Wastewater purification

The water treatment consortium operates in the associated municipalities of Cairo Montenotte, Carcare, Dego and Altare and in the af. liated municipalities of Cosseria, Plodio, Bormida, Mallare and Pallare, for a total area of approximately 200 km² in Liguria region (I). The consortium water treatment plant serves as the foundation for initiatives to restore and protect the environment in the area in question, where current industrial activities have been built on long standing traditions and have survived to this day as a result of a long and laborious process of evolution.

The urban and industrial sewage treatment plant is based on the biological action of active sludges in two distinct treatment lines: one for treating the sewage, the other for treating the sludge itself.

Currently, all components of the water treatment plant are fully operational, serving an equivalent population of approximately 35,000 inhabitants, a figure due in part to the contribution of effluent from industrial districts, for a total of over 3 million cubic meters of effluent treated annually and 1400 tons of sludge produced by the process of anaerobic digestion.

New funding will enable the completion of the main consortium sewage duct, that stretches for approximately 25 km from Altare and Carcare to the Dego treatment plant. These funds will also be used to construct spillways to

protect the main duct in the event of high load due to flash floods which, over the past decade, have been a frequent phenomenon. A number of improvements and upgrades will also be made to the water treatment plant itself for greater control and reliability in the treatment process. In light of the chemical, physical and microbiological results already achieved during the first four years of operation, the waste water could feasibly be reused for irrigation and industry, meaning significant water savings.

Certain components of the plant, such as screens, desilting tanks and surplus sludge tanks, will be upgraded to meet current operational demands, and a remote control system for the entire complex will be realized, linked to new, latest generation analytic and electromechanical control and monitoring instruments, installed at each of the components of the plant.

The control system has been based on a completely open architecture based on the ControlCare Field Controller by Endress+Hauser. The system may be expanded in future whenever necessary without decreasing performance, while maintaining the same prerequisites for functional simplicity. Thanks to the use of standard FOUNDATION fieldbus™ function block technology, the Field Controllers form a single distributed control architecture based on an HSE (High Speed Ethernet) network. The function blocks are interconnected via links constituting the central nervous system for control.

Each Field Controller deploys a PROFIBUS^® DP local digital network (integrated Master PFB DP) and manages the discrete utility signals on local I/O boards. Furthermore, the PROFIBUS^® DP and PA network extends locally

into each zone (cell) of the plant to manage data from digital monitoring instruments.

The data made available by PROFIBUS^® digital instrumentation are typically primary and secondary measurements (where available) and the diagnostic status of the instrument.

Motor (inverter) function is also controlled. The inverter functions are managed via the bus by sending parameters to given memory addresses of the device. A number of status and diagnostics data are also available.

In addition to the units described above, the automatic sampling machines, which may be programmed via bus and provide information on sampling status and malfunctions, and the discrete data acquisition boards (remote I/O) are also managed.

A MODBUS RTU Wireless network based on radio-modems is managed by one of the Field Controllers in native mode (master Modbus RTU) for data acquisition from the bridge crane (in constant, slow rotation) level sensor.

The treatment plant is completely outfitted with intelligent sensors and measurement instruments using PROFIBUS^® technology to perform the following functions:

	On line analytical measurements (pH, Redox, Oxygen, Turbidity)
	Flow rate measurements using magnetic field and ultrasound measurement methods
	Ultrasonic and hydrostatic level measurements
	Temperature measurements
	Inlet / outlet automatic sampler
	Pump and blower control (inverters)

Wastewater purification plant: network architecture overview

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The primary functions of the control system are as follows:

	control over the lifting system in uptake procedures
	control with PID regulation over the motors of 2 lift pumps
	control over motorized valves
	bypass management
	fine screening
	activation of belts and coordination with pool management
	management of 2 motorized shutters and control over water flow management in
	Oxygen regulation in oxygenation tanks
	control over 3 compressors with PID motor speed regulation
	Belt management at mechanical filtration section outlet
	Sampling machine control
	Acquisition of process measurements, instrument diagnostic status and of the status of 50 service motors

On the basis of this architecture, a monitoring and local management system was created which is open to remote management. The functions of the monitoring system are as follows:

	monitoring of the plant, subdivided into graphic video screens representing each functional cell
	configuration of parameters for control and regulation functions
	log and trend data management
	alarm management
	event management
	report management

In addition to the above are intelligent instrumentation maintenance management and asset management functions. The latter of these deserves a chapter in its own right as, in addition to illustrating the innovation introduced into this system by the use of FDT/DTM technology, it is also a modern, web-oriented instrument for the comprehensive and effective management of problems related to the documentation, maintenance and asset management of the plant.

The water treatment plant control system has been designed for maximum distribution of control functions, using

architecture based on the ControlCare Field Controller by Endress+Hauser. The distribution of functions allows a more rationalized management of process resources and networks. The process monitoring and servo control systems are integrated into a digital field network.

The Endress+Hauser ControlCare Field Controller is completely compatible with the IEC61131-3 standard via the ".exible function block" already included in the FOUNDATION fieldbus™ standard. The advantage of this architecture is the fact that the IEC61131-3 sequence management functions are perfectly integrated into the function block management typical of process control.

The monitoring system integrates with the control system via an OPC based communication architecture (OLE for Process Control).