ANSWER you must complete heroic again after obtaining catalyst to receive an additional 12 blighted essence (24%) and then the chest run gives you 6 blighted essence (12%) for 36% total.

Can you still get blighted essence?

Once you destroy the Taken Blight in the Lost Sector, drop down the hole and keep going forward until you reach the first red jump. After the first red jump, but before the crawl, look for a small crack in the wall. Jump into it to find the chest. Open it, and you'll receive some Blighted Essence.

Can you complete whisper catalyst in one week?

You can only do the heroic version of the whisper quest once per week. You only have to complete the catalyst once.