The Organisational Structure of an Agent-Based Model for the Management of Wastewater Systems
Abstract
:1. Introduction
2. Materials and Methods
- Detect and name the stakeholders of the system;
- Formalise roles defining them, listing their goals, who depends on whom and who is responsible for what;
- Describe the interactions between the roles to handle their dependencies in terms of interaction scenes;
- The interactions defined in the previous step have to be linked into a meaningful interaction structure;
- Clearly state how agents are going to enact the different roles they have to play during the execution of the model.
3. Modelling Process
3.1. Organisational Structure
- The Social Structure, which defines the roles and how they relate with each other.
- The Interaction Structure, which describes how the roles interact and how they coordinate in terms of scenes and landmarks to achieve.
- The Communication Structure, which lists the messages that agents should use—its kinds and purposes, and what words can be used as their content (i.e., pragmatics and semantics).
- The Normative Structure, which represents the norms that state what behaviours are acceptable, what is permitted and forbidden.
3.1.1. Case Study: The Wastewater System
3.1.2. Social Structure
- Hierarchical: one of the roles acts as an authority over others and therefore, whenever a superior requests something to its related inferior, the latter has to comply with that request. These are detailed as H in Figure 2;
- Network: when the roles depending on each other coordinate as peers to achieve a shared objective. This dependency is marked using an N in Figure 2;
- Market: when some roles act as producers and consumers, the former being providers of services or products at a given price; it is shown as M in Figure 2.
- The reference prices are given by the CompetentAuthority with regards to volume and concentration of discharges (ObtainDischargeReferencePrice);
- The characteristics of the wastewater (i.e., volume and concentrations of pollutants) to be discharged, which are provided by the IndustrialWWRetainer as part of the wastewater discharge negotiation process.
- An agreement is not achieved, and wastewater is kept stored until prices go down (if storage capacity allows doing so);
- An agreement is achieved, and some (or all) wastewater is discharged; the actual discharge may comply or not to what was previously agreed.
- Reference prices from the CompetentAuthority;
- The treatment efficiency of (ObtainTreatmentEfficiency) and;
- The characteristics of the wastewater whose discharge is being negotiated by an IndustrialWWRetainer.
- How much household wastewater is being received (ObtainHouseholdDemandForecast);
- Whether there is any meteorological phenomena expected (ObtainMeteoDemandForecast);
- Whether the CompetentAuthority has imposed any limitations on the effluent (ObtainWWTPEffluentLimits);
- Treatment efficiency in the WWTreater (i.e., WWTP ) (ObtainTreatmentEfficiency).
3.1.3. Interaction Structure
3.1.4. Social Model
3.2. Behaviour and Decision-Making
- is the reference price for discharging a mass unit of pollutant r and the competent authority determines it;
- is a peak coefficient that expresses the deviation between the pollutant r concentration in the wastewater mass sent by the industry and the pollutant concentration limits agreed with the competent authority.
3.3. Negotiation
4. Results and Discussion
- Linking goal-driven behaviours;
- Allowing them to choose which scene they will navigate to (i.e., discharge wastewater to a WWTP or store it in a retention tank), and how (which WWTP or tank to use in either case);
- Selecting among the set of actions available to transition from landmark to a landmark (within scenes) and from one scene to the next one.
- Orange nodes stand for blocked scenes (i.e., scenes no agent has participated in, neither in the past nor at the present moment).
- Blue nodes stand for paused scenes, nodes that have been participated in by some agent in the past but not currently.
- Green nodes stand for active scenes, with actual participating agents.
5. Conclusions
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Acknowledgments
Conflicts of Interest
Appendix A. Description of the Roles (Those of the System Not Specified in the Paper)
- WSensor: This role is focused on analysing the characteristics of a water body (e.g., a wastewater mass or a water mass in a river) (ObtainWCharacteristics). This analysis includes:
- Determining concentration of pollutants (ObtainPollutantConcentrations);
- Measuring the volume of water (ObtainVolume);
- MeteoRetainer: role responsible for storing water coming from meteorological conditions (e.g., rain) (StoreMeteoWW). This stored water is analysed (ObtainMeteoWWCharacteristics) and its destination is assessed (AssessMeteoWWDestination) (e.g., the storage tank is overflown and it cannot retain more water). Depending on the assessment result, water is either:
- -
- Discharged to a WWReceiver (DischargeMeteoWW);
- -
- Bypassed to the river (BypassMeteoWW), which also requires informing the CompetentAuthority of such event (InformBypassMeteoWW);
- -
- Kept stored, if possible.
The relation between the MeteoRetainer and WWReceiver is a network dependency. Both roles act as equals since none of them have an authoritative power over the other nor they are consuming any service provided as in a market. This relation is motivated by the willingness to coordinate their actions and achieve the system’s goal of providing a certain level of water quality which emanates from the CompetentAuthority goals. - HouseholdWWDischarger: This role generates wastewater produced by residential areas and discharges it to the sewage system (DischargeHouseholdWW). It provides the wastewater characteristics that it generates to roles that may need it (ObtainHouseholdWWCharacteristics) such as WWReceiver as part of its goal ObtainHouseholdDemandForecast.
- WWReceiver: this role takes care of negotiating the reception of wastewater masses (NegotiateDischarge). This includes providing discharge prices for (CalculateIndustrialWWDischargePrices) and the treatment capacity available for industrial wastewater (CalculateIndustrialWWAvailability). To calculate discharge prices, actors enacting the WWReceiver role use the discharge reference prices provided by the CompetentAuthority, the current treatment efficiency in (ObtainTreatmentEfficiency) as well as the characteristics of the industrial wastewater that a given wants to discharge, which are provided by the IndustrialWWRetainer as part of the wastewater discharge negotiation process. Concerning treatment capacity availability, it depends on:
- -
- The wastewater being received from households (ObtainHouseholdDemandForecast);
- -
- Meteorological retainers status (ObtainMeteoDemandForecast);
- -
- Current efficiency in the WWTreater (ObtainTreatmentEfficiency;
- -
- Current effluent limits imposed by the CompetentAuthority (ObtainWWTPEffluentLimits).
Once the influent is received, the WWReceiver determines its destination, either to be sent for treatment or bypass it directly to the river. This decision depends on the (EvaluateInfluentDestination) wastewater characteristics (ObtainInfluentCharacteristics), current treatment efficiency (ObtainTreatmentEfficiency) and available capacity (CalculateAvailableCapacity). Finally, it also keeps a record of the influent characteristics received (LogInfluentCharacteristics) for the SewageInspector (as part of the VerifyDischarge task) and WWTreater (in order to calculate treatment efficiency). - WWTreater: a role responsible for processing the wastewater to reduce its pollutants concentration (WWTreatment). Once the treatments ends, treated water is discharged as an effluent to the river. This effluent is analyzed (ObtainEffluentCharacteristics) and information is logged so the CompetentAuthority can audit it (VerifyWWTPEffluent). Given the effluent and influent characteristics (ObtainInfluentCharacteristics/ObtainEffluentCharacteristics), WWTreater can calculate treatment efficiency (CalculateTreatmentEfficiency). This calculation is used to keep as efficient as possible (AchieveAdequatePerformance). It is also used to support WWReciever during the discharge price negotiation described before.
- CompetentAuthority: this is the role that takes care of ensuring the river has a certain quality level determined by applicable legislation (EnforceWaterQualityPolicies). To do so, it should assess river water quality continuously (AssessRiverWaterQuality) by means of collecting river sensor data (CollectRiverSensorData); these data are requested by entities playing the WSensor role. Such entities are expected to be physically located along the river basin. According to the results of this assessment, it may request a SewageInspector to verify that every is compliant with what they agreed with concerning wastewater discharges (VerifyDischarge).Depending on the current status or even exceptional meteorological conditions, it is possible that the CompetentAuthority requires establishing exceptional restrictions on the system (EstablishExceptionalRestrictions) to ensure river water quality. The CompetentAuthority also uses the above mentioned assessment for two main purposes: First, providing discharge limits for the industry set (CalculateIndustryPermissionLimits) and effluent limits for the set (CalculateWWTPEffluentLimits). In this way, the CompetentAuthority can establish pollutant reductions in certain river sections and in general, in the river as a whole. Second, determining reference prices for wastewater discharges (CalculateDischargeReferencePrices).These elements are used by both IndustrialWWBroker and WWReceiver as part of their negotiation process when discharging industrial wastewater.Finally, CompetentAuthority also checks are compliant with the effluent limits established (VerifyWWTPEffluent).Given that the CompetentAuthority has to ensure that the rest of roles are compliant with water quality legislation, all the dependencies that are related to this role are hierarchical ones, since the system requires the CompetentAuthority to have a power relation on all the roles to oblige them to coordinate appropriately.
- SewageInspector: actors enacting this role are responsible for monitoring activity in the urban sewage system: verifying industrial discharges (VerifyDischarge) that are being produced; checking that the influents that are received by the WWReceiver (ObtainLogWWTPInfluents) that the effluents sent by IndustrialWWRetainer (ObtainLogIndustrialDischarges) match and that there is no strong deviation that places into a hazardous or unsuitable state (e.g.,, too many industries discharging more water or with more pollutant concentration than that which was previously agreed, thus affecting processes negatively). The result of this verification is reported to the CompetentAuthority to act accordingly.
Appendix B. Landmark Patterns
Appendix C. Trace of the Model Simulation
Listing 1. Trace of an execution with two industries and one WWTP. |
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Dependency | Scenes |
---|---|
CollectRiverSensorData | EnforceWaterQualityPolicies ComputeWWTPEffluentLimits |
LogIndustrial WWDischargeCharacteristics | IndustryWWDischarge |
LogInfluentCharacteristics | WWTPReceiveInfluent |
ObtainEffluentCharacteristics | WWTPTreatInfluent |
ObtainHouseholdWWCharacteristics | MeteoWWGenerate |
ManageIndustrialWW | IndustryWWGenerate |
ManageStoredWW | IndustryManageWWTank IndustryAssessWWDischarge |
ObtainDischargeReferencePrice | IndustryAssessWWDischarge |
ObtainDischargeReceiverPrice | IndustryAssessWWDischarge |
ObtainWWTPEffluentLimits | WWTPAssessDischargePrice |
VerifyDischarge | VerifyDischarge |
ObtainTreatementEfficiency | WWTPAssessDischargePrice |
ObtainInfluentCharacteristics | WWTPTreatInfluent |
LogEffluentCharacteristics | WWTPTreatInfluent WWTPBypassfluent |
ObtainEffluentCharacteristics | WWTPTreatInfluent |
ObtainIndustrialWWCharacteristics | WWTPAssessDischargePrice |
AssessMeteoWWDestination | MeteoWWGenerateScene |
ObtainIndustrialWWCharacteristics | IndustryManageWWTank WWTPAssessDischargePrice |
ObtainMeteoDemandForecast | WWTPAssessDischargePrice |
ObtainHouseholdDemandForecast | WWTPAssessDischargePrice |
ObtainLogWWTPInfluents | VerifyDischarge |
ObtainLogIndustrialDischarges | VerifyDischarge |
InformBypassMeteoWW | MeteoWWBypass |
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Oliva-Felipe, L.; Verdaguer, M.; Poch, M.; Vázquez-Salceda, J.; Cortés, U. The Organisational Structure of an Agent-Based Model for the Management of Wastewater Systems. Water 2021, 13, 1258. https://doi.org/10.3390/w13091258
Oliva-Felipe L, Verdaguer M, Poch M, Vázquez-Salceda J, Cortés U. The Organisational Structure of an Agent-Based Model for the Management of Wastewater Systems. Water. 2021; 13(9):1258. https://doi.org/10.3390/w13091258
Chicago/Turabian StyleOliva-Felipe, Luis, Marta Verdaguer, Manel Poch, Javier Vázquez-Salceda, and Ulises Cortés. 2021. "The Organisational Structure of an Agent-Based Model for the Management of Wastewater Systems" Water 13, no. 9: 1258. https://doi.org/10.3390/w13091258