Wastewater treatment plant automation is not merely connecting measurement devices to software. A reliable system covers the validation of data received from field sensors, the continuity of the communication infrastructure, the early detection of abnormal conditions, and the traceable storage of historical measurements.
In municipal wastewater treatment plants (WWTPs), this approach helps operators evaluate plant performance and respond to problems faster. In facilities within the scope of legislation, the processes of measurement, recording, validation and official data transmission must additionally be assessed.
1. Why is wastewater treatment automation necessary?
Manual controls and laboratory analyses performed at intervals provide important information about the process. However, they cannot alone continuously monitor sudden changes occurring between measurements. Automation reduces this gap by providing operators with up-to-date measurement data and historical trends.
What problems does a wastewater monitoring system solve?
- Late-detected measurement changes: alarms can be generated for abnormal changes in pH, flow or other parameters.
- Data loss: during communication outages, a local recording mechanism can store data until the connection is re-established.
- Maintenance delays: calibration dates, sensor maintenance times and device failures can be tracked.
- Fragmented reporting: data from different measurement points can be assessed on a common screen.
- Lack of traceability: timestamps, alarm history and user actions can be recorded.
There is an important distinction here: process control manages the plant's physical equipment, whereas monitoring software collects, analyses and reports measurement data. Both layers can work together, but they do not perform the same function.
SAİS legislation and the 5,000 m³/day threshold
The Continuous Wastewater Monitoring Systems Communiqué, published in the Official Gazette No. 29303 dated 22 March 2015, initially took an installed capacity of 10,000 m³/day and above as the basis. With the amendment published in the Official Gazette No. 30833 dated 16 July 2019, the scope was updated to an installed capacity of 5,000 m³/day and above for the relevant facilities.
This threshold is not the same concept as the plant's daily actual flow. The definition of installed capacity in Article 4 of the Communiqué is based on the maximum treatment amount specified in the plant's project approval file. When assessing scope, one should not look only at the instantaneous flow.
The following articles in particular should be reviewed:
| Legislative provision | Subject |
|---|---|
| Article 1 | Purpose of the Communiqué |
| Article 2 | Scope and installed capacity threshold |
| Article 3 | Legal basis |
| Article 7 | Obligations of the facility |
| Articles 8–14 | Installation, measurement system, devices and data transmission |
| Articles 15–19 | Performance test, calibration, validation and comparison |
| Articles 20–24 | Application, system approval and sanction provisions |
| Article 27 | Internal audits |
The current provisions applicable to the facility, amendments and any special scope conditions should be checked via official legislation.
Why should the MARBİN practice be examined separately?
For facilities in the Marmara Region, the real-time monitoring circular No. 2021/14 dated 2 July 2021 is also important. According to the technical information published by the Ministry, the inlet and outlet flows of some facilities within the relevant scope with an installed capacity of 1,000–5,000 m³/day are monitored online. The scope and the parameters to be applied should be checked according to the facility's location, nature and current official regulations.
Therefore, MARBİN and SAİS should not be considered as a single system applying the same requirements to every facility.
2. How is wastewater plant automation planned in 5 steps?
A successful installation begins with an examination of the existing infrastructure. Before purchasing hardware, measurement points, communication protocols, legislative scope and data requirements should be determined.
Step 1 — Identify the existing infrastructure and needs
The PLCs (Programmable Logic Controllers), RTUs (remote terminal units), sensors, analysers and SCADA system at the facility should be inventoried. Not only the manufacturer of the devices but also which data they provide and in which format they present this data matter.
At this stage, installed capacity, discharge point, existing measurement devices, electrical infrastructure, communication quality and applicable legislative provisions are assessed.
Step 2 — Select sensors and measurement points
Suitable devices are determined for pH, temperature, conductivity, flow and other parameters depending on the facility's requirements. The parameters and device characteristics required under SAİS should be assessed together with the relevant provisions of the Communiqué.
The usability of existing sensors depends on measurement range, accuracy, output type, maintenance status and compliance with the relevant technical specifications.
Step 3 — Plan PLC integration and communication
Sensor data can be transmitted to the central software either directly to a data acquisition unit or via a PLC. Suitable analog input modules are required for analog signals, input/output connections for digital signals, and appropriate protocol drivers for communication-enabled devices.
When designing the communication infrastructure, cable distances, electromagnetic interference, network security and how connection outages will be managed should be considered together.
Step 4 — Establish central monitoring, alarm and recording mechanisms
The central software should store measurements with timestamps and be able to distinguish communication outages, sensor failures and values outside the defined thresholds. An alarm should not only generate a notification but also provide the description and event history that help the operator diagnose the problem.
For example, a pH value leaving the defined range and no data being received from the pH sensor at all are different alarm types. Treating these two situations as the same alarm can lead to unnecessary interventions or real problems being overlooked.
Step 5 — Validation, reporting and commissioning
Once the installation is complete, it should be tested that each measurement point produces correct data, that timestamps are consistent and that communication outages do not disrupt the recording mechanism. Alarm scenarios, authorisation and data export functions should also be validated.
If official data transmission to the Ministry is involved, the software collecting data alone should not be considered sufficient. The technical specifications of the relevant system, the application process, approval requirements and the official data transmission method should be confirmed separately.
3. PLC/SCADA integration and technical communication
At the heart of a wastewater monitoring system is a data flow extending from the field to the centre. In PLC-independent architectures, a similar structure can be established via measurement devices and data acquisition hardware.
Example PLC/SCADA integration diagram
Sensors and analysers → Field connections (4–20 mA / digital / Modbus) → PLC or data acquisition unit → Local recording and buffering → Secure gateway → Central monitoring software → Alarm, reporting and archive
In projects requiring official SAİS data transmission, it should additionally be verified that the relevant device and communication chain meets the Ministry's current technical requirements. A general-purpose cloud connection does not by itself mean official integration.
Modbus TCP vs Modbus RTU comparison
Modbus is a communication protocol used by industrial devices to share measurement values and status information. TCP and RTU are Modbus variants used with different physical communication methods.
| Feature | Modbus TCP | Modbus RTU |
|---|---|---|
| Communication medium | Ethernet network | Usually RS-485 serial line |
| Speed | Generally higher depending on network infrastructure | Depends on serial line speed |
| Distance | Typically a 100 m segment on Ethernet copper cable; network equipment or fibre can be used for longer distances | In an appropriate RS-485 design it can reach about 1,200 m; speed and field conditions are decisive |
| Cabling | Ethernet cable and network equipment | Twisted pair, appropriate termination and line design |
| Cost | Low incremental cost if Ethernet infrastructure exists | Can be economical for simple serial connections |
| Use case | PLCs, SCADA, gateways and Ethernet-enabled devices | Legacy devices, serial analysers and field equipment |
These values are general references for design; they are not guaranteed performance limits. Especially in the RS-485 line, cable quality, termination, grounding, number of devices and electromagnetic noise should be assessed.
How does a 4–20 mA analog signal work?
4–20 mA is a current loop signal commonly used in industrial measurements. The lower limit of the measurement range is usually matched to 4 mA and the upper limit to 20 mA. A non-zero starting value makes it easier to distinguish some fault conditions from the normal measurement range; however, fault detection depends on the device's configuration.
For example, if a sensor with a 0–14 pH measurement range is configured to show pH 0 at 4 mA and pH 14 at 20 mA, then 12 mA corresponds to approximately pH 7.
General conversion:
Measurement = Lower limit + [(Read current − 4) / 16] × (Upper limit − Lower limit)
In this calculation, the PLC must scale the current input correctly. A broken cable, incorrect analog input configuration or an incorrectly defined engineering unit can cause measurements to appear incorrect.
Sensor output types
| Output type | Advantage | Points to note |
|---|---|---|
| Analog (4–20 mA) | Common, simple and suitable for industrial use | Scaling, cabling and analog input accuracy |
| Digital input/output | Suitable for status, fault or trigger information | May not by itself provide continuous numeric measurement |
| Modbus RTU/TCP | Can digitally transmit multiple measurement and status values | Register map, data type, addressing and communication settings |
The right choice should be made not only according to the connection the sensor supports, but also according to the facility's existing control architecture and the criticality of the measurement.
4. Calibration, data reliability and field experience
The value of a wastewater monitoring system depends not only on producing data but on that data being reliable. Sensor fouling, electrode ageing, blockages in the sampling line and delayed analyser maintenance can affect measurement quality.
Maintenance and calibration plan by sensor
The periods below are starting ranges for example maintenance planning; they should not be interpreted as periods mandated by legislation. Exact intervals should be determined taking into account the device manufacturer's instructions, field conditions, measurement stability and the relevant provisions of the Communiqué.
| Sensor / device | Example control interval | Important check |
|---|---|---|
| pH sensor | Weekly check; calibration as needed | Reference buffer solutions, electrode cleaning |
| Conductivity sensor | Weekly check; monthly validation assessment | Reference solution, cleanliness of probe surface |
| Temperature sensor | Monthly functional check | Comparison with a reference measurement |
| Flow meter | Daily data consistency check; maintenance per manufacturer plan | Zero value, flow conditions, total flow |
| Dissolved oxygen sensor | Weekly field check | Membrane or optical surface, manufacturer procedure |
| COD / TSS analyser | Daily functional check and periodic validation per manufacturer plan | Reagents, sampling line, standards and comparison measurements |
Under SAİS, Articles 15–19 of the Communiqué should be reviewed in particular for calibration, validation, performance testing and integrated comparison tests. In the Communiqué's definition of the integrated comparison test, a quarterly interval for industrial facilities and a six-month interval for domestic/municipal facilities is specified. These tests are a different requirement from the example field maintenance schedule above.
Typical problems that may be encountered in a municipal WWTP
Data interruption due to sensor fouling: Consider a facility where the values become unstable because of substances accumulating on the surface of the outlet water measurement sensor. The software can detect that measurements are not changing or that no data is received from the device; however, it must be confirmed by a field inspection that this is due to fouling. The solution is to apply measurement quality checks in addition to the cleaning and maintenance procedure.
Warning due to calibration delay: If a pH analyser's calibration date has passed, the system can give a maintenance warning to the responsible personnel. This notification does not prove that the measurement is definitely incorrect; it indicates that the validity of the measurement needs to be re-evaluated.
Local buffering during a communication outage: When the internet connection is lost for two hours at a facility, the data acquisition unit can store the measurements in its local memory. When the connection returns, the records can be transferred to the central system while preserving their timestamps. For this to happen, the buffering capacity, the transmission queue and the retransmission mechanism must be designed and tested in advance.
These scenarios are example field situations; they are not case studies taken from a specific customer facility.
5. Common mistakes and installation checklist
Five common mistakes in automation projects
| Mistake | Why does it occur? | Solution |
|---|---|---|
| Neglecting sensor calibration | Maintenance responsibility and schedule not defined | Create calibration records, task assignments and delay alarms |
| Insufficient local buffering | Duration of internet outage and data volume not accounted for | Plan memory capacity suitable for the outage duration and controlled retransmission |
| Wrong protocol selection | Device communication characteristics not verified before installation | Test PLC, sensor and gateway compatibility |
| Setting wrong alarm thresholds | Measurement range, process behaviour and delays not taken into account | Determine thresholds according to technical requirements, test and version them |
| Not optimising data transmission frequency | Bandwidth, device capacity and official requirements not assessed together | Determine monitoring and official transmission needs separately |
Pre-installation checklist
- The facility's installed capacity and legislative scope were verified.
- The existing PLC, SCADA, sensor and analyser inventory was drawn up.
- The parameters to be monitored and measurement points were determined.
- Analog signal scales and Modbus register information were verified.
- The electrical, grounding and communication infrastructure was checked.
- The local recording capacity and internet outage scenario were tested.
- Calibration and maintenance responsibilities were assigned.
- Alarm thresholds and notification recipients were defined.
- User permissions, timestamps and record history were checked.
- The required official application, testing and approval processes were assessed.
- The success and failure states of data transmission were tested.
6. Legislation, sanctions and data transmission frequency
Sanction: software alone is not sufficient
Article 24 of the Continuous Wastewater Monitoring Systems Communiqué regulates penal actions and sanctions. Article 2 of the Communiqué covers scope, Article 7 facility obligations, Article 14 data transmission, Article 17 calibration, and Article 23 on-site inspection and approval of the system. These provisions should be assessed together.
For penal consequences, not only the Communiqué but also the current provisions of Environmental Law No. 2872 that may apply to the relevant act should be examined. Without verifying the full text of the legislation, it would not be correct to give a specific fine amount or automatic sanction outcome.
Legal notice: Monitoring software can help reduce the risk of data loss, enable early detection of incidents and organise records; however, it does not replace legal advice. The facility's obligations should be assessed in line with current legislation and the technical conditions of the relevant authority.
What should the data transmission frequency be?
Three different frequencies should not be confused with each other:
- Sensor measurement frequency: how often the device takes a measurement.
- Software recording frequency: at which intervals measurements are recorded in the local or central database.
- Official data transmission frequency: by which method and at which intervals data is transmitted to the relevant Ministry system or other official platform.
These intervals do not have to be the same. For the data transmission, signal states and technical requirements to be applied under SAİS, Articles 10, 11 and 14 of the Communiqué and the technical documents in force should be taken as the basis. The fact that a general software records, for example, once a minute does not mean that the official transmission conditions are met.
Conclusion: Reliable automation begins with accurate measurement
Wastewater plant automation is an engineering effort in which sensor selection, PLC integration, reliable communication, local data storage, alarm management and regular calibration are addressed together. In a successful implementation, not only must the screen show data, but the source, quality and history of that data must also be traceable.
Aqualon Control Center's wastewater monitoring module can be assessed in terms of compatibility with existing plant infrastructure and data monitoring needs. Before starting the project, it is recommended to verify device compatibility, data transmission requirements and the technical conditions within the scope of SAİS.
Official source links referenced in this article
- Sürekli Atıksu İzleme Sistemleri Tebliği — 22.03.2015, Resmî Gazete, Sayı 29303: https://www.mevzuat.gov.tr/
- Sürekli Atıksu İzleme Sistemleri Tebliğinde Değişiklik Yapılmasına Dair Tebliğ — 16.07.2019, Resmî Gazete, Sayı 30833: https://www.resmigazete.gov.tr/eskiler/2019/07/20190716.htm
- MARBİN — Marmara Bölgesi'nde Bulunan Atıksu Arıtma Tesislerinin Gerçek Zamanlı İzlenmesine Dair Genelge: https://www.csb.gov.tr/
- 2872 sayılı Çevre Kanunu: https://www.mevzuat.gov.tr/
- Su Kirliliği Kontrolü Yönetmeliği: https://www.mevzuat.gov.tr/