Cadmium adsorption by mixed-culture biofilms

under metabolizing and non-metabolizing

conditionsJose Roberto Diaz

University of Puerto Rico at MayaguezAugust 3, 2006

Advisors: Dr. Robert Nerenberg Dr. Jeremy Fein

Mentors: Leon Downing Brian Ginn

Outline• Introduction• Objectives• Experimental method• Results and discussion• Conclusions• Future work• Acknowledgements

Introduction• Heavy metals are a

common cause of pollution

•non-degradable•accumulate in the

environment •causes of land and

water pollution • Conventional

treatment methods increasingly expensive heavy metals in the

atmosphere

Introduction• microorganisms treat heavy metal-

polluted wastes• accumulate trace levels of ions• major role in modification,

activation and detoxification• Immobilized systems have higher

surface areas and biological mass concentration

• ability of mixed cultures to adhere

• form biofilms• provide higher loading rates

than suspended systems

Introduction• Biofilms used in wastewater treatment systems

• resistant to inhibitory and toxic metals• tolerant to high metal concentrations• high affinity for metallic cations• anionic nature of polymers inhibit entrance of cationic

molecules to biofilm

• Immobilized-cell bioreactor technology provides cost-effective means for eliminating pollutants

Introduction• Live vs. Dead

Objectives

• Determine extent of Cd adsorption onto mixed-culture bacterial system under two conditions:

1. biofilm growth, metabolically active

2. biofilm growth, metabolically inactive

To waste

Experimental method

Acetate Feed = 16mM Phosphate buffer with 16.6356g CH3COOK (10 g/L acetate) to provide acetate as the electron donor

Continuous flow packed bed reactor

Q = 1mL/min

Retention time of 60 min

Air

N2

reactor is inoculated with Mishawaka activated sludge

Biofilm Growth Air is humidified to provide O2 as the electron acceptor

Experimental methodCd Adsorption Bulk solution:-no ammonium

-2 ppm Cd

-70 ppm Acet (dead)

-150 ppm Acet (live)

divide to test tubes

(5 mL each)

mix for approximately 2 hours

centrifuge and filter

add one-tenth of a gram of biofilm to each test tube

Cd in bulk liquid by

ICP-OES

Acetate by

Ion Chromatography

analyze samples

Cs-irradiation

35,000 rads/hr

Results and discussion

• Live or Dead?• Acetate consumption• Cd Adsorbed

Live or Dead?• metabolically active • metabolically inactive

Live-Dead staining

ImageLive

CountDead Count

Ratio (L:D)

1 1170 26 45.0000

2 944 19 49.6842

3 743 13 57.1538

4 1205 27 44.6296

5 710 11 64.5455

6 2579 41 62.9024

7 855 16 53.4375

8 577 13 44.3846

9 3214 91 35.3187

10 1835 57 32.1930

11 2727 57 47.8421

12 1598 28 57.0714

average 49.5136

stdev 10.0497

Image Live CountDead Count

Ratio (L:D)

1 346 96 3.6042

2 2175 1432 1.5189

3 311 186 1.6720

4 1038 87 11.9310

5 350 108 3.2407

6 71 85 0.8353

7 127 99 1.2828

8 187 107 1.7477

9 177 25 7.0800

10 93 61 1.5246

11 256 41 6.2439

12 530 621 0.8535

average 3.4612

stdev 3.3676

Metabolically Active BacteriaAcetate Control (150 ppm)

0

20

40

60

80

100

120

140

160

0 20 40 60 80 100 120 140

time (min)

Aceta

te Co

nc. (p

pm)

Run 1

Run 2

Acetate Consumption (live)20 ppm Acetate

05

1015202530

1 2 3 4 5 6 7

Sample#

Ace

tate

co

nsum

ed (p

pm)

20 ppm Acetate

18

20

22

24

26

28

1 2 3 4 5 6

Sample #

Ace

tate

co

nsum

ed (p

pm)

150 ppm Acetate

145147149151153155157

1 2 3 4 5 6 7 8 9 10

Sample #

Ace

tate

co

nsum

ed (p

pm)

Acetate Consumption (dead)50 ppm Acetate

0

20

40

60

80

1 2 3 4 5 6 7 8 9 10

Sample #

Ace

tate

co

nsum

ed (p

pm)

80 ppm Acetate

-100

-50

0

50

100

1 2 3 4 5 6 7 8 9 10

Sample #

Ace

tate

co

nsum

ed (p

pm)

70 ppm Acetate

0

20

40

60

80

100

1 2 3 4 5 6 7 8 9 10

Sample #

Ace

tate

co

nsu

med

(p

pm

)

Cd Adsorption for Metabolically Active Bacteria

0

5

10

15

20

25

30

35

40

45

1 2 3 4 5 6 7

Sample #

% C

d Ads

orbe

d 20 ppmAcetate20 ppmAcetate 2150 ppmAcetate

average %Cd adsorption = 26.9518

Cd Adsorption for Non-metabolically Active Bacteria

0

10

20

30

40

50

60

70

1 2 3 4 5 6 7 8 9Sample #

% C

d Ad

sorb

ed 50ppmAcetate80ppmAcetate70ppmAcetate

average % Cd adsorption = 48.9928

Cd Adsorption for Metabolically Active and Non-metabolically Active Bacteria

0

10

20

30

40

50

60

70

0 50 100 150 200

Acetate Consumed (ppm)

Cd A

dsor

bed (

%)

Active

Inactive

Discussion• bacteria are surviving the radiation

treatment• Non-metabolizing bacteria are still

consuming acetate in some samples more than others

• Metabolizing bacteria seem to be adsorbing less Cd (≈27%) than samples that have non-metabolizing bacteria (≈49%)

• possible reasons why

Conclusions• Radiation treatment is not effective in

killing bacteria and must be modified• Non-metabolizing bacteria certainly

showed an effect on how much Cd was adsorbed

• Samples with varying amounts of acetate adsorbed around the same percent of Cd for metabolizing and non-metabolizing bacteria

Future work

• Different method of killing bacteria• Non-metabolizing vs. metabolizing

in suspended growth system• Different electron acceptors and

donors for growing biofilm

Acknowledgements• EMSI• Dr. Valli

Sarveswaran• Leon Downing• Brian Ginn• Dr. Jeremy Fein• Dr. Robert

Nerenberg• CEST