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MICROBIOLOGY^ OF^ WASTE
TREATMENT
A.^ Treatment^ process 1.^ Common^ characteristic
โ^ complex^ interactions,^ multi
โsubstrate,^ multiโspecies
interactions. โ^ Aerobic^ treatment^ systems
are^ less^ well^ understood^ than
the^ less^ widely
used^ anaerobic^ treatment^
systems,^ which^ are^ microbiologically
better
understood.2.^ Most^ (80%)^ are^ small^ treatment
facilities^ (<1^ MGD),^ and^ most
(>85%)^ have^ at
least^ secondary^ treatment .3.^ Wastewater^ treatment
in^ U.S.^ began^ in^ beginning^
of^ the^ last^ century.
Filtration^ along^ with^ chlorination
was^ the^ major^ reason^ for^ decline
of
mortality^ by^ bacterial^ pathogens
such^ as^ typhoid,^ cholera^ and
other
waterborne^ diseases.
MICROBIOLOGY^ OF^ WASTE^ TREATMENT^ โข^ In^ the^ U.S.^ in^ the^ 1800s,
population^ increased^ from
5M^ to^ 75M^ (currently
300M) โข By the^ early^ 1900s^ many^ cities
had^ sewer^ systems^ to^ collect
wastewater^ and
โtreatmentโ was^ limited^ to^
dilution,^ removal^ from^ source,
irrigation^ foragriculture. โข Driving^ force^ for^ centralized control^ and^ treatment^ was public health,^ cholera, typhoid,^ etc. โข First biological^ treatment, trickling filter^ in^ Madison,^ WI in 1901. โข First activated^ sludge^ plant, 1916, San^ Marcos,^ TX
Definitions:COD^ โ^ Chemical^ Oxygen^ Demand,
used^ to^ determine^ the^ total
organic^ carbon^ in^ a
wastewater^ of^ sample. Defined^ as^ the^ amount^ of^ oxygen
needed^ to^ oxidize^ the^ organic
carbon^ in^ the
sample^ completely^ to^ COand^2
H^ O^ in^ the^ presence^ of^ potassium^2
dichromate:
organics^ +^ oxygen^ +^ KCr^2
3+Oto CO+ H O + Cr 2 7 2 2
Total^ solids^ โ^ includes^ both
organic^ and^ inorganic^ material
which^ results^ from the
mass^ remaining^ from^ a^ water
or^ wastewater^ sample^ after
drying^ in an^ oven^ at
low^ temp.^ [Biomass]Suspended^ solids^ โ^ that^ portion
which^ is^ retained^ on^ a^ glass
fiber^ filter^ and^ dried.
Dissolved^ solids^ โ^ that^ portion
which^ goes^ through^ the^ glass
fiber^ filter^ and^ dried.
Volatile^ solids^ โ^ that^ portion
of^ total^ solids^ which^ are^ lost
on^ burning^ at^ 500ยฐC
[organic^ fraction]
Table^ 7.2.^ Typical^ characteristics
of^ domestic^ wastewater^ (mg/L)
ConcentrationParameter^
strong^ medium^ weak
BOD^5
COD^
1,000^500
Organic^ N^
NHโN^3
Total^ N^
Total^ P^
Total^ solids^ [biomass]^
1,200^720
Suspended^ solids^
Major^ objectives^ of^ waste^ treatment1.To^ remove^ pathogen^ and
parasites.
2.To^ reduce^ the^ BOD^ (organic
content)^ of^ wastewater.
3.To^ reduce^ levels^ of^ major
nutrients,^ N^ &^ P^ which^ can
adversely^ affect
receiving^ waters.
Aeration^ tank Primaryclarifier
Final clarifier wastewater
effluent recycle Excesssolids
Aeration^ tank Primaryclarifier
Final clarifier
wastewater
effluent recycle Excesssolids
Activated^ Sludge^ unit^ process โข There^ are^2 main^ goals^ of^
the^ aerobic^ activated^ sludge
process
1.^ biological^ oxidation^ of
the^ readily^ degradable^ organic
fraction
2.^ flocculation^ and^ settlement
of^ the^ biomass^ (sludge)^ from
the^ treated
effluent.3. Equation^ describing^ activated
sludge^ process^ โ^ simplest^ description
C^ H^ ON^ +^ 9Oโโโโโโโโโ>^1019
C^ HO^ N^ +^ 5CO+^ H^ O^57
This^ describes^ "waste^ stabilization",
e.g.^ conversion^ to^ CO^2
It^ is^ โstabilizedโ because^ it^ no
longer^ exerts^ an^ โoxygen^ demandโ
4.^ Operation^ of^ process^ โ^ defines
a^ set^ of^ conditions^ for^ the^ successful organisms. e.g. there is^ considerable^ selective^ pressures
operating. a.^ heterogeneous^ waste^ โ^ complex
polymers,^ proteins,^ carbohydrates,
lipids b.^ short^ detention^ time,^ rapid
dilution^ rate c.^ rapid^ settling^ ability5.^ Hence,^ organism^ population
shoulda. be nutritionally versatile^ and^ be^ heterogeneous^
population b.^ rapid^ growers,^ short^ generation
time c.^ form^ flocs^ and^ attach^ [prevents
washout^ and^ lessens^ predation] 6.Microbial^ numbers^ are^ high both^ in^ numbers^ and^ diversity.
Meaningfulness^ of^ census data^ is^ limited^ given^ the^ limited
detection^ methods,^ table^ 8.1. 7.Protozoaa.^ important^ for^ effective
operation^ of^ the^ unit^ process b.^ not^ just^ a^ consequence^ of^ the
system,^ but^ a^ desired^ result.^
They^ function^ as "polishers"c. e.g. presence^ of^ high^ numbers^ of^ rotifers^ associated
with^ low^ BOD. d.^ Table^ With protozoaWithout^ protozoaBOD (mg.L)^15 60 COD 130 (^220) org N 8 17 susp.^ solids^30
(^1006) bact. numbers 5^130 (x^10 /ml)
Flocculation^ and^ settling โข Flocsare^ loose^ aggregates^ of^
microorganisms,^ protozoa,^ inorganic
matter^ in^ a^ matrix^ of extracellular^ polymers. โข^ Good^ flocculation^ and^ settling
are^ important^ for^2 reasons1. effluent quality โ suspended^ solids^ removal,^ BOD^ removal,
90 โ^ 99%^ reduction^ in bacterial^ numbers.2. high^ substrate^ removal^ โ^ in^ aeration
unit^ because^ it^ is^ recirculated
into^ the unit,^ this^ maintains^ an^ active^ population. โข Poor settling^ โ^ the^ most^ frequent^ problem
encountered^ in^ waste^ treatment
plants.
-^ Causes^ of^ poor^ settling1.Poor^ floc^ formation โ Dispersed
growth,^ no^ floc^ formation,^ no
settling^ of microbes; โ^ waste^ is^ too^ concentrated^ or
detention^ time^ is^ too^ short.
2.^ Pinโpoint^ flocs^ โ^ flocs^ too
small,remain^ in^ suspension.^ Can
be caused^ by temperature^ fluctuations.3. Density^ problem^ โ^ rising^ sludgeSolids^ rise^ to^ surface^ in^ settling
tank,^ get^ washed^ out^ causing
poor^ effluent^ quality. โ^ nitrification^ in^ aeration^ tank:
โโ NHโโโ>NO โโโ>NO^3
โ^ with^ denitrification^ in^ settling
โ basin: NO โโโ>N^ O^ โโโ>^ N^322 โ remove sludge before denitrification^ can^ occur โ manage cell concentration and dissolved^ oxygen^ in^ aeration tank โ^ anaerobic^ sludge^ โ^ if^ left^ too
long,^ anaerobiosis^ will^ take^ place
in^ the^ settling basin^ with production^ of^ CO^ ,^2
CH^ ,^ H^ S.^42
Bulking^ sludge^ โ^ Major^ operational
problem^ with^ the^ others^ being
relatively^ minor
problems. โข^ Very^ different^ from^ 'rising^ sludge',
bulking^ sludge^ is^ a^ problem^ of
poor^ compactability SVI^ ml/g^ =^ SV^ x^1000 MLSSSVI = sludge volume^ index,^ SV^ =^ vol^ after^30 min
settling^ of^1 L MLSS^ =^ mixed^ liquor suspended^ solids,^ dry^ weight^ of^ 1Lnormal SVI = 50 โ^150 ml/gbulking SVI = 200 โ2000ml/g
-^ Bulking^ is^ frequently^ associated
with^ high^ numbers^ of^ filamentous
organisms^ that^ are normal^ inhabitants^ of^ activated
sludge,^ but^ the^ cause^ and^ effect is
difficult^ to^ establish.^ On the^ one^ hand,^ you^ see^ lots^ of^
filaments^ in^ bulking^ sludge.^ On
the^ otherhand,^ do^ the organisms^ create^ the^ condition
or^ do^ the^ conditions^ select^ for
the^ organisms?
Table^ 9.2^ Comparison^ of^ physiological
characteristics^ of^ flocโformers
and^ filamentous
organisms
Bacteria Characteristics^
floc^ former^ filamentous Maximum^ substrate^ uptake^ rate
high^ low Maximum^ specific^ growth^ rate
high^ low Endogenous^ decay^ rate^
high^ low Decrease^ in^ specific^ growth^ rate
from^ significant^ moderate low^ substrate^ conc.Resistance^ to^ starvation^
low^ high Decrease^ in^ specific^ growth^ rate
due^ significant^ moderate to^ low^ DOPotential^ to^ sorb^ organics^ under
excesshigh^ low Ability^ to^ use^ nitrate^ as^ electron
acceptor^ yes^ no Exhibits^ abundant^ uptake^ of^ P
yes^ no
-^ Removal^ of^ pathogens,^ parasites,
viruses^ =^99 to^ 99.9% 3 major^ mechanisms1.^ they^ do^ not^ compete^ or^ grow^ well^ under^ the^ given^ conditions2. they are consumed by^ protozoa3. they flocculate and settle^ out
-^ Current^ wastewater^ quality^
issues pharmaceuticals and personal^ care^ products โ antibiotics, hormones,^ surfactants,^ enzymes,treatment plants were not^ designed^ for^ these^ products โ extremely low concentrations,^ are^ they^ seen^ as^ substrates?
How^ do^ the^ drugs^ get^ into^ the^ water?People^ take^ pills.^ Their^ bodies^ absorb^ some^ of^ the^ medication,^ but^ the^ rest^ of
it^ passes^ through^ and^ is^ flushed^ down the^ toilet.^ The^ wastewater^ is^ treated^ before
it^ is^ discharged^ into^ reservoirs,^ rivers^ or
lakes.^ Then,^ some^ of^ the^ water is^ cleansed^ again^ at^ drinking^ water^ treatment
plants^ and^ piped^ to^ consumers.^ But^ most
treatments^ do^ not^ remove all^ drug^ residue.And^ while^ researchers^ do^ not^ yet^ understand
the^ exact^ risks^ from decades^ of^ persistent
exposure^ to^ random combinations^ of^ low^ levels^ of^ pharmaceuticals,
recent^ studies^ โโ^ which^ have^ gone^ virtually
unnoticed^ by^ the^ general public^ โโ^ have^ found^ alarming^ effects^ on
human^ cells^ and^ wildlife. ''We^ recognize^ it^ is^ a^ growing^ concern^
and^ we're^ taking^ it^ very^ seriously,''^ said
Benjamin^ H.^ Grumbles,^ assistant administrator^ for^ water^ at^ the^ U.S.^ Environmental
Protection^ Agency. Members^ of^ the^ AP^ National^ Investigative
Team^ reviewed^ hundreds^ of^ scientific reports,^ analyzed^ federal^ drinking water^ databases,^ visited^ environmental
study^ sites^ and^ treatment plants^ and^ interviewed
more^ than^230 officials, academics^ and^ scientists.^ They^ also^ surveyed
the^ nation's^50 largest^ cities^ and^ a^ dozen
other^ major^ water providers,^ as^ well^ as^ smaller^ community
water^ providers^ in^ all^50 states. Continued.
