Organic matter is initially synthesized in aquatic ecosystems mostly through algal photosynthesis, and the C:N:P. ratio is well known to be close to the Redfield ratio (106:16:1). However, during the decomposition of organic matter, the behavior and the rates of mineralization of C, N, and P can vary.

If phosphorous content is assumed 20% of nitrogen content then the required ratio of COD: N: P in an aerobic reactor should be calculated from the following formula 41/EYobs:5 :1. For anaerobic treatment, the value of C: N: P ratio of 250: 5: 1 is observed at an observed yield value of 0.16 and 100% removal efficiency.When treating wastewater, it is usually stated that the ratio of COD:N:P in the wastewater to be treated should be approximately 100:5:1 for aerobic treatment and 250:5:1 for anaerobic treatment . For anaerobic treatment, the required nitrogen and phosphorous concentrations is lower than the case for aerobic treatment due to the fact that anaerobic treatment produces only 20% sludge compared to aerobic treatment. the COD:N requirements for anaerobic treatment on loading rates. For highly loaded processes (0.8-1.2 kg COD/kg VSS/d), the recommended a value of 250:5. For lower loading rates, the value can be increased from 250:5 by multiplying it with a factor which equals to the loading rate in kg COD/kg VSS/d divided by 1.2. This calculation solves for the carbon to nitrogen ratio of up to three materials. Enter the mass of each material (wet weight), percentage of carbon, percentage of nitrogen, and percentage of moisture, then click on the calculate button. If you have less than three materials be sure to enter zeroes in the fields for the missing materials.

Please see attached table

Regards

Prem Baboo

Regarding whether to measure total COD (Chemical Oxygen Demand), nitrogen, and phosphate, or total carbon, total nitrogen, and total phosphate, it depends on the specific requirements of your analysis and the information you need.

- If you're interested in the organic content and overall pollutant load, measuring total COD, total nitrogen, and total phosphate would be advisable.

- If you need more specific information on the elemental composition and stoichiometry for biological processes (such as microbial growth or nutrient removal), measuring total carbon, total nitrogen, and total phosphate would be more appropriate.

In many cases, both sets of measurements may be useful for a comprehensive understanding of wastewater composition and treatment needs. Choose the set of parameters based on your specific goals and analysis requirements.

@Miloud Chakit thanks for your insights