One idea is to keep that theme going (around measure 34) while having a much slower, very ominous them "riding on top of" (maybe in the horns?). You could slow down the theme of measure 34 or build something out of it. Try inverting it, running it backwards, etc.

To end this piece maybe just have the themes "pile-up on eachother" and end in a fury. Bruckner does stuff like this at the end of his symphonies (although his are on major chords). You could just have every crash together in a dissonant or minor chord manner.

Another idea is to do some wild evil sounding modulations. Progressions by minor thirds always sound disturbing so sometimes that works. Maybe a few tri-tones?

Your material here is good. Just keep plugging away and you will have major success!!!