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Wastewater > Disinfection > Flashcards

Disinfection Flashcards

1
Q

Relationship between chlorine dose, chlorine demand, and chlorine residual.

A

Dose = demand + residual

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2
Q

Basic purpose of wastewater disinfection.

A

Destruction of harmful or undesirable microorganisms

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3
Q

Typical chlorination units used in the wastewater industry:
chlorine dose * chlorine demand * chlorine residual

A
  • Dose: pounds/day * Determined by weighing the chlorine container daily
  • Demand: mg/L * Determined by subtraction (dose - residual = demand)
  • Residual: mg/L * Determined by measuring chlorine remaining after at least 30 minutes of contact time)
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4
Q

Factors that enhance the effectiveness of chlorine disinfection of wastewater effluent.

A
  • Warm wastewater temperature
  • Low effluent BOD; and suspended solids
  • Long contact basin detention time
  • Neutral to slightly acidic effluent pH
  • Adequate chlorine residual
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5
Q

This chemical, when present in wastewater effluent, can cause serious interference with disinfection.

A

Nitrite, produced during nitrification, can cause high chlorine demand

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6
Q

The type of chlorine residual found in most wastewater effluents

A

Combined residual chlorine, in the form of chloramines. Combined residual is typical because most effluents contain ammonia.

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7
Q

Characteristics of chlorine gas:
Density
Color
Smell
Reactivity

A
  • Approximately 2.5 times heavier than air
  • Yellow green color, visible when gas is 100 ppm or higher
  • Acrid, burning sensation detectable at 1 ppm
  • Supports combustion and very corrosive in the presence of moisture
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8
Q

Used to detect small chlorine gas leaks.

A

Waive an ammonia soaked rag near the suspected leak - white cloud indicates leak

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9
Q

Typical containers used for gas chlorine.

A
  • 150 lb cylinder
  • 2000 lb container or “one ton” container
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10
Q

“Rule of thumb” for removal of chlorine from cylinders.

A

Maximum removal rate: approximately 1/4 of full cylinder net weight/day
150 lb cylinder = 40 lb/day
2000 lb container = 500 lb/day

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11
Q

The total weight of a full “one ton” chlorine cylinder.

A

A full “one ton” chlorine container weighs approximately 4000 pounds
Container wt. = 1800 lb
Chlorine wt. = 2000 lb

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12
Q

Chlorine is available in these physical states

A
  • Gas chlorine: Molecular chlorine. Cl
  • Liquid, solution chlorine: Sodium hypochlorite, NaOCl
  • Solid, granular chlorine: Calcium hypochlorite, Ca(OC1)2
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13
Q

Microorganism group used to determine the effectiveness of disinfection of wastewater effluent.

A
  • Fecal coliform bacteria (monthly ave. not to exceed 200/100 ml sample
  • E. coli (monthly ave. not to exceed 126/1 00 ml sample
  • enterococci (monthly ave. not to exceed 33/100 ml sample
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14
Q

The fecal coliform limit for a secondary effluent.

A

Fecal coliform bacteria

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15
Q

The disinfection standard for “reuse” of wastewater effluent.

A

Less than 2.2 total coliform bacteria/1 00 ml sample

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16
Q

The most commonly used chemical for effluent de-chlorination.

A

Sulfur dioxide

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17
Q

Method used to determine the 24-hour chlorine dose.

A

Weigh the chlorine container(s) at 24 hour intervals

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18
Q

Observe this to determine the present chlorine dose rate.

A
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19
Q

The difference between the amount of chlorine added and the amount of chlorine residual that remains after the contact time

A
20
Q

The chemical used to determine the chlorine residual in wastewater effluents.

A
21
Q

The color that develops when DPD reacts with residual chlorine

A
22
Q

These can cause chlorine demand in wastewater.

A
23
Q

Typical uses of chlorine in a wastewater treatment plant

A
24
Q
A
  • Chlorine (most common method in U.S.)
  • Ultraviolet light (UV)
  • Ozone (least common method in U.S.)
25
Q
A

Approximately 158° F

26
Q
A
  • Dysentery
  • Polio
  • Typhoid fever
  • Cholera
  • Hepatitis A
  • Gastroenteritis
27
Q
A

Pathogens

28
Q
A
  • Viruses
  • Bacteria
  • Protozoa
29
Q
A

Coliform bacteria

30
Q

The effect of chlorine on the pH of wastewater.

A

Chlorine gas tends to lower the pH, due to the formation of hydrochloric acid and hypochlorous acid.

31
Q

High effluent water temperature will have this effect on the chlorine residual.

A

The chlorine residual will tend to be lower because the chlorine is reacting faster

32
Q

This remains after a specified contact time and the chlorine demand has been met.

A

Residual chlorine

33
Q

This is the most effective form of chlorine disinfectant.

A

Hypochlorous acid, also called “free” residual chlorine

34
Q

If the chlorine dose exceeds the ammonia concentrate by eight times, this will occur.

A

Breakpoint is reached. Combined forms of chlorine are destroyed and any additional chlorine dose will produce free residual.

35
Q

The term “available chlorine.”

A

The oxidizing power of a chlorine compound

36
Q

Baffles serve this purpose in a chlorine contact basin

A
37
Q

Bubbles observed across the surface of a chlorine contact basin indicate the need to do this.

A
38
Q

Chlorine reacts with ammonia nitrogen compounds in wastewater to form this.

A
39
Q

This may occur if chlorine is removed from a container too fast, or the container temperature is allowed to drop below 50° F.

A
40
Q

Characteristics of high test hypochlorite (HTH™ ).

A
41
Q

The wavelengths used for UV disinfection

A
42
Q
A

Sulfur dioxide gas (SO2)

43
Q
A

Sulfur dioxide reacts almost exactly 1:1 with chlorine

44
Q
A
  • Liquid chlorine drawn from lower valve on ton containers
  • Heat is applied in the evaporator to provide conversion to gas chlorine
  • High withdrawal of liquid chlorine does not cause container cooling and icing
45
Q
A
  • The complete destruction of all life
  • Processes designed to kill or inactivate most microorganisms in water and wastewater, including essentially all
    pathogens
46
Q

Characteristics of liquid hypochlorite chlorination:
Delivered concentration
Chemical formula
Storage
Dosing equipment
Compatible piping, valves, storage tanks
Reactivity
Safety

A

Delivered concentration
12.5%

Chemical formula
NaOCl (sodium hypochlorite)

Storage
For 30 days can result in 15% drop in strength

Dosing equipment
Hypochlorinator which incorporates a variable output positive displacement pump (diaphragm or peristaltic)

Compatible piping, valves, storage tanks
PVC, tephlon™, polyethylene

Reactivity
Can react (sometimes with violence) with many substances:
Metals
Ammonia salts
Organic compounds
Acids (causes rapid release of Cl2 gas)

Safety
Pronounced irritant; can cause severe burns to skin and eyes. Inhalation hazard (Cl2

Wastewater (10 decks)

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