Frequently Asked Questions

PeCOD® COD/BOD Analyzer

COD Application

Why is COD higher than BOD?

COD is normally higher than BOD because more organic compounds can be chemically oxidized than biologically oxidized. This includes chemicals toxic to biological life, which can make COD tests very useful when testing industrial sewage as they will not be captured by BOD testing.

What is the COD BOD ratio in domestic sewage influent?

BMS have recorded average ratios of 2-3 mg/l COD to 1 mg/l BOD over its 30 years of business. Influent COD in normal domestic sewage is therefore generally 600 – 900 mg/l and it is then treated to at least 30 -100 mg/l before discharge to minimize pollution potential.

How should COD samples be stored?

MANTECH recommends storing samples in the laboratory fridge vs preserving samples. If you do choose to preserve your samples, use H2SO4 to adjust the pH of your samples to ~2.

What is the difference between chemical oxygen demand and biochemical oxygen demand?

Chemical Oxygen Demand (COD) analysis is a measurement of the oxygen-depletion capacity of a water sample contaminated with organic waste matter. Specifically, it measures the equivalent amount of oxygen required to chemically oxidize organic compounds in water. The traditional COD method is the wet chemistry method, dichromate COD (CODCr). This involves a two hour digestion at high heat under acidic conditions and involves hazardous chemicals such as mercury and dichromate. Biochemical Oxygen Demand (BOD), also often referred to as biological oxygen demand, is a test performed to measure the potential of wastewater and other waters to deplete the oxygen level of receiving waters. The BOD test involves taking an initial dissolved oxygen (DO) reading and a second reading after five days of incubation at 20°C. For this reason, this test is often written as BOD5 for short. MANTECH has developed an automated COD method utilizing a new, rapid and green technology called the PeCOD® COD Analyzer. This method directly measures the amount of oxidizable material in a sample via photoelectrochemical oxidation in a microcell, eliminating the need for time-consuming digestion and hazardous chemicals as only an electrolyte solution is required for analysis.

What is chemical oxygen demand (COD)?

Chemical Oxygen Demand (COD) analysis is a measurement of the oxygen-depletion capacity of a water sample contaminated with organic waste matter. Specifically, it measures the equivalent amount of oxygen required to chemically oxidize organic compounds in water. COD is used as a general indicator of water quality and is an integral part of all water quality management programs. Additionally, COD is often used to estimate BOD (Biochemical Oxygen Demand) as a strong correlation exists between COD and BOD, however COD is a much faster, more accurate test.

What happens if COD is high?

Higher COD levels mean a greater amount of oxidizable organic material in the sample, which will reduce dissolved oxygen (DO) levels. A reduction in DO can lead to anaerobic conditions, which is deleterious to higher aquatic life forms.

What causes high COD in wastewater?

COD increases as the concentration of organic material increases. It also increases if inorganic compounds susceptible to oxidation by the oxidant (typically dichromate) are present. Water with high COD typically contains high levels of decaying plant matter, human waste, or industrial effluent.

General Information

What is the difference between the PeCOD® L50 and the PeCOD® L100?

The L50 is the newer, more cost efficient model of the PeCOD®. It uses the same method, reagents, and software as the L100. Improvements were made with the fluidics and space requirement in the L50 model.

What are the specifications of the external battery pack for the PeCOD® L50?

Type of Battery: Rechargeable NiMH battery, Battery Voltage: 12V, Battery Capacity: 3.8 Ah, Battery Life: Entire day of typical PeCOD® use, Charging Time: Approximately 9.5 hours

What is the difference between the benchtop and portable PeCOD®?

The PeCOD® L50 analyzer is applicable for both benchtop and portable use, with the external battery and carrying case.

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.

What is the typical initial PeCOD® shipping weight and dimensions?

An investment in the safe, green, and fast PeCOD® Analyzer includes the PeCOD® L50 Analyzer, starter kits, and consumables. This is typically packed in two cartons with the following weight and dimensions: Box 1 (starter kits and consumables) – 16” x 15” x 14”, 32lbs/41cm x 39cm x 36cm, 15kg, Box 2 (PeCOD® L50) – 16” x 15” x 16”, 21lbs/41cm x 39cm x 41cm, 10kg

How much bench space do I require for a typical PeCOD® L50 set-up?

The typical benchtop PeCOD® L50 set-up requires 36 inches x 18 inches of bench space which includes space for a laptop to access MANTECH Pro Software™

How is the PeCOD® Analyzer calibrated?

Calibrations are comprised of 6 different stages. The first stage is called the “Normalization Phase” and lasts 100 seconds. During this time, the LED strength is adjusted to maintain a baseline electrical current of 20 mA. This is performed on the blank solution, containing range specific electrolyte and COD free deionized water. Once the LED is set, oxidation of the blank solution will occur. This is comprised of 3 stages, visualized by 3 distinct curves. The stages are known as the Burn-In, Pre-Burn, and Oxidation of port B. The blank acts as a zero reference for the calibration based on the charge generated from the DI and electrolyte mixture. The area under the curve is used to quantify charge. Once the Port B stages have completed, the Port A stages will begin. The calibrant and electrolyte mixture is introduced across the TiO2 sensor, where similar Pre-Burn and Oxidation curves are generated. The concentration of the calibrant is determined based on the sample COD range. Once the specified number of calibrations have completed, the calibrant solution can be run as a sample (referred to as a QC check). It is expected that the COD result will be + / – 5% of the standard COD value. To view an example of the stages of a PeCOD® calibration, view our video here.

What information is required for PeCOD® analysis?

PeCOD® can greatly increase the efficiency and transparency of chemical oxygen demand (COD) or estimated biochemical oxygen demand (BOD) results of a laboratory, factory, wastewater treatment plant and more. To perform this analysis, let us know the COD or BOD concentration range to measure, how many samples will be analyzed per day or per week, how you measure COD currently and whether you do on-site treatment and if so, tell us the treatment train.

What items are required for each PeCOD® configuration (benchtop, automated, or online)?

Based on the PeCOD® model (benchtop, automated, or online), each system configuration will differ.

How do I prepare my water/wastewater sample for PeCOD® analysis using a homogenizer?

Homogenizing your sample prior to analysis takes approximately 4 minutes. View the steps that outline how to correctly homogenize a water/wastewater sample for PeCOD® analysis here.

Can the PeCOD® analyzer analyze sludgy/dirty samples with large particles?

For samples containing particles larger than 50μm, a pre-filtration or homogenization step is required. For biochemical oxygen demand (BOD) analysis, a simple pre-filtration step is required. MANTECH has a Sample Filtering Guide for PeCOD® Analysis. For chemical oxygen demand (COD) analysis, no filtering required as we recommend a homogenizer that gets all particles to a 1micron size. View MANTECH’s recommendations here.

Will PeCOD® correlate with my BOD results?

The PeCOD® measures COD through a rapid 10-minute photoelectrochemical oxidation, allowing for the accurate monitoring of a wide range of concentrations in real-time. These COD readings can be used to reliably estimate BOD by applying a correlation coefficient. When compared to the standard BOD test, the PeCOD® can estimate BOD concentration within a 95% confidence level. You can view some examples of correlation coefficients of PeCOD®/BOD that have been determined for different types of industrial wastewater here.

What temperature should my PeCOD® samples be analyzed at?

The temperature range that PeCOD samples should be analyzed is between 10 to 30°C. For samples that are outside of this temperature range, the addition of electrolyte (which is stored at room temperature) prior to analysis will help to bring the sample solution to an acceptable temperature range.

What pH range can the peCOD method measure in?

The peCOD method requires that the pH of a sample AFTER being mixed with electrolyte must be between 4 – 10. To determine if a sample must be pH-adjusted, mix the sample with PeCOD® electrolyte at the proper mixing ratio for your COD range, then test the pH of the mixture. For example, the sample may have a pH of 3.0, but then after preparing with electrolyte, the pH is in the required range, therefore, it is acceptable for immediate PeCOD® measurement. If samples have been preserved in acid, they should be neutralized using sodium hydroxide prior to analysis to avoid a low reading, as well as damage to the sensor. When the sample pH is below 4, the photocatalytic oxidation at the TiO2 sensor is affected, leading to poor reproducibility and charge values below theoretical expectation. Below a pH of 2, the TiO2 displays instability. When the pH is above 10, the charge measured for the reference and sample solution yield lower than expected values, again caused by interference at the TiO2 sensor. Sulphuric acid should be used to lower the pH of samples with a pH of 10 or more.

What is the allowable COD/chloride concentration combinations for PeCOD® analysis?

There are limitations to ensure that after dilution with electrolyte the chloride concentration will be <200mg/L. This means that the allowable chloride concentration of the original sample varies depending on the COD range since each range has a different ratio of sample to electrolyte.

How do inorganic compounds affect PeCOD® COD determination?

View table that summarizes the impact of a range of common inorganic anions and cations on the determination of COD using the PeCOD® technique here.

Will PeCOD® correlate with my Dichromate COD results?

There is a strong correlation between the PeCOD COD results and the dichromate COD results. To determine this, the two methods were compared vs. the theoretical oxygen demand (ThOD) for 34 organic species. See MANTECH’s technical bulletin for more information on the study.

What is the cost per sample using PeCOD®?

On average, the cost per sample can range anywhere from $3-5 per sample depending on analysis range and bulk discounting. The cost per sample varies depending on the COD/BOD range and the number of samples analyzed, as this affects consumable usage such as calibrant, electrolyte and sensors. In general, the cost per sample decreases with an increase in the number of samples. There are several reasons for this, one being that the sensor should be replace monthly, therefore running more samples per month will yield a better return on sensor usage. In addition, the PeCOD® requires a daily calibration; by running more samples per calibration users save on consumable costs associated with calibrant. There are no disposal costs for the PeCOD, whereas disposal costs accumulate via the traditional dichromate method with every sample vial. Compare cost per sample by electrolyte here

Does PeCOD® conform to regulatory standards?

PeCOD® is utilized as an internal process control tool to make impactful real-time decisions.The PeCOD® conforms to regulatory standards such as the ASTM International Method D8084, the Ministry of Environment, Conservation and Parks, Ontario (MECP) method E3515, and the Health Canada Guidance on drinking water. The ASTM International method for photoelectrochemical oxygen demand is approved for measuring organics in freshwater sources and treated drinking water. The Ontario MECP method E3515 replaced the standard dichromate methods due to the fact that no harmful chemicals are used in the peCOD method. This method now includes PeCOD® as an approved alternate COD method in the Municipal and Industrial Strategy for Abatement (MISA). The PECOD method is also referenced in the Health Canada Guidance on Natural Organic Matter in Drinking Water. COD has been added as a parameter with a <5ppm limit, only the peCOD method is referenced for the parameter, and peCOD is also referenced as a “parameter” to monitor in source waters for drinking water plants.

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.

How does the PeCOD® analyzer determine oxygen demand?

The PeCOD® analyzer performs advanced oxidation on a small volume of sample. As the reaction proceeds, electrical charge is generated proportional to the oxygen being consumed. The PeCOD® analyzer captures this generated charge, plotting the output current from the reaction over time as shown below. The area under the curve generated by plotting current over time is proportional to the oxygen demand of the sample. A blank charge is also determined for each sample, and subtracted from the total charge to ensure accuracy.

PeCOD® Consumables

How can I make Calibrant and Check Standard solutions?

View our instructions for producing 1L calibrants, check standards and for more information on these solutions here.

What is the acceptance range for MANTECH’s pre-mixed secondary standards?

The acceptable values for MANTECH’s pre-mixed secondary standards is +/- 20%.

What is used as a quality check standard for PeCOD®?

A separate standard produced by Sigma Aldrich is used for quality control testing of PeCOD® systems. This allows for verification of results and ensures that the system in use produces trusted values. This secondary standard can be diluted into different concentrations, making its use applicable to all COD ranges of solution used with the PeCOD® analyzer. The Sigma Aldrich SKU number for this standard is QC1130.

What are the PeCOD® electrolyte and calibrant solutions composed of?

PeCOD® reagents are composed of salt- and sugar-based solutions for safe operation and require NO hazardous waste removal. The PeCOD® electrolyte solution is mainly composed of a low-concentration lithium nitrate solution. The PeCOD® calibrant and check standard solutions supplied by MANTECH are composed of sorbitol. These solutions contain a trade recipe preservative that allow for the longer shelf life, compared to solutions prepared manually. Calibrant and check standard solutions prepared manually, following the PeCOD® Standard Recipe, can be used for up to two weeks. View the PeCOD® electrolyte and calibrant solutions Safety Data Sheets here.

How long will the PeCOD® Electrolyte, Calibrant, and Standard solutions last?

Both Calibrant and standard solutions are good for one year after they are made. Electrolyte has a shelf life of two years after it is produced. All labels have the expiry date in the box just above the MANTECH logo.

What are the COD/BOD ranges for the PeCOD® and what are the mixing ratios?

This depends on the reagent range. There are 4 COD reagent ranges for the PeCOD®. The advanced blue range is the lowest range and analyzes samples up to 25mg/L with a mixing ratio of 3:1 (sample to electrolyte). Green is the second lowest range and measures up to 150mg/L with a mixing ratio of 1:1.The yellow range determines COD up to 1,500mg/L with a mixing ratio of 1:9. The red range can analyze samples up to 15,000mg/L and has a mixing ratio of 1:49. For more information, read MANTECH’s technical bulletin here.

How many PeCOD® samples can be analyzed with the reagent starter kit?

It depends on the reagent range and number of analyses per sample. View full details here.

What is the shelf life of a PeCOD® sensor?

If left unopened and sealed in the package, PeCOD® sensors have a shelf life of 12 months. Once opened and in use, sensors can be expected to last for approximately 1 month or 200 samples (whichever comes first).

How long does a sensor last in the PeCOD® Analyzer?

Sensors are expected to last for approximately 150 runs (this includes samples, calibrations and QC checks), or for a minimum of 3-4 weeks when used consistently day after day. For more information, read MANTECH’s technical bulletin here.

TOC Application

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 natural organic matter?

Natural organic matter (NOM) is a critical target for drinking water treatment because it causes a negative effect on water quality by color, taste and odor, and can react with disinfectants to form disinfection by-products (DBP). There are several tools for measuring NOM in source and ground water that include total organic carbon (TOC), dissolved organic carbon (DOC), UV absorbance at 254 nm (UV254), specific UV absorbance (SUVA), and chemical oxygen demand (COD).

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 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.

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