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Membrane bioreactor for advanced Membrane bioreactor for advanced wastewater treatment and reusewastewater treatment and reuse

Claudio Lubello Riccardo Gori

Civil Engineering Department - University of Florence - Italy

4th INTERNATIONAL SYMPOSIUM ON WASTEWATER RECLAMATION, RECYCLING AND REUSE

12-14 November 2003, Mexico City12-14 November 2003, Mexico City

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Textile wastewater characteristics produces

Impacts on water resources

Quantitative: High water consumption

Qualitative: Textile wastewater contains slowly- or non-biodegradable

organic substances

Necessity of wastewater reuse Limitations of wasterwater reuse

This work is focused on the treatment of textile industry wastewater using Membrane Bio-reactor (MBR)

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Industrial activities and water supply in Prato

0 20 40 60

Textile wet process

Dyeing

Scouring

Carbonizing

Printing

Washing

Finisching

Chemistry industry

More

Number of industries with high water demands in Prato

0 2 4 6 8

Million of cubic meters of industrial water consumption in

Prato (2002)

The industrial district of Prato area extends over 700 Km2 with about 45.000 workers engaged and 8.000 medium and small

textile activities

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Textile industries carry out several fiber treatments using variable quantities of water from five to forty times the fiber weight. Consequently generate large volumes of wastewater to be disposed of. Such treatments include:

•Dyeing preliminary treatments (bleaching, desizing, mercerization);

•Textile ennobling treatments (from dyeing to post-dyeing treatments, such as those required to increase colorant fastness, in wet and dry conditions);

•Finishing, including operations such as fulling or impregnation with products giving special characteristics to fibers.

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Effluent characteristics from the textile industries (Barclay and Buckley, 2000)

Process Composition Nature

Sizing Starch, waxes, carboxymethylcellulose, polyvinyl alcohol

High in BOD and COD

Desizing Starch, glucose, carboxymethylcellulose, polyvinyl alcohol, fats and waxes

High in BOD and COD, suspended and dissolved solids.

Scouring Caustic soda, waxes, grease, soda ash, sodium silicate, fibres, surfactants, sodium phosphate

Dark coloured, high pH, high COD, dissolved solids

Bleaching Hypoclorite, chlorine, caustic soda, hydrogen peroxide, acids, surfactants, sodium phosphate

Alcaline, suspended solids

Mercerising Caustic soda High pH, low COD, high dissolved solids.

Dyeing Various dyes, mordants, reducing agents, acetic acid, soap

Strongly coloured, high COD, dissolved solids, low suspended, solids, heavy metals.

Printing Pastes, stanch, gums, oil, mordants, acids, soaps

Highly coloured, high COD, oily appearance, suspended solids

Finishing Inorganic salts, toxic compounds Slightly alkaline, low BOD

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In this way, the effluent is enriched with compounds having high environmental impact and difficult to treat directly, through conventional biological processes.

Priority pollutants are Dyes and Surfactants.

Typical wastewater concentrationsDyes 10 – 50 mg/l;Surfactants 20 – 50 mg/l.

Wastewater treatment problemsLow biodegradability;Biomass interactions.

Environmental impactsAlterations of gaseous exchanges; Light penetration reduction;Toxcity; Visual impact.

Technical problems for wastewater reuseFoamColor

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This study is part of a larger research framework whose target is to identify the most appropriate technologies to boost reuse of purified waters for industrial purposes, in the area of Prato, and in the well-watered Pistoia nursery district.

Study area

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1990

Accomplishments

•Refining Water Plant (RWP)

•Distribution system for 30 industries located in First Macrolotto area

1994

Accomplishments

•2 pipelines to withdraw and return water from Bisenzio river

•Distribution system for 30 industries located near the centre of Prato’s city

1999

Accomplishments

•Distribution system for 35 industries located in Second Macrolotto area

The water recycling system in Prato allows connected enterprises to use , as a water supply source in addition to groundwater:

1) Treated water from the Baciacavallo WWTP - about 400 m3/h (more than 3 million m3/year)

2) Surface water from Bisenzio river - about 60 m3/h (0,5 million m3/year)

Bisenzio river

Evolution of industrial aqueduct of Prato

Center of the city of Prato

II Macrolotto area

Intake basin

Ombrone river

I Macrolotto area WWTP RWP

Wastewater from Prato

draining system

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The Baciacavallo plant is the main wastewater treatment plant in the area of Prato, its capacity is of about 750.000 p.e. and has a maximum flow capacity of 6000 m3/h.

The treated wastewater is partially reintroduced in the surface water system and partially (100 l/s) is further refined and reused to feed the industrial and fire-fighting waterworks of one of the main industrial areas in Prato.

The pilot-scale plant is part of the treatment chain, and operates in parallel with the oxidation-nitrification treatment of the Baciacavallo plant, therefore, downstream the primary sedimentation.

Wastewater

Effluent

Preliminary treatments

Primary sedimentation

Biological oxidation

Secondary sedimentation

Clariflocculation

Ozonation

Equalization

MBR Pilot PlantPermeate

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Variable Mean Max Min STD

Q (m3/d) 119.200 130.700 31.930 108.894

COD (mg/L) 686 1.263 167 241

TSS (mg/L) 228 1.060 52 145

N-total (mg/L) 18,4 27,2 8,2 4,6

MBAS (mg/l) 5,9 9,6 0,0 0,9

Non-ionic surfactants (mg/l)

31,5 44,2 9,2 5,4

Absorbance at 420 nm 0,302 0,489 0,02 0,069

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The biological reactor operates at constant level and the bio-mass is maintained in aerobic conditions via aeration, through 6 small bubble diffusers. The ultra-filtration module (Rhodia, UFP10) is of the external type, with plate and frame membranes, where a cross-flow type filtration is performed.

E ff luentf ro m

prim arytratm ent S trainer

B io lo gical reacto rA ir

D rain

UFP10Module

A uto m aticsam pler

P

O 2Q

V

Perm eate

Sludge

Influent

Permeate outle t

C o ncentrate recyclein the bio lo gical reacto r

C o ncentrate

P erm eate recycle in thebio lo gical reacto r

C o ncentrate recyclein the m o dule

P

T

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Pin=1,8 – 2,5 bar

Pout1,0 – 1,7 bar

The module consists of 4

elements in series (each one made

up of 7 membranes) for a total

filtering surface of about 3 m2. The membrane is of the organic

type, made up of acrylonitrile

copolymers, with a 3 m thickness

and a pore cut-off of 40 KD

(approximately, this corresponds to

a pore average size of 0,02 – 0,03

m). The average module inlet flow

rate is of 30 m3/h, which turns into a

cross-flow velocity of 2,1 m/s.

The pilot plant (plate and frame)

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Results and discussion

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Biomass development and characteristics

0

2

4

6

8

10

12

14

16

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24-apr 04-mag 14-mag 24-mag 03-giu 13-giu 23-giu 03-lug 13-lug 23-lug

Tim e (days)

TS

S C

on

cen

trat

ion

(g

/l)Concentrazione solidi nel bioreattore

The initial concentration of the biomass introduced in the bio-reactor was of 5 gTSS/l. Fluctuation in solid particle concentrations, together with inlet wastewater characteristics variability, led the pilot plant bio-mass to operate with extremely variable organic loads. After an initial start-up period, the bio-mass grew with a linear trend until it reached about 16 gTSS/l, in the space of 120 trial days.

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0,0

50,0

100,0

150,0

200,0

250,0

0 20 40 60 80 100 120 140 160

Time (days)

Pe

rme

ate

flo

w (

l/h)

0,0

50,0

100,0

150,0

200,0

250,0

Pe

rme

ate

sp

ec

ific

flo

w

(l/h

/mq

)

Flusso di permeato Flusso specifico di permeato

P

PP

P

The trend of permeate flow extracted from the pilot plant was comprised between 35 and 65 l/h m2, considerably lower than the 100 l/h m2 specified by the manufacturer. During the experimental period, on the basis of the previously described criteria, 4 chemical cleanings of the module were required, actually with a monthly frequency. The cleaning system proved to be efficient in restoring the flow conditions. However, the permeate flow descending trends were not regular and this can be explained on the basis of following phenomena: substantial fluctuation, even unexpected, of solid particle concentrations in the aerated mixture, due to sludge escape; change in the sludge viscosity and filterability characteristics

Permeate flow

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Tests conducted on COD fractionation, in its soluble and particulate components, provided a total COD average value of 869 mg/l, whose soluble component corresponded to 34.7%.Figure compares the COD trends, at the pilot plant outlet, from the Baciacavallo plant secondary settling and from the final ozone treatment. After about 2 weeks from start-up, a quick COD decrease at the outlet was observed; these values stabilized within 40 and 60 mg/l (mean value: 56,8 mg/l), in the third week, seldom exceeding the upper threshold. The removal efficiency, 93% on average, proved to be considerably higher with respect to that obtained only with biological treatment and secondary settling in the Baciacavallo plant.

COD Monitoring

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Nitrogen monitoring

Nitrification process results were extremely satisfactory. With respect to the full scale plant, the nitrification process efficiency appeared considerably higher. The nitrification process proved to be complete since no nitrite accumulations were found in the oxidation tank (all values were below the 0.05 mg/l threshold).

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Color monitoring

Permeate 0,041 - 0,119

Inlet 0,153 - 0,504 0,322

0,075

0.000

0.050

0.100

0.150

0.200

0.250

0.300

0.350

0.400

0.450

0.500

0 5 10 15 20

Tempo (settimane)

As

so

rba

nza

infl

ue

nte

a 4

20

nm

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

Re

nd

ime

nto

di r

imo

zio

ne

(%

)

Assorbanza influente Assorbanza permeato Rendimento

Absorbance values a 420 nm

Range Mean

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Average removal

MBR pilot plant

WWTP (with ozone)

77,2 %

77,6 %

Color monitoring

0,000

0,020

0,040

0,060

0,080

0,100

0,120

0,140

0,160

0 2 4 6 8 10 12 14

Tem po (settim ane)

Ass

orb

anza

a 4

20 n

m

Eff luente chiarif locculazione Eff luente ozono Permeato MBR

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Clariflocculation outlet

MBR effluent

Ozone effluent

0,090 0,074 0,070Abs. a 420 nm

Color monitoring

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Color monitoring

Color inlet

Membrane removalAdsorbtion and biodegradation

Color permeate

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Color monitoring

Adosrption removal Nel caso dell’impianto pilota la capacità di adsorbimento è incrementata da:

High biomass concentration High adsorption capability of MBR sludge

MBR Sludge

200xWWTP Sludge

400x

assenza di macrostruttura del fiocco di fango presenza di batteri dispersi ridotta presenza di microfauna

1

2

1 – Traditional activated sludge

2 – Activated sludge disintegrated by boiling

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Inlet Permeate Secondary Effluent

Ozone outlet

MBAS

Average 5,3 0,4 0,58 0,35

STD 0,45 0,06 0,08 0,06

Max 6,2 0,52 0,75 0,51

Min 4,2 0,25 0,41 0,25

Non-ionic surfactants

Average 34,1 0,26 1,22 0,97

STD 3,9 0,21 0,30 0,21

Max 40,8 0,98 2,05 1,23

Min 26,4 0,09 0,57 0,62

As a general rule, the pilot plant proved to be efficient in surfactant removal from textile wastewater; however, with respect to removal efficiency obtained in the full scale plant, the MBR technology effect appeared different between anionic and non-ionic compounds.

In the case of non-ionic surfactants, a considerable removal efficiency was found (higher than 99% on average). In this case, a significant removal increase was noticed, both with respect to the conventional activated sludge treatment and to the ozone treatment; the latter, as everyone knows, shows a lesser efficiency with respect to MBAS.

Surfactants monitoring

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Conclusions

• The pilot-scale plant demonstrated that the MBR treatment makes it possible to obtain high purification efficiency of textile wastewater.

• Extremely satisfactory results were obtained both on conventional parameters such as COD, suspended solids, ammonium, and on compounds typical of this type of wastewaters such as dyes and surfactants. In the case of dyes and surfactants, removal efficiency similar or higher than that obtained with the Baciacavallo plant complete chain, were reached. These results appear to be extremely important, but only a very limited literature is available on them.

•As regards treatment applicability, it is advisable to specify that the system adopted provides for the use of ‘plate and frame’ membranes with an external module. This system has high energy consumption and is suitable for small flow rates treatment (2000 – 3000 m3/d) with high pollutant concentrations.

• It would be therefore proper to experiment also alternate membrane typologies (for example, hollow fiber membranes) more suitable for high flow-rates treatment.