ch 11 + 12: Disinfection + Pumps

Question 1

Define sterilization

Answer 1

the process where all microorganism are destroyed and thus, no longer in the system.

Question 2

What are the concerns regarding sterilizing your water?

Answer 2

• when ‘all’ microbes are removed, any non-ideal organisms that make it into the system can flourish due to lack of competition
• sterilizing your system can be cumbersome and time consuming

Question 3

Define probiotics

Answer 3

healthy bacteria in the system maintain a natural balance and limit the growth of harmful bacteria

Question 4

define disinfection

Answer 4

use commercially produced agents to destroy many specific organisms.

Question 5

why use disinfection over sterilization?

Answer 5

disinfection does not discourage growth in a system, and the cost of implementing it is lower than with sterilization.

Question 6

What three factors does the effectiveness of disinfection depend on?

Answer 6

1- the concentration/intensity of the disinfectant
2- the contact time
3- water quality parameters (incl. ph, temp, turb

Question 7

name 4 methods of disinfecting your water

Answer 7

• hydrogen peroxide
• chlorination
• ozone
• UV

Question 8

describe how hydrogen peroxide is a good disinfectant

Answer 8

• very effective at oxidizing water

- reacts with organic matter rendering wastewater ‘harmless’

Question 9

describe the two concerns with using hydrogen peroxide as a disinfectant

Answer 9

• handling issue need to be addressed (dangerous goods)

- if it does not dissipate after use in the water it will negatively affect biological growth downstream

Question 10

Chlorine is a good disinfectant; what is its contact time, ‘how much’ should you add, how do you neutralize it, and what are the concerns?

Answer 10

• contact time: 60 minutes
• add: excess
• neutralize: dechlorination by carbon, sodium sulphite, ozone, UV, ferrous salts, sodium thiosulphate
• with high ammonia levels, the chlorine can react to form chloramines, which are quite toxic.

Question 11

UV light: what are some concerns with this system?

Answer 11

• because it is light dependant, if there are suspended matter in the system they will block the light, reducing the amount of penetration, which will reduce the effectiveness of the system.
• light only penetrates a shallow depth

Question 12

how does UV work?

Answer 12

it destabilizes organic material with light

Question 13

name a few pros and cons for UV

Answer 13

P: V. effective
-no change in taste odour, ph, conductivity
-no chem
-simple to use/install
-no toxic chem to ship
C: hard water produces build up on sleeve, reducing effectiveness
-iron/manganese will potentially stain quartz sleeve
-bulbs must be replaced frequently ($)
-quartz sleeve must be periodically replaced ($)

Question 14

what are pros of ozone?

Answer 14

P: -v. effective

• short contact time in water pre filtered to 5um
• no harmful residuals
• generated on site = reduced handling
• elevates the DO in the effluent stream
• breaks up large chain organic molecules, easier to biodegrade
• removes nitrate
• low levels of ozone polymerizes organic matter

Question 15

what are cons of ozone?

Answer 15

• complex technology ($)
• v. reactive and corrosive
• off gases very irritating and potentially toxic
• above pH of 8, its effectiveness diminishes
• in SW systems it reacts with bromine to form persistent toxic compounds. (thus you need an additional carbon filtration after)

Question 16

define a pump

Answer 16

a machine capable of adding energy to a fluid

Question 17

NPSH: define

Answer 17

net positive suction head
-absolute total head at the inlet of a pump above the fluid vapor pressure
(does fluid flow into system with gravity, or does it draw water into the chamber)

Question 18

positive NPSH

Answer 18

a situation where the pumps inlet is below the water supply, or the fluid is under enough pressure to force the water into the pump chamber without the pump having ot carry out any work.

Question 19

what is another term for positive NPSH?

Answer 19

flooded suction

Question 20

negative NPSH

Answer 20

a situation where the pumps inlet is above the lever where the water can reach under non-pumping conditions. The pump must create a vacuum to draw water into the chamber.

Question 21

what does negative NPSH require?

Answer 21

priming

Question 22

Name four types of heads

Answer 22

• pressure head
• static head
• friction head
• total dynamic head

Question 23

define pressure head

Answer 23

-the total head (or pressure) that the pump provides at the outlet or is required to work against.

Question 24

define static head

Answer 24

-the vertical distance a pump lifts water and includes both the lift and the suction

Question 25

define friction head

Answer 25

the energy losses associated with the pipe walls, fittings and instrumentation

Question 26

define total dynamic head

Answer 26

the pressure head + the static head + the friction head. Accounts for all head losses throughout the system.

Question 27

define braking power

Answer 27

the amount of energy or power applied to the pump when it is in operation.

• the larger the pump, the greater the power requirements
• generally the pump rating

Question 28

what are the two pump ratings for braking power?

Answer 28

• watts

- horsepower (hp)

Question 29

name the 7 keys to extending pump life

Answer 29

1- never overwork your pump
2- if you have a backup pump, rotate their in-service use periodically
3- to not subject the pump to incompatible fluids
4- retain and regularly service the suction strainer
5- do not operate the pump if water is not able to flow out of it
6- reduce the amount of pump vibration by dampening the unit
7- service the pump regularly