Something to do with energy efficiency would relate very well to chem eng. Improving efficiency is one of the best things a chemenger can do to reduce costs.
You could go from the safety aspect, and talk about something that has gone very wrong. Chernobyl is overused, I would go for something like Deepwater Horizon.
Plant safety is an important part of chem eng. It's all very well inventing cold fusion, but if your plant explodes when you turn it on you would look a bit silly.
So, analysis into what went wrong over in the gulf of mexico would be my choice.