ENE 483

Activated carbon (chemical functional groups) utilizes the

Adsorption of organics

The minimum hardness that ion exchange softening can achieve is

0 mg as CaCO3

the 5 steps/softening reactions

1. *neutralization of carbonic acid* to remove pH. no hardness removed. 2. *precipitation of carbonate hardness due to calcium*. convert all bicarbonate to carbonate 3. *precipitation of carbonate hardness due to mg2+*. add lime. 2 steps 4. *removal of noncarbonate hardness due to ca2+*. add soda 5. *removal of noncarbonate hardness due to mg2+*. add lime and soda

lime

Ca(OH)2

excess lime adds hardness as

Ca2+

When hard water is softened by ion exchange, which substance is typically exchanged for calcium and magnesium and will appear in the product water?

H+

soda ash

Na2CO3

difference between RO/NF anD UF/MF

RO removes ions, UF separates suspended particles

EBCT

V/Q

concept of ion exchange

a charged ion in solution is exchanged for a similarly charged ion attached to an immobile particle, like a resin bed

Select all true statements: a: Carbonate hardness is called temporary hardness because the hardness minerals associated with alkalinity are removed during the heating of water. b: Carbonate hardness is called permanent hardness because the hardness minerals associated with alkalinity are removed during the heating of water. c: Total hardness = carbonate hardness + noncarbonate hardness d: Hardness is the sum of all monovalent cations.

a, c

adsorption

accumulation of molecules on a surface (a surface layer of molecules) in contact with an air or water phase

array

arrangement of stages

If the finished water from an ion exchange unit has a salty taste, a probably cause for the problem may be: a: The resin needs to be regenerated b: The rinse stage was unsuccessful c: Iron oxide is coating the resin beads d: Too much chlorine was present

b

In order to maximize the service life of an ion exchange unit, a: The water should be prechlorinated. b: Iron, manganese, or the combination of the two should not exceed 0.3 mg/L in the water applied to the resin. c: The water should not be prechlorinated. d: Iron, manganese, or the combination of the two should not exceed 3.0 mg/L in the water applied to the resin.

b,c

which type of hardness is temporary

carbonate

If iron in the ferric form is found in the raw water entering an ion exchange softener, the following is likely to occur: a: The resin will reduce the ferric iron to ferrous iron, which will be exchanged. b: The ferric ions will be exchanged for sodium on the resin. c: Nothing will change d: Ferric iron will precipitate and the ion exchange resin will act as a filter.

d

absorption

dissolution of molecules within a phase, e.g., within an organic phase in contact with an air or water phase

ebct

empty bed contact time

pressure vessels

enclose membrane elements

stages

group of pressure vessels. operate in parallel

neutralization of carbonic acid helps, but does not reduce...

helps reduce sludge, does not remove hardness

the purpose of recarbonation is to

lower the pH by adding carbon dioxide (to stop precipitation)

LSI >0 =0 <0

oversaturated, CaCO3 will precipitate equilibrium undersaturated, CaCO3 will dissolve

pHs =

pCa2+ + pAlk +C pCa2+ = negative log [Ca2+] in M pAlk = neg log Alk in Eq/L C = empirical constant (function of ionic strength and temperature), see Table 4-5

LSI =

pH - pHs

during softening, raising/lowering pH will cause precipitation

raising

sfr

service flow rate

SLR

surface loading rate

granular activated carbon

to remove organic matter that would otherwise cause lots of by-product during chlorination