Water Treatment Technologies Flashcards
First law of ecology
everything is conected to everything else
can’t be removed through filtering
dissolved inorganic matter
examples of dissolved inorganic matter
® Minerals leaching into groundwater leading to hardness, alkalinity, and other mineral contents
® Fertilizer runoff, mostly phosphates, nitrate, and sulfates
® Industrial discharges of all kinds, especially from metal finishing trade
® Salinity (principally chlorides) from sea water or saline ground water intrusion
® Natural impurities from decay of vegetable and animal matter
® Domestic waste, general biological debris and decay products, soap, detergents
® Industrial discharges (e.g. food processing and intensive agriculture, tanning, papermaking, and organic chemical
industry)- fats, oils, and solvent
® Residues of pesticides
Dissolved organic matter
examples of suspended impurities
• Colloids (organic and inorganic: clay, and iron or manganese oxides)
• Suspended Inorganic
• Suspended Organic
(Plant and animal particles; Industrial and domestic products)
sources of colloids
® Industrial wastes from e.g. china clay or paper processing
® A component of sewage solids
examples of suspended inorganic impurities
sand, Industrial materials from coal washings, mining wastes, lime
and other sludge, oxide dust, fly ash, flue washings, etc.
living matters impurities
• Microorganisms
® Algae, viruses, protozoa, micro-fungi, etc.
® Occurrence is promoted by nutrients and favorable breeding grounds (e.g. domestic sewage)
® Exposure to light promotes algal growth
® E. coli is a common contaminant tested
• Larger life
® Fish, worms,crustaceans, insect larvae, etc.
® Occur naturally and may breed in large numbers where food is plentiful
® Aquatic plants, floating and rooted
gases which occur in all natural waters
o2 and co2
underground sources contain this gas
high co2, h2s (from volcano)
can result from biological decay from industrial discharge
NH3
gas which is often dosed deliberately
Cl2
algal growth effect on gas
removes co2 and raise 02 to supersat in daytime
T or F: water treatment method would depend on nature of impurities
true
T or F: dissolved impurities and living matter can be removed by filtration
false, only suspended matter can be removed
microorganisms: must disinfect
commonly involved in removal of suspended solids and color and also in bacteria removal
sedimentation
coagulation
filtration
Passing the water through a layer of sand or other material that retains the suspended solids
Filtration
limitations of filtration
- Capacity of the sand to remove impurities is compromised
- Backwashing (reversing the flow) is recommended so that the filter would not clog
Permitting water to remain quiescent in large settling basin so
that the suspended solids may settle to the bottom
Sedimentation
T or F: Sedimentation can remove dissolved matter and suspended matter that are too small
false
involves coagulants ie aluminum sulfate –most used and effective
coagulation
mechanism of coagulants
(Coagulants: certain chemicals applied to the water wc produce an insoluble gelatinous and flocculent precipitate and precipitate absorbs and entraps the suspended solids in the water and thus hastens their sedimentation)
bacteria removal vs solid
bacteria need final disinfection (with chlorine or other acceptable agents to ensure destruction of bacteria that may cause disease)
how many minutes should bacteria be hoild?
3-5 minutes starting from time bubbles form
method of removal or Neutralization of Tastes, Odors, Objectionable
Minerals, and Dissolved Gases
aeration, treatment with certain chemicals
copper sulfate to control algae) and activated carbon (carbon absorbs toxins, remedy water with odor and taste
exposing water in thin films or droplets to the o2 of atmosphere to volatize or vaporize organic conaminants
aeration (to remove volatile compounds esp pesticides wc cannot be removed by filtration)
How to remove hardness or softening
ion exchange
membrane filtration such as reverse osmosis or nanofiltration
Common treatment processes for surface water source
aeration (air stripping)
disinfection
a waterfall aeration process wherein raw water trickles over a medium within a cylinder to mix water and air
packed tower aeration
used to control spread of communicable water diseases; kills pathogenic microorganisms found in drinking water
disinfection
effects of disinfecting agent in water supply
- bacterial: capacity to destroy pathogenic microoganisms in a given treatment process
- residue/remnant: ability to disinfect water that is re-contaminated in the
distribution system due to seepage of pathogens into the pipes
Things to consider in residue/remnant effect
- Handling is an important consideration on how water can
be contaminated again. - a property that is unique to chlorination (Residual chlorine is important in order to address the contamination that is acquired as the water passes from the source to its final destination since pipes that carry
water can also contaminate it)
Factors affecting effectiveness of disinfection
- Contact duration between disinfecting agent and pathogens
- Nature and concentration
- Dosage and strength of disinfecting agent
- Characteristics or condition of water during disinfection
Conditions for effective disinfection:
- Low Suspended Solids (1 mg/L)
§ Suspended solids may prevent the action of disinfecting agents with the pathogens - Low Organic Matter and Other Oxidizable Subs
§ May react with disinfectants and reduce the effect the
disinfecting agents have on the pathogens
most widely used disinfectant for water supplies
chlorination (min contact time: 30 minutes; residual must be 3-5 ppm)
treatment method with residue effect
chlorination
When is the best time to put chlorine in drinking water?
afte three processes
Properties of chlorination
- Poisonous, corrosive
- 2.5 times heavier than air
- Greenish yellow gas
- Fatal if inhaled in large quantities
- Sharp, suffocating
odor - Causes irritation to mucus lining of
the lungs
commercial preparation of chlorine
- Liquid chlorine
- Gas chlorine
- High test hypochlorite (HTH), granular (75%)
- Bleaching agent, NaOCl
§ Cannot be used since it has detergent and not pure chlorine
Another method of disinfection which uses a strong oxidizing agent wc is naturally occurring component of fresh air and serves as protective layer produced by the reaction between UV rays of sun and earth’s upper atmosphere
ozonization
T or F: ozone is a very reactive and unstable gas with a short half-life before it reverts back to oxygen
true
*Most powerful and rapid acting oxidizer talo niya cl (all bacteria, mold, yeast spores, organic material,
and viruses)
Ozone is usally used on
® Microflocculation ® Viral inactivation ® Turbidity reduction ® Bacterial disinfectant ® Taste, odor, and color removal ® Iron and manganese oxidation ® Organics removal
Ozone concentrations for inactivation
- 0.5 - 0.6 mg/L: 99.9% enteric viruses
- 1.1 mg/L: 99.99% Cryptosporidium oocysts
- 0.5 mg/L: G. lamblia
uses corona discharge principle
ozone genration
Explain corona discharge principle
SEE DIAGRAM PUTA
- Dry air or oxygen is passed between high-voltage electrode and ground electrode separated by a dielectric material
- In excess of 80% of the applied energy is converted to heat
that, if not rapidly removed, caused the ozone to decompose
method of disinfection which uses oxidizing and germ-killing effect through UV lamp
UV Radiation
*most natural purification and disinfection principle
How does UV radiation inactivate pathogens
destroy DNA thus preventing replication
Most sensitive to UV radiation are viruses and bacteria in vegetative forms such as:
- Salmonella typhosa
- Mycobacterium tuberculosis
- Vibrio cholerae
- Hepatitis virus
- Shigella dysenteriae
(higher doses: g lamblia cysts and cryptosporidium oocysts)
T or F: spores need higher doses of UV to be destroyed
true
germicidal lamp that converts electrical power into UV-C
UV Generators
Membrane Filtration Processes
• Feed (Solution which enters the system and is pressurized)
• Permeate (Solution (usually purified water) which passes through the
membrane and is collected for use)
• Concentrate (brine, retentate- Solution, which exists from the system, that has not passed
through the membrane; Enriched in particular rejected material)
• Applications of Membrane Filtration
- Suitable for removal of particulates from pre-treated water in
the range of 0.1-100 micrometers
§ Provided that the total suspended solids do not exceed 100 ppm
one of the most important membrane process; a pressure drive process that retains virtually all ions and passes water
reverse osmosis
*effectively removes most organics, bacterial and particulate matter and also inorganic contaminants with rates of 60-99%
Pressure applied in reverse osmosis must exceed what?
osmotic pressure of salt solution against semipermeable membrane leaving salts behind, only pure water can pass through the other side
final product of reverse osmosis
purified water, beneficial minerals can be removed
process that uses semi-permeable membranes to separate macromolecules in solution; applied to municipal systems and removes organic contaminants
ultrafiltration
important factors in retention in ultrafiltration
size of solute
molecular shape of solute
Ultrafiltration vs reverse osmosis
membranes have looser pore structure than reverse osmosis
• Membrane properties involved in ultrafiltration
• Available in cellulose, acetate, polysulfone, acrylic, noncellulosic polymers
• Have been prepared from polymers such as: polycarbonate,
polyvinyl chloride, plolyamides, polyvinyl fluoride
Applications of ultrafiltration system
- Municipal water treatment plants (both surface and groundwater supplies)
- Removal of total organic carbon, trihalomethane and color
- NF membranes exhibit as high as 40% rejection of salts (May react with disinfectants and reduce the effect the disinfecting agents have on the pathogens)
nanofiltration involves water softening using what
low-pressure reverse osmosis membranes
nanofiltration softening and organics removal is usually done on
low total dissolved solids and slightly brackish water
molecular weight cut off membranes for nanofiltration
<200-500 as opposed to tight RO membranes
other characteristics of nanofiltration
• Rejects hardness
• Repels bacteria and virus
• Removes organic-related color without generating undesirable
chemical compounds (e.g. chlorinated hydrocarbons)
Distillation process
® Water is heated to boiling point then changed to gas, leaving
non-volatile impurities
® Water is cooled then changed once more to water that is now free from dissolved and dissolved matter
® Distillation process may retain 0.3% to 0.5% of water impurities after treatment
® Bacteria may re-colonize on the cooling coils during inactive
periods
Impurities removed by distillation
- Almost all impurities from water (99.5% of impurities)
- Microorganisms
- Dissolved solids
- Nitrate
- Most organic compounds
- Sodium
- Heavy metals
- Hardness
- Radionuclides
T or F: any form of volatile organic contaminants and certain pesticides can be rmoved by distillation
false
uses of distillation
see treated water quality
- Small scale application in laboratories
- Preparation of purified water in pharmacy for injection
- Production of potable water from sea and brackish water
water softening uses
ion exchange process (one type of ion contained in water is absorbed into an insoluble solid material and replaced by an equivalent quantity of another ion in the same charge)
resin used in ion exchange process has what
sodium ion (when hard water passes, it exchanges with calcium and magnesium ions; used again for regeneration)
• Uses of ion exchange process:
- For upgrading municipal or private water in industry
- Water softening
- Purification of boiler needs
Why must hard water be softened?
- Interferes with all types of cleaning tasks
- Dishes and glassware washed with hard water may be spotted when dry
- Causes films on glass shower doors, walls, and bath tubs
- Hair washed in hard water may feel sticky and look dull
- Scale build up in hot water heater
- Scale deposits corrode and clog plumbing
Impurities Removed by Activated Carbon (AC) Filters
• Organic chemicals that cause taste, odor, color problems, mutagenicity, toxicity • Chlorine and chlorination by-products • Inorganic such as arsenic, chromium, mercury • Pesticides and solvents • Polychlorinated biphenyls • Polycyclic aromatic hydrocarbons • Radon • Toxic contaminants
Impurities Not Removed by Activated Carbon (AC) Filters
• Microbes • Sodium • Nitrates • Fluoride • Hardness • Lead and other heavy metals are removed only by specific types of AC filter
(See exposure time and effect on bacteria)
(See exposure time and effect on bacteria)
