What is the oxygen sag curve?

Oxygen sag or the oxygen sag curve refers to the reduction in dissolved oxygen plotted over a distance along a water body from a point at which sewage or other pollutants have been discharged.

How does an oxygen sag curve work?

The curve obtained when the concentration of dissolved oxygen in a river into which sewage or some other pollutant has been discharged is plotted against the distance downstream from the sewage outlet (see graph). Samples of water are taken at areas upstream and downstream from the sewage outlet.

Where do oxygen sag curves occur?

Oxygen sag curves occur when the oxygen dissolved in the water is depleted. This is caused by the addition of anything which increases the BIOLOGICAL OXYGEN DEMAND such as biological waste and sewage. they are found mostly in slow flowing streams.

Which equation helps us to plot the oxygen sag curve?

The classical way of solving for the dissolved oxygen sag equation is the Streeter-Phelps equation, which dates back to 1925 (Streeter-Phelps, 1925; Tchobanoglous and Schroeder, 1984). O0 = dissolved oxygen concentration immediately upstream of effluent discharge (mg/liter).

What causes an oxygen sag curve?

oxygen sag curve The curve obtained when the concentration of dissolved oxygen in a river into which sewage or some other pollutant has been discharged is plotted against the distance downstream from the sewage outlet (see graph). Samples of water are taken at areas upstream and downstream from the sewage outlet.

What is a high BOD level?

Biochemical Oxygen Demand (B.O.D.) is a measure of the quantity of oxygen used by microorganisms in the oxidation of organic matter. If the B.O.D. is high, that means that microorganisms are using most of the Oxygen. This situation makes it difficult for larger aquatic animals to survive.

How do you make an oxygen sag curve?

When pollutants (waste or excess fertilizer) enter the water, BOD and DO levels change, producing the oxygen sag curve. DO and BOD levels create characteristic zones in a stream around the point source of pollution known as the Clean zone, Decomposition Zone, Septic Zone, and Recovery Zone.

What happens if BOD is high?

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.

Why is BOD done for 5 days?

The standard oxidation (or incubation) test period for BOD is 5 days at 20 degrees Celsius (°C) (BOD5). The BOD5 value has been used and reported for many applications, most commonly to indicate the effects of sewage and other organic wastes on dissolved oxygen in surface waters (see TECHNICAL NOTE).

Do sag curves have a critical point?

The critical point on the oxygen sag curve is called the critical deficit, Dc. This point (see Figure 1) has the lowest dissolved oxygen content and will determine the impact on living organisms in the stream.

What is a good BOD level?

A BOD level of 1-2 ppm is considered very good. There will not be much organic waste present in the water supply. A water supply with a BOD level of 3-5 ppm is considered moderately clean.

What is BOD and do in water?

BOD is a measure of the amount of oxygen required to remove waste organic matter from water in the process of decomposition by aerobic bacteria (those bacteria that live only in an environment containing oxygen). BOD is used, often in wastewater-treatment plants, as an index of the degree of organic pollution in water.

When do you use the oxygen sag curve?

oxygen sag curve The curve obtained when the concentration of dissolved oxygen in a river into which sewage or some other pollutant has been discharged is plotted against the distance downstream from the sewage outlet (see graph).

When was the first oxygen sag model made?

Figure 1: OXYGEN SAG Oxygen Sag Model One of the earliest mathematical water quality models was developed by for the O hio River b y H.S. Streeter and E.B. Phelps in 1925. Hence the model is referred to as the Streeter-Phelps model.

What does oxygen sag mean in self purification?

OXYGEN SAG: The oxygen sag or oxygen deficit in the stream at any point of time during self purification process is the difference between the saturation DO and DO content at that time. Oxygen Deficit, 9.

Why is the oxygen dissociation curve an S shaped curve?

The oxygen dissociation curve plots the % saturation against the partial pressure of oxygen, and its contribution to the total oxygen content. This is an S shaped curve due to the alterations in hemoglobin’s affinity for oxygen in response to other physiologic factors. Please note the dotted line at the bottom of the graph.

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