The Dao contamination qi was left behind during the ancient Immortal times. It was suppressed in various locations by the great ones in the past through different techniques.
Within the Immortal World alone, there were two known locations where the Dao contamination qis were sealed. They were the Spiritual Mountain and Nether Abyss Blood Ocean.
The Underworld River Forefather had set up several seals in the past that separated the Blood Ocean and forced it to exist in the Immortal World's spatial rift.
One of the entrances to the Blood Ocean was where the Dao contamination qi was found.
With that, Chu Kuangren visited the Blood Ocean and did the same thing. Soon, he absorbed all the Dao contamination qi contained in that location.
Lastly, he returned to the Imperial Palace, hoping to study and understand the Dao contamination qi further.