12) Drinking Water Treatment

what are things in water that we cannot have? examples of each?

pathogens (viruses, bacteria, protozoa), debris (minerals, ions, sand, dirt), organic matter (decaying material)

what is important about pathogens in water? (difference)

some pathogens require many particles of virus to get sick, others only require some

how did addition of chlorine affect the levels of pathogens in water?

decrease

what are the three types of guidelines that raw water must be treated for?

physical, chemical, and biological

what are examples of physical guidelines?

total solids, colour, turbidity, taste, odour

what are examples of chemical guidelines?

pH, alkalinity, hardness, total dissolved solids, total organic carbon, biological oxygen demand, chemical oxygen demand

what must be removed from drinking water?

pathogens, turbidity, colour, taste, odour, organic matter, and other contaminants

what must be removed from waste water?

BOD, COD, pathogens, nutrients, organic matter, contaminants

drinking water must be ____?

safe for human consumption

waste water must be ____?

safe to return to rivers/lakes, won’t affect wildlife and minimize ecological impacts

what are alternative sources of raw water?

ocean water, saline groundwater, wastewater

what is involved in conventional drinking water treatment?

screens, flocculation, sedimentation, filtration, disinfection, distribution

what do screens do?

keep out fish, mussels, large particles form coming into facility

what is flocculation/coagulation?

coagulants are added that bind and neutralize particles and organic matter to creat flocs

what are flocs? what happens with them?

coagulated pieces of organic matter, coagulants are positive because organic matter is usually negatively charged

what are examples of coagulants?

aluminum sulfate and ferric chloride

what is the flocculation mechanism?

particles are negatively charged and attract positive ions around them create the stern layer, then negatively charged ions create the double layer

why are coagulants added? what is the result?

to increase the ions dissolved in solution, which compresses the electrical double layer and reduces the repulsion forces

what is sedimentation?

large flocs settle at the bottom of tanks, and clear water is collected at the top of the tank

what is filtration?

small particles and pathogens are filtered out

what are examples of filter media?

sand, anthracite, activated carbon

what is activated carbon? what are they used for?

adsorbs organic compounds and remove organic matter and trace contaminants (pesticides, taste, odour)

what is geosmin?

molecule produced by cyanobacteria and actinomycetes, can be tasted at only 5ng/L, can be removed with powdered activated carbon

what is methylisoborneol?

has muddy taste, can be tasted at only a few ng/L

what is disinfection?

chemical disinfection and UV light are applied to water to inactivate pathogens

what are common chemical disinfectants?

chlorine (HOCl), combined chlorine (ammonia + chlorine = NH2Cl), chlorine dioxide (ClO2), ozone

what happens after chemical disinfectants are added?

water is sent to a storage tank to allow disinfectants to react and inactivate pathogens

what are the inactivation goals for protozoa and viruses?

99.90 % and 99.99 % respectively

what is pathogen inactivation dependent upon?

disinfectant concentration and contact time with the pathogen

list the chemical disinfectants in order of decreasing oxidizing strength

ozone, chlorine dioxide, hypochlorous acid, monochloramine

what is chlorine as a disinfectant? extra info?

HOCl, pka=7.5, chlorine is not stable at high concs so it must be produced on site

what is combined chlorine as a disinfectant?

series of reactions between chlorine and ammonia, mostly used as a residual disinfectant for the distb system

what is info about UV light?

200-400nm, disrupts DNA in microorgs to prevent replication, fast disinfection (10 secs)

what is distribution?

water can travel through pipes up to 5 days, chlorine residuals and sustained water pressure protects treated water

what are examples of disinfection byproducts (DBP)?

trihalomethanes, haloacetic acids, ozone, chlorine dioxide, combined chlorine

which DBPs does chlorine disinfection primarily result in?

trihalomethanes, haloacetic acids

true or false: the most regulated DBPs are the most toxic

false, the most toxic are usually not regulated (not good)

what are some associated health risks from DBP exposure?

increased risk of bladder cancer, low birth weight and preterm delivery

explain the tradeoffs of disinfection

acute risk are the pathogens that cause waterborne diseases, chronic risks are long term exposure to low level concentration of DBP, acute risks are greater than chronic risks so we disinfect

what is information on using saline waters to source freshwater?

energy intensive and very expensive, use on oceanic or saline groundwater in areas with limited access to freshwater

what is membrane technology?

water can be purified by passing or forcing it through a membrane with small pores, permeable components go to product stream and impermeable components go to waste stream, membranes need significant pressure to drive water across membrane

what are disadvantages of membrane filtration?

membranes can fail to filter water after time and need to be cleaned with disinfectants, then may degrade as reaction to disinfectants, energy and cost intensive, 1/3 of water is wasted, DBPs pass through

what is information about using waste water effluents as freshwater source?

can be reused in agriculture or potable water industrially, public acceptance is a big component

what is involved in the wastewater reuse treatment process?

microfiltration, reverse osmosis, advanced oxidation

what is advanced oxidation processes (AOP)?

UV light and an oxidant (H2O2, O3)

what does AOP do?

generate OH radicals that react with organic contaminants to break them down to CO2 (gets rid of everything else by oxidation)