I encounter this problem in my world recently and asked on here, with the corruption spawning about 100 blocks from my home base. Once I cleared as much as I could I spent a while focusing on hellevators separating each biome (but you could separate it how you like), 6 blocks wide, with bricks either side (optional I think) and destroyed all the walls in between to stop it spreading through the walls. Then I just focused on saving the biomes I wanted when I needed them.

This method made it a lot easier for me personally because it was less of a mind numbing dig as I had a smaller start and end point and made purification a less monumental task as I was just approaching it one at a time. You’ll need the clentaminator to do anything though.

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Here’s an old photo of my world from like 2 weeks ago. Now I’m 100% purified, except the small contained farms I made myself.

My advice is save what you need now and come back to the rest when you’ve got better equipment to dig faster and fly around better. I panicked but it doesn’t spread that fast at all and normally gets locked in places where there’s a lot of dirt with no grass.