1.) Why does the Food equation (mass of BOD entering the aeration tank) have 1 ppm = 1* 10^6 mg/L ?? I thought 1 ppm = 1 mg/L.

Also, when you cancel the units out, you get lbm and ppm leftover. However, the answer just has 8,340 lbm. Where did the ppm go?

2.) When I calculated the values in the MLVSS equation, I get 0.003053. In order to get their answer of 3053 mg/L, I have to multiply by 10^6. I am to assume the 0.003053 was unitless and if I wanted mg/L then I needed to multiply by 10^6? I thought that the units for MLVSS were already in mg/L.

3.) Finally, the problem states that the plant has an 85% BOD removal efficiency. Why is this value not used for this problem? I understand why the 67% efficiency was used for the primary tank, but why should I ignore the 85%?

Any help would be greatly appreciated. The units in this problem are driving me crazy!

Thanks,

Jen