There's a New Way to Measure BOD. It Doesn't Require Long Waits for Lab Results

Sentry technology uses bioelectrode sensors to give clean-water plant operators real-time insights to variable conditions in biological treatment processes.

There's a New Way to Measure BOD. It Doesn't Require Long Waits for Lab Results

The SENTRY device is deployed inside a sleeve attached to a PVC pipe with U-bolts and suspended in the wastewater stream.

BOD in wastewater influent varies with time, sometimes changing slowly and regularly, other times changing suddenly.

Inflow and infiltration, a sudden high-strength discharge from an industrial facility, a toxic load from an unauthorized chemical release — these and other events can have significant impacts on biological processes, effluent quality and permit compliance.

Classically, plant operators have monitored influent and effluent BOD by way of grab samples analyzed in a laboratory. Now Island Water Technologies has introduced the SENTRY sensor platform, giving operators real-time information about wastewater quality and biological activity in their processes.

The system uses bioelectrode sensors to continuously monitor the metabolic activity of process biology so operators can detect changes quickly and make adjustments as needed. Patrick Kiely, Ph.D., is the founder and CEO of Island Water Technologies; Richard MacEwen manages the water and sewer utility in Charlottetown, Prince Edward Island, and is an early adopter of the SENTRY technology. The two talked about the SENTRY offering in an interview with Treatment Plant Operator.

TPO: What problem were you looking to address with this technology?

Kiely: Wastewater streams into biological treatment plants are always changing. There are fluctuations during the day and through the week. Many designers tend to assume that a biological reactor will perform at a steady state, but that’s not the case. And biology often doesn’t respond well to changes. Fluctuating wastewater streams can have serious impacts on the cost of energy for treatment and can lead to fines for being out of permit compliance. We looked at the marketplace and found no product that gave operators real-time insights into biological activity in their processes.

TPO: How do operators watch their processes in the absence of this technology?

Kiely: They analyze grab samples to measure wastewater quality parameters such as BOD or COD once a day or sometimes once a week. Then they have to deal retroactively with imbalance events when they manifest themselves in the effluent. Our technology provides a new level of granularity for understanding when things are happening or when things are going wrong, to the minute.

TPO: What is the basic nature of the SENTRY technology?

Kiely: Our bioelectrode sensor has two conductive surfaces. We make the surfaces active and set the surface for respiration. Biology from the wastewater stream grows on those surfaces. The microorganisms then consume the wastewater organics that are close to the sensor surfaces and, instead of respiring to oxygen or CO2, they donate electrons to the electrode surface. We measure the flow of electrons coming from that biosurface. The resulting value is then displayed on an online dashboard.

TPO: How often are these measurements taken?

Kiely: A new data point comes up on the screen every minute. So in effect, for an operator, it’s almost like a real-time respirometer for that biofilm. We can put the sensors anywhere in the wastewater process so the operator gets a visual interpretation of the biological activity anywhere in the system. It’s a real-time tool for understanding when the system is doing well or not doing well.

TPO: How is the data actually presented?

Kiely: We provide three levels of information. The first is instantaneous events. The bioreactor is stable, and then something happens. Now the operator can see in real time how the biology has responded. It’s quantifiable. The second level is aggregated data. We can take data from days, weeks, months or years, aggregate it, and provide nice insights on times of day or days of the week when biological activity is highest or lowest. The third level makes use of the linear relationship between biological activity and bioavailable carbon (BOD, COD or TOC). So instead of displaying the information on a graph as microbial activity, we can use that correlation and display it as the metric the operator is most interested in.

TPO: What is involved in installing this technology?

Kiely: The device looks like a pH probe. We put a sleeve over it, attach it to a PVC pipe with U-bolts and suspend it in the wastewater stream. We can install sensors throughout the process, from primary clarifiers to nutrient bioreactors to the effluent stream. The sensors are typically installed in two to three hours. On the online dashboard, we can set alerts so if the reading goes above or below a certain threshold, the operator receives a notification.

TPO: How is the purchase of this technology structured?

Kiely: We provide the equipment at no initial cost to the client. We provide training over the first 30 to 60 days to make sure they understand the information and that the information is relevant to their process. After that, we provide a subscription-based service. To access the data, they log on to their own secure website.

TPO: What role has Charlottetown played in developing this technology?

MacEwen: We’re interested in technology development and helping entrepreneurs make progress, especially if it can also help us. We’re a small utility in a small province and willing to help to make thing better for anyone on Prince Edward Island. Right now we’re helping with trials at our wastewater treatment plant, which has a design flow of 6.8 mgd and an average flow of 4.7 mgd. We have four sensors installed: two on the influent and two on the effluent.

TPO: How have you benefited from the technology so far?

MacEwen: It can give us a real-time measurement of BOD. Typically it’s five days from when you take a BOD sample to when you know what the BOD is. You can use COD as an approximation, but even that takes a few hours and you’re only getting one data point from the sample. The SENTRY technology gives us a continuous monitoring indication of what the BOD is coming into the plant and going out.

TPO: What observations have you made based on the information?

MacEwen: It can show us how our BOD drops on a rainy day when we see I&I. Or, if someone dumps something into our system that they shouldn’t, we can detect that with the sensors. For example, a dairy processing facility had an accidental discharge, and we could see that BOD load come through. It helps us understand what is happening. You can see a bump in the BOD load, and that helps explain why you may be having trouble downstream.

TPO: Where else is this technology deployed?

Kiely: We had two years of working with commercial partners before we launched it. We’ve installed systems in Thousand Oaks, California; Ontario; Atlantic Canada; and China, Germany and Hungary. There are all sorts of applications with municipal and industrial treatment facilities.



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