Activated Sludge practice quiz
10 questions, free, no sign-up. Answers and reasons appear when you check your answers, and you can try again as many times as you like.
Ten questions on activated sludge control: internal recycle, MCRT and sludge age, settleometer practice, clarifier loading, F/M, permit limits and aeration.
Practice quiz: it does not give a certificate. Certificates are issued to paid students after passing the certification quiz for their class.