Are any special seals needed in the pumps when used in low pH or highly corrosive waters?

It will depend on the type of pump being used.  If it's an electric submersible pump or a piston pump then, yes, you need a special seal in order to resist corrosive applications or high organic applications. It depends on what you’re dealing with exactly, but for low pH or highly corrosive waters, it would be necessary to use special seals, and electric or piston pumps. However, air-powered pumps are designed specifically with seals that are meant to resist that kind of application. QED has used air-powered pumps at several sites where the pH is between 1.5 and 2. While we have special materials for the pump body construction, the seal material actually does a nice job of resisting low pH waters or leachate.  At the Puente Hills landfill we are using a piston pump called a seal-less piston pump.  In this pump there is no actual seal down at the piston, there is a seal at top of the stuffing box, and it seems to handle a pH of 2 at a temperature of nearly 200 degrees Fahrenheit, or about 90 degree Celsius, which we encounter there.