NUMBER 57 July 2004 International conference 17-18th June 2004, Cranfield University, Great Britain Struvite its role in recovery and recycling

SUMMARY REPORT The conference organised by Cranfield University School of Water Sciences, with Questions asked support from CEEP, brought together some 70 scientists, water industry experts and other John Driver, industrial actors interested in struvite recovery from consultant, opened the sewage and from animal manures. conference by recalling the predictions made at the first The conference showed that today there is a international conference on very wide interest in struvite recovery, with phosphorus recovery and scientific research underway in countries across recycling, Warwick University the world: USA, Australia, , Canada, UK, 1998. At the time, the European phosphate industry South Africa, UK, , Spain, believed that calcium phosphate , The , Greece, , recovery from sewage would be the route to provide Italy, Poland … industry with a significant proportion of its raw material needs from secondary sources. This has not Work underway ranges from detailed come about, and today struvite is seen as the feasible investigation of the chemical parameters of route for phosphorus recovery. struvite precipitation, (e.g. the team at Patras University, Greece), through development of The technical feasibility of struvite recovery in both pilot reactors at the laboratory and semi- sewage treatment and manure installations is now industrial scale, to operation of full-scale proven, however, as Mr Driver emphasised, there struvite recovery reactors (several in Japan, are now two major obstacles: regulatory and social Thames Water UK at the Slough sewage issues regarding the classification of recovered treatment works, installations treating calf phosphates as “waste” and perception of re-use in manure and potato factory waste streams in The agriculture of products recovered from sewage ; Netherlands). economics in that recovered struvite will not in the foreseeable future be economically competitive with Experience of re-use of recovered struvite was mineral fertilisers because of their low costs. also presented, including field trials of struvite as an agricultural fertiliser, use in horticultural For struvite recovery and recycling to develop products for garden centres, and industrial significantly, a political initiative is therefore recycling in the Thermphos International needed, both to classify recovered struvite as a phosphorus furnace in Vlissingen The secondary raw material not a “waste”, and to require the water and animal waste industries to move Netherlands. towards recycling of phosphorus resources. Possible initiatives in this direction are appearing in Germany and Sweden, for example.

precipitated from a food industry factory waste Struvite re-use stream (see ???).

Willem Schipper, Thermphos Mr Schipper emphasised that today Thermphos International, presented would therefore welcome further supplies of struvite operational experience of or K-struvite as a secondary raw material. industrial re-use of recovered K-struvite in the company’s Andrew Johnson et al., industrial thermal phosphorus TERRA / TES Eco Systems / production process at Thames Water, and a poster Vlissingen, The Netherlands. by Emma Sharp, Cranfield For some years now, University, presented Thermphos is successfully processing calcium experience of re-use of struvite phosphates recovered from municipal sewage at the recovered from the Slough Geestmerambacht waste water treatment plant. municipal waste water Recently, Thermphos has also conducted a trial on treatment plant operated by Thames Water. A full- the processing of K-struvite (potassium magnesium scale pilot struvite recovery unit (7m3/hour) treats phosphate) precipitated at a cooperative calf manure sludge digester centrifuge effluent (after a buffer treatment installation at Putten The Netherlands. tank to float off organic particles) from one quarter of the plant’s capacity (total capacity 260,000 pe). The factory tested compatibility of K-struvite as a The struvite production unit has been operating since raw material with the existing process, by processing 2002 (see SCOPE Newsletter n°41), testing different one year of the Putten installations K-struvite operating conditions. The Slough struvite production over 4 days (K-struvite was thus 3% of precipitation unit precipitates 80% of inflow soluble process input phosphate). Magnesium is fully phosphate to struvite. Heavy metal levels in the compatible with Thermphos’ thermal process and recovered product are low. comes out in the slag (in place of the calcium in the usual calcium phosphate rock raw material), but Following simple washing and air drying steps (both with improved slag characteristics. Potassium was a carried out as manual operations at this scale) the question mark, as it is not a usual constituent of struvite produced is a reasonably clean material with phosphate rock and, as a “volatile” metal, might be a free moisture content of ~5%. expected to accumulate in the dust-sludge recycle and may need to be bled off. The test showed, Recently, use of magnesium hydroxide plus pH however, that at this level of K-struvite use the adjustment has been tested instead of magnesium incorporation potassium posed no problems, and chloride. This proved more expensive and resulted also that no other detectable operating problems in smaller struvite crystals and higher levels of occurred. organic impurities in the precipitated struvite.

Thermphos have also been looking into the Struvite quality has been improved by avoiding feasibility of using recovered MAP struvite operating during centrifuge start-up phases, when (magnesium ammonium phosphate) in their process. high organics levels are present. Although ammonium would be problematic in the phosphorus furnace, it should in fact be driven off Thames Water have estimated that if biological during the prior raw material sintering stage, with nutrient removal (BNR) and struvite recovery were the resulting ammonia or NO being retained in the x installed at just 7 target waste water treatment plants, plant’s gas scrubbing circuits. Full scale testing is this would result in around 1,000 tonnes/year of planned shortly using struvite which will be struvite. Current production is however insufficient

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for the logistics of agricultural recycling. TERRA concern about possible contamination of the food are therefore developing its use as a phosphorus chain. Above all, the organisations were concerned source in an organic garden fertiliser, after to maintain the “organic status” of their members’ combination with other ingredients widely used in land and it could be inferred that whilst they are such fertilisers (rape seed meal, feather meal, kali open-minded about the possibilities for the use of vinasse), with a struvite content of around 10%. recovered struvite, they will first require to be Their business model is to sell the fertiliser, along convinced that their organic status can be with other branded products through a network of maintained. garden centres to whom TERRA already sells compost products produced from sewage sludge The organic organisations indicated that they do not currently have sufficient knowledge concerning Growth trials using the struvite-containing organic sewage struvite, and would be interested in fertiliser show good results compared to both a information concerning: energy balance, levels of commercial inorganic and organic fertilisers. heavy metals and other possible sewage contaminants, costs, plant availability of struvite Florian van Sothen, Member phosphorus and nitrogen. of the task force on phosphate recovery within the German Water Struvite reactor design and operation Association (ATV-DVWK), presented the results of a Denis Mangin, LAGEP - survey of organic farmers’ University Lyon 1, France, organisations and of the grain mills’ association in summarised how interactions Germany, asking their opinions and positions on the between the crystallization idea of use of sewage-recovered struvite in organic reaction and local mixing farming. Three out of four German organic farmers effects can enable effective are members of such organisations. Although reactor design and operation: organically-grown products currently make up only 3% of the German food market this is seen as a fast • impact of possible localised growing sector and, importantly, a sector with a high high concentration effects around reagent level of public trust. injection points (leading to scaling and to production of fines because of high local 45% of sewage sludge in Germany is presently used supersaturation); for farmland spreading, but the use of sewage sludge • significance of reactor hydrodynamics in is increasingly not accepted by the public, and it is influencing the chemical and physical processes strictly not allowed on organic farms. Although the of struvite precipitation (including the forms of survey showed that most organic farmers’ crystal/aggregate produced); organisations had not heard of the potential for the recovery and recycling of phosphate from sewage • poly-nucleation on the surface of fines (or primary treatment in the form of struvite, they are, agglomeration), occurring probably at the earlier nonetheless, open to the idea of using sewage stage of particle formation and leading through recovered struvite, with the objective of contributing growth to star-shaped poly-crystals, appears as a to closing resource recycling loops. Particular significant mechanism. These structures can interest was shown by the two largest German readily agglomerate, by meshing and by catching organic farmers’ organisations (in terms of land fines, because of their multi-pointed form. surface farmed). The organisations are, however, Experiments with a 10 litre stirred reactor and pure concerned that acceptance of sewage recovered chemical solutions were presented, in which sand struvite might turn against them through public and recovered struvite pellets being used as seed

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material. In both cases, struvite precipitation Phosphate recovery from inflow liquor was >90%, occurred mainly as fines, and not on the surface of resulting in struvite with a P-content of 12.5% and the seed material, so seeding was then abandoned. very low heavy metals in particles of 0.4mm Unseeded experiments resulted in large particles, diameter. mainly poly-crystals, and many fines, but the latter were not lost in the outflow and were retained in the reactor. Further work is needed to confirm that Integration into sewage treatment larger particles can be produced with longer run times than the 3-5 day runs in this work, and this is Bernd Heinzmann, Berlin now underway at the University of Valencia (see Wasserbetriebe (Berlin below). Water), presented pilot tests of integrating a struvite recovery A full report of this experimental work is available process into a very large at http://www.nhm.ac.uk/mineralogy/P-recovery/ biological nutrient removal (see “Lagep report”). waste water treatment plant. The plant has been suffering Questions were raised concerning the relatively major nuisance struvite high concentration of sodium hydroxide solution deposits in anaerobic digester outflow pipes and used to adjust pH: addition of a more dilute reagent installations. might limit local supersaturation at injection points, and thus reduce production of fines. Test installations have been designed to avoid struvite precipitation upstream of the recovery unit The stirrer mixed reactor was presented as offering and to reduce organic contamination of the struvite. the advantage over fluidised bed reactors or reactors Mixing in the anaerobic digester followed by mixed by air bubbles, that the required mixing can pumping out under pressure to avoid degassing. be obtained by adjusting the stirrer design and Struvite is then precipitated in an aeration chamber power, independently of through-flow rate required with magnesium chloride dosing. An English in FBRs to ensure bed fluidity (thus avoiding the translation of the presentation of this work made at need for recycle or return streams to ensure adequate the German Federal Environment Agency (UBA) residence times) and independently of aeration phosphorus recycling seminar 6-7 February 2003, (which affects pH and ammonia offgassing). Berlin is available at However, the feasibility of stir-mixing aerated http://www.nhm.ac.uk/mineralogy/P-recovery/ (see columns was questioned. “Case study: Berlin Wasserbetriebe”), summarised in SCOPE Newsletter n° 54. Hideyuki Ishikawa et al., Ebara Corporation Japan, The liquor is then passed through a hydrocyclone, presented the ongoing before going into the sludge centrifuge, in order to investigation of a double reactor separate struvite particles >0.05mm diameter from struvite precipitation unit the less dense organic particles. Using a double (inflow inflow 0.56-0.95 cyclone, up to 50% of the waste water treatment m3/hour m3/hour) operating on plant inflow phosphorus could be recovered as anaerobic digester sludge struvite particles. The system proved operational centrate. The main reactor tank under testing, and the recovered struvite showed is a fluidised bed precipitation nutrient values, heavy metal and organic contents reactor, the second smaller tank is used to grow compatible with limits for fertilisers. seeds washed out of the fluidised bed reactor up to 0.3mm diameter, for use as seeds in the main reactor Berlin Water is now looking at a better integration of (see summary in SCOPE Newsletter n°49, page 4). the process into the plant scheme by combining a

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struvite precipitation unit, operating on the sludge Aurora Seco, University of Valencia, Spain, stream between the first and second stages of sludge presented experimental work digestion, and magnesium addition directly into the integrating the Lyon reactor second stage digester with hydrocyclone separation (above) into a complete pilot of struvite particles in a recycle stream in this second scale (40 l/h) BNR sewage stage of sludge digestion. treatment plant fed with real sewage. The struvite reactor is Raffaella Boccadoro, installed downstream of the Marche Polytechnic sewage stream thickener, University Ancona, et al. anaerobic digester and presented ongoing dewaterer. Its capacity is development and testing of however too large for continuous operation on this the full-scale pilot phosphate sidestream, so a smaller reactor will probably be precipitation unit operating at developed. Treviso waste water treatment plant, Italy (in conjunction Results of 13 runs of 5-12 days using the struvite with Venice University and Verona University). A reactor under different operating conditions were full report of work at this installation up to 2003 is presented. The reactor usually achieved stability presented at http://www.nhm.ac.uk/mineralogy/P- after 4 days. Soluble phosphorus removal efficiency recovery/ (see “Phosphorus recovery trials at was shown to be pH dependent in the range 8.5-8.9, Treviso”) and summarised in SCOPE Newsletter but phosphorus recovery efficiency was variable,, n°49, page 7 and previous work in SCOPE probably because of some loss of fines in the Newsletter n°44, page 8. The phosphate precipitation outflow leaving the top of the reactor. installation, operating on the plant’s sewage sludge centrate liquor line is now effectively producing Accurate control of pH was shown to be very struvite with low organic content (<2% dry weight), important in reactor operation. Installation of a low calcite content, nitrogen content >4% and “fuzzy logic” computer pH control system helped to phosphate >12%, thus conforming to requirements achieve stable operating conditions. 60-90% of for fertilisers in Italy. reactor inflow phosphates were then reliably recovered as readily dried struvite particles. The plant has experienced some scaling problems with phosphate precipitation occurring in piping Significant precipitation of phosphorus and instead of in the reactor tank. This is being magnesium are however being encountered in the addressed by reducing the struvite super-saturation : pilot installation’s digester. Further work will aeration is often not necessary to achieve address this question and look at the integration of precipitation in the reactor tank (sufficient pH the struvite precipitation reactor into the whole pilot increase through CO2 off-gassing occurs by mixing installation, including aspects such as CO2 degassing only), the addition of magnesium is not necessary. in the centrate dewaterer and magnesium recycle from the struvite reactor to the sewage treatment The plant has also experienced problems of organics installation inflow. in the reactor, resulting in foaming and operating problems, including carry over of fines out of the reactor. This is being addressed by installation of a decanter tank installed between the sludge digester dewatering and the phosphate recovery plant.

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water liquors. Models are important tools for process Struvite chemistry and modelling control. In the case of struvite, the modelling is complex because of the interference of various Aikaterini Kofina and Petros different possible magnesium and calcium mineral Koutsoukos, University of precipitations (ion competition and simultaneous Patras, Greece, presented precipitation). The model presented is based on ongoing systematic pH- kinetics (rates of reaction) rather than on static controlled experiments which equilibrium data, consistent with the situation in are feeding an increasingly continuously operated waste water treatment detailed data bank concerning installations which are effectively permanently in a struvite precipitation parameters non-equilibrium state. in multi-ion solutions representative of waste water. The three phase (aqueous / gas / solid) mixed weak Phosphate, magnesium, ammonium ions are acid/base kinetic model for struvite precipitation has maintained at 1:1:1 ratios to test super-saturation; been under development for some years (see paper sodium, chloride, nitrate, carbonate and glucose are presented at the Second International Conference on included ; pH s of 8.5 and 9.5 were investigated. Phosphorus Recovery and Recycling and also in Environmental Technology, volume 22, number 11, Current work is investigating the effects of 2001). The model now takes into account ion pairing + concentrations of other non-competing ions on kinetics, and includes H as a specific parameter struvite precipitation: sodium and sulphate were (rather than treating pH as a consequence of other shown to have a threshold inhibition effect, retarding conditions). It was tested on results from struvite precipitation. precipitation experiments carried out by K. Suzuki (see paper above at this conference) in swine wastewater and Van Rensberg (Cape Town At pH 8.5, struvite crystals were formed as long prisms, whereas at pH 9.5 rhomboid shapes were University) in anaerobic sewage sludge digester found. The specific surface area of the crystals was liquor. The model predicted measured data 2 accurately, except for calcium concentration changes rather high (150 m /g) suggesting that they may be in the swine wastewater. porous. Further work is needed to look at this question. Isik Kabdasli, Istanbul Technical University, et al. When left at room temperature the struvite, initially formed as a hexahydrate (MgNH PO *6H O) presented studies of struvite 4 4 2 precipitation induction time evolved to a monohydrate (MgNH PO *H O), with 4 4 2 (key chemical kinetics factor) the well formed crystals changing into a complex in synthetic waste waters platelet structure. containing relatively low ammonium concentrations See summary of several recent papers on struvite (35mg/l, that is 2.45 mMolar chemistry by this team in SCOPE Newsletter n°55, 1:1:1 concentrations of magnesium, phosphate, page 3. ammonium) and other ions typically found in waste liquors (calcium, sodium, chloride, sulphate, Dick Loewenthal et al., carbonate). pH was in the range 8.5 – 9.2. UV- University of Cape Town, visible absorbance measurement by South Africa, presented the spectrophotometer proved a reliable tool for ongoing development of a detecting precipitation and thus measuring induction chemical kinetic model for time. struvite precipitation in waste

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Sodium and sulphate both showed significant depend on levels of free ammonia present, this being retarding effects on precipitation (increase in affected by air stripping and by pH, as well as initial induction time). Carbonate showed no significant ammonium ion concentration. The use of effect. Calcium concentrations had varying effects magnesium oxide as a reagent for struvite depending on pH. precipitation is liable to result in the presence of free ammonia, because its poor solubility reads to molar Kristell Le Corre, Cranfield overdosing and thus to pH increases. He suggests University, Great Britain, et that high levels of free ammonia could result in al. also presented results of struvite crystals forming as long needles, and lower studies of struvite precipitation levels lead to rhomboid crystals. induction time measured by absorbance, particle size and Suschka also suggested that, because magnesium crystal form. In this case, oxide is a cheap by-product in Poland (prices magnesium : phosphate : comparable to calcium hydroxide = lime), its ammonium ratios were fixed at addition along with phosphorus addition to cause 1:2:2 and magnesium concentrations ranged from struvite precipitation could be a viable solution for 1.2 – 3.5 mMolar. pH was adjusted to 9.0. The ammonium removal from sludge liquors. This would effects of calcium and carbonate ions on struvite avoid the return of ammonium to the sewage works precipitation were investigated with Mg : Ca : CO3 head, thus improving biological nutrient removal. ratios of 2:1:1, 1:1:1 and 1:2:2 being tested. Phosphorus could be provided either from internal sewage works liquors and/or by addition of Calcium and carbonate addition was shown to retard phosphoric acid or superphosphate fertilisers. precipitation (increase induction time) but also to increase light absorbance (this may be due to A full report of experiments up to 2003 is available precipitation of small calcium carbonate particles = at http://www.nhm.ac.uk/mineralogy/P-recovery/ calcite). Calcium and carbonate addition resulted in (see “Suschka” in the bibliography) smaller average precipitated particle size after just three minutes reaction, and after 20 minutes: a larger Bruce Jefferson et al., average size for high calcium and carbonate Cranfield University, Great concentrations (2x Mg molar) and a smaller average Britain, presented studies of size for low calcium and carbonate concentrations struvite scaling rates and (0.5x Mg molar), both when compared to the 1:1:1 propensities of different magnesium : calcium : carbonate ratios. materials: stainless steel, PTFE poly tetra fluoro ethylene This concurs with the results of Kabdasli above, that (Teflon), PMMA poly calcium ions have variable effects on struvite methylmethacrylate, both precipitation, and suggests that further work is smooth and after modification via surface abrasion needed on this interaction. using silicon carbide papers. Results using coupons of the materials attached to struvite precipitation Jan Suschka et al., University stirrers showed that most scaling occurred on of Bielsko-Biala, Poland, stainless steel, and least on PMMA, with scaling presented results of struvite being accentuated when materials were modified. precipitation experiments in Work up to 2002 is summarised in SCOPE anaerobic sewage sludge Newsletter n°50, page 7. digester liquors, concentrating on the fate of ammonia. He Work is currently underway to try to compare suggested that the form of scaling results with data concerning surface struvite crystals produced may properties observable via Atomic Force Microscopy

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(AFM). To date, this suggests that scaling is not struvite recovery by facilitating struvite precipitation correlated to “roughness” (as measured using this onto a 1 mm steel wire mesh, submerged in the apparatus) but is correlated to surface adhesion reactor. forces. At present, work is ongoing to try to modify the AFM point (stylus) by growing struvite onto it, After 30 days of submersion in the reactor, one in order to then measure the struvite – struvite kilogramme of struvite was easily recovered by adhesive surface force. scraping from the wire mesh. This product was >99% pure struvite after simple washing. However, more than ¾ of the struvite precipitating in the Struvite recovery from manures reactor was still accumulating in the base of the reactor, with high organic content. Kazuyoshi Suzuki et al., National Institute of Livestock The installation achieved 70% removal of phosphate and Grassland Science Japan, from inflow water without magnesium addition, and presented operation of different 90% with magnesium addition. configurations of a pilot struvite recovery installation in pig Running costs were estimated at 2,000 US$/year for manure wastewater. Pig manure energy consumption and 1,000-3,000 US$ for is generally treated differently magnesium dosing, for a 1,000 fattening pig farm. in Europe, where animal faeces, Experiments with a demonstration installation are urine and wash water are mixed, ongoing. whereas in Japan, faeces go to a separate treatment line. He estimates that around 13%, 24% and 17% of initial phosphorus, magnesium and calcium are See summary of 2002 published paper in SCOPE found in the liquid fraction of the swine wastewater. Newsletter n°50, page 6

Nuisance phosphate deposit problems occur in swine Rachid Laridi et al., INRS wastewater treatment plants. The potential for (University of Québec, struvite recovery from swine wastewaters is Canada) and CRIQ presented estimated at 10,000 tonnes P/year. experiments into struvite precipitation from swine wastewater, following the Dr Suzuki presented a 4m3/day stirred, aerated occurrence of nuisance struvite reactor for struvite precipitation and recovery from deposits downstream of iron swine wastewaters. pH increase results from the and coagulant addition to aeration. Magnesium is added as magnesium reduce suspended solids loads to a trickling filter. chloride, and vegetable oil is added to avoid foaming The reason for these nuisance deposits (despite the caused by organics. reduction in soluble phosphorus resulting from the iron addition) is thought to be the +78% increase in This reactor has been operated continuously for 2 soluble magnesium during this treatment. The years. The solids recovered were 2.0- 25% struvite release of magnesium occurs following coagulant with significant organic content, and had to go to addition, due possibly to ionic exchange with Fe or composting before agricultural re-use. compression of the diffusive layer at the solid/solution interface. Relatively pure (95%) struvite deposits were observed on the air injection tubes and reactor walls. Mr Laridi reported 1 litre beaker scoping A 34 day test showed better struvite precipitation experiments, then testing of different stirred reactors onto coarse and metal surfaces, than onto smooth of 15, 120 and 450 litre capacity using raw swine plastics. It was therefore decided to try to improve

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wastewater after ferric chloride addition and settling. No magnesium addition was required but pH Other processes adjustment was necessary. An optimal pH of 8.5 and a hydraulic residence time of 30 minutes enabled 84- Alex Weidelener, Stuttgart 98% phosphorus removal (and 15% ammonia University Germany, et al. removal) to be achieved in the smaller reactors, but presented a proposed process not in the 450 litre reactor, probably because of for extraction of soluble inadequate mixing (under-sized stirrer). phosphorus from sewage sludges using acid, followed by Further work is currently underway to better struvite precipitation. Acid understand the magnesium release mechanism and addition to the sludges to pH 2 to optimise ferric chloride addition to combine proved more effective that magnesium release, effective settling of organics and alkali (pH13). To enable struvite recovery by pH a limited immobilisation of soluble phosphorus. increase after sludge acidification, however, iron and calcium ions must be neutralised to avoid their Ipek Celen et al., University precipitation with phosphates. Sodium citrate proved of Tennessee, USA, presented effective in neutralising calcium and sodium experimental work on struvite sulphate in neutralising iron. precipitation in liquor collected from a pig farm manure Participants suggested that this process appeared holding lagoon. The liquor was however as excessively complex and potentially dosed with sodium hydroxide costly (reagents for acidification, pH increase, ion only (NaOH) and with NaOH neutralisation …) except in specific circumstances. plus magnesium chloride in 1 It was noted that Thermphos can recycle the litre beakers. Results were compared with the phosphorus from sewage sludge incineration ash in MINTEQ software model. their furnace in Vlissingen, The Netherlands, provided that sludges produced at sewage works A pH increase to 8.5 (no magnesium addition) using iron-based chemical P-removal are separated resulted in a 55% removal of soluble phosphorus as prior to incineration (bio-P and aluminium P- both struvite and calcium phosphates (monetite removal sludge ashes are compatible with the CaHPO4 and brushite CaHPO4.2H2O), whereas process, but not high iron levels). magnesium addition plus pH adjustment enabled 98% phosphorus removal as struvite only (in this Demet Antakyali et al., case, no reduction in soluble calcium). The Stuttgart University experimental results corresponded well with the Germany, discussed the MINTEQ model predictions for both phosphorus potential interest of struvite removal efficiencies and for the precipitation recovery for ammonium product, after the addition of struvite to the model removal from sewage works data base. sludge digester liquors and presented experimental struvite precipitation results.

Like Suschka (above), she emphasised the influence of high ammonium concentrations in sludge digester dewatering liquors returned to the head of sewage works operating biological nutrient removal (BNR). Sludges are often spread on farmland, and there is an increasing demand for mobile sludge dewatering

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units to facilitate sludge management and transport. Matthias Hartmann, Bauhaus- In this case, levels of ammonium from the sludge University Weimar, Germany, dewatering unit (treating relatively large quantities presented work concerning the of sludge compared to sewage works capacity, over precipitation of struvite and a short time) could have a major impact on works hydroxyapatite (HAP) from nitrogen removal when the dewatering liquor is urine. Precipitation can occur returned to the works inflow – indeed, certain spontaneously in urinals German regional statistics showing that BNR plants (blocking piping) and in storage achieve in reality only 60-70% nitrogen removal. To of urine samples (up to 50% of improve this performance, the sludge liquor should initial phosphates). be treated before being supplied to the WASTE WATER TREATMENT PLANTs. Laboratory precipitation experiments with addition of magnesium oxide, magnesium hydroxide, Struvite precipitation, achieved by magnesium and magnesium chloride, calcium hydroxide and calcium phosphate addition and pH adjustment if necessary, chloride were presented. Both magnesium chloride could provide an efficient route to remove and magnesium hydroxide resulted in >90% ammonium from these return liquors, with compact phosphate precipitation after 30 minutes at 2x molar installations (short reaction and settling time) ratio (to phosphorus), whereas magnesium oxide or compatible with mobile units. calcium addition resulted in slower and/or less effective phosphorus removal. Magnesium oxide Laboratory tests using digested sludge dewatering addition resulted in a phosphate product with <12% liquors from three BNR sewage works (ammonium P content, which may be too low for use as a > 1,000 mg/l) showed 80% nitrogen removal from fertiliser. Magnesium chloride was rejected as liquors at pH 8.5 after 30-40 minutes. Magnesium leading to undesirable increases in effluent salinity. oxide (MgO), although poorly soluble (thus requiring longer reaction times and above 1:1 molar Magnesium hydroxide at 2x molar ratio was thus dosing) was the most cost-effective solution. identified as the optimal solution for phosphorus Effectiveness was improved if MgO was dosed recovery. before phosphate addition. Calcium concentrations did not have significant effects at the magnesium and ammonium concentrations studied, because in Poster presentations this case the amount of calcium in sludge liquor coming from municipal sewage works is generally Phil Schneider et al., James Cook University, not very high. Townsville, Queensland, Australia: pilot scale tests of a 40 litre capacity, seeded fluidised bed reactor, With magnesium chloride (rapid struvite for recovery of struvite from piggery wastes, precipitation), very pointed crystals formed. With including dynamic modelling using PHREEQC and MgO, the crystals did not show sharp corners. gPROMS.

The study concluded that struvite precipitation David Montag, RWTH Aachen Unviersity, provided a good solution. One company contacted in Germany: the PRISA process, involving struvite Germany indicated that they would buy struvite for precipitation within sludge treatment (combination 100€/tonne. of different process water streams) in biological nutrient removal sewage treatment systems, using a high-efficiency struvite crystallising reactor. Field trials of plant availability of nutrients in the recovered struvite, used as a fertiliser, are currently underway, and analysis of heavy metals and organic

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chemical contaminants are also being carried out to of dairy manure (ammonium concentration 900- ensure compatibility with agricultural use. 1,200 mg/l), by addition of magnesium chloride and potassium phosphate. Over 2 months operation, with Jozef Hoffmann, Wroclaw University of a pH at average 8.3 and 1:1:1 magnesium and Technology, Poland, et al. presented results from a 1 phosphate addition (to molar ammonium litre laboratory agitated struvite precipitation reactor concentration), >80% ammonium removal was tested for phosphorus removal from industrial and achieved. At pH9.8 and Mg:N:P ratio of 1.2:1:1.4, fertiliser factory waste streams, by magnesium and then 92% ammonium removal was achieved. The ammonium addition. Near 100% P-removal is resulting precipitate was 3%N, 9%K2O, 25% P2O5, achieved by 1.3x molar addition of magnesium and compatible with use as an NPK fertiliser under ammonium at pH9. European regulations.

David Philo, Kralingseveer Waste Water Treatment Julita Kowalczuk and Mieczyslaw Szustakowski, Plant, The Netherlands: this waste water treatment University of Zielona Gora, Poland: samples of plant, which treats around half of Rotterdam’s swine manure, after sedimentation, were boiled, then sewage with biological nutrient removal, has, since struvite precipitation was tested by addition of 2001, been experiencing considerable nuisance magnesium chloride and ammonium chloride, and struvite deposits in the outflow pipes and pumps pH adjustment using concentrated ammonium from the plant’s two 5,000