The Dego wastewater treatment plant, with a catchment area of approx. 200 square kilome-ters, is operated jointly by several communities in Italy.
Dego wastewater treatment plant (Italy)
The plant treats both industrial wastewater and municipal sewage using the microbiological activated sludge process and has two distinct flows: one for the treatment of sewage and one for the treatment of sludge.
Recent investment has allowed the refurbishing of the main sewer which runs 25 km from Altare and Carcare to Dego. In addition, storm basins have been installed to provide protec-tion against flooding due to the heavy downpours that have become increasingly frequent
over the past decade. The plant itself has been reequipped with modern Profibus instrumen-tation and a new control system as well as the latest electromechanical analytical and sam-pling systems. Due to their distance from the control room, several plant units, e.g. pumping controls, are integrated into to the control system by remote wireless connections.
The control system for the water treatment plant has been designed with distributed architec-ture and comprises five Profibus Field Controllers (ControlCare, E+H) each being responsi-ble for a particular area or task. The Profibus DP/PA and wireless network was then
designed around the tasks to be performed. The Field Controllers use standardized function blocks for continuous control supplemented by hybrid function blocks for sequential and logic control. The latter can be programmed in any of the five IEC 61131-3 languages. The Profibus inputs and outputs are mapped to corresponding function blocks, as are local I/O and MODBUS I/O from the wireless network. The Field Controllers are connected to the su-pervisory system through a High Speed Ethernet backbone. The complete system can be easily extended by adding additional controllers to the backbone.
The choice of Profibus DP/PA for the instrument network substantially reduces the amount
of wiring, only two wires being required to supply power to and to transmit the values from up to 32 devices per segment. The main advantage is the ability to acquire both primary and secondary values (where available) as well as the diagnostic status of the instruments.
Profibus is also used to integrate the motor drives, which are controlled by sending com-mands over the bus and also deliver numerous diagnostic messages.
The successful implementation oft he Dego project with over 600 I/Os and 3000 OPC tags proves the high capability of Profibus technology with distributed architecture in automation of wastewater treatment plants.