Ancient city builds future-proof water supply system

Como, Italy - A unique water supply system, employing advanced process control, has been developed for the historic Italian city of Como.

Built in an artificial cavern blasted into the surrounding mountains, it supplies twice as much water as the old system it replaces and will help the city evolve and develop.

Like many established cities, Como is adapting as the local and world economies change. Once small and self-contained, it was a centre for manufacturing and textile industries.

Now the manufacturing tends to be small scale and high value, service industries are taking root and more and more people are choosing to live there and commute to work in larger metropolitan areas.

Lake Como is the natural water source for the city and now local engineers from ACSM Spa have excelled in building a new purification and supply system that is both futuristic and future-proof.

Serving a population of 85,000, water supply is a complex task, which requires a sophisticated control system.

Located in the foothills of the Alps, there were no places suitable and large enough in Como to build the new plant, but this was turned into a positive.

One of the fundamental design criteria was to develop a secure facility that would not be susceptible to terrorist attack, vandalism or the ravages of extreme winter weather.

The answer was to build underground, so the first part of the project was excavating 35,000 cubic metres of rock to form the tunnels and caverns for the treatment plant and supply pipelines.

A new reservoir was also constructed, based on a disused air raid shelter.

The purifying plant produces clean drinking water, 24 hours a day seven days a week, and pumps it into the main network in the Como Aqueduct.

This feeds three storage tanks supplying the east, central and west districts of the city.

The water is lifted by a bank of 1000kW pumps. Normally these are powered from the local mains grid, but a group of emergency 1200kW electric-generators have also been installed in the plant.

This entire system is run completely automatically using a Movicon Scada Platform – an Italian made control system, which is available in the UK through Products for Automation. The system is operated by remote control from the ACSM offices in the city centre.

Water is extracted from the lake at a depth of 45m, which means it is at a virtually constant temperature and never freezes – Como is so deep because it is an alpine lake formed millions of years ago when tectonic plates collided and one rode up over the other to create the mountain range.

Currently the city requires 400-500 litres of water per second during the day (less at night), or 12,000,000 cubic metres a year. The new plant produces 600 litres of clean drinking water a second around the clock, so has capacity to cope with increasing demand.

The purification process starts with two10,000cu.m storage tanks holding lake water and alternately feeding it to a pre-ozonisation basin, where it is held for three minutes to reduce bacterial activity.

The water then passes through six layers of sand filter and into the ozonisation basin for a 10-minute treatment.

Six more filters follow, these being active granular charcoal, the water taking 15 minutes to pass through them into a final disinfection tank and then onto the district accumulation tanks.

The plant has been designed with high levels of redundancy and multiple failsafes so that it will continue to work in almost all possible circumstances.

Each stage of the process is duplicated and includes appropriate water pumps, valves, sensors, alarms, air injectors, backwash systems, chemical dosing pumps, ozoning bubblisers, temperature gauges, etc.

On top of this are support and secondary systems, such as lighting, ventilation fans, telephones, the power supply and its backup generators. This mass of highly technical equipment is all controlled by the Movicon Scada Platform.

The plant in the cavern is managed by two redundant PLCs and monitored with four supervision stations based on the Movicon Platform; two inside the cavern and two in the ACSM remote control room in town.

The stations inside the plant are connected directly to the redundant controllers, which supervise the plant’s automation in general.

Each station is also connected to one of the stations in the control room by dual telephone lines. Thus all four stations can be used to monitor and control the plant.

In order to avoid any problems the architecture is such that commands to the plant cannot be carried out from more than one workstation at a time.

Furthermore, one station is always denoted as the master, from which all the other take their lead.

Each workstation can become the master by pressing the appropriate button on the video screen page relating to system control.

The cavern plant’s supervisory PCs, situated in the remote control room, contain different screen pages, each dedicated to a different task.

These PCs communicate directly with the plant’s control system and transmit the communication signals to the two supervisor stations in the control room.

Besides displaying information deriving from the water purifying process, the two supervisors in the control room also record these signals on files in open format based on a relational database.

The operators can thus safely manage the plant locally or remotely in guided step-by-step procedures.

The supervisor stations display the plant’s data in clear, real time graphical screens. They also record and backup all commands and parameter readings for both real time and historic log analysis.

One of the main tasks of the control system is management of the many alarms. It grades the alarms by importance, to speed up appropriate interventions in the event of breakdowns.

The alarms in the water purifier system are displayed in the Movicon system video screen pages of each workstation.

When an alarm occurs, its description and status are instantly shown on this page. All alarms and events are recorded and the operator can use drop down menus to quickly analyse them for developing trends.

Como’s new water supply system is groundbreaking on many levels, and at its heart the Movicon Scada system ensures every detail of its complex working is monitored and if necessary, adjusted.