A critical challenge facing today’s clean-water plants is tightening effluent limits on nutrients, most notably phosphorus. Reliable nutrient reduction depends in part on accurate measurement at key stages in the process.

Today, innovative technologies are enhancing nutrient measurement, giving operators important insights to nutrient levels received in influent. Digital monitoring tools allow operators to monitor nutrients in real time so that they can optimize the process and comply consistently with permit requirements.

One such tool is the Alyza IQ analyzer from YSI (a Xylem brand). It accurately measures orthophosphate or ammonia in wastewater in real time, using minimal reagents and so reducing operating costs and waste generation. The online cabinet-style analyzer is weatherproof and can be deployed anywhere in the treatment process.

A special valve in the analyzer cuts reagent use to 5 µL per measurement. The device is offered in single- or two-channel versions. It can be used alone or as part of a Xylem IQ SensorNet system. Sean Donnelly, vice president for analytics with Xylem, talked about the technology in an interview with Treatment Plant Operator. 

What was the reason for bringing this technology to market?

Donnelly: Among the biggest challenges today is monitoring the quality of our natural water resources, and one definite threat to that quality is the nutrient level in the waters. Alyza IQ is a platform of real-time continuous-monitoring wet chemistry analyzers, designed with the primary purpose of monitoring nutrients within municipal wastewater treatment plants.

How do you envision operators using these instruments?

Donnelly: Operators are looking for data with two objectives in mind. The first is to clearly define the discharge levels leaving the plant. The Alyza can be used to monitor the levels of ammonia or orthophosphate in the effluent. It helps them understand daily that they are within their permit limits. The second objective is to control the process itself.

How does the technology play a role in controlling the process?

Donnelly: It’s used on one hand to monitor ammonia as a way to optimize the aeration process. This has two effects. It reduces the discharge of ammonia, but it also can limit the time the blowers are engaged, which reduces energy cost. On the orthophosphate side, it can help operators monitor and control the amount of metallic salts they add to bring the phosphorus down chemically, or help verify that a biological removal process is actually working.

What advantage does this system have over traditional ways of monitoring nutrients?

Donnelly: It delivers continuous real-time data, as opposed to operators having to run laboratory tests and come back later with the results.

In brief, how does this technology perform the measurements?

Donnelly: Talk me through the components. The Alyza IQ is a wet chemistry analyzer. What differentiates it from other technologies is a mini-fluidic system that vastly reduces the consumption of reagents. Reagent is added to a continuous sample passing through the analyzer. That results in a color change; the intensity of the color is directly related to the concentration of ammonia or orthophosphate.

What are the benefits of reducing reagent volume?

Donnelly: One is that we reduce the amounts of chemicals on the site and the long-term reagent cost. Another is that the instrument can be in service longer, for three- to six-month intervals between reagent changes.

How are the reagents dispensed into the process?

Donnelly: The reagents are packed in what people would refer to as IV-type bags similar to those used in medical environments. We call them ChemBags; they’re self-contained units with a special valve that prevents any dripping. So from a safety point of view, operators never really come in contact with the reagents, even when changing the ChemBags.

How does the analytical function of the device operate?

Donnelly: It doesn’t require any external evaluation or interface. The algorithms reside within the unit, which can stand alone and deliver data directly to a SCADA system or PLC, or can be integrated with our IQ SensorNet system.

How is calibration performed?

Donnelly: The unit includes auto-check and auto-calibration system. It repeatedly checks and calibrates itself. We offer one-point or two-point calibration. There is also an on-board diagnostic system that helps with predictive or preventive maintenance. A simple example is that the unit gives an alert when it’s time for a reagent change.

What is advantage of two-point versus one-point calibration?

Donnelly: Calibration on two concentration values will yield a better correlation of measurements between those two values.

How was this technology designed for ease of service?

Donnelly: We looked to make it easy to exchange reagents, and we made sure the instrument itself is readily accessible. It comes in a self-contained cabinet in which operators have easy access to the valves, connectors or other service points.

Where in the process would this instrument typically be deployed?

Donnelly: Most often, at end of the process just before discharge, and in the secondary treatment stage. The instrument cabinets are usually mounted on railings right beside the basin. They can be installed outdoors, as they function in a broad temperature range, from about zero to 100 degrees F.

Why are single- and two-channel versions offered?

Donnelly: The two-channel version enables operators to use one unit to take and analyze samples from two locations within the plant.

What kind of user interface is provided?

Donnelly: Operators can read data directly from the instrument if they so wish, but it also connects directly into a PLC or the SCADA system. It also can be an integral part of a Xylem IQ SensorNet, which opens a whole world of network sensor capability across dissolved oxygen, pH, turbidity and other measurements. It’s a comprehensive suite of parameters that can be integrated in a network, providing access to all the data from a single point.

How does this technology fit into the larger picture of protecting water resources? 

Donnelly: We are focused on solving the issue around discharge of nutrients to the waters. We also offer the EXO NitraLED UV sensor for measuring nitrate in freshwater environments. The better the Alyza IQ works to control nutrient discharges, the lower the measurements we’re going to see with the NitraLED in the natural water. You can’t separate the utility from the environmental monitoring. They are really linked. It’s interesting to close the circle.