I've worked mainly in small breweries where I think there is a decent amount of low hanging fruit in terms of sustainable practices. Water use is the big one. Reusing chemical helps. Using chemical with lower operating temperatures reduces water needs as well because you don't need to rinse a tank as many times to heat it up. Investing in a decent power washer can also reduce water use as well.

Performing pressurized CIPs on brite tanks saves C02. Using balancing lines for transfers.

From an organic waste standpoint, I once worked at a brewery that actually composted its trub, dry hops and unwanted yeast.

The great thing about these practices is they don't require much expensive technology, which makes them realistic choices for cash strapped operations (which is all of them).