I have talked with many people searching for wastewater training information and always feel a little bad in telling them that this site does not focus on wastewater. The entire focus of this material is on potable (drinking) water treatment and distribution. Although I am very highly certified in potable water treatment (T4) and distribution (D5), I have never worked in wastewater, nor do I hold any certification in it.
I do know from talking with people in that field, that many people in wastewater have had very good success with my water math courses, especially with learning the math basics, but having never worked in the field I can’t personally vouch for it. I also know from seeing some wastewater practice questions that there are certain problems they will not cover.
Unfortunately, having never worked in that industry or tested for a certification, I’m not familiar with any place to refer people to for that information.