Algae blooms in drinking water reservoirs can require treatment on the spot, as well as adjustments at the water treatment plant to avoid taste and odor problems.

It’s helpful if utilities drawing from reservoirs can anticipate algae blooms and so be prepared with the appropriate treatment regimens. For that and other purposes, LG Sonic has released the PO4 phosphate sensor.  

The device monitors phosphate concentrations in real time and at different water depths. Being stable at highly variable temperatures and fully autonomous in operation, it provides accurate readings over a wide measurement range. Automatic calibration ensures consistently accurate measurements; regular self-cleaning reduces on-site maintenance.

The sensor is mounted on the company’s legacy MPC-Buoy. It has a robust design and uses high-stability reagents. It delivers data to the company’s MPC-View online software. Lisa Maria Brand, company co-founder and chief technology officer, talked about the technology in an interview with Treatment Plant Operator.

What was the reason for bringing this technology to the market?

Brand: For more than 10 years we have been working on solutions to control algae in an environmentally friendly manner, specifically for lakes, reservoirs and other water bodies. We believe that to provide a good solution, it’s necessary to look holistically at what is going on in the reservoir — why the algae are blooming. A big part of that is knowing where the nutrients are coming from.

How does this technology differ from traditional ways of monitoring nutrients?

Brand: Before, utility managers were looking merely at nutrients as a point-source problem. They weren’t differentiating for whether nutrients were leaching in from the sediment or flowing in from a river or some other point-specific source. But the treatment method is completely different if you have nutrients coming from sediment. If you don’t want to just throw chemicals into reservoir and kill everything in sight, you have to know where the problem is coming from.

What are the primary applications of the system for drinking water utilities?

Brand: We designed it for treating raw water reservoirs or for measuring phosphate in those reservoirs. Sometimes algae problems occur seasonally or periodically, and managers often don’t know why at a given moment an algae bloom starts occurring. The sensor then can detect when nutrients are flowing into the reservoir. That gives managers a much better way to implement treatment strategies. If they know what water quality they are taking in, then they are better equipped to deal with it.

How is the sensing system deployed?

Brand: The sensor is deployed on our legacy MPC-Buoy, the same one we use to control algae and monitor water quality. Customers can easily add on the phosphate sensor. The buoy is solar-powered, and the data is transmitted to the software where treatment strategies are determined. That makes it much easier to use the data than with a standalone system.

How can the system detect where phosphorus is coming from?

Brand: It can take samples and measurements from different depths. So it can be placed at a site where you expect an inflow of phosphorus. Then by comparing measurements from the bottom and the surface, you get a good indication of where the phosphorus is coming from. Today most water companies take phosphorus samples once a month. Even if they take them once a week, they are missing a great deal of data. If they get a release from an agricultural facility, for example, they can miss it and think the phosphorus is leaching from the sediment.

Would a reservoir typically have multiple buoys?

Brand: Depending on the size of the reservoir, we usually have several buoys deployed. Some just use ultrasound to control the algae, while others monitor water quality. Clients who also want to measure phosphorus can add that capability on buoys in locations where they expect phosphorus to enter the reservoir.

How does the device actually take the samples and measurements?

Brand: It takes a water sample and mixes it with a reagent. In the presence of phosphate a chemical reaction generates a color, the intensity of which is then measured to determine the concentration. There are blue and yellow methods. We chose the yellow method because it is more accurate and uses a higher-stability reagent.

How often are the samples taken?

Brand: Our clients can determine that, but we optimize the system for three samples per day; three times at different depths. The more samples they take, the sooner they have to visit the buoy and replace the reagent. At three samples per day, they would have to replace the reagent every three months. Before and after each reading the system calibrates itself.

What are the physical components of the technology?

Brand: There is a winch with a tube that can go to the different depths. There is a pump that draws the samples and a filter to exclude debris and heavy particulate matter from the samples. Then there is the sensor itself, a canister for the reagent and a canister for waste.

What happens to the data collected by the sensor?

Brand: Online software is accessible to us to provide the decision-making protocol for the algae treatment. It is also available to our clients with the option to forward it to their own PLC systems.

What other capabilities can the buoy-based technology provide?

Brand: It can act as a vertical profiler. So besides measuring phosphate, users can add other modules for water-quality parameters like chlorophyll a, phycocyanin (blue-green algae), pH, turbidity, dissolved oxygen and temperature, to provide a complete vertical profile of the water column.