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Application of magnetic microsorbents for separation, concentration and recovery of phosphate from wastewater streams

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Application of magnetic microsorbents for separation, concentration and
recovery of phosphate from wastewater streams
Asya Drenkova-Tuhtan*, Carsten Meyer**, Michael Schneider***, Karl Mandel****, Carsten
Gellermann*****, Matthias Franzreb******, Heidrun Steinmetz*******
* Institute for Sanitary Engineering, Water Quality and Solid Waste Management (ISWA), University of
Stuttgart, Bandtäle 2, 70569 Stuttgart, Germany, asya.drenkova@iswa.uni-stuttgart.de
** ISWA, University of Stuttgart, Bandtäle 2, 70569 Stuttgart, Germany, carsten.meyer@iswa.uni-stuttgart.de
*** Fraunhofer ISC, Neunerplatz 2, 97082 Würzburg, Germany, michael.schneider@isc.fraunhofer.de
**** Fraunhofer ISC, Neunerplatz 2, 97082 Würzburg, Germany, karl-sebastian.mandel@isc.fraunhofer.de
***** Fraunhofer ISC, Neunerplatz 2, 97082 Würzburg, Germany, carsten.gellermann@isc.fraunhofer.de
****** Karlsruhe Institute of Technology (KIT-IFG), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-
Leopoldshafen, Germany, matthias.franzreb@kit.edu
******* University of Stuttgart, Bandtäle 2, 70569 Stuttgart, Germany, heidrun.steinmetz@iswa.uni-stuttgart.de
Abstract: Advanced nanocomposite magnetic particles are developed and tested for the adsorptive elimination
and recovery of phosphate directly from wastewater streams (PO4-P10mg/L). The phosphate loaded adsorbers
can be extracted from the liquid phase via inexpensive low gradient magnetic separation, regenerated in a
suitable solution where simultaneously phosphate desorption and concentration take place, and then reused again
in multiple cycles. Laboratory experiments demonstrate the reusability of the particles in 60 consecutive
adsorption/desorption cycles where under optimal reaction conditions >90% total efficiency and P-recovery can
be achieved. The desorption solution can be enriched with phosphate ions through repetitive application of the
same solution and used as a potential P-rich resource or alternatively serve as a source for further precipitation of
a solid P-product (e.g. struvite). In addition, pilot-scale tests were performed to verify the feasibility to upscale
the technology.
Keywords: Phosphate recovery; Sorption; Wastewater effluent
Introduction
The element phosphorus is essential for life but rock phosphate is a non-renewable and
irreplaceable limited resource which the fertilizer industry and modern agriculture heavily
depend on. Although the global phosphate rock reserves are estimated to cover the demand in
a very broad time range from a couple of decades up to a few centuries (Cordell and White,
2015), this would depend on factors like political situation, agricultural development,
population growth, exploitation of new deposits, etc. Nevertheless, there is a general
consensus that the quality of the remaining natural mineral reserves is deteriorating
progressively and that the costs will increase in the future. As a consequence, in 2014 the
European Commission declared phosphate rock to be one of 20 critical resources for the
European Union (EU Commission, 2014).
Therefore, suggesting alternatives for phosphate recovery from secondary P-rich sources,
such as municipal wastewater, is of high importance. Numerous technologies have been
developed so far and most of them focus on phosphorus recovery from the sewage sludge or
sludge ashes after incineration. The majority of them are based on costly processes with
intensive chemicals consumption (Niewersch et al., 2014) or certain pre-conditions involving
e.g. additional expensive infrastructure such as a sludge mono-incineration facility.
Alternatively, phosphorus may also be recovered directly from the wastewater effluent, where
it is in a relatively low concentration distributed over a higher hydraulic load, assuming that
no earlier targeted elimination takes place. Adsorption is known to be one of the most
effective methods for removal of dissolved compounds in a low concentration range (μg/L-
mg/L). Applying a suitable adsorber may also allow recovery of the phosphate through
desorption in a suitable regeneration solution.
Material and Methods
The engineered composite microsorbents (20 to 25 µm) consist of superparamagnetic
nanosized magnetite particles (magnetic carriers) which are enclosed in a SiO2 matrix and
their surface is modified with a phosphate selective adsorber material (Mandel et al., 2013). A
broad range of potential selective phosphate adsorbers was pre-screened and finally ZnFeZr
hydroxide precipitate was selected for further detailed tests (Drenkova-Tuhtan et al., 2016).
The wastewater for the experiments was collected from the effluent of the sewage treatment
plant for education and research at ISWA, University of Stuttgart and was spiked with
phosphoric acid (H3PO4) to reach a desired initial PO4-P concentration of 10 mg/L.
Reusability of the particles was demonstrated in a 2 L lab-scale test within 60
adsorption/desorption cycles. A flow diagram of the phosphate removal and recovery process
is presented in Fig. 1.1. The solid-liquid separation was performed in a magnetic separation
column equipped with permanent magnets and the supernatant was collected and filtered
through a 0,45 µm syringe filter prior to analysis. Phosphorus concentrations of the samples
were determined spectrophotometrically with the ammonium molybdate method.
Results and Conclusions
A summary of the adsorption/desorption efficiency for every cycle is presented in Fig. 1.2.
Several reaction parameters (particles/adsorber concentration, contact time, pH, suspended
solids in wastewater and washing of the particles) were varied in different phases
(corresponding to the vertical lines) in order to improve and optimize the performance.
In the first ten adsorption cycles the particles concentration was set initially to 1 g/L, pH 7-8
and contact time 1h. The P-loaded particles were regenerated in a 1M NaOH solution for 1h
at pH 13, where simultaneous desorption of the phosphate ions took place, and then particles
and reclaimed solution were reused again in the next cycle. After 10 cycles, the constantly
reused P-rich desorption solution was sent for detailed analysis, and a new fresh
desorption/regeneration NaOH solution was applied from cycle 11 onwards. It was
continuously reused for the rest 50 cycles and gradually concentrated with phosphate ions.
After several adjustments of the process parameters, it can be concluded that particles dosage
of approximately 5 g/L (corresponding to 0.865 g/L ZnFeZr adsorber at 17 wt% loading),
contact time 20 min in both adsorption and desorption phases, pHads=7, pHdes13 are optimal
for the removal and recovery of phosphate from unfiltered wastewater effluent with ~ 10
mg/L PO4-P. At optimal conditions (cycle 48-60) the observed total efficiency was > 90%.
Optionally, a solid product can be further precipitated from the P-rich reclaimed solution.
A major advantage of the presented method is the dual benefit of phosphate elimination
(down to µg/L concentrations) and its subsequent recovery, thus having the potential to be an
attractive alternative to the conventional P-elimination processes at a WWTP. The goal of the
ongoing research is upscaling the technology by treating a total of 6.3 m3 wastewater.
Figure 1.1 Flow diagram of the phosphate elimination and recovery process with magnetic microsorbents.
Figure 1.2 Phosphate adsorption and desorption efficiency over 60 cycles of particlesreuse and adjustment of
the process parameters.
References
Cordell, D. and White, S. (2015), Tracking phosphorus security: indicators of phosphorus vulnerability in the
global food system. Food Sec., 7 (2015), 337–350.
Drenkova-Tuhtan, A.; Schneider, M.; Mandel, K.; Meyer, C.; Gellermann, C.; Sextl, G.; and Steinmetz, H.
(2016), Influence of cation building blocks of metal hydroxide precipitates on their adsorption and desorption
capacity for phosphate in wastewaterA screening study. Colloids Surf. A, 488 (2016), 145–153.
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Mandel, K.; Drenkova-Tuhtan, A.; Hutter, F.; Gellermann, C.; Steinmetz, H. and Sextl, G. (2013), Layered
double hydroxide ion exchangers on superparamagnetic microparticles for recovery of phosphate from waste
water. J. Mater. Chem. A, 1 (2013), 18401848.
Niewersch, C.; Ewert, W.; Hermanussen, O.; Kabbe, C.; Mele, C.; Paillard, H,; Stoessel, E.; Wagenbach, A. and
Stemann, J. (2014), Sustainable sewage sludge management fostering phosphorus recovery and energy
efficiency. Report D5.1 P-REX project supported by the European Commission, April 29th, 2014.
... Particularly in tropical soils, where reduced levels of available P are associated with elevated levels of Fe and Al oxyhydroxides, large doses of phosphate fertilizers are necessary for high yields, directing the main focus of this concern to agriculture-based countries such as Brazil (Roy et al., 2016). P recycling and reusing strategies have thus become recently studied (Drenkova-Tuhtan et al., 2016;Fink et al., 2016). The reuse of P can be achieved by immobilization, from the locations where it previously caused an environmental problem, such as in eutrophic or wastewater, for later use as phosphate fertilizer in agriculture. ...
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Increases in agricultural productivity associated to the crescent use of finite reserves of phosphorus improved the demand for ways to recycle and reuse this nutrient. Biochars, after doping processes, seem to be an alternative to mitigate the large use of P reserves. Sugarcane straw and poultry manure were submerged in an MgCl2solution in a 1:10 solid/liquid ratio and subsequently pyrolyzed at 350 and 650 °C producing biochar. Increasing concentrations of P were agitated with biochars in order to obtain the maximum adsorption capacity of P with the aid of Langmuir and Freudelich isotherm. MPAC was extracted, successively, with H2SO4(0.5 mol L-1), NaHCO3(0.5 mol l-1a pH 8.5) and H2O, until no P was detected in the solution. Biochars without the addition of Mg did not have the ability to adsorb P but had this property developed after the doping process. The poultry manure biochar presented higher MPAC (250.8 and 163.6 mg g-1of P at 350 and 650 °C, respectively) than that of sugarcane straw (17.7 and 17.6 mg g-1of P at 350 and 650 °C, respectively). The pyrolysis temperature changed significantly the MPAC values for the poultry manure biochar, with an increase in the adsorbed P binding energy for both biochars. H2SO4showed the best extraction power, desorbing, with a lower number of extractions, the greater amount of the adsorbed P. These materials doped with Mg and subjected to pyrolysis have characteristics that allow their use in P adsorption from eutrophic and wastewaters and therefore its use as a slow release phosphate fertilizer, indicating to be competitive in quality and quantity with available soluble chemical sources in the market.
... DAMO technology [3] can mitigate the detrimental CH 4 emission and link that with nitrogen removal. An interesting technique for removal and recovery of phosphorus was recently published by Drenkova-Tuhtan et al. [35], applying nanocomposite magnetic particles for adsorption and desorption of phosphate from wastewater. ...
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Thirteen metal hydroxide adsorbers were synthesized via precipitation by systematically varying different two-, three- and four-valent metal precursors, namely Mg2+, Ca2+, Zn2+, Fe3+, Al3+ and Zr4+. The resulting materials were classified in four groups based on their structure, morphology and BET surface area. Two of the groups could be classified as layered double hydroxides (LDH). The rest of the materials could be either only partially related to a LDH-like structure or formed non-layered precipitates. The phosphate removal performance of each adsorber (dose 200 mg/L) was tested in spiked distilled water and municipal wastewater (10 mg-P/L) at pH 7-8. The phosphate adsorption capacity of the materials after 1 h varied between 32 mg-P/g (for a rod-like-sample, lacking a layered structure) and 51 mg-P/g (for a sample appearing as a mixture of particulate matter covered with a web-like structure). Longer contact time (24 h) did not increase significantly the adsorption efficiency. None of the materials was ideally selective for phosphate, especially the ones with a clear LDH structure and highest surface area (110 m2/g) which adsorbed up to 25 mg/g Cl− and other competing anions. The adsorbed phosphate could be desorbed (> 90% in most of the cases) by treatment with an alkaline solution (0.5 M NaOH or 1 M NaOH + 1 M NaCl) which turned out to be the best option for regeneration among many other tested combinations.
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Superparamagnetic microparticles modified with an ion exchange system are reported for the recovery of phosphate from waste water by a magnetic separation technique. Layered double hydroxides (LDH), anionic clays, are precipitated from an aqueous solution and deposited by an ultrasonic treatment on superparamagnetic microparticles consisting of Fe3O4 multicores embedded in a SiO2 matrix. Deposition can be conducted in a batch process as well as in a continuous way, using an ultrasonic flow cell. The obtained composite particles show good magnetic separability and have a specific surface area of around 100 m2 g−1. Zr doped LDH shows improved phosphate adsorption in waste water. After magnetic separation and regeneration, the composite particles are re-used which is demonstrated for four cycles. Phosphate ions are concentrated in the regeneration solution. Simple, low cost, and a fast continuous synthesis of the composite particles paves the way for application beyond lab scale in real waste water treatment plants.
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Phosphorus underpins global food systems by ensuring soil fertility, farmer livelihoods, agricultural productivity and global food security. Yet there is a lack of research and effective governance at global or national scales designed to ensure the future availability and accessibility of this global resource. The world’s main source of phosphorus, phosphate rock, is a finite resource that is becoming increasingly scarce, expensive and subject to geopolitical tensions as one country, Morocco, controls three-quarters of the world’s remaining high-grade reserves. Given the criticality of phosphorus and the vulnerability of the world’s food systems to phosphorus scarcity, there is a strong need to stimulate appropriate sustainable phosphorus practices and technologies, and simultaneously, to initiate effective international governance mechanisms, including policy/research coordination and accountability. Sustainability indicators are increasingly being used as tools to facilitate accountability, implementation, evaluation and communication for global sustainability challenges. This paper presents the first comprehensive set of phosphorus vulnerability and security indicators at global and national scales. Global indicators include: phosphate price, market concentration and supply risk, relative physical phosphorus scarcity and eutrophication potential. National indicators include: farmer phosphorus vulnerability, national phosphorus vulnerability, national phosphorus equity and soil phosphorus legacy. Monitoring and tracking such indicators at the national and global levels can ultimately provide evidence of key phosphorus vulnerabilities or ‘hotspots’ in the food system, support effective phosphorus governance to stimulate targeted and effective action, raise awareness of this food security challenge, and evaluate the effectiveness and performance of global or national sustainable phosphorus projects.
Press release URL: www.europa.eu/rapid/press- release_IP-14-599_en.htm, website consulted on
European Commission (2014), Press release, Brussels, 26 May 2014. URL: www.europa.eu/rapid/press- release_IP-14-599_en.htm, website consulted on Oct. 27 th, 2015.
Sustainable sewage sludge management fostering phosphorus recovery and energy efficiency
  • C Niewersch
  • W Ewert
  • O Hermanussen
  • C Kabbe
  • C Mele
  • H Paillard
  • E Stoessel
  • A Wagenbach
  • J Stemann
Niewersch, C.; Ewert, W.; Hermanussen, O.; Kabbe, C.; Mele, C.; Paillard, H,; Stoessel, E.; Wagenbach, A. and Stemann, J. (2014), Sustainable sewage sludge management fostering phosphorus recovery and energy efficiency. Report D5.1 P-REX project supported by the European Commission, April 29 th, 2014.
Sustainable sewage sludge management fostering phosphorus recovery and energy efficiency. Report D5.1 P-REX project supported by the European Commission
  • E Stoessel
  • A Wagenbach
  • J Stemann
Stoessel, E.; Wagenbach, A. and Stemann, J. (2014), Sustainable sewage sludge management fostering phosphorus recovery and energy efficiency. Report D5.1 P-REX project supported by the European Commission, April 29 th, 2014.