Alternative methods to decontaminate Bacillus spores from large fermentor

We have a 200L fermentor that experiences recurring contamination by Bacillus spores. We have tried caustic, dilute bleach, heat, etc. Are there any alternative methods to decontaminate a large fermentor of Bacillus spores? Quaternary amines? UV light? Please help.

Equipment: Bacterial fermentor decontamination