STP plants currently are releasing treated water with 0-2 PPM level of Dissolved Oxygen (DO), this is having negative impacts on the environment thus negating the basic core environmental objectives of the Sewerage Treatment.
A DO concentration of 0 PPM indicates that the water is completely devoid of oxygen, which can be extremely harmful to aquatic life. A DO concentration of 2 PPM is considered the minimum DO level for supporting aquatic life, and even at this concentration, some sensitive species may be negatively affected.
Low Dissolved Oxygen (DO) concentrations in treated water can have a significant impact on both agriculture and river waters.
In agriculture, low DO concentrations in irrigation water can affect crop growth and yield. Plant roots require oxygen to function properly, and low DO levels in irrigation water can reduce the oxygen supply to the roots, leading to reduced crop growth and yield. Additionally, low DO levels in irrigation water can promote the growth of anaerobic bacteria, which can negatively impact soil health and lead to nutrient loss.
In river waters, low DO concentrations can lead to a range of negative impacts on aquatic life. Aquatic animals, such as fish and insects, require oxygen to breathe, and low DO levels can lead to reduced growth, reproduction, and survival rates. Additionally, low DO levels can cause the release of toxic compounds, such as ammonia and hydrogen sulfide, which can further harm aquatic life.
When low DO water is discharged into a receiving water body, it can lead to a process called "hypoxia," where oxygen levels become so low that aquatic life is unable to survive. This can result in fish kills, the loss of other aquatic animals, and the disruption of the entire ecosystem.
Furthermore, low DO concentrations in treated water contributes to the growth of algae and other microorganisms, leading to the formation of harmful algal blooms, which can be toxic to both humans and animals.
Therefore, it is essential to maintain DO levels in treated water to ensure that it is safe for discharge into the environment and does not negatively impact agriculture or river waters.
Therefore, it is important for STP plants to maintain DO levels in their treated water that are in compliance with local regulations and are sufficient to support aquatic life. In some cases, additional aeration or oxygenation systems may be necessary to increase the DO levels in treated water before discharge to ensure that it does not harm the environment.
Regulatory agencies should set minimum DO levels for treated water before it can be discharged into receiving waters, and make it mandatory for the STP plants to comply with these regulations to protect the environment and public health.
Considering the gravity of this issue it is recommended that the measurement and monitoring of DO levels of minimum 4 PPM in the treated water needs to be included in the stipulated KPIs for treated water discharged from all the STPs. Kindly advise.
As a rule of thumb, according to the Environmental Protection Agency (EPA ), dissolved oxygen levels approaching 3 mg/L are in the danger zone for supporting common aquatic life, and then levels below 1 mg/L cannot support any aquatic life..
The dissolved oxygen measurements can provide a great insight into water quality, especially when paired with pH , temperature, and other probe measurements.
when wastewater enters the treatment facility it is usually pretty “dead” in the sense that minimal life exists and the dissolved oxygen content is near zero. (Remember: levels around 8-9 mg/L is optimal for aquatic life, where this water is close to 0 mg/L dissolved oxygen). This is fine for primary treatment where large solids are filtered out as one would strain spaghetti noodles in boiling water.
On the other side, levels of dissolved oxygen can vary from process to process but dissolved oxygen levels that increase beyond 5-6 mg/L could indicate a problem. Since dissolved oxygen increases with mixing and flow, if the mechanical mixer rates are too high (thus increasing DO) they could shear the activated sludge apart which is undesirable. This scenario is more unlikely but something to keep in mind when beginning or adjusting the secondary treatment process.
Dissolved oxygen (DO) is added to the aeration basin to enhance the oxidation process by providing oxygen to aerobic microorganisms so they can successfully turn organic wastes into inorganic byproducts.
The oxygen content of water will decrease when there is an increase in nutrients and organic materials from industrial wastewater, sewage discharges, and runoff from the land.
Thanks Dr. Prem Baboo, Sir you are absolutely right.
I have gone through the available data of most of the STP plants in India and have personally visited various STP plants acros various states, I found out that the DO level of the treated water being discharged is ranging between 0-1.5 PPM. This is actually causing grave damage for the environment eco system irrespective of the fact whether the treated water is released for agriculture or to the rivers.
Government of India is spending crores of rupees for waste water treatment but actually the quality of treated water is playing havoc with the environment.
Ironically CPCB or NGT has never included minimum DO level parameters for stipulating the KPIs for STP plants.
No one is bothered.
The use of treated water for Agriculture with extremely low DO levels will only create more demand for pesticides and fertilizers.
Humanity dependent on river water is bound to suffer due to the impact of release of low level DO in river waters.
it is really alarming.
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