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enveng test 1 > Three Waters - Drinking Water > Flashcards

Three Waters - Drinking Water Flashcards

1
Q

drinking water should be essentially free of disease causing microbes, but often this is not the case

A

a large proportion of the worlds population drinks microbially contaminated water, especially in developing countries

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2
Q

what are the burdens of providing microbially safe drinking water supplies

A
  • the efficiency of removal or inactivation of enteric microbes and other pathogenic microbes in specific water treatement
  • the ability of water treatment processes and systems to reduce waterborne disease
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3
Q

what are the five steps of water treatment

A
  1. coagulation (rapid mixing)
  2. flocculation (slow mixing)
  3. Sedimentation (settling)
  4. filtration (cleaning)
  5. Disinfection
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4
Q

what is turbidity

A

suspended, dissolved and collodial particles in pretreated water that need to be removed to optimize treatment efficiency

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5
Q

what are suspended solids

A

particles held in suspension by the natural action of flowing waters

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6
Q

what are colloidal solids

A

fine silt that does not settle out of water but remain in suspension

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7
Q

what are dissolved solids

A

organic or inorganic molecules that are dissolved into the aqueous phase

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8
Q

what is coagulation

A

destabilization of colloids by addition of chemicals that neutralise the negative charges. adding and rapid mixing of chemicals to remove particles from water

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9
Q

what chemicals are known as coagulants

A

Al3+, Fe3+ (higher valence cationic salts)

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10
Q

what is flocculation

A

gentle mixing (agglomeration) of destabilized particles into a large size particles known as flocs by slow mixing which can be effectively removed by sedimentation or flotation

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11
Q

what are the floc aids known as

A

flocculants, organic polymers

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12
Q

what are the steps of coagulation

A

coagulation added, coagulant forms precipitate, trapping impurities, precipitate and trapped impurities settle to bottom

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13
Q

what happens in flocculation steps

A

negatively charged particles with cloud of counter ions -> add strongly abrosbing species of opposite charge -> neutralized particle with no double layer

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14
Q

microbe reductions by chemical coagulation flocculation

A

microbe reductions of 90-99% if critical process variables are adequately controlled

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15
Q

what is the oldest form of water treatment

A

sedimentation and flotation

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16
Q

what does sedimentation and flotation use

A

uses gravity to separate particles from water

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17
Q

how to estimate smallest particles for sedimentation and floation

A

given a critical velocity for a sedimentation tank

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18
Q

what does auckland use for filtration

A

ultrafiltration

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19
Q

what does granular media filtration do

A

remove suspended particles (turbidity) including microbes

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20
Q

what are the two types of granular media filters

A

slow sand filters, rapid sand filters

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21
Q

what are slow sand filters

A
  • low flow rates (2.5-10 m/day)
  • biological process (1-2cm slime layer)
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22
Q

what do we need to achieve filtration with slow sand filters

A

need a a number of SS filters in parallel

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23
Q

what are rapid sand filters

A
  • high flow rates (60-240 m/day)
  • physical chemical process; depth filtration)
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24
Q

positives of slow sand filters

A
  • effective, widely used in europe and india
  • filter through 3-5 food deep bed of unstratified sand
  • biological growth develops in upper surface of sand, responsible for particle and microbe removeal
  • effective without pretreatment of water by coagulation - flocculation
  • biological layer relys on nutrients and some organic matter that present in water
  • very cheap
  • lots of protozoa + algae
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25
rapid sand filters
- efficient, widely used in NA - stratified with dif layers (3) - removal using physicochemical prosesses - needs pretreatment of water by coagulation -flocculation - backwashing frequency but no need to change top layer
26
roughing filter
used in developing countrys - inexpensive -low maintenance - local materials - remove large solids - remove microbes - not efficient in removal and turbidity and pathogens
27
membrane filters
- recently developed - microfilters - reverse osmosis filters - high 99.99% removal of cellular microbes, viruses - membrane and membrane seal integrity - cost going down
28
log removal
log10 (Cin/Cout) (Cin is influent pathogen concentration, Cout is effluent pathogen concentration)
29
what does granular activated carbon adsorption do
remove dissolved organics
30
what is a poor retention of pathogens esp viruses
granular activated carbon adsorption
31
what can granular activated carbon shed
microbes into water
32
what does granular activated carbon shed develop
biofilm, its biologically active
33
what does sand plus granular activated carbon do
reduced particles and organics and is biologically active
34
how is microbial retention possible
sand plus granular activated carbon
35
what is an adsorber
granular activated carbon adsorption
36
what is a filter adsorber
sand plus granular activated carbon
37
how to remove hardness in water
add lime or soda to remove hardness
38
what does hard water contain
excessive amounts of calcium and magnesium ions
39
what can also contribute to hardness
iron and manganese, to precipitate them as carbonates, hydroxides and oxides
40
how is hardness ions removed
by adding lime (CaO) and sometimes soda ash (Na2CO3) to precipitate carbonates, hydroxides and oxides
41
what is softening
basically a type of coagulation-flocculation process
42
microbe reduction water softening pH
similar to alum and iron coagulation when pH is <10, >99.99% when pH is >11 - microbial inactivation + physical removal
43
what is disinfection
essential barrier to prevention and control of waterborne microbial transmission and waterborne disease
44
most disinfections are
are short lived hence chloride is used more widely
45
why is ozone not a really good
because its life is too short and you need to protect water from pathogens on the way to home
46
what are the good things about radicals
hydroxial radical are chemical entities with unpaired electrons in their outer orbit, have this thing they are desperate to fulfill, snatch electrons from anything they come in contact with. great oxidising agent, more than 2x chlorine
47
why is radicals not used as much as chlorine
because it will bind with anything whether its organic matter or pathogens and becomes OH-. very low lifetime hence not used
48
what is free chlorine
HOCl (hypochlorus acid) and OCl- (hypochlorite ion)
49
what is and what does it provide HOCl (hypochlorus acid) and OCl- (hypochlorite ion)
- is a strong oxidant and relatively stable in water - provides a disinfectant residual
50
what are chloramines
mostly NH2Cl weak oxidant provides a stable residual
51
what is chlorine dioxide
ClO2, strong oxidant, not very stable residual
52
what are different disinfections of microbes in water
free chlorine, ozone, uv radiation
53
what are the concerns of disinfections
concerns due to health risks of chemical disinfectants and their by-products
54
what is ozone
strong oxidant, provides no residual (too volatile and reactive)
55
what is low pressure mercury lamp
low intensity, monochromatic at 254 nm
56
what is medium pressure mercury lamp
high intensity, polychromatic 220-280 nm
57
what does uv radation react with
nucleic acids, pyrimidine dimers and other alterations
58
what is the reason for maintaining residuals during treatment and distribution
to control microbiological growths when the water is biologically unstable
59
microbe type disinfection resistance from least to post
bacteria -> viruses -> protozoan cysts, spores and eggs
60
type of disinfectant, order of efficacy against Giardia from best to worst
O3 <- ClO2 <- iodine/free chlorine <- chloramines (but order or effectiveness varies with type of microbe)
61
what does microbial aggregation do
protects microbes from inactivation
62
microbes within aggregates can not be reach by
the disinfectant
63
what are the particulates effects of water quality on disinfection
protect microbes from inactivation - microbes shielded or embedded in particles
64
what are the dissolved organics effects of water quality on disinfection
protects, consumes or absorbs (UV radiation) disinfectant, coats microbes
65
what are the inorganic compounds and ions effects of water quality on disinfection
effects vary with disinfectant
66
what are the pH effects of water quality on disinfection
effects depend on disinfectant, free chlorine more biocidal at low pH where HOCl predominates, chlorine dioxide more microbiocidal at high pH
67
rector design, mixing and hydraulic conditions better activity in
"plug flow" than in "batch-mixed" reactors
68
what is the most commonly used disinfectant
free chlorine
69
what is the problem for O3 and ClO2
do not remain in water for very long
70
what must be provided for a stable residual
a secondary disinfectant
71
what is a promising disinfectant and why
UV radiatoin because it inactivates Cryptosporidium at low doses
72
what has to be used along with a chemical disinfectant to protect the water through distribution and storage
UV

enveng test 1 (6 decks)

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