Biological treatment in wastewater treatment plants WWTPs consists of two main tanks, aeration
tank and final settling tank. Aeration process using in return activated sludge system is very costly
and it is required to operate WWTPs with low dissolved oxygen (DO) concentration in aeration
process without risking poor effluent quality. To apply this study, a plant model for the addition of
chemicals must be made with the necessary calibration of this model. Laboratory experiments were
started between November 2017 and June 2018. This paper will discuss the impact of DO
concentration on sludge properties by using a pilot plant model WWTP and find the optimum doses
of Hydrogen peroxide H2O2 concentration with using low DO concentration to achieve good
sedimentation. In this study the DO set-point was changed every 3 weeks between 0.5 mg/l and
4.5 mg/l for a few months. Experiments were carried out to The optimal ratio and dosage of H2O2
/Fe+2 was 5 as 30/6 mg/l. BOD, COD, TSS and VSS removal efficiency by using H2O2 /Fe+2 were
91%, 89% 90% & 89%, respectively with DO = 1.5 mg/l at an increased rates were 21.3%, 25.4%,20% & 12.7%, respectively. Results of paper proves that the addition of optimum H2O2 will save 2
mg/l of DO concentration and providing a high cost of using electricity and mechanical equipment
compared to the non-use of H2O2.