Environmental Engineering FOURTH EDITION

202 ENVIRONMENTAL ENGINEERING

sense to entrust unqualified operators with multimillion dollar facilities. Wastewater
treatment requires proper plant design and proper operation. One without the other is
a waste of money.

PROBLEMS

9.1 The following data were reported on the operation of a wastewater treatment

plant:

Influent(mg/L) Effluent(mg/L)

BOD5^200 20

ss 220 15

P 10 0.5

a. What percent removal was experienced for each of these?

b. What type of treatment plant will produce such an effluent? Draw a block

diagram showing the treatment steps.

9.2 Describe the condition of a primary clarifier one day after the raw sludge

pumps broke down.

9.3 Ponding, the excessive growth of slime on the rocks, is an operational problem

with trickling filters. The excessive slime clogs spaces between the rocks so that water

no longer flows through the filter. Suggest two cures for ponding.

9.4 Illegal connections are sometimes made to sanitary sewers. Suppose a family

of four, living in a home with a roof area of 70 x 40 ft2, connects the roof drain to the

sewer. If rain falls at the rate of 1 inh, what percent increase will there be in the flow

from their house over the dry weather flow? The dry weather flow is 50 gal per person

per day.

9.5 Suppose you are an engineer hired to build a wastewater treatment plant. What

would you choose as the five most important wastewater parameters to be tested? Why

would you want to know these values? What tests would you run to determine influent

and effluent characteristics, and why?

9.6 The influent and effluent data for a secondary treatment plant are:

Influent(mg/L) Effluent(mg/L)

BOD5 200 20

ss 220 15

P 10 8

Calculate the removal efficiency. What is wrong with the plant?

9.7 Draw block diagrams of the unit operations necessary to treat the following

wastes to effluent levels of BOD5 = 20 ma, SS = 20 mg/L, P = 1 ma. Assume all

BOD is due to dissolved chemicals, and that all SS are inert.