Dr Ana Soares, Lecturer Biological Engineering Copyrighted

Biological struvite crystal formation in sludge dewatering liquors

Phosphorus: a pollutant or a resource?

Guideline

UWTD

(91/271/EEC)

2 mg/L (10k-100k p.e.)

1 mg/L (>100k p.e.)

New targets 0.01-0.1 mg/L P

Rock Phosphate Monthly Price -

US Dollars per Metric Ton

http://www.indexmundi.com/commodities

World P resources

Gilbert N: The disappearing nutrient. Nature 2009 461: 16–718

Stopped exporting in 1997

Planned bans

on exportation

In gigatonnes

Recovery of phosphorus from wastewater enough?

Municipal

wastewater

treatment

pant P

Options for P recovery

Primary sed. Second. sed. Tertiary treatment

Treated

effluent

Sludge

Sludge

Large

items

Grit

Screens Grit

chamber

Activated sludge

or trickling filter

Sludge

Biogas Anaerobic digester

P recovery from sludge liquors

Struvite chemical precipitation

+ Well known process installed at full-scale with a market

+/- Recovery of 90% of phosphorus (10% left in the wastewater)

- Needs high phosphorus streams >100 mg/L

- Crystallisation through chemical process with chemical addition

Le Corre KS, Valsami-Jones EB, Hobbs PC, Parsons SA: Phosphorus recovery from wastewater by struvite crystallization: A review. Crit Rev

Environ Sci Technol 2009, 39: 433–477.

Pratt C, Parsons SA, Soares A, Martin BD: Biologically and Chemically Mediated Adsorption and Precipitation of Phosphorus from Wastewater.

Trends in Biotechnology

Sludge liquors have high P – other ways to recover P?

Sustainable

(no chemicals)

Versatile

(range of [P] )

High quality effluent

Usable for wastewater

mixed matrix

High yield, good product

quality

Investigate the suitability of selected bacteria to produce struvite in wastewater and dewatering liquors

Bio-mineralization: biological formation of inorganic materials

Over 60 different minerals have been identified, including struvite and CaP

Widespread property in environment/nature

Well studied in biomedical sciences (e.g.: kidney stones)

Bio-mineralization: Known mechanisms

Nucleus Crystal Vacuole Nucleus Crystal Vacuole

Nucleus

Crystal

Extracellular microenvironment

Crystal

Intracellular crystal production

Extracellular crystal production

Bacteria

Bacteria

Bio-mineralization bacteria selection: Literature information

Myxococcus xanthus: soil bacteria, EXTRACELLULAR crystal production observed after 2 days in synthetic media

Bacillus pumilus: soil bacteria, EXTRACELLULAR crystal production observed after 6-20 days in synthetic media

Halobacterium salinarum: Aquatic halophilic bacteria, INTRACELLULAR crystal production observed after 3-4 days in synthetic media

Brevibacterium antiquum: permafrost soil bacteria, INTRACELLULAR crystal production observed after 2-3 days in synthetic media

Bio-mineralization bacteria selection: Cultivation in synthetic media

Strains Growth rate

(1/h)

Dry weight

(mg/L)

Myxococcus xanthus 0.013 2160

Bacillus pumilus 0.039 720

Halobacterium salinarium 0.042 63

Brevibacterium antiquum 0.027 980

Negative control: media without bacteria – no crystal

production

Bio-mineralization bacteria selection: Cultivation in wastewater

Primary sed. Second. sed.

Treated

effluent

Sludge

Sludge

Large

items

Grit

Screens Grit

chamber

Activated sludge

Sludge

Biogas Anaerobic digester Sludge liquors:

PO4-P: 30 mg/L

NH4-N: 629 mg/L

Mg: 39 mg/L

WW

PO4-P: 2.3 mg/L

NH4-N: 70 mg/L

Mg: 17.8 mg/L

Full-scale wastewater treatment plant (UK)

PE 570,000.

Thick./dewatering

Bio-mineralization bacteria selection: Cultivation in wastewater

Typical µmax:

Denitrifiers= 0.1 1/h; Methanogens= 0.02 - 0.002 1/h;

Anammox = 0.001 - 0.004 1/h

Wastewater M.

xanthus

B.

pumilus

H.

salinarium

B.

antiquum

Settled

wastewater

Growth rate

(1/h)

Negligible 0.001 Negligible

0.004

Crystal dry

weight

(mg/L)

- 137 - 113

Sludge

dewatering

centrifuge

liquors

Growth rate

(1/h)

Negligible

0.001 0.002 0.002

Crystal dry

weight

(mg/L)

- 213 - 226

Negative control: Wastewater not inoculated – no crystal production

Crystal characterisation

Crystals formed by B.antiquum in centrifuge sludge liquor were

approximately 250 µm

Crystal characterisation

SEM images in sludge dewatering

centrifuge liquors

struvite

struvite

Scanning electron microscope with energy

dispersive x-ray spectroscopy (SEM-EDX)

Effluent quality

Sludge dewatering centrifuge liquors

Settled wastewater

PO4-P

(mg/L)

NH4-N

(mg/L)

Mg

(mg/L)

PO4-P

(mg/L)

NH4-N

(mg/L)

Mg

(mg/L)

Initial concentration

30.5 629.0 38.9 Initial concentration

7.5 70.0 22.6

After cultivation

with B.

pimulus

2.1 122.5 18.7 After cultivation

with B.

pimulus

2.0 30.0 9.0

After

cultivation

with B. antiquum

1.5 117.5 21.4 After

cultivation

with B. antiquum

2.1 31.0 9.5

B. pimulus

removal

93% 81% 52% B. pimulus

removal

73% 57% 60%

B. antiquum

removal

95% 81% 45% B. antiquum

removal

72% 56% 58%

Bio-struvite vs. chemical struvite (10,000 m3/day wastewater treatment plant producing 500 m3/day of sludge liquors)

* Costs used in chemical precipitation are from 2001 (Jaffer et al.,); struvite price $1500/ton

http://biomassmagazine.com/articles/1838/from-problem-to-profit

Parameter Biological struvite Chemical struvite

Production Kg/day 120 100

Capital costs

£ Fermentation

reactor (10 days HRT)

630,000 Precipitation

reactor

425,000

Blowers and

diffusers

Not

known

Blowers and

diffusers

825,000

Filtration unit 100,000 Desludge pump 75,000

Total capital

costs

£ total 730,000 total

1,325,000

Operating costs £/year Electricity

10,000

Electricity 3,500

Chemical costs 13,000

Total operating

costs

£/year total

10,000

total

16,500

Post treatment Likely not to be required Needs recirculation to the head of

the works

Income = £40,734

Total Opex = £10,000

Income = £33,945

Total Opex = £16,500

http://biomassmagazine.com/articles/1838/from-problem-to-profithttp://biomassmagazine.com/articles/1838/from-problem-to-profithttp://biomassmagazine.com/articles/1838/from-problem-to-profithttp://biomassmagazine.com/articles/1838/from-problem-to-profithttp://biomassmagazine.com/articles/1838/from-problem-to-profithttp://biomassmagazine.com/articles/1838/from-problem-to-profithttp://biomassmagazine.com/articles/1838/from-problem-to-profit

Bio-struvite producing bacteria can be the “anammox” for phosphorus?

Microbial characterization

(μ, Ks, temp, nutrients, pH,

etc.)

Reactor

design

Struvite separation

Conclusions

Bacteria can produce struvite crystals in wastewater in simple way (no optimisation yet!)

Microscope analysis showed presence of crystals as early as 3 days and visible crystals were seen in cultures after 10 days reaching up to 250 µm.

Crystals can be separated by filtration/centrifugation

The final concentration of phosphate in sludge centrifuge liquors reached 1.5 mg/L, indicating a 95% P and 55-86% ammonia removal

The process can potentially be economically attractive

New flowsheets for wastewater treatment

Screen

Primary

Sedimentation

Raw

wastewater

anMBR

1 ry

/ 2 ry

sludge

Thickener

Sludge supernatant ( Return liquor )

Stabilised sludge to land

Anaerobic digester

Sludge recirculation

loop to heat exchanger

Gas

engine

Imported grid

electricity Digested sludge pump

Primary

sludge

pump

Thickened

Primary

sludge

pump

Disposal of gross

solids

Produced biogas

Treated

effluent

Nutrient rich

eluent

N - C

o n

t a c t o

r

P - C

o n

t a c

t o r

Phosphorus removal media

HCO3-

SO42-

SO42-

SO42-

HCO3-

HCO3-

NO3-

Cl-

Cl-

Cl-

Cl-

Cl- PO43-

PO43-

PO43-

PO43- PO4

3-

PO43-

PO43-

Capacity 2 g P/ kg media

Regeneration 5% NaOH

Compare technologies R

eso

urc

e r

eco

ve

ry p

ote

nti

al

Sludge to land Chemical

struvite Adsorption

processes

Phosphorus recovery technology

Bio-struvite

Thank you for your attention

a.soares@cranfield.ac.uk

www.cranfield.ac.uk/SAS

Thank you to: Yorkshire Water and Severn Trent

Further reading:

Soares A, Veesam M, Simoes F, Wood E, Parsons SA, Stephenson T. 2013. Bio-struvite: A new route to recover phosphorus from wastewater. CLEAN - Soil, Air, Water. In Press.

mailto:a.soares@cranfield.ac.ukhttp://www.cranfield.ac.uk/SAS