Professor Navarro B-tech level : Biological treatment of waste water and sludge

Figure 1 illustrates the water cycle in town ; in this course, we wil l study biological treatment applied to waste water and sludge purification, not to drinking water production. 1. Municipal waste water quali ty and discharge standard MWW quali ty is rather constant ; this board illustrates the average chemical composition od MWW and the discharge standard ( from “Pollution control acts, rules and notifications issues thereunder” , Central Pollution Control Board, May, 1998) Parameter unit Average value Discharge standard

in inland surface water

pH 7.5 to 8.5 5.5 to 9 Suspended Solids SS mg / l 150 to 500 100 BOD5 mgO2/l 100 to 400 30 COD mgO2/l 300 to 1,000 250 NH3 mgN/l 20 to 80 50 TKN mgN/l 30 to 100 100 Nitrate NO3

- mgN/l <1 10 P mgP/l 10 to 25 5 2. The necessity to remove BOD, ammonia, nitrates and phosphorus from waste water This board summarizes the origin and the toxicity linked to the presence of various chemicals in MWW. Undesirable compound C

Origin in MWW Toxicity or inconvenient for the receiving water

SS Wastes Turbidity, consumption of oxygen…

Organic carbon : BOD5

Organic matter Consumption of O2 in the medium

Ammonia Organic nitrogen

Ammonification of urea, proteins… Proteins, urea…

Consumption of O2 Toxic for fauna

Nitrates

Absent in MWW Present in water after nitrification of ammonia

Phosphorus

Organic matter and washing powders…

Eutrophication

3. General considerations about biological treatment 3.1. Total removal of carbon, nitrogen and phosphorus

MWW are biodegradable : - the ratio COD / BOD, called biodegradability ratio, is inferior to 3 ; - pH is neutral ; - there are nitrogen, phosphorus, and no toxic. Bacteria will be exploited for purification of MWW. They assimilate carbon (BOD), nitrogen and phosphorus according to the mass ratio : BOD / N / P = 100 / 5 / 1. Assimilation is the intracellular incorporation of a chemical in order to carry out anabolism. However, the ratio BOD / N / P of a MWW presents a large excess of nitrogen and phosphorus ; it can be for example equal to 100 / 20 / 10. It means that a simple assimilation doesn’ t allow to respect the discharge standard. Two other biochemical processes should be performed in order to remove enough nitrogen and phosphorus : - nitrification, and then denitrification, for total nitrogen removal ; - specific intracellular accumulation of phosphates, for total phosphorus removal. 3.2. The separation between biomass and treated water. Once the metabolism is performed, the exploited microbes must be separated from treated water ; there are two techniques : attached or suspended growth. The efficiency of these two technologies depend on the bacterial secretion of an extracellular polymer : figure 2. Biofiltration is performed in one step, but is a discontinuous process : when the medium is clogged, it must be backwashed. This medium both retains SS and is the place of biological purification of MWW. Figure 3 illustrates the structure of a biofilm. Suspended growth is a continuous two-step process : biological purification and then settling in order to separate biomass from treated water . Figure 4 illustrates a biofloc structure. 4. Activated sludge and suspended growth MWW is introduced in an aerated tank : biological purification takes place and flocculating biomass grows. A real food chain develops in this tank, responsible for purification, and including a large variety of organisms : - bacteria - protozoan - metazoan. The identification of these organisms allows to check the running of the process : some organisms are indicators of the treatment quali ty: figures 5 to 14. Figure 15 illustrates a food chain in an aerated tank. Figure 16 illustrates the flow sheet of an activated sludge process ; as biomass grows and circulates from the tank to the clarifier, sludge must be recirculated (in order to maintain a constant biomass concentration in the aerated tank) ; the sludge draw-off allows to remove the excess of produced biomass. 4.1. TKN and BOD removal Organic carbon is assimilated : it provides the cell with matter and energy ; these bacteria are chemo-organo heterotrophic and aerobic ; organic matter is oxidized with O2 and the reaction generates water and CO2. Ammonia and phosphorus are assimilated in different biochemical ways ; in definitive, ammonia is introduced in amino acids and proteins, phosphorus in proteins, ATP, nucleic acids…

In order to remove the nitrogen excess in MWW, nitrification of ammonia must take place in the aerated tank ; it is performed by chemo-litho autotrophic bacteria like Nitrosomonas and Nitrobacter, and generates nitrates. 4.2. Nitrates removal Nitrification produces nitrates, which induces eutrophication of the receiving water ; then nitrates must be removed. Chemo-organo heterotrophic bacteria carry out the denitrification : they need nitrates, but also organic matter ; oxygen inhibits the reaction : nitrates are the final acceptor of electrons and many bacteria prefer using oxygen (they can carry out both respirations). Nitrates are transformed into N2. The process presents two characteristics : figure 17 - mixed liquor is recirculated in an upstream zone : water inlet must contain organic matter (BOD is not assimilated yet) - this zone is anoxic : oxygen inhibits denitrification. 4..3. Phosphorus removal The excess of phosphorus is removed by a specific metabolism, carried out by bacteria li ke Acinetobacter, Moraxella…: figure 18 It is a two – step process : anaerobiosis then aerobiosis ; anaerobiosis means neither nitrates nor oxygen, while anoxia means only absence of oxygen. Anaerobiosis step : these aerobic bacteria are stressed, they excrete a quantity Q1 of P in the medium Aerobiosis step : they incorporate a quantity Q2 of P, and Q2 >> Q1. P is finally extracted from the plant in the same time than phosphated sludge (which treatment should be aerobic). Figure 19 illustrates a plant which removes BOD, N and P from MWW. 4.4. Bulking Bacteria growth can present three forms : - flocculating growth, which should be obtained for activated sludge process ; - dispersed growth which occurs when the activated sludge process is started (for the first weeks, before flocculation) ; - filamentous growth, also called bulking, which occurs with dysfunctions such as presence of toxic chemical in MWW, insufficient aeration of the tank…; this type of growth cause a sharp drop in the quality of treated water due to massive entrainment of SS outside the settling tank. Figures 20 to 25 ill ustrates the main filamentous bacteria responsible for bulking in MWW treatment. Their identification can help to know the origin of the dysfunction. 5. Aerobic attached growth : trickling filters, biofil ters, biodisks Among these three technologies, only biofiltration (figure 26) is an efficient process : it allows to remove both SS and BOD from MWW ; sometime, nitrification and denitrification can occur. Biofiltration is an expensive, discontinuous process ; it is well adapted to large variation of load, and can be implanted in specific geographic area like mountains… The medium can be either sand, or granular activated carbon, or polystyrene balls…on which biofilm takes place.

Trickling fil ters technology (figure 27) is quiet rare : biofilm is fixed on large pozzolan or plastic stones and SS are not removed from MWW ; it is often used as a pretreatment before activated sludge, for very concentrated industrial waste water (high BOD). Biodiscs technology (figure 28) is also rare : the biomass is attached to discs that turn around a horizontal axis and are partially bathed in raw water ; rotation brings the biomass alternately in contact with the water to be treated and the oxygen in the air. Discs are spaced 2 or 3 cm from one another and tun at 1 or 2 rpm ; they are 2 or 3 m in diameter and made of polystyrene ; they must be cover to protect them against harsh weather. This process consumes li ttle electrical energy. A downstream clarifier retains the excess sludge. 6. Extensive processes : lagooning Natural biological purification of pollutants can occur in water : in this way, many different metabolisms are involved ; in fact, the food chain is the same as the activated sludge one but the source of oxygen is photosynthesis and not artificial aeration. The Winograsky column illustrates all the nutritional types which can occur in a layer of water : figure 29. All these natural biological reactions are exploited in lagooning ; figure30 illustrates such a two-step process : in a first microphytes lagoon, SS settle, some fermentations occur ; on the surface, algae generates oxygen which allow aerobic metabolism like BOD removal and nitrification ; the second step consists in assimilation of nitrates and phosphates by macrophytes. This technology needs a lot of space (10 m2 / habitant). 7. Anaerobic bacterial growth for industrial waste water purification and sludge stabilization In anaerobic conditions, organic matter is reduced to methane CH4. This natural metabolism occurs in many different places, like in deep ocean, in the ruminants rumen… Because of the very slow growth of methane-producing bacteria and the cost of the industrial installation, it is applied for very high BOD load, i.e. for industrial waste water (agro-food) or for sludge stabilization in large plants. 7.1. Biochemistry of the process Figure 31 summarizes the different biochemical ways leading to methane : only some of these ways are used in a specific place (note that their should be competitions, for example for H2 between acetate- producing bacteria and some methane - producing bacteria). In a digester, the following ways take place : - acetogenesis OHPA (and not the homoacetic acetogenesis) - both methanogenesis. Methane – producing bacteria are archaebacteria, strictly anaerobic ; their generation time is very long (15 to 30 days). 7.2. Industrial waste water purification : suspended and attached growth Figure 32 illustrates a mixed digester (suspended growth) and settling tank : Analift (Degrémont) ; the degasification device is required to remove the occluded gas, which hinders settling, from the floc. It is suitable for concentrated effluents (distilleries…). The COD load varies from 3 to 15 kg / m 3 . d. Figure 33a il lustrates an attached growth on a support medium : the biofilm grows on a fixed medium, through which the water passes in upflow : Anafiz (Degrémont) ; it is suitable for relatively diluted effluents such as dairies, sweet factories…The COD load varies from 8 to 15 kg / m 3 . d.

Figure 33b illustrates an attached growth on fluidized bed : Anaflux system, Degrémont. The advantages of the process are : - no risk of clogging of the support - rapid start-up -compact unit - accommodation of considerable flow variation. It is suitable for effluents from breweries, canning factories… ; the COD load varies from 30 to 60 kg / m3 . d. 7.3. Sludge stabilization Biological sludge stabilization (reduction of the pathogenic organisms and of organic matter concentration) can be performed in three ways ; - aerobic process in a structure equivalent to the activated sludge : figure 34 - anaerobic process, number of steps depending of the load : figures 35 and 36 - composting : figure 37 Conclusion : the figure 38 summarizes all the biological processes applied to waste water treatment.

individual sanitation

drinking water treatment plant DWP

River

sludge

drinking water consumption

sewage treatment plant STP

Sewer

Figure 1 : Water cycle in town

end use ?

water table

Industries : agro-food, nuclear power plant, steel , iron and steel...

collective sanitation

subsoil

Caption :

raw water for DWP or industries

municipal and industrial waste water ;* the necessity to treat industrial waste water depends on its quality and the regulation

sludge

*

Bacteria secreting an Extracellular Polymer (polysaccharides, proteins…) : Zooglea ramigera, Pseudomonas aeruginosa…

Biofilm on a surface

Attached growth : biofilt ration : one step (no need to separate treated water and depolluting biomass) Applications : - for clear water to avoid rapid clogging of the granular medium : biological treatment of drinking water production (denitrification, iron removal…) - for turbid MWW : discontinuous process : fil tration, washing.

Raw water : biodegradable pollution

Biofilter : granular medium on which a biofilm is developing - SS removal - biodegradation ONE STEP

Treated water

Biofloc in a liquid medium

Suspended growth : two steps : biological purification of raw water by the flocculating biomass then separation of treated water and biomass : Applications : - for the most famous MWW treatment process : activated sludge

Tank : liquid medium containing flocculating biomass : biodegradation : FIRST STEP

Separation treated water / flocculating biomass : SECOND STEP

Treated water

Raw water : biodegradable pollution

Figure 2 : Attached and suspended growth in water treatment

DOC adsorption

Biofilm growth

Biofilm Support

Biofilm death

Biofilm particles

Water flow direction

Figure 3 : Sketch of a biofilm (Maul A., Vagost D., Block J.C., 1989)

13 µm

125 µm

Polymers linking microcolonies

Microcolony

bacterium (1 to 5µm) of the colony, linked by a polymer

Figure 4 : Model of structure microbial floc in activated sludge

Figu

res 5

to 1

4 : b

rief p

hene

tic c

lass

ifica

tion

of m

icro

faun

a in

act

ivat

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udge

Th

e co

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taxo

nom

ic h

iera

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is :

Kin

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: ani

mal

Su

b ki

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m

Bra

nch

Cla

ss

Sub

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s O

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Fa

mily

G

enus

Sub

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PR

OTO

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N

MET

AZO

AN

B

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Fl

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t fam

ous

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s in

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ivat

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udge

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a

A

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The

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Pl

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mon

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, M

onos

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Par

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, T

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, C

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lla

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ticel

la,

Car

ches

ium

, E

pisi

tylis

, O

perc

ular

ia

Eupl

ots,

As

pidi

sca

Rot

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s, G

astr

otri

chs

Nem

atod

es

In th

ick

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rs a

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e or

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w ;

for

each

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, are

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☛ a

sket

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e av

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the

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☛

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f the

mic

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nd th

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latio

n w

ith th

e pr

oces

s man

agem

ent

Figure 5 : Sketch of an organism belonging to the class of nematodes (branch of worms )

0.5 to 1 mm

Crown of cilia constituted by two rotatory discs.

Cuticle

Spurs

Telescopic body

Mastax (pharynx)

Figure 6 : Sketch of a metazoan organism * Sub kingdom of metazoa, branch of worms, class of rotifers, fifteen known genus * bacterio- or protozoophagous ; planktonic or fixed species ; low load and high sludge age : satisfying treatment eff iciency and nitrification

0.5 to 1 mm

Figure 7 : Sketch of a protozoan organism * class ciliate, sub-class of hypotr ichs (seven known genus, main are Euplotes and Aspidisca) * bacteriophagous ; adapted to the surface of the flocs, mobile ; low load and high sludge

Cil ia

Below view Lateral view

Dorsal fissures

30 to 60 µm

Figure 8 : Sketch of a protozoan organism * class of ciliate, sub-class of peritichs (six known genus) * bacteriophagous (free bacteria), fixed at the surface of the floc, low load, well a aerated medium

Peristome with cilia

Retractile peduncle

Macronucleus

Genus Episityli s (partitioned and non retractile peduncle)

Genus Vorticella (the diameter of the peristom is superior to the widest diameter of the body)

30 to 60µm

50 to 80µm

body

Apical cytostom Cil ia Nucleus

Figure 9 : Sketch of a protozoan organism permanent in microfauna of activated sludge * class of ciliate, sub-class of holotr ichs, genus Trachelophylum * adapted to the surface of the floc but no fixed and free swiming, bacterio- and protozoophagous ; high concentration of oxygen, moderate or high load .

30 to 50µm

50 to 100µm

Macro et micronucleus

Cytopharynx (or cytostome)

Cil ia

Figure 10 : Sketch of a protozoan organism : Paramecium * class of ciliate, sub-class of holotr ichs * bacteriophagous ; swimer ; need a lot of oxygen, low load.

Pseudopoda

Figure 12 : Sketch of a protozoan organism : Amoeba * branch of Rhizopoda, class of amoeba * bacterio- ou protozoophagous ; live on the surface of flocs ; few indication about its relation with the quality of the treatment

40 to 70µm

Thequa constituted of siliceous particles

30 to 40 µm

Figure 11 : Sketch of a protozoan organism * branch of Rhizopoda, class of Thaecamoeba, genus Euglypha * li ving on flocs, no fixed, no swimer, bacteriophagous (some consume filamentous bacteria) ; stable sludge, low charge.

Axostyla (pseudopoda like needle))

Figure 13 : Sketch of a protozoan organism : Heliozoa * branch of Rhizopoda * bacteriophagous ; rare in sludge, planktonic ; low load and high sludge.

50 to 70 µm

Figure 14 : Sketch of a protozoan organism: * branch of flagella, class of zooflagellates * swimmer, consumes organic matters and bacteria ; very young sludge, or adapted to IWW containing phenol

Flagelles

Noyau

Vacuole contractile

Vacuole de digestion

membrane cytoplasmique

10 à 20 µm

MWW inlet Tank aeration

Bacteria Decomposers Heterotrophs

Primary consumers : B, P, M

Consumers n : P and M

CO2

CO2

CO2

Atmospheric discharge

Figure 15 : Food chain in an activated sludge aerated tank

Caption: B : bacterium P : protozoan M : Metazoan

MW

W in

let

DO

C, N

H3 a

nd P

Act

ivat

ed s

ludg

e ta

nk

Air

Slud

ge re

circ

ulat

ion

Slud

ge ex

trac

tion

Figu

re 1

6 : S

ketc

h of

a st

ruct

ure

of M

WW

trea

tmen

t with

act

ivat

ed s

ludg

e pr

oces

s (b

iolo

gy)

Tre

ated

wat

er

Settl

ing

tank

Mix

ed li

quor

Nitr

osom

onas

and

Nitr

obac

ter :

C

LA A

e : n

itrifi

catio

n “N

H3

+ O

2

NO

3- + H

2 O

” M

O C

OH

Ae

: “D

OC

+O

2

CO

2 + H

2O“

Flo

ccul

atin

g bi

omas

s ; b

acte

ria, p

roto

and

met

azoa

: fo

od ch

ain

MW

W r

aw

wat

er

Flow

Q

Ups

trea

m an

oxic

zone

A

ctiv

ated

slud

ge ta

nk

Slud

ge ex

trac

tion

Tre

ated

wat

er

(Q)

Settl

ing

tank

Rec

ircu

latio

n of

mix

ed li

quor

(NO

3- )

2 x

Q

Air

Slud

ge re

circ

ulat

ion

Figu

re 1

7 : S

ketc

h of

a st

ruct

ure

of d

enitr

ifica

tion

in a

n up

stre

am a

noxi

c zo

ne

MO

CO

H A

e :

“DO

C +

O2

C

O2 +

H2O

“

Nitr

osom

onas

and

Nitr

obac

ter :

C

LA A

e : n

itrifi

catio

n “N

H3

+ O

2

N

O3- +

H2

O”

“NO

3- + D

OC

N2 +

CO

2”

MO

CO

H A

n :

deni

trifi

catio

n

Acetyl CoA

Reserve of intracellular C : Poly C : (PHB…)

Reserve of intracellular energy volutine : Poly Pi : (Pi)n

n Pi

nPi exterior

Bacterium

Figure 18 : Simplified sketch of phenomena involved in biological phosphate removal in water (Comeau et al., 1986) Caption : metabolism in anaerobiosis metabolism in aerobiosis

- Q2

+Q1

Raw

wat

er

Flow

Q

DO

C, P

, NH

3

Phos

phat

ed sl

udge

ex

trac

tion

Ups

trea

m an

oxic

zo

ne

Act

ivat

ed sl

udge

tank

Tre

ated

wat

er

(Q)

Settl

ing

tank

Rec

ircu

latio

n of

mix

ed li

quor

2 x

Q

Air

Phos

phat

ed sl

udge

reci

rcul

atio

n (Q

to 2

xQ)

Figu

re 1

9 : S

ketc

h of

a st

ruct

ure

of b

iolo

gica

l rem

oval

of D

OC

, N a

nd P

in M

WW

Ana

erob

iosi

s zo

ne

MO

CO

H A

e:

“DO

C +

O2

CO

2 + H

2O“

Nitr

osom

onas

et N

itrob

acte

r :

“NH

3 +

O2

NO

3- + H

2 O

”

“NO

3- + D

OC

N2 +

CO

2”

MO

CO

H A

n :

deni

trifi

catio

n A

ccum

ulat

ion

of P

: | -

Q2|

>>

| Q1|

Excr

etio

n of

P :

+ Q

1 Ac

inet

obac

ter,

M

orax

ella

Figures 20 to 25 : Main filamentous bacter ia responsible for bulking in activated sludge processes

* sketch

* classification (Bergey’s Manual of Systematic Bacteriology, J.G. Holt et N.R. Krieg, 1984-1989) and relationship with water treatment

* morphology, Gram stain, Neisser stain , sulphur granule determination

Nocardia sp. : short and branched filament , non partitioned ,G+, N+, S-

50µm Section 26 : Actinomycetal Stable foam on the surface of the aerated tank ; excess of grease in MWW

Figure 20

Figure 21

500µm

Thiothrix sp : straight or not much curved filament , non branched, without sheath, partitioned, sulphur granule ( ), G-, N-, S+

Section 23 : gliding bacterium, non photosynthetic and without fructification ; order Beggiatoales Septic MWW concentrated in sulphured reduced compounds

200 to 300 µm

Beggiatoa sp. : flexible filament , mobile, partitioned, sulphur granule, G-, N-, S+

Section 23 : gliding bacterium, non photosynthetic and without fructification ; order Beggiatoales Observed in insuff iciently aerated attached growth

Figure 22

sheath

Haliscomenobacter : Thin and straight filament, non partitioned , sheath, G-, N-, S-

cytoplasmic membrane

200µm

Section 22 : sheathed bacteria Insuff iciently aerated sludge

Figure 23

one filament

Microthrix parvicella : thin filament, sinuous, entangled, G+, N+, S-

200 to 500 µm

Insuff iciently aerated sludge ; insuff icient recirculation flow

Figure 24

Sphaerotilus natans : long filament , quiet straight , partitioned, sheath, false ramifications, granules PHB ( ), G-, N-, S-

Section 22 : sheathed bacteria Deficiency of nitrogen, phosphorus or oxygen Too high or too low load

granule of PHB

cell False ramification

sheath

1mm

Figure 25

Air

lavage

procédé

Raw water

Heterotrophic denitrification “ DOC + NO3

- N2 + CO2”

MO COH An

Anoxic zone

Wash air

process

aerobic zone

Attached growth Thin granular medium

‘ ‘DOC + O2 CO2 +H2O“ MO COH Ae Nitrosomonas and Nitrobacter : CLA Ae : nitrification “ NH3 + O2 NO3

- + H2O”

Treated water

recirculation of nitrates

Screened floor

Wash water inlet

Flow of washwater

Wash water outlet

Figure 26 : Sketch of a structure of MWW treatment by biofil tration : biological removal of DOC and N (process Biostyr, OTV)

Raw water Treated water

Channel for treated water outlet

Filter medium

Rotative sprinkler for raw water spreading

Figure 27 : Sketch of a tr ickling fi lter

MO COH Ae : “ DOC +O2 CO2 + H2O” and possible nitrification (MO CLA Ae)

Channel

MWW

Rotative biodisc

Axis of the disc

Figure 28 : Sketch of a biodisc ; water circulates in a plane perpendicular to the plane of this sketch , and parallel to the direction of the axis

Level of water

MO COH Ae : “ DOC +O2 CO2 + H2O”

DOC adsorption on the biofilm

Layer of water : diatomites and cyanobacteria

Oxygenated sludge : oxidizing sulphur aerobic micro-organisms (Beggiatoa, Thiobacillus, Thiothrix)

photoorganotrophic : non sulphurous purple bacteria (low [H2S] ) Rhodospirill um and Rhodopseudomonas (Rhodospirillum, Rhodopseudomonas)

diffusion of H2S

green zone : Chlorobium

Anoxigenic photosynthesis with sulphur ; assimilation of CO2 in carbonates

Sludge + Na2SO4 + Na2CO3 + cellulose : degradation of cellulose and fermentations by Clostridium ; anaerobic sulphatoreduction and fermentations (Desulfovibrio) : upward diffusion of sulphides

red zone : Chromatium

Figure 29 : The Winogradsky column experiment

L

I G H T

algae

Raw water

Settled SS

SS sedimentation

Fermentations

CH4 , NH3 , H2S...

O2

COD CO2 , NO3

- , ...

Sun

bacteria

Waterproof membrane

Treated water to macrophyta lagoon : nitrates and phosphates

Figure 30a : Sketch of a microphytes lagooning

Inlet of water from microphytes lagoon

Treated water

Nitrates and phosphates assimilation

O2

Collecting and revaluation of plants

End of C and N removal

CO2

Figure 30b : Sketch of a macrophytes lagooning

Polymers (Sludge, IWW...)

Miscellaneous organic acids

H2 CO2

CH3 COOH H2

CO2

CH4 CO2

Figure 31 : The different way of anaerobic degradation of organic mater

Hydrolysis and and acidogenesis

acetogenesisOHPA

Homoacetic fermentation

Hydrogenophili c methanogenesis

Acetoclastic methanogenesis

Interspecific transfer of d’H2

Treated water

Settling tank

Anaerobic reactor with suspended growth

Gas removal

Sludge recirculation Sludge extraction

gas extraction

Stirr ing with gas

Figure 32 : Sketch of a structure of IWW treatment, with anaerobic digestion suspended growth

IWW

DOC CH4

IWW

COD CH4

Anaerobic reactor

Attached growth Filter medium Ordered packing or random fill

Treated water

Gas

Sludge extraction

Figure 33a : Sketch of a structure of IWW treatment, with anaerobic digestion attached growth

Biolite recirculation

biogas outlet

treated water

Inlet raw water

Fluidising pump

Figure 33b : The Anaflux System (Degrémont, France)

Raw sludge

A I R

Endogenous respiration : MO COH Ae : important oxygen demand : Biomass and organic matter + O2 CO2 + H2O + NH3 + heating energy � pathogenic micro-organisms removal � nitrification (CLA Ae : Nitrosomonas et Nitrobacter : CLA Ae : nitrification “ NH3 + O2 NO3

- + H2O” Sludge age : 15 to 20 d

Stable sludge

Figure 34 : sketch of a structure of aerobic stabilization of sludge

Raw sludge

COD CH4

Stable sludge

Extraction of biogas

Gas mixing or mechanical agitation

Boiler and heat exchanger

Figure 35 : Sketch of a moderate load digestor

gaz inlet feeding the boiler

Thi

cken

ed

slud

ge in

let

Stab

le sl

udge

outle

t

Gas

Was

te g

as bu

rner

stirr

ing

Boi

ler a

nd h

eat

exch

ange

r

Hea

ted

slud

ge re

circu

latio

n

Figu

re 3

6 : S

ketc

h of

a h

igh

load

dig

esto

r

Beg

inni

ng o

f m

etha

nisa

tion

End

of m

etha

nisa

tion

Partially dried, fresh, raw sludge : organic matter (insuff icient C/N ) + water (60 % ) + mineral matters + pathogenic micro-organisms

MO COH Ae endogenous : bacter ia, mould, mushroom

CO2 + H2O + increase of temperature (50 to 70°C) + NH3 + residual organic matter + mineral matter

Addition of structuring carbonaceous compound (sawdust…) : * sludge aeration , partial dewatering * addition of C

evaporation of water

Pathogenic micro-organisms removal

The final sludge : is dry (dryness = 60 to 70 %)

is not pathogenic is a marketable organic soil improvement

Compost maturation for 2 to 3 months with regular mixing : Nitrification Oxydation of residual organic carbone

Figure 37 : Sketch of sludge composting

Und

esir

able

co

mpo

und

C

Ori

gin

in

MW

W

Ave

rage

co

ncen

trat

ion

in M

WW

Exa

mpl

e of

di

scha

rge

stan

dard

Tox

icity

or

inco

nven

ient

Ph

ysic

al

rem

oval

B

iolo

gica

l pr

oces

s In

volv

ed m

icro

-or

gani

sm

Nut

ri-

tiona

l ty

pe

Rol

e of

C in

th

e m

etab

olis

m

Prod

uct o

f re

actio

n (

� � )

Con

ditio

n fo

r th

e tr

eatm

ent

Org

anic

ca

rbon

: B

OD

5

Org

anic

mat

ter

100 t

o 40

0 m

gO2/l

25

mgO

2/l

Con

sum

ptio

n of

O2 i

n th

e m

ediu

m

pre-

treat

men

t

* su

spen

ded

cultu

res

AS

or

AD

(fo

r ag

ri fo

od

IWW

) **

atta

ched

gr

owth

(D

,Bf,T

f)

bact

eria

, pro

to

and

met

azoa

*

flocc

ulat

ing

* in

bio

film

: fo

od ch

ain

CO

H A

So

urce

of

elec

tron

s and

C

�

CO

2

*oxy

gena

tion

* lo

w lo

ad

Am

mon

ia

org

anic

ni

trog

en

amm

onifi

ca-

-tion

of u

rea,

prot

eins

…

prot

eins

, ur

ea…

KN

= 3

0 to

100

m

g/l

NK

+

nitra

tes

= G

LN =

cons

umpt

ion

of

O2

toxi

c fo

r fau

na

by

clar

ifica

tion

: re

mov

al o

f C,

N a

nd P

lin

ked

to S

S

* su

spen

ded

cultu

res

AS

**at

tach

ed

grow

th

(D,B

f,Tf)

Nitr

osom

onas

an

d N

itrob

acte

r C

LA A

e So

urce

of

elec

tron

s �

NO

3-

*oxy

gena

tion

*low

load

*h

igh

slud

ge

age

Nitr

ates

Abs

ent i

n M

WW

Pr

esen

t in

wat

er a

fter

nitri

ficat

ion

of

KN

0 10

mg/

l eu

trop

hica

tion

*

susp

ende

d cu

lture

s A

S

with

up

stre

am

anox

ic z

one

**

atta

ched

gr

owth

Bf

misc

ellan

eous

: en

tero

bact

e-

-ria

, Ps

eudo

mon

as…

CO

H A

n Fi

nal a

ccep

tor

of e

lectr

ons

�

N2

* ef

fici

ent

nitri

ficat

ion

*

anox

ia

* pr

esen

ce of

or

gani

c m

atte

r

Phos

phor

us

Org

anic

mat

ter

and

was

hing

po

wde

rs…

10 to

25

mg/

l 1

mg/

l

prec

ipita

tion

with

FeC

l 3 A

S w

ith

anae

robi

osis

zo

ne

Aero

mon

as

Acin

etob

acte

r M

orax

ella

CO

H A

e In

trace

llula

r ac

cum

ulat

ion

of P

�

in sl

udge

*neit

her O

2 no

r NO

3- *a

erob

ic

slud

ge

treat

men

t

Figu

re 3

8 : B

iolo

gica

l tre

atm

ent o

f MW

W

Cap

tion

: AS

(act

ivat

ed s

ludg

e) ;

AD

(ana

erob

ic d

iges

tion)

; D

(dis

c) ;

Bf (

biof

ilter

) ; T

f (tr

ickl

ing

filte

r)