ch 11 + 12: Disinfection + Pumps Flashcards
Define sterilization
the process where all microorganism are destroyed and thus, no longer in the system.
What are the concerns regarding sterilizing your water?
- 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
Define probiotics
healthy bacteria in the system maintain a natural balance and limit the growth of harmful bacteria
define disinfection
use commercially produced agents to destroy many specific organisms.
why use disinfection over sterilization?
disinfection does not discourage growth in a system, and the cost of implementing it is lower than with sterilization.
What three factors does the effectiveness of disinfection depend on?
1- the concentration/intensity of the disinfectant
2- the contact time
3- water quality parameters (incl. ph, temp, turb
name 4 methods of disinfecting your water
- hydrogen peroxide
- chlorination
- ozone
- UV
describe how hydrogen peroxide is a good disinfectant
- very effective at oxidizing water
- reacts with organic matter rendering wastewater ‘harmless’
describe the two concerns with using hydrogen peroxide as a disinfectant
- 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
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?
- 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.
UV light: what are some concerns with this system?
- 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
how does UV work?
it destabilizes organic material with light
name a few pros and cons for UV
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 ($)
-quartz sleeve must be periodically replaced ($)
what are pros of ozone?
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
what are cons of ozone?
- 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)
define a pump
a machine capable of adding energy to a fluid
NPSH: define
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)
positive NPSH
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.
what is another term for positive NPSH?
flooded suction
negative NPSH
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.
what does negative NPSH require?
priming
Name four types of heads
- pressure head
- static head
- friction head
- total dynamic head
define pressure head
-the total head (or pressure) that the pump provides at the outlet or is required to work against.
define static head
-the vertical distance a pump lifts water and includes both the lift and the suction
define friction head
the energy losses associated with the pipe walls, fittings and instrumentation
define total dynamic head
the pressure head + the static head + the friction head. Accounts for all head losses throughout the system.
define braking power
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
what are the two pump ratings for braking power?
- watts
- horsepower (hp)
name the 7 keys to extending pump life
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
