COD/BOD Ratio Calculator
Our environmental chemistry calculator computes codbodratio accurately. Enter measurements for results with formulas and error analysis.
Formula
COD/BOD Ratio = COD (mg/L) / BOD (mg/L)
The COD/BOD ratio divides Chemical Oxygen Demand by Biochemical Oxygen Demand. Low ratios indicate biodegradable waste suitable for biological treatment, while high ratios indicate recalcitrant compounds requiring chemical treatment.
Worked Examples
Example 1: Domestic Wastewater Assessment
Problem: COD = 500 mg/L, BOD = 250 mg/L, Flow = 1000 m3/day
Solution: COD/BOD = 500 / 250 = 2.0\nBiodegradable fraction = 250/500 = 50%\nCOD Load = 500 * 1000 / 1000 = 500 kg/day\nBOD Load = 250 * 1000 / 1000 = 250 kg/day
Result: Ratio = 2.0 (Biodegradable) - Biological treatment effective
Example 2: Industrial Effluent Evaluation
Problem: COD = 3000 mg/L, BOD = 400 mg/L
Solution: COD/BOD = 3000 / 400 = 7.5\nBiodegradable fraction = 400/3000 = 13.3%\nNon-biodegradable COD = 3000 - 400 = 2600 mg/L
Result: Ratio = 7.5 (Poorly Biodegradable) - Chemical pretreatment required
Frequently Asked Questions
What does the COD/BOD ratio indicate?
The COD/BOD ratio is a key indicator of the biodegradability of wastewater. A low ratio (below 2.0) means most organic matter is biodegradable and can be efficiently treated using biological processes like activated sludge systems. A ratio between 2.0 and 4.0 indicates partial biodegradability, suggesting a combination of biological and chemical treatment may be needed. Ratios above 4.0 indicate predominantly non-biodegradable organic compounds that require advanced chemical oxidation or physical treatment methods.
What are typical COD/BOD ratios for different wastewaters?
Domestic sewage typically has a COD/BOD ratio of 1.5 to 2.5, indicating high biodegradability suitable for conventional biological treatment. Food processing wastewater ranges from 1.5 to 3.0 depending on the product. Pharmaceutical and chemical manufacturing wastewater often has ratios above 5.0 due to recalcitrant organic compounds. Textile industry effluent ranges from 3.0 to 10.0 because of synthetic dyes and finishing chemicals. Paper mill wastewater typically shows ratios between 2.5 and 4.0.
How are COD and BOD measured differently?
COD is measured by chemical oxidation using potassium dichromate under acidic conditions at high temperature, giving results within 2-3 hours. BOD is measured by incubating a sample with microorganisms for 5 days at 20 degrees Celsius (BOD5) and measuring dissolved oxygen consumption. Because COD chemically oxidizes all organic matter (biodegradable and non-biodegradable) plus some inorganic reducing agents, it always gives a higher value than BOD. The BOD test only measures the portion that microorganisms can metabolize.
Why is the COD/BOD ratio important for treatment plant design?
The COD/BOD ratio directly influences treatment plant design decisions, sizing, and operational parameters. A ratio below 2.5 allows engineers to design conventional activated sludge systems with confidence, knowing biological treatment will achieve 85-95 percent removal. Higher ratios require incorporating chemical treatment stages such as Fenton oxidation, ozonation, or electrochemical oxidation before biological stages. The ratio also affects sludge production estimates, aeration requirements, and the selection of specialized microorganism consortia for bioreactors.
How do I get the most accurate result?
Enter values as precisely as possible using the correct units for each field. Check that you have selected the right unit (e.g. kilograms vs pounds, meters vs feet) before calculating. Rounding inputs early can reduce output precision.
Is my data stored or sent to a server?
No. All calculations run entirely in your browser using JavaScript. No data you enter is ever transmitted to any server or stored anywhere. Your inputs remain completely private.