The other method for chemical oxygen demand (COD)
COD drinking water and wastewater analyser
Rapid COD testing procedure, results within 15 minutes
COD test kit with no toxic or hazardous chemicals
Highly adaptable for wastewater and drinking water COD testing applications, the Mantech PeCOD COD analyzer is the fastest available method for quantifying COD.
The PeCOD COD analyser provides operators with real time COD measurement data needed to make timely, impactful decisions that enhance environmental protection while generating substantial savings on chemical and energy use. PeCOD is an accurate and reliable other method for COD and an alternative to COD measurement using a spectrophotometer.
The PeCOD is very user friendly and accurate. Though for me the best aspect of the PeCOD is how fast the test us. This revolutionary piece of equipment is a fast but powerful way of COD analysis, giving consistent and quality results every test.
James Bissell, Bridgenorth Aluminium
How to Prepare a PeCOD Sample by Filtering
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.
What is chemical 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. 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 is biochemical oxygen demand?
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. In other words, the BOD test is performed to determine what effect dirty water, containing bacteria and organic materials, will have on animal and plant life when released into a stream or lake.
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.
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.
Why is COD higher than BOD?
COD is normally higher than BOD because more organic compounds can be chemically oxidised than biologically oxidised. 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 does high BOD indicate?
BOD indicates the amount of putrescible organic matter present in water. Therefore, a low BOD is an indicator of good quality water, while a high BOD indicates polluted water. Dissolved oxygen (DO) is consumed by bacteria when large amounts of organic matter from sewage or other discharges are present in the water.
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. Some examples of correlation coefficients of PeCOD/BOD that have been determined for different types of industrial wastewater are provided in the table below.
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.
What are the reasons for differences between the PeCOD COD and Dichromate COD results in some cases?
Chemical Oxygen Demand (COD) results may differ when measured via the PeCOD COD method versus the traditional dichromate COD method for certain sample matrices. There are various reasons for this difference. One is that chloride, ammonia, and some heavy metals have been known to interfere with PeCOD readings and provide inaccurate results. Another reason could be the time delays between analyses. It is best to analyze samples via PeCOD and dichromate on the same day to limit uncertainties due to sample degradation.
How does the PeCOD method compare to BOD, TOC, and conventional COD?
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.
Why does KHP measure high on PeCOD?
KHP (Potassium Hydrogen Phthalate) has historically been a common reference standard used in a variety of chemistry applications including the traditional dichromate COD test, where it does provide a result close to the theoretical COD result, and for TOC analysis. KHP is not recommended for use in the PeCOD COD analysis as it over reports compared to the theoretical COD amount. This is predominantly due to some pre-concentration of the molecule on the surface of the PeCOD sensor prior to analysis which is a peculiarity of KHP with the PeCOD COD method.
It is important to note that for all COD methods there are specific molecules whereby the individual analytical result is not well aligned to the theoretical value. For instance, organic compounds such as propionic acid, diethylamine or nicotinic acid could not be used as a COD standard for the dichromate COD method due to poor correlation to theoretical results but could be suitable for the PeCOD COD method. It is therefore important to chose a standard that provides a strong correlation to the theoretical result for the method employed, is a good reflection of the samples to be analysed, is suitable for general laboratory use and is readily available. For details on preparing sorbitol and glucose-based COD standards for the PeCOD COD method, read our technical bulletin 2017-029: PeCOD Standard Recipe.
How do inorganic compounds affect PeCOD® COD determination?
The following tables summarize the impact of a range of common inorganic anions and cations on the determination of COD using the PeCOD® technique. For each inorganic species, solutions containing 0, 20, 50, 100, 250, 500 ppm (by mass) of the anion or cation, 60ppm COD (as sorbitol) and 1M LiNO3 (containing 20ppm COD spike) were prepared and analyzed, unless otherwise stated. Therefore, the below ion concentrations represent the concentration in the cell (i.e. if analyzed in a different range, the interference levels may vary due to different electrolyte dilution effects).
|Ammonium||NH4+||No interference for NH4+ ≤ 500 ppm. Note: Similar results are obtained for Ammonia|
|Carbonate||CO32-||No interference for CO32- ≤ 500ppm using chloride resistant sensor|
|Chlorate||ClO3–||No interference for ClO3– ≤ 500ppm|
|Chloride||Cl–||No interference for Cl– < 200 ppm. COD reduced by up to 20% at Cl- levels of 500ppm using Chloride resistant sensor. Other halides (F-, Br-, I-) would be expected to behave in the same manner|
|Nitrate||NO3–||No interference, NO3– can be used as PeCOD electrolyte|
|Nitrite||NO2–||No interference for NO2– ≤ 500ppm|
|Perchlorate||ClO4–||No interference, ClO4– can be used as PeCOD electrolyte|
|Phosphate||PO43-||No interference for PO43- ≤ 500ppm|
|Sulfate||SO42-||No interference for SO42- ≤ 500ppm|
|Sulfite||SO32-||Interference for SO3 ≥ 20 ppm, giving COD high by 90% at 250 ppm SO32-|
|Sulfide||S2-||Interference for S2- > 0 ppm, giving COD high by >100% at 50 ppm S2-|
|Aluminum||Al3+||No interference for Al3+ ≤ 500ppm|
|Calcium||Ca2+||No interference for Ca2+ ≤ 500ppm|
|Chromate||Cr3+||Interference for Cr3+ > 2 ppm, giving low COD|
|Ferric Iron||Fe3+||No interference for Fe3+ ≤ 500ppm|
|Ferrous Iron||Fe2+||Interference for Fe2+ > 100 ppm, giving low COD|
|Magnesium||Mg2+||No interference for Mg2+ ≤ 500ppm|
|Potassium||K+||No interference for K+ ≤ 500ppm|
|Silver||Ag+||Interference for Ag+ > 10 ppm, giving low COD|
|Sodium||Na+||No interference for Na+ ≤ 500ppm|
|Zinc||Zn2+||No interference for Zn2+ ≤ 500ppm|
What pH range can the PeCOD method measure in?
pH Range: 4.0 – 10.0 (after mixing with electrolyte)
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.
Do I need to filter my samples for PeCOD analysis?
Samples must be filtered prior to peCOD analysis to ensure that no particulates greater than 50 micron (um) are primed into the peCOD. Particulates larger than 50um can cause clogging, which can lead to damage of the internal fluidics of the machine. To prevent clogging and ensure proper sample preparation, MANTECH has a Sample Filtering Guide for PeCOD Analysis.
For pulp and paper and wastewater applications, MANTECH recommends using a 35um polyethylene (PE) syringe filter. These filters can contribute trace amounts of organics, which are negligible for wastewater applications. For drinking and source water applications it’s important to use a filter that does not contribute organics to the filtered sample. One of MANTECH’s research partners has recommended a 0.45um polyethersulfone (PES) filter; however, other filter types may also be acceptable, if no organics are contributed by the filter. Since these applications traditionally see less particulates, having a smaller pore size filter hasn’t shown an impact on the peCOD results.
How much bench space do I require for a typical PeCOD L50 set-up?
The typical benchtop L50 set up requires 36 inches x 18 inches of bench space.