{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}


Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
UNIVERSITY OF CALIFORNIA, LOS ANGELES Civil and Environmental Engineering Department CEE 153 Introduction to Environmental Engineering Science Example Problems for Problem Set # 3 _____________________________________________________________________________ 1. Water “hardness” is defined as the concentration of calcium and magnesium ions (Ca ++ and Mg ++ ). One way to “soften” water is to add a chemical that will combine with these ions to form a solid precipitate that can then be settled out. For calcium hardness, soda ash (Na 2 CO 3 ) may be added to produce the following reaction: Ca ++ + Na 2 CO 3 CaCO 3 (s) + 2Na + where the calcium carbonate CaCO 3 is in solid form. a) A water treatment plant must soften a total flow Q = 1 m 3 /sec that has a calcium ion concentration of 100 mg/L. What mass of soda ash must be added each day to remove completely the calcium hardness? [22,848 kg] b) The softened water passes into a settling basin. If the solid CaCO 3 particles in the settling basin have a settling velocity w s = 100 m/day, what should the area A of the settling basin be if the objective is to remove 80% of the CaCO 3 solids? [3456 m 2 ] 2. In a wastewater treatment plant sludge from the primary clarifier and waste-activated sludge from the secondary system are mixed and thickened in a gravity thickener. The primary sludge contains 1250 kg of dry solids per day with a 4% solids content by volume (relative to the total volume including liquid) and the waste-activated sludge contains 525 kg of dry solids per day with a solids content by volume of 1.2%. After thickening the mixture has a solids content by volume of 3%. Assume that all dry solids have a density of 1000 kg/m 3 . a) Calculate the volume of thickened sludge produced each day. [59 m 3 /day] b) Calculate the percent volume reduction in the thickener. [79% = volume after thickening/volume before thickening]
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
3. A water treatment plant with a flow Q = 1 m 3 /sec adds FeCl 3 to increase the concentration of suspended solids. The reaction of FeCl 3 with water that produces the solids (in the form of Fe(OH) 3 ) is: FeCl 3 + 3H 2 0 Fe(OH) 3 + 3HCl This reaction may be assumed to happen very rapidly and to result in the formation of small particles. After FeCl 3 addition and reaction, the flow passes through a flocculation
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}