The amount of DO available in water depends upon several factors. Factors such as physical, chemical and biological factors. it also depends on elevation (MSL) of water body. Temperature is one of the imp factor higher is the temperature of the water less is the amount of DO and less is the temperature of water higher is the concentration of DO. 

K2Cr2O7 is oxidizing agent. 

You might find this helpful for part of your question in that colder water can hold more dissolved oxygen, and that is why when stream temperatures get  high, some intolerant fish and aquatic organisms are stressed or seek refuge. K2Cr2O7 can digest organics, and that may be why you question its affect.  If you want to evaluate DO, suggest it is done in the field if evaluating environmental water conditions before you add the oxidant.  If you have need to know effects, perhaps someone else with more specific knowledge will respond, or you can determine dissolved oxygen before and after adding the K2Cr2O7 for digestion.

http://www.mainevlmp.org/wp-content/uploads/2014/01/Maximum-Dissolved-Oxygen-Concentration-Saturation-Table.pdf

Environmental waters can also be supersaturated with oxygen ( > 100 % DO).  I have seen this for relatively stagnant water in which there is photosynthesis during the day.

Dear Arind,

The "saturation level" is the maximum concentration of dissolved oxygen that would be present in water at a specific temperature, in the absence of other factors. Scientists have determined the saturation DO level for various temperatures. Saturation levels also vary with elevation. Percent saturation is calculated by dividing the measured dissolved oxygen concentration by the saturation level and multiplying by 100.

With my best regards

Prof. Bachir ACHOUR

As you are talking about DO, not BOD; the maximum value of DO that can be attained by a water body is around 14mg/L. 14.6mg/L at 00C to be precise. The DO level depends on temperature, partial pressure etc. So, you can not expect getting a DO value more than 14.6 mg/L. Although in groundwater, pond water the DO value remains around 4-6mg/L.

K2Cr2O7 is an oxidant used along with concentrated sulfuric acid to determine the COD.

Dear Dr. Pravin Mukund ,

the Do level of water mostly depend on the temperature of water , in the case of pure water at 2o centigrade may be 8 but not more than that. for your better information get the standard DO table corresponding with the temperate of water

The DO values obtained in Late rite mines in Odisha more than 20 at places at 27deg. centigrade by titrimetric method.