Lecture 10 Pt 1 and 2: waste water treatment

Coastal water pathogens

infectious hepatitis, guardia, toxoplasma, vibrio sp.

Pathogens in wastewater and drinking water

salmonella, shigella, e. Coli, vibrio cholerae

autochthonous

indigenous water column organisms

allochthonous

transient, harmless or pathogenic water organisms

coliforms

bacteria naturally present in the environment, indicators of harmful bacteria’s presence

water

quality, 8-9 DO is good water and below 4 is gravely polluted

biochemical oxygen demand (BOD)

measures amount of O2 required for aerobic degradation of organic material in a water sample

BOD5 test index

index of the pollution potential of an organic pollutant, higher the number more polluted the water is

BOD5 test

fill 300mL airtight bottle with P diluted wastewater sample, can now add commercial seed starter, measure initial DO then incubate for 5 days at 20 degrees and measure second DO

BOD equation

(D1-D2)/P

value of the BOD test

estimate wasteloading to treatment plants, evaluate efficiency of treatment, predict effect of effluent releases on DO in the receiving stream

Pollution dispersion in a stream

where its’ dumped is the decomposition zone then septic zone (no fish) then recovery zone and back to normal clean water

aquatic ecosystem health

balance between oxygen and reduced organic nutrients

routine environment monitoring

BOD, COD, Free ammonia, phosphorus

chemical oxygen demand (COD)

amount of O2 consumed in complete oxidation of organic matter, amount of oxygen required to oxidize chemical organic matter

COD and BOD when recalcitrant compounds are present

the COD will be higher than the BOD if a recalcitrant compound is present in the water

COD test

acidic conditions, uses strong oxidizing agent like potassium dichromate to oxidize organic compounds, takes a few hours

potassium dichromate

used in COD test, is incredibly strong oxidant

objectives of municipl wastewater treatment

remove and reduce nutrients, remove and inactivate pathogens, reduce organic carbon content to reduce BOD

Jean R. Marcotte plant

in Montreal, is the largest in North American and third largest in the world, treats 50% of the provinces wastewater

preliminary treatment

protects equipment downstream by filtering with screens to remove solids and large sticks/animals, bar screen, grit chamber, and mesh screen

comminutor

across flow path in preliminary treatment shreds solids to around 8mm

primary treatment

physical and chemical process, slows wastewater so solids can settle and adds flocculants to assist, removes 90% of organic matter

Alum and FeCl3

primary treatment flocculants

wastewater clarifier

sediment tank, scrapes grease and foam from top and lets sludge settle to the bottom where its taken from drainage pipe, top fluid flows over the edge into secondary treatment

Secondary treatment

Microbiological process with activated sludge, trickling filter, and sludge digester

aerobic secondary treatment processes

nitrification, pathogen removal, nutrient removal

activated sludge (aerobic)

reduce 90% BOD in 4-8 hours, needs a lot fo O2, any nutrients are converted to biomass, flocs form during aeration and settle out after, recycle the settle flocs

activated sludge: decreasing BOD of wastewater

Addition of oxygen encourages aerobic bacterial growth which uses up nutrients

activates sludge: NH4

toxic and at high concerations in wastewater, but in tank nitrification happens which converts the NH4 into NO2 (nitrosomonas) and NO3 (nitrobacter)

activated sludge: pathogen removal

pathogens are trapped in flocs and consumed by predators because the conditions for pathogen growth are very bad

activated sludge: removal of nutrients

after settling cleaner water flows out, some sludge recycled back to tanks but most sent to anaerobic digester or discarded

sequence batch reactor

variation of activated sludge, sequence of fill, react, settle decant, fill and repeat

floc microbiology

filamentous no cardia spp. form flocks with zoogloea, flavobacterium, and pseudomonas, and ciliates, amoebas, rotifers, and nematodes prey on bacteria which helps maintain structure

poorly settled floc causes

low aeration, low sulfide and acidic organic substrates, not enough predators

sludge bulking

BOD very high relative to nutrient content extracellular polysaccharides form causing the flocs to get way out of balance

floating sludge bulking causes

hydrophobic/porous organisms, dentirificaiton (gas), fats, oils and grease

bulking control

predation, chemical amendments, chlorination, re aeration

bulking

any settlement treatment when Filamentous organisms hold the flocs apart and preventing settling, causes high BOD in effluent

trickling filter (aerobic)

Waste water sprayed over layers of sand and gravel where biofilm has been formed, same principles as activated sludge, need to backwash

biofilms in trickling filters

algae and fungi but also bacteria, polysaccharides adhere, whole food web and micro environments

sludge digesters (anaerobic)

slow, batches, very expense, mixing zone at bottom then sludge and fluid zone then finally a biogas zone

low rate digestion

just layers in the bioreactor

high rate single stage digestion

is mixed and heated to speed up the process

high rate two stage digestion

two tanks both heated, then one has mixing and the second doesn’t mix and lets everything settle

high rate two phase digestion

two tanks but both are mixing and heated one is acid phase digestor and the second is methane phase digester

pros and cons of sludge digester

generate CH4, reduce organic material, can use sludge to fertilize, accumulate heavy metals, expensive, skilled workers, difficult to keep conditions right

sludge digester microbial process

denitirficaiton, fermentation and methanogenesis, CO2 converted to CH4 and H2S which are vented, fermentation yields heat, effluent has organic acids and recalcitrant organic compounds

sludge stabilization

digester brakes sludge to simple components and residual sludge, destroys pathogens, similar to dirt and is good fertilizer (except has heavy metals)

lime stabilization

chemical stabilization, dewater the sludge, change pH to very high to kill all microbes

secondary treatment effluent

can be released at this phase or sent to tertiary treatment or second round of secondary treatment

tertiary treatment

removes specific compounds, expensive and not always needed, nutrients are removed (phosphorus) and ins final clarifier

PO4 removal in tertiary treatment

precipitate PO4 then filter out with membranes, and biological removal step

Sewage ponds/lagoons

Sequence of ponds, need nice sun and land, simple and low cost

aerated lagoon

inexpensive, shallow with aerators on the surface to transfer air to basin for oxidation rections and mix to optimize contact with reactants

facultative sewage pond system

very shallow, aerobic and anaerobic zones, reduce BOD up to 95%, requires 7-50 days retention

Aerobic degradation

similar to sludge digestion effluent fluent dispersed into well drained soil for aerobic bacteria, have to remove sludge periodically

wetlands

natural wetlands purify the water and remove organic very very well (Florida)

artificial wetlands

construct wetlands to treat raw sewage, storm water, and other effluent, simple and low cost, provide habitats but uses a lot of land and need preliminary treatment, could release pollutants into the environment