Any alkali can be used, I used lye as an example. At least it was intended as such. But since the quality and type of developing agent in peaty water is utterly unknown, I would go for very high pH - dilute lye. This brown goop also tends to be slightly acidic.

Besides, I don't think this kind of developer can be "optimised" in any way. It will remain a curiosity, and not a source of cheap high-quality developer. So the type of alkali is unimportant - but I know I'm going to use lye (sodium hydroxide).