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Phosphorus Recovery from Wastewater

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Presentation on theme: "Phosphorus Recovery from Wastewater"— Presentation transcript:

1 Phosphorus Recovery from Wastewater
END-O-SLUDG Conference Sludge and Phosphorus Management in Europe: Present and Future Peter Vale, Severn Trent Water Ltd 3rd December 2013

2 Contents Drivers for P recovery from wastewater
P a water quality issue P a finite, irreplaceable resource The Process - How do we recover P as struvite? Full scale implementation

3 Drivers

4 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

5 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

6 How do we remove P from sewage?
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.

7 How do we remove P from sewage?
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

8 Is P recovery the key to sustainable P removal?
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) “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:

9 Data courtesy of UKWIR / Birmingham University
The UK’s (simplified)phosphorus life cycle (2009 data) Applied mineral fertiliser 74,500 tonnes Human Consumption Lost to Environment (water bodies) Wastewater Treatment Sewage sludge to incineration 5,000 tonnes Applied organic fertiliser 80,000 tonnes Applied organic fertiliser derived from sewage sludge 33,000 tonnes 37,000 tonnes Losses from agriculture 12,500 tonnes 15,500 tonnes Losses in sewage effluent 24,000 tonnes 9,500 tonnes Data courtesy of UKWIR / Birmingham University

10 How do we recover P in the form of struvite?

11 What is Struvite? Mg2+ + NH4+ + PO43- MgNH4PO4∙6H2O
Naturally occurring Forms easily in some wastewater plants Increases O & M costs Impacts plant reliability But, also a valuable slow release fertiliser PhotograpH courtesy of PAQUES bv

12 Recovery of P as Struvite in sewage treatment plants
A combination of two processes is required: 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) 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) PO4 Bio-P bacteria O2 CO2 Facultative Bacteria Poly-P PHB Energy (ATP) Energy Cell Growth Anaerobic Aerobic

13 Example Commercial Technologies (1): Ostara’s Pearl® Process
Ostara Plant at Durham AWWTP,US SCHEMATIC and photograph courtesy of Ostara Nutrient Recovery Technologies Inc

14 Example Commercial Technologies (2): Paques’ Phospaq Process
MgO NH4+ PO43- Air Struvite removal MgNH4PO4 · 6 H2O PHOSPAQ Phospaq Plant at Lomm, NL SCHEMATIC and photograph courtesy of Paques BV Other technologies are also available!

15 Struvite quality Information and Images courtesy of Paques BV
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 requirements Paques © Cd Cr Cu Hg Ni Pb Zn As EU standard (mg/kg P) 31 1875 19 750 2500 7500 375 struvite product (mg/kg P) 0.9 17 42 <0.3 26 6.6 336 <6 Content compared to EU standard 3% 1% 2% <2% <1% 4%

16 Implementation in Severn Trent Water

17 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

18 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

19 Business Case for P Recovery through Struvite at Stoke Bardolph STW, Nottingham
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 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. Protects Anammox Plant Anammox process can be inhibited by high P in liquors

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

21 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.

22 Acknowledgements

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