Environmental decision support systems: A new approachto support the operation and maintenance of horizontalsubsurface flow constructed wetlands

Claudia Turona,∗, Joaquim Comasa, Jaume Alemanya, Ulises Cortesb, Manel Pocha

a Laboratory of Chemical and Environmental Engineering (LEQUIA), University of Girona, Campus Montilivi s/n, E-17071 Girona,Catalonia, Spainb Knowledge Engineering and Machine Learning Group (KEMLG), Technical University of Catalonia, Campus Nord, Edifici Omega 135,C/Jordi Girona 1-3, E-08034 Barcelona, Catalonia, Spain

a r t i c l e i n f o

Article history:

Received 21 November 2006

Received in revised form

23 February 2007

Accepted 15 April 2007

Keywords:

Constructed wetlands

Ecological engineering

Environmental decision support

system

a b s t r a c t

This paper describes the development and operation of an Environmental Decision Support

System (EDSS) to improve the operation and maintenance of horizontal subsurface-flow

constructed wetlands (EDSS-maintenance). Constructed wetlands (CWs) allow wastewater

treatment in a sustainable manner since they involve low energy consumption, low con-

struction and functioning costs and low environmental impact. However, operation and

maintenance activities are essential to guarantee reliability in CWs performance. The defini-

tion of operation and maintenance protocols depends on several quantitative and qualitative

aspects such as wastewater treatment plant configuration, CW design, influent characteris-

tics, sensitivity of the receiving media, etc. Bearing this in mind and considering the limited

technical knowledge about CWs, the need for a new tool to support CW performance is clear.

In this sense, EDSSs offer a new approach because they can tackle problems of complex and

uncertain systems. The EDSS-maintenance provides operation and maintenance manuals

Operation and maintenance specifically defined for every CW. To achieve it, the required knowledge was implemented

within a rule-based system, which forms the backbone of the EDSS. Several features pre-

sented in this paper demonstrate how the EDSS-maintenance provides a proper platform to

support the necessary collaborative work in the ecological engineering problem of horizontal

subsurface flow CWs operation and maintenance.

The first task when solving an environmental problem

1. Introduction

The term ecological engineering implies restoring, creatingand maintaining sustainable ecosystems that have value forboth humans and nature. The collaboration between ecol-

ogists and engineers is essential in these developmentsbecause, while competent at describing environmental prob-lems and maybe even managing ecosystems, ecologists are

∗ Corresponding author. Tel.: +34 972 418 804; fax: +34 972 418 150.E-mail addresses: claudia@lequia.udg.cat (C. Turon), quim@lequia.u

ia@lsi.upc.edu (U. Cortes), manel@lequia.udg.cat (M. Poch).0925-8574/$ – see front matter © 2007 Elsevier B.V. All rights reserved.doi:10.1016/j.ecoleng.2007.04.012

© 2007 Elsevier B.V. All rights reserved.

not well versed in prescribing solutions to problems. Likewise,engineering curricula do not routinely include ecology, therebythe science that could help engineers most in environmentalproblem-solving is overlooked (Mitsch and Jørgensen, 2003).

dg.cat (J. Comas), jaume@lequia.udg.cat (J. Alemany),

is formulating a precise definition of the problem. Thenext one is analysing the problem to understand its impor-tant features and identify what is required to solve it. The

lam(mdsip(aSapqtu

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iterature illustrates how engineering problem-solvingpproaches entail different mathematical and statisticalodels, numerical algorithms and computer simulations

Krishnamoorthy and Rajeev, 1996). On the other hand, inany environmental problem-solving processes, inference or

eduction from a set of facts by means of intelligent reasoningystems plays a major role. The optimal approach, however,mplies using a tool which include both numerical com-utations for detailed engineering and intelligent systems

mainly knowledge-based systems) for the logical analysisnd reasoning tasks. In this sense, Environmental Decisionupport Systems (EDSSs) have generated high expectationss devices able to confront environmental managementroblems because they link quantitative models with moreualitative approaches, providing both traditional compu-ations and intelligent behaviours such as explanations,nderstanding and interpretations.

Since being coined, the term ecological engineering haseen widely applied in the field of Wastewater Treat-ent Plants (WWTPs) (Peterson and Teal, 1996; Etnier and

uterstam, 1997; Ou et al., 1997; Harmersley et al., 2001; Gebernd Bjorklund, 2002). WWTPs are one of the hidden neces-ities of life in populated areas. In small communities andn developing countries this necessity becomes severely lim-ted by the costs of wastewater collection and of treatmentacilities. Moreover, inadequate budgets and poor access toquipment, supplies and repair facilities preclude proper oper-tion and maintenance (USEPA, 1999). In the past, severalDSS approaches have been developed within the domain ofigh-loaded WWTPs (pilot or full scale activated sludge sys-ems with anaerobic, anoxic and/or aerobic configurations),

ainly as support tools for plant managers who are facedith problematic situations that frequently occur in the pro-

ess (Serra et al., 1994; Punal et al., 2002; Rodriguez-Roda etl., 2002; Sorour et al., 2002; Wiese et al., 2005). However, fewecision support systems for the operation of WWTPs with-ut electromechanical daily management requirements, suchs constructed wetlands (CWs) or other natural or low-loadedystems, can be found in the recent literature.

CWs, or modified natural wetlands, are used as wastewa-er treatment systems all over the world, especially in smallommunities and developing countries, because they can pro-ide high treatment efficiency with low energy consumptionnd low construction costs (Alexandre et al., 1998; Core Group,000; Kadlec et al., 2000). In addition, compared to high-loadedystems (i.e. activated sludge technologies), CWs are easiero operate and more efficient to maintain (Alexandre et al.,998; Kivaisi, 2001). However, reliability and design lifetimeave become of paramount importance when comparing CWsith competing technologies (Bavor et al., 1995). Despite being

ppropriate and sustainable for wastewater treatment in com-unities with strained budgets, operation and maintenance

ctivities are crucial to guarantee the performance of CWsKadlec and Knight, 1996; Knight, 2000; Rousseau et al., 2004).he notion that natural systems are able to manage them-elves is false: deficient supervision is the most common cause

f disturbances and, also often, of lower treatment efficien-ies in CWs. As pointed out by Kadlec and Knight (1996) andousseau et al. (2004), another cause of operational problems

s the lack of know-how in terms of: (1) the physical, chemical

and biological processes occurring in a CW and (2) the tasksneeded to carry out the operation and maintenance processes.Confronting this lack of technical knowledge is a complextask since the operation and maintenance requirements varyaccording to (1) the design and configuration of the facilities,(2) the amount and quality of the influent wastewater and(3) the sensitivity of the receiving media. Moreover, processknowledge is typically built up from the experience of opera-tors and engineers but this experience too often leaves withthem when they move on (Olsson et al., 2003).

Both first-order (Kadlec, 2000) and mechanistic mathemat-ical models (Wynn and Liehr, 2001; Hafner and Jewell, 2006)have been proposed mainly as a design tool for CWs. Morerecently, a few examples of knowledge-based systems in eco-logical engineering can also be found in the bibliography (e.g.Janssen et al., 2005; Lee and Scholz, 2006). Nevertheless, thecomplexity of these treatment systems makes them very dif-ficult to represent using a single modelling technique, i.e. thereis still room for improvement by using a combined approachintegrating numerical models and knowledge-based systems.In this sense, the success experienced when developing EDSSsfor the management of high-loaded WWTPs and the ability ofartificial intelligence methodologies to represent diverse typesof knowledge and provide intelligence capabilities in decisionmaking led us to develop an EDSS to support the operation andmaintenance of CWs (EDSS-maintenance), specifically for thehorizontal subsurface flow CW (HSFCW), which is the mostcommon CW design (Vymazal, 2005).

The aim of this paper is to explain the development andoperation of the EDSS-maintenance as a useful tool to supportplant managers who deal with operation and maintenance ofHSFCWs. The paper starts with a description of the method-ology used. Next, the EDSS-maintenance development andoperation are presented, placing special emphasis on theoutcomes provided by the system. Finally, the benefits andusability of this support system are discussed and some con-clusions are drawn.

2. Methodology to developEDSS-maintenance

The methodology used to develop the EDSS-maintenance isproposed by Poch et al. (2004). This procedure involves the fol-lowing steps that will be described in detail in the followingchapter: (1) environmental problem analysis, (2) data collec-tion and knowledge acquisition, (3) model selection, (4) modelimplementation and integration, and (5) evaluation process.This methodology has been previously applied with success inseveral EDSSs (Comas et al., 2003; Devesa et al., 2004; Alemanyet al., 2005; Comas et al., 2006; Rodrıguez-Roda et al., 2006).

3. EDSS-maintenance development

3.1. Environmental problem analysis

Operation and maintenance activities are crucial to guaranteesatisfactory pollutant removal efficiencies and preclude oper-ational problems in HSFCWs. Experience shows that thesetasks and the frequencies of these actions and monitoring

measurements can differ from one HSFCW system to another.This variability is due to (1) the design and configuration of thefacilities, (2) the amount and quality of the wastewater and (3)the sensitivity of the receiving media. Therefore, it is neces-sary to define operation and maintenance protocols accordingto the characteristics of each facility.

3.2. Data collection and knowledge acquisition

The EDSS-maintenance was planned as a tool to support plantmanagers to improve operation and maintenance of HSFCWs,especially when facing problematic situations that frequentlyoccur in these facilities. Thus, an important step in the EDSS-maintenance development was the acquisition of knowledgeabout: (1) the most common HSFCW problems, (2) the causesbehind these disturbances, (3) monitoring programs to iden-tify these abnormal situations and, last but not least, (4)preventive and corrective actions to solve the operationalproblems and attain optimal HSFCW performance. The knowl-edge acquisition phase relied on two different sources (Fig. 1):

• Literature review: specialized books (Cooper et al., 1996;Kadlec and Knight, 1996; USEPA, 1999; Kadlec et al., 2000),journal articles (Blazejewski and Murat-Blazejewska, 1997;Thullen et al., 2002) and web pages (Hygnstrom et al.,2002) were checked to identify the most common HSFCWproblems. This literature review led to an initial characteri-zation of the identified disturbances, resulting in a generalknowledge base, which in turn led to the formulation of aquestionnaire to obtain more specific information.

• Site visits and interviews: according to the general knowledgebase, the surveys posed questions about (1) the charac-teristics of the small communities, (2) their correspondingreceiving media, (3) the configuration and design of thefacilities and (4) the operation and maintenance protocolsusually carried out. The surveys were first distributed to the

thirteen HSFCWs located in Catalonia (north-east of Spain)and then collected during on-site visits and personal inter-views which required the collaboration of plant operatingpersonnel, WWTP managers and environmental experts.

Fig. 1 – Knowledge acquisition step for theEDSS-maintenance development.

Fig. 2 – Reasoning procedure followed to obtain operationand maintenance protocols.

Data and knowledge acquired from the bibliography, sur-veys and interviews were analysed. From this study, 24problems were identified as the most frequent disturbances inHSFCWs. These abnormal situations are related to (1) vegeta-tion growth, (2) water distribution, (3) the presence of rodents,(4) the general state of the facilities and (5) effluent quality.These problems result from (a) the characteristics of the influ-ent, (b) the WWTP configuration and design, (c) the weatherconditions, (d) inadequate operation and maintenance and, (e)the appearance of other disturbances. Globally, the knowledgebase built includes 58 potential causes (Fig. 1).

The knowledge acquisition step also allowed the defini-tion of the required measurements or controls to identify theHSFCW problems and causes. The knowledge base includesa total of 38 measurements (Fig. 1), 23 of them are needed toidentify the HSFCW disturbances. Besides, 68 possible actionswere defined although it was not feasible to define whichof them are preventive and which are corrective since thedescribed actions can be applied in both senses (Fig. 1). Finally,the knowledge base also includes the 37 potential effects(Fig. 1).

Regarding information about the properties of the receiv-ing media, the analysis of the survey and interviews led toa description of the effects of the 24 HSFCW problems on theenvironment, showing that the intensity of these effects variesaccording to the sensitivity of the receiving media. Therefore,analysing both the effects and the environmental character-istics of the receiving media, three sensitivity categories wereestablished: very sensitive, sensitive and resistant.

Analysis of the acquired data and knowledge also allowedthe establishment of the reasoning process to define operationand maintenance protocols (Fig. 2). The causes behind thedisturbances are the starting point of this process, becausefrom these factors it is possible to predict the potentialdisturbances as well as to define the preventive action. Thesemeasures aim at keeping away the causes from appearingor at avoiding the effects of these causes. Continuous orrepeated observations or measurements to determine thelevel of compliance with performance requirements andpollutant levels are needed (monitoring tasks). The monitor-ing program is defined to identify simultaneously both theproblem and the cause of each disturbance. Since a particularproblem can be originated by different causes, it can be solvedapplying different corrective actions. Since the intensity ofthe effects of a problem varies depending on the sensitivity of

the receiving media, it is proposed to define the frequency ofthe measurements and preventive actions in accordance withthis sensitivity, i.e. the more sensitive the receiving mediumis, the more frequently controls and preventive actions will

Table 1 – Template for the monitoring program and preventive actions

Problems Measurements Causes Frequencies

Very sensitive Sensitive Resistant

P1: abnormal vegetationgrowing during thestart-up

M1: visual control of thegrowing vegetation

C1: weeds growing; C2:low water level; C3: highwater level; C4: organicoverload; C6: presenceof rodents

Two or threetimes a week

Two or threetimes a week

Weekly

P12: inappropriatewastewaterdistribution

M28: verify the state oftubes distributingwastewater

C38: inadequate designand/or construction;C40: suspended solids

tion;umurmat

Daily Daily Weekly

bmmp

3

Sfttsa

accumulasolids accC42: ice fo

e needed. All this information related to problems, causes,easurements, preventive actions and corrective actionsust be included within the operation and maintenance

rotocols provided by the EDSS-maintenance.

.3. Model selection

ince the definition of operation and maintenance protocolsor HSFCWs requires qualitative and quantitative informa-

ion, heuristics and the use of reasoning processes similaro those of human beings (expert judgement), a rule-basedystem (RBS) was selected as a suitable model to representll the acquired knowledge about HSFCW management. Clas-

Table 2 – Template for the corrective actions

Problems Causes

P1: abnormal vegetationgrowing during the start-up

C1: weeds growing M2: visgrowinthe wa

C2: low water level M3: m

C3: high water level M3: mverifymatrix

C4: organic overload M5: mthe in

C6: presence of rodents M10: vroden

P12: inappropriate wastewaterdistribution

C38: inadequate designand/or construction

M27: vdistribM28: vdistrib

C40: suspended solidsaccumulation

M27: vdistribM28: vdistrib

C41: solids accumulation M27: vdistrib

C42: ice formation M28: vdistrib

C41:lation;ion

sification, diagnosis and monitoring tasks can be addressedefficiently using a RBS (Krishnamoorthy and Rajeev, 1996). Therule-based knowledge base of the RBS becomes the core of theEDSS.

3.4. Model implementation and integration

The acquired knowledge is transformed into a graphical rep-resentation according to the selected model. This easy to

understand representation allows simple editing and revi-sion by HSFCWs experts. The knowledge about the HSFCWproblems was organized into two different specific templateswithin a database. In the first template, the knowledge was

Measurements Corrective actions

ual control to verify theg of weeds; M3: measureter level

AC1: remove weeds; AC2: flood theCW; AC56: install a water levelcontroller

easure the water level AC3: increase the water level; AC56:install a water level controller

easure the water level; M4:if water flows over the

AC4: decrease the water level; AC37:dose the wastewater; AC56: install awater level controller; AC57: install amechanism to dose wastewater

easure the organic load influent

AC7: decrease the organic load

erify the presence ofts

AC5: follow the protocol specified inP6—presence of rodents

erify the state of theuting wastewater channel;erify the state of theuting wastewater tubes

AC46: improve the wastewaterdistribution system

erify the state of theuting wastewater channel;erify the state of theuting wastewater tubes

AC36: improve the pretreatmentand/or the primary treatment; AC43:clean the wastewater distributionsystem; AC46: improve thewastewater distribution system

erify the state of theuting wastewater channel

AC36: improve the pretreatmentand/or the primary treatment; AC43:clean the wastewater distributionsystem; AC46: improve thewastewater distribution system

erify the state of theuting wastewater tubes

AC43: clean the wastewaterdistribution system

divided into six columns, the first of which lists the 24potential problems (Pi), while the second one contains the23 measurements (Mi) necessary to identify the potentialproblems. Each visual control was considered as a differentmeasurement, e.g. the visual control to check the grow-ing of Phragmites australis (M1) is different than the visualcontrol to verify the state of the tubes for the wastewaterdistribution (M28). The second column also includes some rec-ommended preventive actions. The third column lists the 58identified causes and, finally, the last three columns containthe frequencies to carry out the measurements and preven-tive actions, according to the three sensitivity categories ofthe receiving media. Table 1 provides an example of how theknowledge was organized in this first template.

The second template includes the information about thecorrective actions. Table 2 shows part of this template. Again,the first column lists the 24 potential problems (Pi) but nowthe second and third columns include the 58 identified causes(Ci) and the 34 measurements to identify the causes (Mi),respectively. As in the first template, each visual observation isconsidered as a different measurement. The last column liststhe 68 corrective actions (ACi) identified.

The knowledge about the receiving media was organizedand documented in a decision tree (Fig. 3). This diagram allowscategorizing the sensitivity of the receiving environment asvery sensitive, sensitive or resistant. This categorization allo-cates the frequencies of the actions that must be taken andthe frequencies of the controls considered in the monitoringprotocol.

The knowledge contained in the database tem-plates and in the decision tree was transformed into:IF 〈condition〉 THEN 〈conclusion〉 heuristic rules.

3.5. Evaluation process

First, the verification for consistency and completeness ofthe EDSS-maintenance involved checking the complete rule-

Fig. 3 – Decision tree for the definition

based knowledge base. Rules were manually verified in orderto detect redundant rules, subsumed rules, unnecessary IFconditions, circular rules, dead-end rules and missing rules.Next, the validation phase began. The EDSS was faced up withhistorical examples and real HSFCW cases. The operation andmaintenance protocols provided by the EDSS-maintenancefor each one of these situations were directly compared withthe solution of a panel of experts (i.e. user’s assessmentwas selected as reference standard). Every time this two-stage evaluation procedure required changes (reformulations,redesign, refinements or extensions), the EDSS-maintenancewas re-evaluated to assure its consistency.

4. EDSS-maintenance operation

The steps followed during the EDSS operation to provide themost adequate operation and maintenance protocol for a par-ticular HSFCW may be summarized as follows:

• Data gathering: for each HSFCW, the user introduces therequired data to the EDSS-maintenance: (a) communitycharacteristics (i.e. number of inhabitants, presence ofindustries, etc.), (b) receiving media properties (i.e. flow rate,nitrate polluted area, etc.), (c) treatment plant configuration(i.e. pre-treatment unit, primary treatment technology, etc.),and (d) HSFCW design (i.e. size of the HSFCW, wastewaterdistribution system, etc.). This data can be obtained througha limited field survey complemented with expert interviews.

• Diagnosis: the RBS is activated and, following the reasoningprocess described in Fig. 2, the EDSS-maintenance identifiesthe potential causes of failures, the problems themselves,the measurements to detect problems and causes, and the

preventive and corrective actions.

• Decision support: in the third and final step, the EDSS-maintenance proposes the most appropriate operation andmaintenance protocols, according to the characteristics of

of the receiving media sensitivity.

inten

tEaw

5

TstWt(famt(

mmptvt

Fig. 4 – EDSS-ma

each wastewater treatment system, which aim at sum-marizing all the information inferred by the RBS. Theseprotocols are organised into two documents which becomethe final outcomes of the EDSS: (1) the monitoring notebookand (2) the operating manual.

The user-friendly interfaces to introduce input data ando provide the operation and maintenance protocol make theDSS-maintenance an easy to use application. Fig. 4 offersschematic representation of how the EDSS-maintenanceorks.

. Monitoring notebook

he monitoring notebook includes the list of needed mea-urements to define the functioning state of the HSFCW andhe list of recommended preventive actions for a specific

WTP. These two lists are provided by means of tables. Everyable summarizes controls to be done with a same frequencyTable 3). The monitoring notebook has to be filled in with theollowing information: (i) the date and time when monitoringctivities are carried out; (ii) the responsible person; (iii) theeasurement results obtained and (iv) the problems encoun-

ered and corrective actions applied (in the ‘observations’ field)Table 3).

Although in most of the cases the frequencies of measure-ents and actions depend on the sensitivity of the receivingedia, there are a few exceptions where the frequency is inde-

endent of the sensitivity of the receiving media because ofhe associated environmental effects. For instance, while theisual control to check the state of the water distribution sys-em (M27) is carried out on a daily basis if the receiving media

ance operation.

is very sensitive or sensitive but weekly if the environment isresistant, the visual control to check the state of the fence (M20)is performed weekly in all cases. The state of the water distri-bution system is crucial to keep a low environmental impactto the receiving media while the state of the fence is not.

Since the EDSS-maintenance protocols are adapted to thecharacteristics of each facility, the list of measurements andpreventive actions vary among different HSFCWs. The follow-ing three examples illustrate the dependency of the operationand maintenance protocols on the wastewater treatment sys-tem characteristics:

• If the HSFCW is new or less than 1 year old, the problem“P1—abnormal vegetation growing during the start up” willappear on the list problems, and, as a consequence, themeasurement “M1—visual control of the vegetation growth”will be included in the monitoring notebook. On the otherhand, if the HSFCW is older than 1 year, the problem P1 andthe measurement M1 will not be considered in the operationand maintenance protocols (Fig. 5 (up)).

• If the HSFCW has a mechanism to control the water level inthe gravel beds, “P13—inappropriate water-level controllerregulation” can be a problem, and therefore, the mea-surement “M30—check the water-level controller” will beincluded in the monitoring notebook. However, if the facil-ity does not have a water-level controller, the P13 will notbe included in the list of problems, while the preventiveaction “AC —install a water-level controller” will be rec-

56

ommended instead (Fig. 5 (middle)).• If the WWTP has been protected by a fence, then the prob-

lem “P17—unsuitable fence and gate characteristics” will beconsidered as a possible disturbance and the measurement

Table 3 – Daily controls of a notebook table provided by the EDSS-maintenance for a specific HSFCW located in asensitive area

“M20—check the state of the fence and the gate” will beincluded in the monitoring notebook. On the other hand, ifthe facility does not have a protecting fence, then the EDSS-maintenance will not provide P17 nor M20 but instead it willpropose the preventive action “AC23—install a fence” (Fig. 5(bottom)).

5.1. Operating manual

The operating manual document provided by the EDSS-maintenance for every HSFCW has two objectives: (1)explaining in detail the required measurements and pre-ventive actions specified in the monitoring notebook, and(2) describing the procedure to be followed once a problemappears. This second objective involve (2a) identifying thecauses that have originated the disturbances and (2b) apply-ing the most appropriate actions. To attain these objectives,the operating manual is a document that defines the modus,the causes, the monitoring program, the preventive and cor-rective actions and the effects for each situation of potentialfailure identified for a given HSFCW. The operating manual,including the list and description of measurements requiredto identify and solve the factors causing a disturbance, willdiffer between different HSFCWs.

The modus definition for a given problem is always thesame but the number of modus described in the operatingmanual varies according to the potential problems identi-fied. For instance, whatever the characteristics of a HSFCWare, if the system is less than 1 year old, the problem“P1—abnormal vegetation growing during the start up” will beincluded in the list of potential failures. As a consequence, themodus “MD —poor Phragmites australis development during

1

the growth stage” will be integrated into the operating man-ual. Otherwise, i.e. if the HSFCW is older than 1 year, then theproblem P1 and the modus MD1 will not be described in theoperating manual.

Despite some problem causes are common to all HSFCWs,a few of them vary among different WWTPs. For example,while the cause “C3—high water level” can be the origin ofthe problem “P9 – high water level – water flow over thematrix” in all HSFCWs, the cause “C25—inappropriate gravelmatrix” will only be the starting point of “P8—gravel clog-ging” in the HSFCWs built with an improper gravel size(Fig. 6).

The EDSS-maintenance proposes corrective actions inaccordance with (1) the causes that originate the problem,(2) the WWTP configuration and (3) the HSFCW design. Fig. 7illustrates two examples where the corrective actions willbe different according to the cause of the problem and theHSFCW design. The reasoning process schematized in Fig. 7(up) reflects that if problem “P15—deficient dike structure”is caused by “C45—growth of trees and bulrushes”, then theEDSS-maintenance will recommend the actions “AC48—repairthe dikes” and “AC15—remove the trees and bulrushes”. How-ever, if the origin of P15 is the cause “C6—presence of rodents”,then EDSS will propose the actions “AC48—repair the dikes”and “AC6—apply the recommendations described in problemP7: presence of rodents”. Corrective actions between two dif-ferent wastewater treatment systems can also be differentdue to two different HSFCW designs. As shown in Fig. 7-bottom, if problem “P4—weed growth” appears and the HSFCWhas a mechanism to modify the water level, then the EDSS-maintenance will recommend the action “AC3—increase thewater level”. Otherwise, the system will propose the action“AC56—install a water-level controller”.

The type of effects and their intensity depends on thecharacteristics of the receiving media. For instance, whenthe problem “P —high concentration of suspended solids”

24

appears and the receiving media is soil, the EDSS will advisethe effect “E37—clogging of the receiving media”. On theother hand, if the receiving media is a river, then the effect“E36—increasing of the water turbidity” will be advised (Fig. 8).

Fig. 5 – Flow diagram for the definition of the monitoringnotebook (obtained from the database templates): (up)rrp

6

6

Tdwcbarbdve(

consideration of the impact of wastewater treated into thereceiving media when defining the monitoring program andthe preventive actions for CWs. This novel characteristicdenotes a step forward towards the integration of all signif-

easoning path for the age of the HSFCW; (middle)easoning path for water level control; (bottom) reasoningath for the fence.

. Discussion

.1. Complete knowledge base

he methodology followed during the EDSS-maintenanceevelopment leads to a complete rule-based knowledge base,hich allows tackling all common HSFCWs problems and

auses, proposing measurements to identify these distur-ances and recommending preventive as well as correctivections. This methodology also enables an expressive rep-esentation of the acquired knowledge easy to understandy any stakeholder and its posterior implementation. Since

ifferent knowledge sources (literature, databases and inter-iews), expertises (chemistry and biology of the processes,cological, wastewater engineering, etc.) and points of viewdifferent stakeholders) were consulted during the knowledge

Fig. 6 – Flow diagram with the reasoning path for theidentification of causes.

acquisition step, results provided by the EDSS-maintenanceare multidisciplinary and unbiased. This approach does notprovide a conflict due to contradictory results, but on thecontrary, an added value since it allows reaching the best-informed and most appropriate compromises, converging intoan optimal operation and maintenance protocol, dependingon the characteristics of the wastewater treatment system.

Another relevant aspect in the EDSS-maintenance is the

Fig. 7 – Flow diagram with the reasoning path forproposing corrective actions: (up) proposed according to thecause behind a problem; (bottom) proposed according tothe HSFCW design.

son

Fig. 8 – Flow diagram with the rea

icant management and ecological aspects in the integratedwater management paradigm, which has been adopted, atEuropean level, by the Water Framework Directive (EC-WFD,2000).

Although EDSS can already be found for the managementof the natural ecosystems that inspired CWs, i.e. the wetlandsecosystems (Quinn and Hanna, 2003; Janssen et al., 2005), theyare so far new in the ecological engineering field. EDSS willcontinue to be a hot topic to deal with the complexity of envi-ronmental problems (Carson et al., 2006).

6.2. Optimising operation and maintenance

The EDSS-maintenance turns out to be a tool to support theoperation and maintenance of CWs, promoting involvementof stakeholders during its development and, at the same time,increasing transparency in the decision-making processes.Again our approach is in line with the Water FrameworkDirective recognition of the necessity for the provision ofdecision support tools to improve on water and wastewatermanagement (EC-WFD, 2000). The EDSS-maintenance pro-vides operation and maintenance protocols adapted to thespecificity of each wastewater treatment facility. Therefore themonitoring notebook and manual of operation are defined ina practical manner according to the influent characteristics,receiving media, configuration and design of a given CWs.As pointed out by Russell (1999), although referring only tomosquito management, operational strategies for pollutioncontrol will vary from place to place, from time to time, andfrom design to design. In this sense, Kadlec and Knight (1996)specifies that the frequency of operational monitoring for CWsystem control is dictated by the size and capacity of thesystem, the sophistication of the owner’s staff and samplingequipment, and specific factors related to influent quantityand quality variability and climatic factors. Since differentcauses can originate the same problem, universal correctiveactions usually do not work. On the contrary, CW operationand maintenance is best achieved with corrective strategies

specific to each problem and cause, and sometimes integrat-ing various complementary actions. It has been shown thatproper operation and maintenance, a part from avoiding dis-turbances, could also lead to higher treatment efficiencies

ing path for effects identification.

of CWs (Kadlec and Knight, 1996; Vymazal, 2002; Meulemanet al., 2003). The adaptation of the measurements and theirfrequencies to each facility entails also economical savingsbecause unnecessary control measurements are not carriedout. Besides, having access to monitoring programs allowsdetecting the problems with anticipation (Kadlec and Knight,1996) while preventive actions preclude severe consequences.Therefore, the availability of all this information in a computa-tional format enables gaining time when detecting and solvinga HSFCW problem as well as improving the consistency andquality of the operation and maintenance guidelines.

The use of the EDSS-maintenance guarantees the system-atic and objective management of the information registeredby the experts and, consequently, facilitates the sharing andrapid re-use of HSFCW technical knowledge and experiencesamong plant managers, helping to overcome the most com-mon causes of operational problems: lack of know-how, loss ofknowledge when operators or engineers move on, and lack ofrequired time for knowledge management in the day-to-dayoperation (i.e. integrating a large number of data in differentformats, reasoning about them and making decisions on theprocess operation requires time and skilled plant managers).

This paper shows how the EDSS-maintenance providesa proper platform to support the necessary collaborativework in the ecological engineering problem of CW opera-tion and maintenance. Although the original knowledge baseof the EDSS-maintenance has been developed for HSFCWs,this approach is flexible in the sense that its extension forother configurations (vertical subsurface constructed wet-lands, hybrid constructed wetlands, etc.) as well as for othernatural wastewater treatment systems is under development(i.e. waste stabilization ponds (Turon et al., 2006)). The use-fulness of such a knowledge-based approach could also bedemonstrated for CW design, learning or modelling purposes.

7. Conclusions

In this paper, arguments that EDSSs are proper tools to sup-port the operation and maintenance of HSFCWs are provided.During the EDSS-maintenance development, several sourcesof knowledge and expertises were explored, including the

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nvironmental characteristics of the receiving media, to dis-over the required knowledge for avoiding, detecting andolving all the HSFCWs problems. This knowledge was imple-ented within a knowledge-based system, which forms the

ackbone of the EDSS. The EDSS-maintenance provides aonitoring notebook and an operating manual specifically

efined for every HSFCW according to the characteristicsf the influent, receiving media and design and configura-ion of the wastewater treatment system. These protocolsnclude the measurements to monitor the functioning ofhe wetland, preventive actions and, for every potential fail-re, the modus, causes, corrective actions and the effectsn the environment. Several features highlighting the ben-fits of using the EDSS-maintenance and its outcomes haveeen discussed. Although verification and laboratory vali-ation steps of the EDSS-maintenance prototype have beenarried out, additional work should be conducted to testhe protocols when dealing with a full-scale field validationnd to confirm the assumption that operational costs can beeduced and treatment efficiencies increased. Further devel-pment is also required to improve the knowledge base of theDSS-maintenance with new knowledge obtained from basicesearch about the HSFCW and experience gained during theeld validation.

cknowledgments

his research has been supported by the Agencia Catalana de’Aigua of the Generalitat de Catalunya through the projectSistema de suport a la desicio per a l’establiment de protocols’explotacio a les depuradores del PSARU 2002”. The authorslso wish to thank the responsible of the Agencia Catalanae l’Aigua for their collaboration and confidence in the pos-ibilities of EDSS. The research work of Claudia Turon wasupported by the Departament d’Universitats, Recerca i Soci-tat de la Informacio de la Generalitat de Catalunya i el Fonsocial Europeu under the contract (2003 FI 00921). The authorslso benefited from the partial support of the Spanish CICyTroject DPI2003-09392-C02-01.

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