Technology Aqua Metrology Takes the Guesswork Out of Chemical Dosing for Nutrient Reduction

An automated system for chemical phosphorus control uses on-site generation of high-quality ferrous reagents.

Technology Aqua Metrology Takes the Guesswork Out of Chemical Dosing for Nutrient Reduction

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While some clean-water plants transition to biological methods for phosphorus removal, many still rely on chemical methods.

Typically, they dose the wastewater with ferric chloride or ferrous sulfate; the iron binds with the phosphates to form precipitates. A key issue is dosing correctly to minimize chemical costs while ensuring permit compliance. In addition, the chemicals need to be shipped to the site and stored; they also need to be handled safely by operations staff.

Now Aqua Metrology Systems has introduced a fully automated ferrous/ferric reagent generation system designed to provide affordable and sustainable chemical phosphate removal. The company says its generation system, SafeGuard H2O, delivers 60% cost savings. The technology uses a certified iron precursor and an in situ electrolytic generator to create a ferrous/ferric reagent on demand.

The process includes automatic dosing based on continuous, real-time monitoring of phosphate levels in the influent and effluent, ensuring optimal treatment and compliance with regulatory and operational targets. Vladimir Dozortsev, senior product manager with Aqua Metrology, talked about the technology in an interview with Treatment Plant Operator.

What was the motivation for developing this technology?

Dozortsev: We started developing the technology about six years ago. The intent was to provide intelligent phosphorus removal technology that is cost-effective and fully automated, enhanced by online monitoring and, most important, able to achieve much more ambitious treatment goals than conventional methods.

How does this solution differ from conventional chemical phosphorus treatment?

Dozortsev: The conventional approach uses liquid ferric chloride or ferrous sulfate reagents. The user buys bulk chemicals, has them delivered to the site and doses them into the system. One associated issue is toxic nature of the reagents. They are highly acidic and very concentrated, and sometimes need specially trained personnel and a lot of precautions for handling. Another concern is the logistics of bulk chemical supply. The cost may be unstable, and availability of the reagent may be problematic.

Are there any issues with the quality of these reagents?

Dozortsev: They are often made from scrap metal, and the solution may contain multiple contaminants, some of which, like lead and cadmium and others, may be very toxic.

Is there an issue with accurate dosing when using the conventional method?

Dozortsev: If the process doesn’t have enough online monitoring, the operators don’t know how efficient the chemical treatment is. If they don’t know the concentration of the target contaminant, they may either under-dose or overdose. If they overdose they waste reagent and produce sludge for no reason. If they underdose they don’t treat effectively.

What is the benefit of generating the reagent on site?

Dozortsev: It is advantageous to produce reagent on demand because some reagents, like ferrous sulfate, have an expiration date. If you buy and store it, it may degrade. You think you dosed X, but in reality you may have dosed 80% or 60% of X, or less.

In basic terms, how does your reagent generation process work?

Dozortsev: We produce ferric or ferrous reagent on demand from a metal precursor. We electrolyze mild steel and produce the solution of dissolved reagent in a way that is 100% efficient. Based on parameters we control, we know how much reagent we produced per second, per minute, per day. And we can dose the precise amount at the time when it’s needed. Users don’t need to carry liquid reagents. They just store metal. The electricity demand is very modest and can be supplied from renewable sources like solar or wind.

What ensures the quality of the reagents?

Dozortsev: The metal precursor we use is certified. If it has impurities, we know what they are. We know how much manganese it has, how much carbon. We never use steel that has dangerous or unpredictable contaminants.

In the generation process, where does the chloride or sulfate come from?

Dozortsev: In the case of ferric chloride, for example, the reagent generator contains a certain amount of chloride, in the form of sodium chloride, with a small amount of hydrochloric acid to keep the pH in the correct range. We use an amount of chloride that matches the amount of iron in a stoichiometric iron-chloride ratio.

How does the monitoring process operate?

Dozortsev: We monitor the electrolyzer itself for critical parameters like current and voltage. We also monitor the influent for all contaminants that may affect our efficiency. Once we know how much phosphate is present, we know the optimum dose of reagent needed to achieve the desired removal. Then we monitor the effluent to make sure we achieve the target level. The difference between the influent and effluent concentrations is the amount of phosphate removal. Users can see a live diagram of how much phosphate has been removed and what amount of iron we used to remove it.

How are the automated controls executed?

Dozortsev: Input on phosphate concentration from the influent monitor is sent to a PLC. The machine then knows what dose of iron to produce and adjusts the generation parameters to match. Then the input from the effluent analyzer reports the residual amount of phosphate. By analyzing all inputs, the dosing device adjusts in real time to achieve the treatment goal.

How much operator attention does the technology require?

Dozortsev: Because the system can be fully controlled, monitored and optimized remotely, there is minimal need for on-site supervision. This makes the technology well suited for smaller treatment plants that do not have personnel trained to operate bulk-chemical-based systems.   


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