However, if the BOD value is higher than COD values, it just says that the root is caused by the used oxidants in the COD analysis but this wastewater is still bio-degradable. COD is generally greater than BOD. However, high presence of microbiologically oxidisable chemicals such as ammonium could boost BOD readings.
Can BOD ever be higher than COD?
BOD can be higher than COD determined by dichromate oxidation in a few cases. The most common is a sample with very degradable organic matter and high organic nitrogen or ammonium such as wastewater from fish processing.
What happens if you have a higher BOD value?
The greater the BOD, the more rapidly oxygen is depleted in the stream. This means less oxygen is available to higher forms of aquatic life. The consequences of high BOD are the same as those for low dissolved oxygen: aquatic organisms become stressed, suffocate, and die.
What does high BOD and COD mean?
The more variable the ratio values, as in, the higher the COD/BOD ratio, the greater the percentage of slowly biodegradable and non-biodegradable material in the sample. And that means the BOD5 test will give a lower value than is truly representative of the oxygen demand in the sample.
Why COD is higher than BOD in wastewater?
The COD test uses a chemical (potassium dichromate in a 50% sulfuric acid solution) that “oxidizes” both organic (predominate) and inorganic substances in a wastewater sample, which results in a higher COD concentration than BOD concentration for the same wastewater sample since only organic compounds are consumed
Is BOD always less than COD?
No, BOD is always less or equal to COD, since BOD gives you only the biodegradable organic content of a aquatic sample, while COD gives you the biodegradable and the non-biodegradable organic content, thus the total organic content.
Can BOD be equal to COD?
COD, Chemical Oxygen Demand, is a measure of the total quantity of oxygen required to oxidize all organic material into carbon dioxide and water. COD values are always greater than BOD values, but COD measurements can be made in a few hours while BOD measurements take five days.
Why is BOD high in polluted water?
So, the higher the amount of organic pollutants in the water, the higher oxygen is required by the bacteria and this oxygen required by the bacteria is known as BOD. So, the amount of pollution in a water body is directly proportional to the BOD.
What does BOD tell us about water quality?
Nitrogen and Water
A small amount, but it is essential for life in the water. Biological oxygen demand (BOD) generally represents how much oxygen is needed to break down organic matter in water.
What is the range of BOD for good quality of water?
BOD values range widely; generally, pristine waters have a value below 1 mg l−1, moderately polluted waters 2–8 mg l−1, and treated municipal sewage 20 mg l−1. Standards for the discharge of effluent from WWTPs have the range 20–30 mg l−1 and require a minimum flow in receiving waters to ensure sufficient dilution.
What is BOD to COD ratio?
Typical values for the ratio of BOD/COD for untreated municipal wastewater are in the range from 0.3 to 0.8 (see in table 3). If the BOD/COD ratio for untreated wastewater is 0.5 or greater, the waste is considered to be easily treatable by biological means.
Which is better BOD or COD?
COD is always higher than BOD because chemical oxidation is easier than biological oxidation.
What is the permissible limit of BOD in wastewater?
The Significance of BOD in Wastewater Treatment
BOD is listed as a conventional pollutant under the U.S. Clean Water Act. Typical maximum values range from 10 mg/L for direct environmental disposal and 300 mg/L for disposal to sewer systems.
What is the limit of COD?
The chemical oxygen demand (COD) concentration in a treated effluent, if observed to be persistently greater than 250 mg/l before disposal to any receiving body (public sewer, land for irrigation, inland surface water and marine coastal areas), such industrial units are required to identify chemicals causing the same.
Why is BOD done for 5 days?
BOD occurs in 2 general stages. While calculating the oxygen demand, the carbonaceous stage is taken into account. This stage is almost completed in 5 days, which means that most of the organic content of the sewage is oxidized under aerobic conditions in 5 days. Hence ,BOD for 5 days is calculated.
How do you reduce BOD COD wastewater?
You can reduce COD and BOD by adding hydrogen peroxide to the wastewater solution. The hydrogen peroxide will chemically attack the organics in the wastewater, degrading them and reducing the measured COD and BOD.
How do you convert BOD to COD?
Typically, the average BOD result is divided by the average COD result to find a “conversion factor” between the two parameters. One would then multiply their COD results by this factor to estimate BOD. COD values are almost always higher than BOD values for the same sample.
What problems can arise from high BOD?
High BOD is harmful to ecosystems as fish and other aquatic life may suffocate in oxygen-depleted waters. 4 Furthermore, it is important that wastewater treatment processes are designed to handle the high organic matter loading present in wastewaters.
Does BOD increase with temperature?
The BOD removal rate in the bioreactor increased when the temperature increased from 20 degrees C to 30 degrees C, 40 degrees C, and 50 degrees C, but it decreased when the temperature increased from 50 degrees C to 60 degrees C. Higher temperature enhanced the endogenous respiration of microbes in the bioreactor.
Why is BOD important in water quality?
The BOD is an important parameter for assessing water quality. It deals with the amount of oxygen consumption (mg O2 L− 1) by aerobic biological organisms to oxidize organic compounds. Sewage with high BOD can cause a decrease in oxygen of receiving waters, which in turn can cause the death of some organism.
What happens if COD is low?
IMPORTANCE OF COD FOR WASTEWATER
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.
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