2.2. Measurement of Total Carbon

So the other method that is used is called as chemical oxygen demand. So here I think we don’t rely on biodegradation, there is a direct oxidizing agent that is used. So, you have organic compounds or we call it as organic load in the presence of acidic and oxidizing conditions gives you CO plus H2O plus organic compounds contains a C, H, O, and N generally some ratio.

Chemical Oxygen Demand (COD) is a method used to measure the amount of organic compounds in water. Instead of relying on living organisms to break down these compounds (as in Biochemical Oxygen Demand, or BOD), COD uses a chemical oxidant to oxidize the organic load. The result of this reaction provides a direct measure of the organic material present.

Think of COD like using a strong cleaner on a stained carpet. Instead of waiting for natural processes to clean the stain, you apply a chemical cleaner that quickly breaks down and removes it. Similarly, COD uses a chemical to quickly measure the organic pollutants in water.

The standard method calls for the use of CrO3 + H2SO4. It is called chromic acid, chromium trioxide with concentrated sulfuric acid. And usually back titration is used which is called the excess method.

To analyze COD, a standard method utilizes chromium trioxide (CrO3) and sulfuric acid (H2SO4). The process involves adding excess oxidant to the water sample and then titrating the leftover acid to determine how much was consumed by the organic compounds. This method allows precise measurement of COD because any unreacted oxidant can be precisely quantified.

Imagine you're pouring detergent into a bucket of dirty water. You add a lot of detergent to ensure it cleans everything. After cleaning, you check how much detergent is left to understand how much was used in the cleaning process. This is similar to how COD testing checks how much oxidant reacted with the pollutants in the water.

COD is more an indicator; it does not rely on the conditions that you have and it’s also faster than the BOD. You can do it fairly quickly, you can also do it simultaneously, there are equipment to do that.

While COD is a useful indicator of organic content in water, it's important to note that it isn't condition-dependent like BOD. It can be conducted more quickly and simultaneously for multiple samples, but it doesn’t always tell the full story of water quality as it might include other inorganic materials that could interfere with results.

Consider COD like a quick pulse check of a patient. While it can indicate general health status quickly, it doesn’t provide detailed insight into what specific issues (like cholesterol or blood pressure problems) may be present. For detailed analysis, further tests (like BOD or specific nutrient tests) may be necessary.

There is another method which is called as total organic carbon (TOC) to correct whatever we said in the COD. We are only interested in carbon here.

Total Organic Carbon (TOC) focuses specifically on measuring organic carbon content in water, differentiating it from COD, which includes various organic and inorganic compounds. TOC provides a more refined understanding of organic pollution and helps in monitoring processes like biodegradation.

TOC measurement is like focusing specifically on the sugar content in a juice, while COD would measure the overall sweetness, including all types of sweeteners. If you want to know about the natural sugar levels (organic carbon), TOC gives you just that.

So, the analysis of this is a little more sophisticated. We measure initially what is called as total carbon TC because carbon in water can also be inorganic, in the form of carbonates.

To measure Total Organic Carbon, we first determine Total Carbon (TC), including both organic and inorganic forms. Since carbonates contribute to the total carbon count, it's important to remove these from the measurement, usually done through acid treatment to release CO2. After this, only organic carbon remains for further analysis.

Imagine baking a cake where you need to account for both flour and sugar. First, you gather all ingredients (total carbon) and then identify and set aside the flour (inorganic carbon) by dissolving it in water. What remains is the sugar (organic carbon) that you'll measure for sweetness.

The organic carbon is added to a catalyst which basically does oxidation, all the carbon is oxidized. It’s catalytic oxidation at high temperature and it will release carbon dioxide or carbon monoxide which is measured using near infrared detector.

The TOC measurement process involves oxidizing organic carbon to produce carbon dioxide or carbon monoxide, detected by infrared spectroscopy. This highly sensitive technique helps quantify the carbon content accurately, providing precise readings of organic carbon concentrations in water samples.

Think of this process like converting wood into ash by burning it. The carbon in the wood is released as gas (like CO2) during combustion, just like organic carbon is oxidized in TOC analysis and measured. The ashes remaining after burning would represent the remnants of what was originally there.

The total Organic Carbon instrument is expensive. Compared to BOD and COD which are very cheap.

TOC analyzers tend to be more costly than other methods like BOD or COD due to their advanced technology and capability for lower concentration detection. Furthermore, regular calibration is necessary to ensure accuracy, requiring known amounts of carbon to establish a relationship for results.

It's like owning a high-end camera for detailed photography. While cheaper cameras can take satisfactory photos, the more expensive one provides high clarity and detailed images. You must regularly calibrate your camera lens to keep capturing those high-quality photos effectively.

--