Frequently Asked Questions

TOC Analyzer

General Information

What is the primary mechanism of PeCOD® chemistry?

The primary driver of the peCOD method chemistry is advanced oxidation induced by photocatalysis with Titanium Dioxide (TiO2). Pure TiO2 is only photo-active at wavelengths below 380 nm. This is because a certain amount of light energy is required to bump the electrons around and cause the behaviors that we associate with photocatalysis. The UV LED in the PeCOD® COD Analyzer operates at a peak wavelength of 365 nm, with a minimum 360 nm and maximum 370 nm, ensuring that efficient photocatalysis is achieved.

What are THMs?

THMs (trihalomethanes) are disinfection by-products (DBP’s) formed when residual chlorine reacts with elevated levels of naturally occurring organic matter found in water. THMs are present in most drinking water supplies and are dependent on several factors such as type of organic material present and chlorine dosage.

What is UV254?

UV254 is a water quality test which uses ultraviolet light of 254nm wavelength to measure natural organic matter in water and wastewater.

What is total organic carbon?

TOC (Total Organic Carbon) is the amount of carbon based organic contaminants in a water system. TOC does not identify each specific organic contaminant present, but rather an absolute quantity of all carbon-bearing molecules. In other words, TOC is a way to measure organic contaminants that may pose a threat to drinking water or wastewater systems.

What is oxygen demand?

OD (Oxygen Demand) measures the chemical reactivity of organics by the demand for oxygen, as shown in the diagram below. It can be used as an additional tool in the characterization of NOM (Natural Organic Matter) to predict DBP (Disinfection by-product) formation. This metric also allows for rapid feedback and optimization of coagulation and disinfection dose requirements.

How does the PeCOD® benefit water treatment optimization?

The speed and ease of use of the PeCOD® is key as you are placing this knowledge directly in the operators’ hands, rather than having it be a result they wait to get back from an external lab.

A common benefit of PeCOD® implementation for this application is optimization of coagulant dosing.

The traditional method up to this point has been consistent dosing based on laboratory testing results (jar testing is a very common method of developing coagulant dosing requirements). They then increase their dosing for events that they know to cause NOM spikes. The problem is they often don’t know the extent of the NOM spikes, so they increase their dosing to what has been deemed as ‘enough’. More often than not this is over-dosing, not really causing downstream issues but incurring more cost than is needed for these events. However, when the extra dose is not enough and they under-dose, NOM gets through and reacts with the disinfection chemicals creating DBPs.

The missing ingredient is knowing when these NOM spikes occur, and to what extent. The events could be anything from seasonal variation based on climate to rapid spikes from storm events, but the benefit of knowing is the same. Plants that have enough funding to do so monitor UV and TOC online, however research has shown that this is not enough. PeCOD® is another piece of the NOM puzzle and is truly the more important measure when looking at how NOM will react and be affected by treatment. If you know the COD of the NOM coming in and can match it to known dosing requirements, you minimize the possibility of DBPs forming.

The speed and ease of use of the PeCOD® is also key here, you are placing this knowledge directly in the operators’ hands, rather than having it be a result they wait to get back from an external lab. When they can truly understand the technology and it’s value, it has a secondary effect of getting them more involved with optimizing the treatment processes. We see with numerous cases (mostly in WWTPs at this point) this occurring, where they get the PeCOD® for measuring one or two points then realizing the benefit it can have through monitoring their whole plant.

How does the PeCOD® method compare to BOD, TOC, and conventional COD?

BOD and COD methods differ from TOC because they measure the amount of oxygen that is depleted by organic species in water. There are several common methods to test wastewater and drinking water for organic pollutants, natural and chemical.  Chemical Oxygen Demand (COD), Biochemical Oxygen Demand (BOD) and, Total Organic Carbon (TOC) compromise the three main methods of testing water samples.  BOD and COD methods differ from TOC because they measure the amount of oxygen that is depleted by organic species in water.  Moreover, TOC is a measure of all carbon (both organic and inorganic), rather than the oxygen that is reduced by these species.  As written by a TOC manufacturer, “TOC on its own sheds no light on the oxidizability of the measured carbon or the amount of oxygen needed for its biodegradation.”  Specific to COD, it measures the reactive fraction of the TOC.  This is also known as oxidizability in the European Union. View the full article: Comparison of COD, BOD and TOC Methods for organics, which summarizes the advantages and disadvantages of the COD, BOD and TOC methods, and compares them to the PeCOD method.

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