System features help operators maximize water treatment benefits.
by Tal Niv (Shaniv Control and Automation Ltd.) and Ed Nugent (PcVue Inc.)
November 21, 2015

Water quality is a critical issue in Sri Lanka, where industrial pollution and contamination from dumping waste are top contenders in a long list of factors impacting the area. Restaurants reportedly were using water from illegal boreholes rather than the town's public supply. The effects of using poor water have been reported in the form of skin diseases, hepatitis and other grave health issues.

In light of health risks, there has been a push to quickly address the water supply. One system already improving the water quality situation is a supervisory control and data acquisition (SCADA) system managing hundreds of mobile reverse osmosis (RO) stations.

RO Stations Restore Water Quality

RO is used to remove the majority of contaminants from water by pushing it under pressure through a semi-permeable membrane. Typically groundwater contains a wide array of dissolved minerals. The RO process removes naturally dissolved minerals (such as salt) and dissolved industrial contaminants, creating demineralized water that is safe to consume. In Sri Lanka, RO stations have been placed at wells to supply clean drinking water for residents.

The testing of the RO process' effectiveness on water quality is typically done via electrical conductivity. Conductivity is determined by the quantity of ionized substances such as acids, bases and salts that are dissolved in water. Demineralized water is a poor electrical conductor.

The SCADA system for this water-monitoring project is well under way. The system is monitoring the state of the RO stations to assess if they are working properly. It checks water quality and reports on such indicators as pH and conductivity values while monitoring the status of the stations' pumps. Each RO station has about 10 tags monitored for this purpose.

Approximately 80 RO stations have been installed at wellsites. The RO stations use programmable logic controllers (PLCs), which communicate with cellular modems connected to the SCADA system via a server.

The supervisory control and data acquisition (SCADA) system alerts operators to adverse conditions in mobile reverse osmosis stations.Figure 1. The supervisory control and data acquisition (SCADA) system alerts operators to adverse conditions in mobile reverse osmosis stations. (Courtesy of the authors)

Alarms are configured in the SCADA system to alert operators to adverse conditions at the station. These alarms are raised when any changes to station status occur. Alarms also drive animations in the graphical user interface, producing color changes, changing text strings and driving the appearance of graphical symbols.

Credentialed operators with appropriate user rights can acknowledge alarms. User rights provide a level of security within the SCADA application. Alarms or changes to any status points are acquired by the SCADA server in the control station. This ensures the control station is aware of acknowledged alarms and allows workers to track the status of multiple wells.

Use of Mobile Telecommunications

The SCADA application uses the built-in map feature configured for a geographical information system (GIS) decision-making display within the SCADA graphics. The map feature uses a standard map provider, in this case Google Maps, which is overlaid with markers created by the user. It can display real-time information representing the RO stations. The SCADA GIS allows the operator to locate and track the RO stations with ease.

To acquire the status of each station, the SCADA system connects to a communications server. The server uses general packet radio service (GPRS) and long-term evolution (LTE) for telecommunications. GPRS is a packet-centric mobile data service on the 2G and 3G cellular communications global system for mobile communications (GSM). LTE, a 4G technology, has become the accepted standard for wireless communication of high-speed data for mobile phones and data terminals. The server can transmit data at speeds of up to 60 kilobits per second using an energy-efficient method to send and receive data. It is a good choice for remote applications because of its proven reliability and battery efficiency, particularly when monitoring and supervising remote RO stations.

The SCADA software has been configured to allow the operator to change the identification and physical location of the RO stations without the help of a SCADA specialist. The operator maintains the SCADA map displays by editing the identification or the latitude and longitude for any of the RO station markers. The displays provide an overview of the system-wide operating status and a visualization of all RO station statuses and locations.

This allows the control station to accurately track the water quality at any given well. The SCADA system and communications server are working in harmony and are an effective, affordable and flexible solution.