Stricter effluent limits for wastewater plants place a growing importance on the accurate measurement of parameters in the treatment process.

Today’s operators assign high importance to operating efficiency, whether saving energy in the treatment processes or maximizing biogas production in anaerobic digesters. Today’s instruments can provide significant help in these areas, and more.

Instruments strategically placed in the treatment process deliver vital flow and parameter data in real time, enabling prompt and correct adjustments to the process as conditions change. Devices can be configured to communicate with SCADA and other master control systems, enabling process feedback loops and allowing operators to track parameters remotely or from the control room.

Alan Vance, water/wastewater industry manager, and Steve Smith, liquid analysis product manager, both with instrumentation, service and solutions provider Endress+Hauser, talked about developments in the design and use of analyzers in an interview with Treatment Plant Operator.

Why are analyzers so important in the water and wastewater industry today?

Vance: Analyzers are essential to measuring the critical parameters of water quality. These instruments still measure their primary variables as they have for years, but analyzers today can measure additional parameters, are much smarter, cost less to maintain and provide better diagnostics.  

How is measurement of water-quality parameters different today?

Vance: Historically, operators had to go out and take manual samples and bring them back to the lab to test for pH, TSS, dissolved oxygen and other parameters. But if two or three hours elapsed between the sample and the result, it would be difficult to detect and adjust for a process hiccup. In the last 10 to 15 years, plants have been adding more online instruments, from single pH or DO sensors to colorimetric analyzers. Now they can measure critical parameters 24/7/365, and this data is stored and trended in the plant control system.

What is the net benefit of that capability?

Vance: Over time, plant operators can continuously improve their processes so they are running at the optimum efficiency, such as by reducing plant power consumption related to aeration blowers. As they add points of measurement, they gather the data needed to see what is going on with the process and to make necessary adjustments. Lab samples continue to play a critical role, but in more of a quality-control capacity.

How and where are these analyzers deployed within the processes?

Vance: Plants monitor various analytical parameters at the headworks and throughout the process, so at the end they know they are meeting or outperforming the permit limits set by their state regulatory agency or the U.S. EPA.

What does it mean to say today’s instruments are much smarter than years ago?

Vance: There is two-way digital communications now between the plant control system and the instrument. Operators can view instrument data and other performance factors from the control room. In addition, there are more sophisticated diagnostic and troubleshooting functions. For example, diagnostics might tell an operator that the sample supply to an analyzer has been interrupted. The intelligence built into these instruments provides useful data to help plant personnel make better decisions.

What kinds of improvements have been made in diagnostics?

Vance: The technology is such that now operators can verify the functionality of a flowmeter, a level sensor or an analytical sensor right in place. For example, they can look at a flowmeter and the internal parameters that it reads and verify that the meter is still within the original wet calibration specifications it had when it left the factory. So, the operators do not have to pull that meter out, put another one in and send the original unit back to us to verify the calibration.

Does a similar concept apply to analytical instruments?

Smith: Yes. With the diagnostic technology integrated into devices today, instruments can assess themselves. If operators see a value that seems a bit out of the norm, they can get reassurance that it’s out of the norm not because the instrument is functioning incorrectly, but because something has happened in the process.

Are there also improvements in areas such as calibration intervals?

Smith: Yes. Operators can remove an instrument from the process, such as a pH sensor, bring it back to the lab, run the calibrations, analyze the instruments and keep that information in a database, so they can monitor the instrument’s progress over time. They may find they don’t need to bring the instrument in as often for calibration or maintenance; they can just clean it up and put it back in the process. By using databases and computing, they can determine when it makes sense to calibrate the instrument and when it makes sense just to replace the sensor.

What are some newer opportunities to apply modern analytical devices?

Smith: Historically, plants have controlled the activated sludge process by using sensors to measure dissolved oxygen. The problem is that DO is simply a means to an end. It really doesn’t tell you whether the conversion (from ammonium to nitrogen gas) is happening efficiently or not. We now have ion-selective sensors that can be put directly into the basin that provide real-time monitoring of ammonium and nitrate levels. So now operators can control the process based on what they’re actually trying to accomplish.

Do these kinds of technologies also apply on the solids side of the process?

Vance: We see a lot of wastewater plants upgrading or adding digesters. They want to know the flow to the digester, the pH level, the temperature and the level of sludge in the digester. One of the most critical devices is a flowmeter that monitors biogas coming off the digester. Plants are looking for instruments to improve the control of digesters so they can optimize biogas production. Instruments are available to measure both the biogas volume and methane content.

What are customers’ expectations these days in terms of instrumentation?

Smith: Operators are looking for ways to reduce manual grab samples and trips to the lab. They’re looking for instruments to duplicate the measurements historically made in the lab that they can place in situ and use in the process. They want those instruments to operate for long periods with minimal maintenance and calibration. They prefer instruments capable of self-cleaning, self-monitoring and easy integration to their control systems.

What specific types of instruments do you see as being in the greatest demand?

Vance: Flow measurement is a huge priority. Plants are putting a flowmeter on every line they can, whether it’s at a remote pumping station or within the plant walls. The other area where we are seeing more demand is in colorimetric analyzers for ammonium, orthophosphate and total phosphorus, not because these didn’t exist before, but because there have been dramatic improvements in the technology. Plants are replacing older colorimetric analyzers with modern analyzers that are more cost-effective to operate and provide more features and capabilities.

As a whole, how well are water and wastewater treatment plants taking advantage of the instrumentation technology available?

Vance: We see more plants adopting modern technologies, instruments and digital communications. When plants upgrade, they typically replace all the motor controls, drives, pumps and instrumentation. There is also more talk about how it all fits together with digital communication and how the instruments are tied into the entire control system. Plant personnel are using Ethernet, Ethernet I/P and PROFIBUS, words you didn’t hear them mentioning 10 or more years ago. Plants are moving more and more toward digital communications.