Removal of color from process streams is important in drinking water treatment and in various industrial applications.

To control color, it is first necessary to know how much of it exists both before and after a treatment process. That in turn depends on monitoring. One way to monitor color is by taking grab samples at specified intervals and analyzing them in a lab. A more timely and accurate way is to use instrumentation to monitor color online in the liquid stream.

For that purpose, Hach has introduced the NV3300 scanning UV sensor, an online device for industrial and municipal plant operators who need to monitor color changes. The instrument is a colorimetric probe designed to provide reliable online readings without the use of reagents.

Continuous monitoring enables operators to detect even slight changes in water color so that they can respond quickly and adjust the process if need be. Kyle Perez, product manager for open innovation with Hach, talked about the technology in an interview with Treatment Plant Operator.

TPO: What was the rationale for bringing this technology to market?

Perez: In emerging markets, and in industrial applications domestically, there is a need for color measurement in process control. In high-growth markets, many entities are regulated for color in the same way as turbidity, organics, and other parameters are regulated in the U.S. and Europe. In addition, on the industrial side, textile plants and other industrial facilities that use dyes typically use a color control mechanism to ensure that their process is removing color to a sufficient level before discharge to a municipal wastewater treatment facility.

TPO: If color isn’t measured with an instrument like the NV3300, how is it monitored?

Perez: It’s typically done with lab measurement of grab samples taken at some interval, usually once daily at most and probably in more cases weekly. Now if you have a change in influent or an upset to your system and you’re only testing once a day, you might not see the change. Everything looks good for two weeks, but suddenly you’re discharging more color than you thought. Operators want continuous measurement so that as soon as there is a spike in the color reading, they know about it and can address it.

TPO: Does this technology apply to drinking water treatment?

Perez: Color is regulated in many international markets, especially South America. Even where it’s not regulated, there are two situations in drinking water where color can be an issue. One is where you have algae blooms or algae issues in surface water. The other is in facilities with old piping where rust and metals get into the water. So color measurement is typically used to monitor for the yellowish tint from rust and metals or the greenish tint from algae. On our probe, we offer four wavelengths and three measurement methods designed around those applications.

TPO: In simple terms, how does this technology measure color?

Perez: An LED light source shines through a window. There’s another window opposite from it and a path length where the sample flows between. We measure how much of that light source is being absorbed and at what wavelength. The color sensor reads at intervals greater than or equal to one minute. The sensor has nanocoated measuring windows to minimize fouling of the optical system. Options include automatic ultrasonic or high-pressure air cleaning, and a titanium housing for media like seawater and some industrial process waters.

TPO: How is the instrumentation deployed in the field?

Perez: The sensor is typically mounted on a wall with a flow cell to which the sample is delivered from the source (such as a pipe) by way of tubing. Alternatively, the sensor can be mounted vertically or horizontally directly in an open area process, (such as where the water is not confined to a pipe. We offer two controllers: a two-port controller that can house two sensors and a larger controller that can operate four sensors. Both can communicate with a SCADA system via standard protocols.

TPO: Can one controller accommodate two of the color sensing probes?

Perez: Yes. Probes could be positioned in two locations in a process. For example, a plant looking to remove color from water could mount one sensor upstream and one downstream from the treatment step and monitor percent removal. The sensor cables can extend up to 110 meters.  

TPO: Can probes besides the NV3300 be used with this monitoring and control platform?

Perez: Yes. Hach intends to release additional sensors to this platform. We have already released the NX7500 multiparameter UV scanning sensor, which measures nitrate and nitrite, specific organic parameters like TOCeq, DOCeq, BODeq, CODeq, TSSeq, and more. This probe has a wide variety of applications, primarily in municipal wastewater, municipal drinking water, and environmental monitoring applications.

TPO: What has been done to prove this technology before release?

Perez: We have run pilot tests in Europe and in Latin America, where color is monitored from a compliance perspective and not just for process control. It is proven via testing to measure color to specific standards to enable operators to meet regulatory requirements in line with the DIN EN ISO 7887 (methods B and C) standard or the DIN EN ISO 6271 standard.