Phosphorus Recovery from Wastewater

END-O-SLUDG ConferenceSludge and Phosphorus Management in Europe: Present and Future

Peter Vale, Severn Trent Water Ltd3rd December 2013

Contents

1. Drivers for P recovery from wastewater− P a water quality issue− P a finite, irreplaceable resource

2. The Process - How do we recover P as struvite?

3. Full scale implementation

Drivers

Phosphorus and Water Quality• Phosphorus (P) is the most common cause of water quality failures in

England (it is the main cause of eutrophication in freshwaters).− Concentrations of P in English rivers have been falling since 1990, due to major

reductions in inputs from STW’s.

− Despite this investment, 45% of rivers and 76% of monitored lakes currently exceeding the P standard for good status.

− Pop. growth will increase the amount of P entering STW’s which in some areas could reverse improvement (if nothing is done about it).

Extracts from Environment Agency, England’s Waters: Challenges and Choices. June 2013

History of P removal in Severn Trent Water

• From 1990 (AMP2) STW have been implementing P removal from sewage

• By end of current AMP (2015) the sewage from the large majority of customers served will have P removal

• Up to now P removal has been driven by UWWTD

• The WFD will require much tighter effluent phosphorus limits

How do we remove P from sewage?

1. Chemical precipitation with metal salts

− The conventional technology - very widely used in the UK

− Currently the only option available for small works

− Often need tertiary filtration to remove metal• Fe and Al are both ‘specific pollutants’

• Sand filters on large works

• Reedbeds on small works

− Cost & security of supply issues, e,g for ferric sulphate• Cost has risen by 80% in 5 years

• production capacity has reduced by 15% in the last few years, predicted that demand will outstrip capacity in the next 2/3 years.

How do we remove P from sewage?

2. Enhanced Biological Phosphorus Removal (EBPR)

− Phosphorus is removed biologically, by phosphate accumulating organisms (PAOs)

− Only suitable for ASP’s• A ‘standard’ ASP will remove ~ 20% of P

(uptake of P essential for normal cell growth)

• Reconfiguring the ASP as a BNR plant can give upwards of 90% P removal

− Facilitates P recovery through struvite

Stained PAOs

− P is necessary for agriculture and is an essential, irreplaceable component for life• 160 million tons of phosphate rock

mined annually

• 75,000 tonnes of mineral P used as fertiliser in UK (2009)

• Finite reserves− In 2008, work published that estimated

global reserves at 50 – 100 years!

− Known reserves now substantially increased, (USGS report 2013)

− Morocco controls approx 75% of reserves – so security of supply issues & hence strategically important to UK (and Europe)

Is P recovery the key to sustainable P removal?

“Phosphorus is as critical for all modern economies as water”

“without phosphorus we cannot produce food.”

“In the past 14 months, the price of phosphate rock - has surged by more than 700 per cent”

Quotes from “The Times”, June 23, 2008:

Applied mineral fertiliser74,500 tonnes

Human Consumption

Lost to Environment (water bodies)

Wastewater Treatment

The UK’s (simplified)phosphorus life cycle (2009 data)

Applied organic fertiliser

80,000 tonnes Applied organic

fertiliser derived from

sewage sludge33,000 tonnes

Losses from agriculture12,500 tonnes

Losses in sewage effluent24,000 tonnes

37,000 tonnes

15,500 tonnes

9,500 tonnes

Sewage sludge to

incineration5,000

tonnes

DATA COURTESY OF UKWIR / BIRMINGHAM UNIVERSITY

How do we recover P in the form of struvite?

• Naturally occurring

• Forms easily in some wastewater plants

• Increases O & M costs

• Impacts plant reliability

Mg2+ + NH4+ + PO4

3- MgNH4PO4∙6H2O

What is Struvite?

PHOTOGRAPH COURTESY OF PAQUES BV

• But, also a valuable slow release fertiliser

Recovery of P as Struvite in sewage treatment plants

• A combination of two processes is required:

1. Enhanced Biological P Removal− P concentrated in sludge (sludge ~4/5% P

versus ~2% P)− ‘Extra’ P easily releasable (by contrast if dose

Fe/Al then P is locked up.− Bio-P organisms also concentrate Mg in sludge

(& co-release with P)

2. Anaerobic Digestion− Extra P in SAS is re-released in the digester

(under anaerobic conditions)− Recovery of P easiest in digested sludge liquor

(centrate), − but can be recovered from digested sludge or ‘P

stripped SAS” filtrate

VFAs

rbCOD (fermentable substrate)

PO4Bio-P bacteria

O2

CO2

Facultative Bacteria

Poly-P

PHB

Poly-P

PO4

PHB

Energy (ATP)

Energy

Energy

Cell Growth

AnaerobicAerobic

Example Commercial Technologies (1): Ostara’s Pearl® Process

SCHEMATIC AND PHOTOGRAPH COURTESY OF OSTARA NUTRIENT RECOVERY TECHNOLOGIES INC

Ostara Plant at Durham AWWTP,US

Example Commercial Technologies (2): Paques’ Phospaq Process

SCHEMATIC AND PHOTOGRAPH COURTESY OF PAQUES BV

Phospaq Plant at Lomm, NL

MgO

NH4+

PO43-

Air Struvite removal

MgNH4PO4 · 6 H2O PHOSPAQ

Paques ©

Other technologies are also available!

Struvite quality

Cd Cr Cu Hg Ni Pb Zn AsEU standard (mg/kg P) 31 1875 1875 19 750 2500 7500 375

struvite product (mg/kg P) 0.9 17 42 <0.3 26 6.6 336 <6Content compared to EU standard 3% 1% 2% <2% 3% <1% 4% <2%

• Average crystals size of 0.7 mm

• Field crop tests by DLV Plant institute

• Tested on potatoes, carrots, sprouts

• Equal performance to existing P fertilisers

• Now sold to fertiliser company

• Complies to EU fertiliser requirementsPaques ©

INFORMATION AND IMAGES COURTESY OF PAQUES BV

Implementation in Severn Trent Water

Initial Pilot work

• 2009: STW began working with Ostara, pilot trials of “Pearl Reactor” ran at Derby− Process very effective at removing P− High quality prill product produced− Technical viability of P recovery proved

Full scale implementation at Stoke Bardolph STW, Nottingham

• 1 mg/l P permit comes in to force in 2014

• Existing ASP being upgraded to EBPR

• Mainstream Process volume to be ‘freed-up’ by sidestream carbon, nitrogen and phosphorus removal processes− UASB for chicken rendering trade input− Anammox process for sludge liquor N removal− Phospaq for P recovery through struvite

• 550 kg PO4-P per day will be recovered as Struvite (will be the UK’s largest source of recovered P)

• Struvite to be sold to a fertiliser blender for incorporation in a liquid suspension fertiliser

Business Case for P Recovery through Struvite at Stoke Bardolph STW, Nottingham

1. Reduces capital cost (£5 million saving vs conventional soln.) and increases robustness of mainstream Bio-P process

− Removes ~ 80% of P from returns (and some ammonia)− Reduces required process volume

2. OPEX savings estimated at £165K/yr− Reduces nuisance value of struvite coating pipes and

pumps• Savings on maintenance, interventions and “anti-struvite”

chemicals

− Reduces any supplementary iron requirements− Provides an additional revenue stream

• valuable slow release fertiliser • Contract signed with a fertiliser blender for incorporation into

a liquid suspension fertiliser.

3. Protects Anammox Plant− Anammox process can be inhibited by high P in liquors

Construction of P recovery treatment plant, Stoke Bardolph STW, November 2013

Conclusions

• Treated sewage sludge already a significant and valuable P fertiliser.

• Recovery of P through struvite would allow up to 40% more P to be recycled.

• Application as struvite rather than treated sludge can be more targeted and allows more applications.

• Technology commercially available, and product being used as a fertiliser.

• Already happening! – Thames Water, opened Slough facility last month, and Severn Trent Water opening Nottingham facility in summer next year.

Acknowledgements

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