in September 2007 the Guadiana River Basin authority promoted REACAR

network installation5 in order to establish an automated system for online monitoring of effluent

from the WWTP. The main goal was to establish a system to immediately alert the

Administration and the WWTP operator on possible flaws in the process, alerting of a likely

danger of contamination in the shortest possible time. Adasa was the awarded company of the

installation, maintenance and operation of the network, project which was built during the years

2008 and 2009, and was fully operational since mid-2009.

Network Structure

The aim of the network was to have a control system for the detection of abnormal effluent

situations at a reasonable installation and maintenance cost. After an initial analysis of

alternatives, it was determined that monitoring parameters of a typical wastewater treatment

plant effluent (BOD5, ammonia, nitrates, phosphates, etc.) was not best suited for the project, as

the cost of installation and especially maintenance was not acceptable. It was found that the use

of physical and chemical parameters such as ORP, dissolved oxygen and turbidity, together with

the measurement of organic matter in an indirect way (through the sample absorbance at 254

nm) allowed an alternative with reasonable installation and maintenance cost: although it could

not be used for direct effluent control, it allowed for the detection of abnormalities. Moreover,

the technological possibility of incorporating a system for recording low cost images added a

new parameter - visual aspect - that endowed the system with more features.

Under these assumptions, the network is defined with the following elements (Figure 1):

• Measuring Station

• Communication System.

• Control Centre.

Measuring Station Elements

The network design was based on small autonomous stations for portable outdoor installation.

Each station had no external parts, needing only power and water connection points for

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sampling and drainage, without civil works. Thus, the installation process was quick and simple

(Figure 2).

Figure 1. REACAR network structure.

Figure 2. REACAR station installation. From left to right, top to down: a) Station in the truck;

b) Station out of truck; c) Station at final position; d) Station installed.

Inside the cabin, the core of the system is the aquaTest-MO, a physicochemical multi-parameter

(temperature, pH, ORP, conductivity, dissolved oxygen and turbidity) unit developed

specifically for these applications. This unit measures organic matter by absorbance at 254 nm

(SAC parameter, or Spectral Absorbance Coefficient), with turbidity compensation supplied by

DUV Led technology (Deep Ultra-Violet Light Emitting Diode). The equipment is able to

manage the caption system (using a pump controlled by a variable frequency driver) and self-

cleaning system, allowing unattended operation without preventive maintenance for 15 days. In

addition, the equipment has capability to store historical and communications management data,

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so it is only necessary to include a router GSM / GPRS to provide connectivity to the control

centre.

The stations include a sampler controlled by the multi-parameter equipment, so when detecting

anomalous situations, on alarm or remote command, sample collection can be enforced for

further detailed analysis in the laboratory.

Communications System

As communications system for transmission of measurements, alarms and images from station

to Control Center, the GSM network was selected, using the GPRS service, using a VPN

(Virtual Private Network) so equipments of the stations are elements of the Control Centre

network.

Control Centre

Control Centre if composed by a computer with several software applications allowing the

operator to perform:

• Reception of measures

• Reception of images.

• Validation and interpretation of data.

• Reporting.

RESULTS

After an adjustment period during the start up of the first station, the system was configured to

generate a historical record every 15 minutes. For the cameras it was scheduled a daytime image

capture every hour, as initially it was not considered necessary to capture images during the

night. Daily analysis of the information received is performed in the control centre, generating

the report status of each network station, which is sent to the municipality owner of the plants.

The following figures show three examples of sewage outlets, with the graph showing the

evolution of the chemical-physical parameters and images collected by the system:

- Figure 3 corresponds to the output of a plant without problems, where the values are

always correct. The output of the effluent quality is very consistent, although with a high

content of organic matter. There is a daily cycle in the measurements of temperature, pH

and dissolved oxygen, with a high value thereof.

- Figure 4 represents a consistent issue in the operation of the plant, with a very high rate of

change. In the photographs it can be seen that within 4 hours the effluent of the output

changes twice from normal to abnormal.

- Figure 5 is a fairly typical example of discharge at the input of the plant, resulting in

increased organic matter content in the output, as the plant is not able to degrade the

entire load.

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Figure 3. Sample of charts at the output of an urban WWTP

Figure 4. Spill sample. On top, weekly evolution of parameters, with photographs of the

WWTP’s output (September, 22th 2009)

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Figure 5. Punctual spill of WWTP’s input, which causes a plant malfunction

Data availability

In this type of warning networks the concept of good and bad data cannot be regarded as

absolute, since one of the biggest benefits is the large amount of data it can generate, which

provides information likely to be contrasting, and is one of the determining factors to evaluate

the usefulness of the system. Consequently, the extent of data available is also a parameter for

evaluating the network.

Since the system is configured to obtain a value for each parameter every 15 minutes, it is very

simple to calculate availability, since the system should record 35,040 annual registers for each

of the measures (365 days x 24 hours / day x 4 values per hour). Nevertheless, not all of data

will be available, due to power failure, stations breakdown, etc., and among all available data

some will be invalid because of equipment failure, maintenance, etc. Table 1 shows data

summary statistics of valid and invalid data recorded during 2010. Table 2 shows the availability

for each of parameter and each of station, indicating the percentage of availability in terms of

maximum operating days of a station.

Table 1. Data availability statistics for 2010

# Data invalidated % over possible Data

Total Possible data 3.269.280

Total Available Data (valid & invalid) 3.125.905 95,6%

Total Valid data 3.008.994 92,0%

Total invalid Data 116.911 3,6%

2010

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Table 2. Availability measure for 2010

Data Analysis

The large volume of data that is capable of generating the network is not useful if one is not able

to extract the necessary information for management and, thus, see how data evolve over time,

both in short (within hours or days) and long term (months or years). Although in this case, due

to the youth of the system - data available before 2009 only in two stations -, it cannot yet

display long-term variations that create both a profile of the normal discharge of the WWTP and

its potential alterations.

Common features that can be obtained from the analysis of all data are the following ones:

- The value of pH is a very stable parameter in all discharges, ranging between 7.4 and 7.8

(+ -0.2) on a widespread basis.

- The measurement of dissolved oxygen almost always has a minimum around 0. This

means that, although it works well, it is very difficult for the WWTP to be free from

occasional episodes of anoxic landfill.

- The measure of conductivity is the parameter most affected by industrial activity,

resulting in very sharp swings in industrial areas.

- The SAC (Spectral Absorption Coefficient) and turbidity parameters are the best

indicators of the quality of discharge and have very high standard deviations. During

bouts of abnormal discharge they typically reach such high values that they are easily

identifiable and make it easy to assess the intensity and importance of the episode.

CONCLUSIONS

Insufficiently purified effluent discharged to the environment can represent a serious risk of

contamination to the natural systems that the WFD is required to protect. Through the

responsible authorities (in Spain, the Water Boards, as stated in Article 94 of the TRLA2), it is

necessary to control effluent more efficiently to protect the public water from the adverse effects

of discharges.

Days On

Station 01 365 96,4% 97,3% 96,8% 96,9% 97,2% 96,7% 95,1% 94,6%

Station 02 365 84,2% 87,1% 85,3% 86,8% 86,3% 85,6% 72,5% 85,8%

Station 03 365 93,5% 94,7% 94,3% 94,6% 94,0% 94,3% 92,5% 90,0%

Station 04 365 97,2% 97,9% 97,3% 96,9% 97,1% 96,2% 97,5% 97,2%

Station 05 166 95,4% 99,7% 97,0% 99,2% 98,7% 98,6% 84,2% 90,3%

Station 06 365 85,6% 87,6% 85,9% 86,1% 84,0% 85,8% 84,1% 85,7%

Station 07 184 96,8% 99,5% 99,7% 99,4% 97,1% 98,4% 94,4% 88,8%

Station 08 365 89,8% 91,3% 90,3% 90,1% 90,4% 89,2% 89,6% 87,6%

Station 09 365 96,2% 98,2% 97,0% 96,1% 97,3% 97,0% 92,2% 95,7%

Station 10 365 86,6% 90,3% 88,8% 90,2% 89,0% 83,9% 82,7% 81,5%

Station 11 150 92,2% 99,2% 96,3% 90,3% 97,5% 97,3% 82,2% 82,6%

Station 12 365 94,3% 96,4% 95,6% 93,1% 95,1% 95,2% 93,3% 91,4%

Station 13 365 94,9% 98,6% 98,3% 98,3% 98,4% 95,8% 96,2% 78,4%

Station 14 152 93,7% 98,6% 95,8% 98,3% 96,4% 96,8% 76,6% 93,7%

Station 15 365 92,7% 94,0% 92,4% 92,9% 93,5% 93,4% 93,0% 89,6%

Station 16 198 85,5% 99,5% 98,5% 98,5% 98,7% 93,7% 15,4% 94,6%

Total 4.865 92,0% 94,9% 93,7% 93,7% 93,8% 92,9% 86,2% 89,1%

Valid Data Valid Data Valid Data Valid DataValid Data Valid Data Valid Data Valid Data

Oxygen Red Ox SAC Turbidity2010 Temp pH Conduc

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The method defined in current legislation based on a monthly report of punctual analytical is

insufficient to ensure adequate monitoring of the quality of discharges onto the public domain,

and shows that WWTPs with correct analytical results may work very poorly. A permanent

monitoring of the quality of the effluent permits to control if discharges are within the

boundaries of each given authorization, and determine whether this authorization has to been

revised to fit the real situation. In these cases, the REACAR project has demonstrated the

feasibility, both technically and economically, of a system capable of tracking the quality of

effluent to evaluate the overall operation of the WWTP:

• Field installation is simple and quick and can go from arrival to operational in no time.

• The equipment used in this work is specific and, after a year of operation, shows

excellent results.

• System covers the dual purpose of having real-time data and to state the compliance with

WFD effluent quality objectives.

As a result of implantation, detection and correction of malfunctions in plants that generated an

increase in the pollutant load in the freshwater public domain was done, allowing authorities to

secure the objectives of the Water Framework Directive and a revision of quality of discharge

authorization in some cases.

ACKNOWLEDGEMENT

Mr Domingo Fernández, area head of the Water Quality Department of Guadiana River Basin,

for his help in providing information.

REFERENCES

1 Directive 2000/60/EC of the European Parliament and of the Council of 23 October 2000 establishing a

framework for Community action in the field of water policy 2 Real Decreto Legislativo 1/2001, de 20 de julio de 2001, por el que se aprueba el Texto Refundido de la Ley de

Aguas, en adelante TRLA. Modificado posteriormente mediante la Ley 62/2003, de 30 de diciembre (Royal

Decree 1 / 2001 of July 20, 2001, by approving the revised Water Law, hereinafter TRLA. Subsequently

amended by Law 62/2003 of 30 December) 3 Ley 7/1985, de 2 de abril, Reguladora de las Bases del Régimen Local. (Law 7 / 1985 dated April 2,

Regulation of the Local System.) 4 Council Directive 91/271/EEC of 21 May 1991 concerning urban waste-water treatment, as amended by

Directive 98/15/EC. Transposed into Spanish law by the R.D. Law 11/1995, the R.D. 509/1996, which

implements it, and R.D. 2116/1998 amending previous 5 BOE núm. 129 de 12 de septiembre de 2007. 56.226/07. Resolución de la Confederación Hidrográfica del

Guadiana por la que se anuncia concurso abierto número de expediente 9/164-07 para la contratación del

«Suministro e instalación del medios para la implantación de la infraestructura necesaria y bienes destinados al

uso, mantenimiento y explotación de la Red de Estaciones Automatizadas de Control de Aguas Residuales

(REACAR) en la Zona Occidental de la Confederación Hidrográfica del Guadiana (clave 05/1.2.02). (BOE.

129, September 12, 2007. 56.226/07. Resolution of the Guadiana River Basin in which open competition is

announced 9/164-07 file number for the recruitment of 'Supply and installation of the means for implementing

the necessary infrastructure and property for the use, maintenance and operation of the Automated Network

Control Stations Sewage (REACAR) in the Western Zone of the Guadiana River Basin (key 05/1.2.02).