Let IIoT do the dirty work: automating sewage treatment

As global urban population continues to grow, water pollution and water scarcity are increasingly important problems for communities, businesses, and governments. Sewage management is key to both keeping water sources clean and maximizing efficiency in reclaimed water processing.

Sewage system monitoring impacts nearly every aspect of treatment plants. For many plants, monitoring is performed locally using a host computer and programmable logic controllers (PLCs). In such setups, monitoring is only accessible on-site, so traditional systems are restricted by labor cost and data availability.

Multiple operators must be present on site 24x7x365 to meet safety requirements. Isolated, in-house data monitoring not only requires expensive hardware, but also loses many advantages of big data processing, like shared history from other plants. Future monitoring systems that are enabled by the Industrial Internet of Things (IIoT) have already demonstrated advantages in performance, reliability, and affordability.

Raising the bar

Most current sewage systems manage complex, nonlinear processes. With over a thousand different devices that require monitoring, additional complication stems from converting between analog and digital signals. Further, as cost, volume, and safety requirements become increasingly demanding, remote monitoring has become a near-term requirement for sewage treatment plants. An optimal system must efficiently process and store large volumes of real-time data, manage both digital and analog signals, and support network connectivity.

Advantages of introducing

Immense investment in IIoT devices has delivered products that are competitive in price and level of service to the installed base. Cloud processing is typically cheaper and experiences less downtime than on-site servers. Commercial cloud systems are highly tuned for big data processing, and are able to share data, such as logs, between systems or plants.

IoT sensors are relatively low-cost, which allows for additional readings from new system components or multiple measurements of one component. Redundant values from several sensors on the same component can be compared to increase the accuracy of system readings, improving safety and reliability.

Support of remote automatic, remote manual, or on-premise control access provides operators with flexibility to respond to alarms faster. When there is a crisis, teams already have all the critical system information in a centralized cloud database that’s easily shareable.

Benefits of PLCs w/ IIoT

There are many ways to bring automation and IIoT to sewage treatment facilities. Even in a world of IIoT, use of PLCs deliver some unique benefits.

• Stable, reliable control with simple programming. While some current systems rely on a single host computer, using IIoT-enabled control improves reliability and performance by eliminating a single point of failure.
• Energy efficiency, bringing cost and power savings across the plant. Energy use can be further reduced through IIoT control and system-wide optimization.
• Low-profile, compact size for minimal interference with existing infrastructure. For plants that already utilize PLCs to some degree, conversion to an IIoT-enabled monitoring system is further simplified.

A PLC can read data from sensors and initiate responses and adjustments based on current and targeted levels. Operators can set tolerances and desired levels, but the system can promptly make changes autonomously. This improves performance and efficiency by enabling quicker response times and reducing human error. An example applying PLCs to automatically coordinate various sewage treatment systems is shown in Figure 1.

Performance in China

Researchers have already started fielding and testing IIoT technology in sewage treatment plants in China. One particular case study replaced a traditional monitoring system that used PLCs and a host computer with low-cost STM32 processors and IoT connectivity via a WeChat Applet. The plant in this study sought to significantly increase daily treatment capacity from 20,000 tons to 50,000 tons.

To establish reliability, the researchers outfitted each sensor with a standalone backup power supply and a redundant Wi-Fi network to avoid service outages. Specific components were also outfitted with multiple sensors for redundancy. Each user had unique on-site and remote access permissions to maintain security. Comprehensive system logs were recorded through various fault tests of the system to vet automatic responses to changing conditions.

Questions remain on the scalability of their cloud service provider; however, in this simple proof-of-concept, the researchers modernized processors costing thousands of dollars to microcomputers under $100, enabled remote monitoring and control of a sewage treatment system, and utilized cloud computing to meet new capacity demands.

Efficiency in India

The World Economic Forum identified that improving wastewater treatment procedures and management in India was a critical target to reduce pollution and supplement agricultural water demand. This has inspired further research to automate and optimize wastewater treatment, as demonstrated in another recent case study.

In this case, PLCs were applied to control each treatment step: preliminary treatment, primary clarifying, aeration, secondary clarifying, and tertiary treatment. These processes remove physical impurities, like oil and grease, as well as biological impurity. IIoT-enabled sensors tracked various status indicators, including sludge volume, chlorine levels, and pH levels, to regulate and optimize the end-to-end wastewater process to maximize the amount of reusable water.

With the communication between sensors, PLCs, and operators via IIoT, this system enabled successful automation of a practical process. Researchers in this study successfully reclaimed more than 98% of wastewater as safe for agricultural use.

Looking to the future

IIoT brings the power of cloud computing to many new applications, while improving affordability, reliability, performance, and safety. Early pilots of IIoT in sewage treatment plants have demonstrated successes but room for growth remains as these technologies continue to scale in terms of data volume and number of users. On par with industry trends, many industrial treatment plants can expect IIoT investment to show value in the short and long term.

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