Intro To Envi. Eng. Chapter 3

Front 1

Define potable and palatable and explain why we must provide a water that is both potable and palatable.

Back 1

Potable: water consumed as much as they want without any harmful effects
Palatable: water that is pleasing to drink but not necessarily safe
We must provide a water that tastes good (palatable) and safe (potable).

Front 2

Distinguish between dissolved substances, suspended solids, and colloidal substances based on their size and the mechanism by which they can be removed from water

Back 2

Dissolved: <0,1 micrometer in size, distillation, precipitation, adsorption, or extraction can remove.
Suspended: 0,1 to 100 micrometer in size. filtration, sedimentation, and centrifugation.
Colloidal: 0,01 to 10 micrometer in size. high-force centrifugation or filtration with small pore membranes

Front 3

Define and calculate quantities of a given substance in water in percent by weight, ppm, and mg/L, and convert from one unit of measure to the others.

Back 3

1mg/L = 10^-3mL/10^3mlL = 1mL/10^6mL = 1ppm
1mg/L = (10^-3g/1000g)*100 = 10^-4 %

Front 4

Define alkalinity in terms of all the chemical species HCO3-, CO3-2, OH-, H+.

Back 4

Alkalinity is an measure of the concentration of acid and base species in a water. Alkalinity is the sum of all the titratable bases down to about pH 4.5 minus H+.

Front 5

Define buffer.

Back 5

A solution that prevents pH change of a water. For example, CO2 produces a natural buffer:
CO2 <-> CO2 + H2O <-> H2CO3 <-> H+ + HCO3- <-> 2H+ + CO3-2

Front 6

Explain the effect of various chemical additions to the carbonate buffer system. Your explanation should include the effect on the displacement of the reaction (left or right), effect on CO2 (into or out of solution), and effect on pH

Back 6

Addition of acids: hydrogen ion concentration -> carbonate ion (CO3-2) reacts to form bicarbonate ion (HCO3-) and further forms carbonic acid (H2CO3) that dissociates CO2 and water -> release of CO2, pH is low.
addition of bases: the system moves to the right, CO2 is replenished from the atmosphere, and pH is high.

Front 7

Define hardness in terms of the chemical constituents that cause it and in terms of the results as seen by the users of hard water.

Back 7

Chemical constituents: the sum of Mg2+ and Ca2+ ions in water.
Results: when boiled, insoluble carbonates precipitate and form scale in shower head or bottom of water heaters.

Front 8

List the four categories of standards for drinking water.

Back 8

Physical, chemical, biological, radiological

Front 9

List the four categories of physical standards

Back 9

Turbidity, Odor, Temperature, Color.

Front 10

Select the appropriate category of chemical standard for a given constituent, for example, zinc-esthetics, iron-esthetics/economics, nitrates-toxicity

Back 10

Chloride-taste, copper-taste, fluoride-health problem, lead-health problem, manganese-esthetics, sodium-health problem, sulfate-health probelm

Front 11

Define pathogen.

Back 11

Disease-producing organisms such as bacteria, protozoa, virus, and worms.

Front 12

Identify the microorganism group used as an indicator of fecal contamination of water and explain why it was selected.

Back 12

Coliform group which lives in human intestinal tract or in most domestic animals, it was selected because they are easily identified and outnumber the pathogens.

Front 13

Sketch a water softening plant and a filtration plant, labeling all of the parts and explaining their functions.

Back 13

filtration plant: screen -> rapid mix (coagulation) -> flocculation basin (flocculation) -> sedimentation basin -> rapid sand filter -> disinfection -> storage
softening plant (groundwater): rapid mix -> reaction basin -> settling tank -> recarbonation (adjustment of pH) -> rapid sand filter -> disinfection -> storage.

Front 14

Define the Shulze-Hardy rule and use it to explain the effectiveness of ions of differing valence in coagulation.

Back 14

One mole of trivalent ion can reduce the charge as much as 30-50 moles of divalent ion and 1500-2500 mole of monovalent ion. So, trivalent ion is more effective in removing repelling charges around the colloidal materials and destabilizing them.

Front 15

Explain the significance of alkalinity in coagulation.

Back 15

Because coagulants react with bicarbonate ions to form complex, that can destabilize the colloids to adhere each other.

Front 16

Differentiate between coagulation and flocculation.

Back 16

Coagulation is a process of rapid mixing of coagulants and colloidal matters in water so that they form flocs that can precipitate. Flocculation is a process of contacting the particles together so that they can settle down efficiently.

Front 17

Write the reaction chemistry of alum and ferric chloride when alkalinity is present and when no alkalinity is present.

Back 17

Alkalinity present: Al2(SO4)3 + 6HCO3- -> 2Al(OH)3 + 6CO2 + 3SO4-2, FeCl3 + 3HCO3- -> Fe(OH)3 + 3CO2 + 3Cl-
No alkalinity: Al2(SO4)3.14H2O -> 2Al(OH)3 + 8H2O + 3H2SO4, FeCl3 + 3H2O -> Fe(OH)3 + 3HCl

Front 18

Explain the effect of pH on alum and ferric chloride solubility.

Back 18

Optimal pH: 5,5 - 6,5
If there is no bicarbonate ion (=pH is low), alum and ferric complex can be formed but pH decreases readily because of formation of H2SO4 and HCl.If pH is high, CO3-2 is predominant species, so the same pH drop will be observed.

Front 19

Explain how to conduct a jar test to obtain an optimum coagulant dose.

Back 19

First, the different concentrations of coagulants are made. pH of the sample water is optimized to 5,5 - 6,5. Each jar is mixed with series of coagulant dose and mixed rapidly and then settled for 30minutes to 1hour. The water quality was checked by pH measurement and turbidity (or others), and then the optimal coagulant dose can be found.

Front 20

List the four basic types of coagulant aids; explain how each aid works and when it should be employed.

Back 20

Polymers: polymer's active sites adhere to flocs and make larger flocs that settle better
pH adjusters: either acid or base is added to adjust the optimal pH for coagulation.
Activated silica: added when treating low-colored, low-turbidity water. Activated silica form a negatively charged solution that will bind with aluminum or iron flocs.
Clay: added when colored, low-turbidity water is present. Works like activated silica.

Front 21

Using diagrams and chemical reactions, explain how water becomes hard.

Back 21

When rainwater enters the soil, CO2 produced by soil bacteria reacts with water to from H2CO3, and that will further react with limestone to form Ca(HCO3)2 and Mg(HCO3)2.

Front 22

Write the general equations for softening by ion exchange and by chemical precipitation.

Back 22

Chemical precipitation:
Ca+2 + CO3-2 <-> CaCO3
Mg+2 + 2OH- <-> Mg(OH)2
Ion exchange:
Ca(HCO3)2 + 2NaR <-> CaR2 + 2NaHCO3

Front 23

Explain the significance of alkalinity in lime-soda softening.

Back 23

Alkalinity --> providing enough HCO3- for CaCO3 precipitation

Front 24

Calculate the theoretical detention time or volume of tank if you are given the flow rate and the volume or detention time.

Back 24

detention time t = V(volume)/Q(flow)

Front 25

Explain how an upward flow sedimentation tank (upflow clarifier) works, using a vector arrow diagram of a settling particle.

Back 25

settling velocity of particle arrow is downwards and velocity of liquid arrow is upwards. Settled particles are discarded from the bottom of the clarifier and inlet liquid flow from the bottom of the clarifier.

Front 26

Define overflow rate in terms of liquid flow and settling basin geometry and state its units.

Back 26

overflow rate = (volume*time)/surface area = liquid flow rate/surface area (m/s)

Front 27

Calculate the percent of particles retained in a settling basin given the overflow rate, settling velocity, and basin flow scheme (horizontal flow or upward flow).

Back 27

P = 100*(vs/v0) = 100*(vs/(Q/As)) = 100*((vs*As)/Q)

Front 28

Explain the difference between Type I, Type II, and Type III sedimentation.

Back 28

Type I: constant settling velocity is known (sand and grit material)
Type II: flocculation occurs during sedimentation, so settling velocity changes
Type III: particles settle as a mass so there are clear zone and sludge zone in clarifier.

Front 29

Compare slow sand filters, rapid sand filters, and dual media filters with respect to operating procedures and loading rates.

Back 29

Slow sand filters: loading rate 3-7,5 m3/d*m2, uniform sand diameter of 0,2 mm and suspended or colloidal material is applied to the sand then the particles clog to the pore spaces. When the pores are clogged, the top layer of sand is replaced.
Rapid sand filters: backwashing (forcing water backwards through the sand) is applied. loading rate is 120 m3/d*m2.
Dual media filters: deeper filter for particle removal, and coal is placed on top of small particles. loading rate is 300 m3/d*m2.

Front 30

Explain how a rapid sand filter is cleaned.

Back 30

Backwashing (washwater expands the sand filter and removes from the bed. after backwashing, the sand settles back into place).

Front 31

Sketch and label a rapid sand filter identifying the following pertinent features: inlet main, outlet main, washwater outlet, collection laterals, support media (graded gravel), graded filter sand, and backwash troughs.

Back 31

see figure 3-32

Front 32

Define effective size and uniformity coefficient and explain their use in designing a rapid sand filter.

Back 32

Effective size: 0,35-0,55mm
Uniformity coefficient: 1,3-1,7

Front 33

Explain why a disinfectant that has a residual is preferable to one that does not.

Back 33

to prevent recontamination before use

Front 34

Write the equations for the dissolution of clorine gas in water and the subsequent dissociation of hypochlorous acid.

Back 34

Cl2(g) + H2O <-> HOCl + H+ + Cl-
HOCl <-> H+ + OCl-

Front 35

State the purpose of super-chlorination.

Back 35

to remove taste- and odor-producing chlorine-containing organic materials

Front 36

Explain the difference between free available chlorine and combined available chlorine and state which is the more effective disinfectant.

Back 36

Combined available chlorine is formed when ammonia is available in water and used as an indicator of contamination because it is reduced slowly. Free available chlorine is formed when there is no ammonia present in water and it is more effective disinfectant.

Front 37

Sketch a breakpoint chlorination curve and label the axes, breakpoint, and regions of predominantly combined and predominantly free residual.

Back 37

First comes peak of combined residual and then the breakpoint comes and peak of free residual. y axis is residual chlorine concentration and x axis is chlorine dosage.