When James Dyson invented the bagless vacuum cleaner, the idea didn't come out of thin air. Famously he saw a vortex system for capturing dust at a sawmill and realised it could revolutionise the vacuum cleaner market. From wood cutting to domestic cleaning - the same basic principle could be applied to both.
Most innovation is like this - very few ideas are 'new', but are 'borrowed' from other applications. Sustainability is no exception - ideas cross sectoral boundaries and there is the whole fascinating field of biomimicry which borrows from nature (why use poisonous ship anti-fouling if you can copy how shark skin does it?).
This is one reason why I don't specialise in a particular market - my clients cover transport, chemicals, defence, broadcasting, construction, engineering, health, waste, nature conservation and local government to name a few - because much of the value I bring to those clients is cross-pollinating ideas.
So, if you're looking for inspiration, don't just look inside your company, or what your competitors are doing, but be curious and look further afield. You never know where the next idea might come from.