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Editors Message



How To Use SCADA To Avoid Overflows


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If wastewater treatment plant operators have nightmares, it’s a good bet that many of them have to do with sewage overflows. Few events are as catastrophic for a wastewater facility as a surge of water it can’t process being churned out into the public sphere, in violation of environmental regulations, and to the detriment of public health.

Wastewater treatment plants can deploy a fierce ally against overflows by using supervisory control and data acquisition (SCADA) systems. To find out exactly how, Water Online spoke with Doug Johnson, the director of water automation solutions with Emerson Process Management’s Power & Water Solutions.

How is SCADA employed differently in wastewater treatment than on the drinking water side?

There are more similarities than there are differences. In both, SCADA is used to control equipment and processes within the plant as well as in remote areas.

One difference in drinking water is that when you’re talking about remote areas, you are talking more about a distribution system. In a wastewater system, it’s the reverse in that we’re talking about the flow that’s coming into the plant. Despite that reversal, there are a lot of similarities between the systems and what they traditionally do, what they can do with more advanced control, and what they are going to be expected to do in the future.

Controlling the treatment of wastewater within the plant is a more complex process than controlling drinking water processes. Drinking water processes are largely about filtration, disinfection, and moving water around. In wastewater treatment, there are more demanding physical and chemical processes required in order to remove solids and heavier materials. On top of that, there is the added level of complexity involving biological processes. The microorganisms that perform the critical functions of removing nutrients and treating the waste must be maintained in a tightly controlled environment.

What are the consequences of sewage overflow to the environment and what kind of sanctions might a wastewater treatment plant face if they’re responsible for something like that?

The consequences can be quite bad. You’re talking about raw sewage possibly being dumped into a waterway. You’re also talking about public health and safety; and that’s about as serious as it gets. Beyond those concerns, you must keep in mind that this is a highly regulated industry. That means wastewater plants all carry permits, of course, and when they violate those permits, municipalities can be subject to fines and losses.

There are a lot of municipalities right now that are operating under consent orders, meaning they have already reached an agreement to upgrade their infrastructure, often because of sewage overflows that have occurred during wet weather. Upgrades to bring their facilities into compliance can be quite expensive.

What leads to an overflow? How can automation help prevent it?

When there is a lot of rain, there can be more flow than the plant can handle. A lot of it is rain water, which doesn’t necessarily need to be processed before it goes back into a river. But when the mixture includes sewage, then it all needs to be treated. If the plant does not have the capacity to treat it, store it, process it, or divert it to another facility, then it’s going to overflow into a surface body of water.

That’s where some of the advantages of automation come in. If you can predict that flow, you can get ready to handle it. A lot of authorities are now applying combined sewage overflow (CSO) programs that divert excess flow to storage facilities so that they can process it at a more leisurely pace once the wet-weather event has subsided.

If you have access to comprehensive operational data through a unified SCADA system, then you can make proactive decisions instead of just reacting. You can predict, set up contingencies, and determine if you need to divert influent from one plant to another.

Does Emerson’s Ovation™control and SCADA system give plants the data necessary to prevent overflows?

If you have the data that is collected through the Ovation system, then you can use it to help your operations in a lot of different ways. You can better predict what’s going to happen and then manage those situations more effectively so that you don’t end up in an overflow situation.

Another area in which Emerson’s Ovation system can make an impact is in the realm of equipment reliability. Our integrated Ovation Machinery Health™ Monitor monitors pumps, motors, and centrifuges to predict when they might fail. Failures of major equipment like that can contribute to overflow situations. If you can see that a pump’s not acting the way it should, you can take action to prevent a failure from happening in the first place.

The Ovation simulator is another great tool. Training existing operators on the Ovation simulator helps them become more effective and enhances situational awareness. The simulator also reduces the learning curve for new operators.

Another advantage of utilizing Ovation is being able to see what’s happening at the plant remotely. If plant supervisors are at home, they can get alerts on their phones to indicate there are issues that require their attention.

What other advantages does the Ovation system provide to a wastewater treatment plant?

Ovation offers the ability to have offsite backup control centers. In the event of a facility evacuation, you don’t necessarily have to shut the treatment plant down as it can be operated from the offsite control center. The ability to stay online would certainly reduce the risk of overflows.