Lecture 10 pt. 3: drinking water treatment

1) coagulation

Chemicals added to destabilize particles, rapid mixing and floc formation

aluminum sulfate and ferric chloride

added during coagulation

2) flocculation (sedimentation)

gentile mixing to promote contact, flocs form and grow and then sedimented

zeoturb

coagulant/flocculate made from biopolymer, environmentally safe but not as effective as other ones

3) filtration

layers of fine sand then gravel and coal then membrane filter

rapid filtration

used in the USA water moves through sand and activated carbon or anthracite coal to trap organic carbon, less effective in removing biological load

membrane filtration

series of membranes that get smaller and smaller remove a lot of biological load and particles

4) disinfection

kills all pathogens and removes chemicals and contaminants

chlorination

strong oxidant with residual activity, inexpensive and relatively safe

chlorine acceptable levels

80ppb in drinking water of chloroform, bromoform, bromodichloromethand and dichloromethane

chlorine alternatives

mono, di and tri chloromethanes

trihalomethanes

residual activity good, produced by chlorine, but carcinogen produced, do not want this

ozone

o3, fully kills biological organisms and neutralizes fertilizers, does not produce THMs but can produce bromate

sodium bisulphite

at end of ozonation added to neutralize ozone leftover to not give water weird taste

ultraviolet light

effective and no residual activity but hard to optimize, purely physical uses photolysis, leaves no taint but effectiveness decreases with turbidity

bacterial pathogens

salmonella, shigella, e. Coli, vibrio cholera

viral pathogens

enteric viruses, hepatitis A, poliovirus, rotavirus

protozoal pathogens

entabmeoba histolytica, giardia, cryptosporidium parvum

algal pathogens

red tides, dinoflaggelates

coliforms

enteric rod shaped gram negative non spore forming bacteria that can ferment lactose, presence indicates fecal contaminants

Most probable number test

presumptive test (gas produced in lactose broth) confirmed test (gas production in brilliant green lactose bile broth) and complete test (plating on Levines EMB agar)

filter plate method

filter the water through and then plate the filter and screen for bacterial growth

direct count method

grid on a microscope and count how many bacteria

drinking water guidelines

test for e. Coli not everything (that would be very hard)

maximum acceptable concentration

for e. Coli or total Coliforms is none per 100mL sample

MAC for other pathogens

cannot establish for other pathogens, can evaluate cyst and oocyst counts but thats it

Lead guideline

5ppb

arsenic guideline

10ppb

nitrate guideline

45ppb

mercury guideline

1ppb