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 sewageBy end of current AMP (2015) the sewage from the large majority of customers served will have P removalUp to now P removal has been driven by UWWTDThe WFD will require much tighter effluent phosphorus limits
6 How do we remove P from sewage? Chemical precipitation with metal saltsThe conventional technology - very widely used in the UKCurrently the only option available for small worksOften need tertiary filtration to remove metalFe and Al are both ‘specific pollutants’Sand filters on large worksReedbeds on small worksCost & security of supply issues, e,g for ferric sulphateCost has risen by 80% in 5 yearsproduction 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’sA ‘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 removalFacilitates P recovery through struviteStained PAOs
8 Is P recovery the key to sustainable P removal? P is necessary for agriculture and is an essential, irreplaceable component for life160 million tons of phosphate rock mined annually75,000 tonnes of mineral P used as fertiliser in UK (2009)Finite reservesIn 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 fertiliser74,500 tonnesHuman ConsumptionLost to Environment (water bodies)Wastewater TreatmentSewage sludge to incineration5,000 tonnesApplied organic fertiliser80,000 tonnesApplied organic fertiliser derived from sewage sludge33,000 tonnes37,000 tonnesLosses from agriculture12,500 tonnes15,500 tonnesLosses in sewage effluent24,000 tonnes9,500 tonnesData courtesy of UKWIR / Birmingham University
11 What is Struvite? Mg2+ + NH4+ + PO43- MgNH4PO4∙6H2O Naturally occurringForms easily in some wastewater plantsIncreases O & M costsImpacts plant reliabilityBut, also a valuable slow release fertiliserPhotograpH courtesy of PAQUES bv
12 Recovery of P as Struvite in sewage treatment plants A combination of two processes is required:Enhanced Biological P RemovalP 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 DigestionExtra 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” filtrateVFAsrbCOD (fermentable substrate)PO4Bio-P bacteriaO2CO2Facultative BacteriaPoly-PPHBEnergy (ATP)EnergyCell GrowthAnaerobicAerobic
13 Example Commercial Technologies (1): Ostara’s Pearl® Process Ostara Plant at Durham AWWTP,USSCHEMATIC and photograph courtesy of Ostara Nutrient Recovery Technologies Inc
14 Example Commercial Technologies (2): Paques’ Phospaq Process MgONH4+PO43-AirStruvite removalMgNH4PO4 · 6 H2OPHOSPAQPhospaq Plant at Lomm, NLSCHEMATIC and photograph courtesy of Paques BVOther technologies are also available!
17 Initial Pilot work2009: STW began working with Ostara, pilot trials of “Pearl Reactor” ran at DerbyProcess very effective at removing PHigh quality prill product producedTechnical viability of P recovery proved
18 Full scale implementation at Stoke Bardolph STW, Nottingham 1 mg/l P permit comes in to force in 2014Existing ASP being upgraded to EBPRMainstream Process volume to be ‘freed-up’ by sidestream carbon, nitrogen and phosphorus removal processesUASB for chicken rendering trade inputAnammox process for sludge liquor N removalPhospaq for P recovery through struvite550 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 processRemoves ~ 80% of P from returns (and some ammonia)Reduces required process volumeOPEX savings estimated at £165K/yrReduces nuisance value of struvite coating pipes and pumpsSavings on maintenance, interventions and “anti-struvite” chemicalsReduces any supplementary iron requirementsProvides an additional revenue streamvaluable slow release fertiliserContract signed with a fertiliser blender for incorporation into a liquid suspension fertiliser.Protects Anammox PlantAnammox process can be inhibited by high P in liquors
20 Construction of P recovery treatment plant, Stoke Bardolph STW, November 2013
21 ConclusionsTreated 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.