9.1

A schematic of a wastewater treatment plant is shown in Exhibit 9.1.

Exhibit 9.1

1. Treatment to remove grit from the wastewater

   1. decreases BOD

   2. is used to decrease mechanical failure

   3. involves the use of coagulants

   4. can come at any point in the treatment train

2. The primary settling results in

   1. 50% removal of TSS

   2. sludge that is 1 % solids

   3. cost-effective removal of suspended solids by gravity

   4. 25% removal of BOD

3. A major goal of the biological process is

   1. to remove influent TSS

   2. to convert influent BOD to bacterial cells

   3. to decrease hydraulic detention times

   4. to decrease mechanical failure

4. For sewage treatment plants, the biological treatment unit is often some form of activated sludge process because

   1. activated sludge is easier to operate than other biological treatment units

   2. activated sludge has a greater probability of meeting secondary treatment standards

   3. nitrification can be controlled more easily in activated sludge plants

   4. (b) and (c)

5. A small pinpoint floc is observed in the final clarifier. The best corrective action for this problem would be to

   1. increase the recirculation rate

   2. increase the aeration rate

   3. decrease the food-to-microorganism (F/M) ratio

   4. decrease the solids retention time

6. The sludge is wasted from the biological treatment system to

   1. remove bacteria grown in the biological treatment unit

   2. remove the TSS that are captured in the biological treatment unit

   3. control the solids retention time

   4. all of the above

7. Flotation thickening processes

   1. are designed around hydraulic detention time

   2. concentrate primary and secondary sludges to about 5 to 10% solids