The behaviour of pharmaceuticals and heavy metals during struvite precipitation in urine (2023)

Water Research

Volume 41, Issue 9,

May 2007

, Pages 1859-1868

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Separating urine from wastewater at the source reduces the costs of extensive wastewater treatment. Recovering the nutrients from urine and reusing them for agricultural purposes adds resource saving to the benefits. Phosphate can be recovered in the form of struvite (magnesium ammonium phosphate). In this paper, the behaviour of pharmaceuticals and heavy metals during the precipitation of struvite in urine is studied.

When precipitating struvite in urine spiked with hormones and non-ionic, acidic and basic pharmaceuticals, the hormones and pharmaceuticals remain in solution for more than 98%.

For heavy metals, initial experiments were performed to study metal solubility in urine. Solubility is shown to be affected by the chemical conditions of stored and therefore hydrolysed urine. Thermodynamic modelling reveals low or very low equilibrium solute concentrations for cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), nickel (Ni) and lead (Pb). Experiments confirmed Cd, Cu and Pb carbonate and hydroxide precipitation upon metal addition in stored urine with a reaction half-life of ca. 7 days.

For all metals considered, the maximum specific metal concentrations per gram phosphate or nitrogen showed to be typically several orders of magnitudes lower in urine than in commercially available fertilizers and manure. Heavy metals in struvite precipitated from normal stored urine could not be detected.

Phosphate recovery from urine over struvite precipitation is shown to render a product free from most organic micropollutants and containing only a fraction of the already low amounts of heavy metals in urine.


Urine separation as a sustainable sanitary concept is gaining ground. Research on and implementation of this novel technology takes place in a growing number of countries (Peter-Fröhlich et al., 2004; Wilsenach and van Loosdrecht, 2003; Kühni et al., 2002; Larsen et al., 2001; Johansson, 2001). The advantages of urine separation are considerable. Urine represents a small but concentrated stream, so by separating it from the main wastewater stream the nutrient load on the wastewater treatment plant can be reduced significantly (Larsen and Gujer, 1996). Additionally, the nutrients become available for recovery and re-use. Different techniques have been studied to remove and recover nutrients from urine, focusing mainly on nitrogen and phosphate (Maurer et al., 2006; Udert et al., 2003a; Pronk et al., 2006a; Wilsenach and van Loosdrecht, 2006). An efficient phosphate removal technique is the precipitation of struvite. Struvite is a crystal built up from magnesium, ammonium and phosphate in a 1:1:1 molar ratio. Its precipitation from urine is a fast and undemanding process with respect to energy and necessary chemicals. Due to its low solubility in hydrolysed urine (pH 9) the addition of magnesium causes the solution to be supersaturated with struvite, leading to immediate precipitation (Ronteltap et al., accepted).

Struvite can be used as a fertilizer in agriculture (Bridger et al., 1962; Johnston and Richards, 2003). Separate collection of urine, therefore, offers an opportunity to re-use nutrients directly as fertilizers. However, urine also contains substances which are not desirable in agriculture. In a screening assay of 212 pharmaceuticals an average of 64% of each compound was excreted via urine (Lienert et al., 2006). From urine-based fertilizer products, these substances may diffuse into the aquatic environment or accumulate in soils and have an adverse effect on human health and environment (Sanderson et al., 2003; Halling-Sorensen et al., 1998). Although currently no specific threshold values are available for micropollutants in fertilizers, the introduction of potential hazardous substances into the environment should be avoided (Pronk et al., 2006b).

Another potential threat is posed by heavy metals. Under normal circumstances the human intake of heavy metals is low, which is reflected by low concentrations in urine (Ciba-Geigy, 1977). However, their accumulation in the soil is a serious concern for sustainable agriculture. Therefore, strict regulations are in place for heavy metal concentrations in fertilizer products.

In this paper, we quantify the incorporation of pharmaceuticals, hormones and heavy metals to be incorporated into struvite during precipitation in source-separated human urine.

In this paper, we assess the possibility for pharmaceuticals, hormones and heavy metals to be incorporated into struvite during precipitation in source-separated human urine.

To study the behaviour of pharmaceuticals and hormones, experiments with spiked urine are carried out in a batch as well as a continuous flow set-up. The specific metal concentrations per gram of phosphorus and nitrogen are calculated and compared to the values for existing industrial fertilizers. To gain more insight into the behaviour of metals in urine, we perform a kinetic study and set up a thermodynamic model to predict equilibrium concentrations. By performing struvite precipitation experiments in heavy metal-spiked urine we investigate the possibility of metal contamination in struvite. No risk or hazard assessments are performed, rather data are provided which can be used in other studies which aim to perform a comprehensive risk analysis.

Section snippets

Pharmaceuticals and hormones

Pharmaceuticals, hormones and their metabolites found in urine form a broad group of anthropogenic organic chemicals with a variety of structures. Some molecules contain ionic groups (e.g. carboxyl groups) and are, therefore, strongly influenced by pH (Schwarzenbach et al., 2003). Both ionic and non-ionic organic molecules are reported to adsorb to the surface of inorganic minerals (Clausen et al., 2001).

For this study, a mixture of commonly applied pharmaceuticals and hormones is used.

Filters, reagents, stock solutions and urine

Whatman GF/F filters originated from American Membrane Corporation, Michigan; 0.45μm membrane filters from Hach Lange GmbH, Düsseldorf. All pharmaceuticals were obtained from Sigma (Buchs, Switzerland), all other chemicals from Merck (analytical quality). A concentrated stock solution with pharmaceuticals was produced containing 2.24×10−2M (4.10gL−1) diclofenac, 1.34×10−2M (2.76gL−1) ibuprofen, 5×10−3M (1.48gL−1) propranolol, 2×10−2M (4.73gL−1) carbamazepine, 7.4×10−7M (200μgL−1) estradiol E2


Initial batch experiments were carried out with struvite precipitation in urine spiked with propranolol and the hormones estron (E1), estradiol (E2) and ethinylestradiol (EE2). The experiments revealed that of the recovered fractions (mass sum of filtrate and re-dissolved struvite), 99%, 97%, 95% and 100% of, respectively propranolol, E1, E2 and EE2 remained in solution.

Similar results were obtained in batch and continuous experiments with urine spiked with a broader spectrum of


In this paper, the behaviour of pharmaceuticals, hormones and heavy metals during struvite precipitation in source-separated urine was studied. The main conclusions are:

During struvite precipitation, hormones as well as pharmaceuticals (non-ionic, acidic and basic) remain in solution for >98%.

The introduction of a washing step after filtration results in a slightly cleaner product.

The chemical conditions of stored and, therefore, hydrolysed urine influence the solubility of dissolved metals.


The authors would like to thank Rainer Hausherr and Jaqueline Traber for their great assistance with performing the experiments. We kindly thank the Novaquatis management ( for support and coordination of the experiments. For the development of the analytical methods and the measurements we thank Nadine Bramaz, Manuela Richter, Martin Biebow, Christoph Bill, Raimund Wütrich, Daniel Sutter, Mischa Zschokke, Rene Schönenberger, Philippe Trachsler, Elvira Keller, Alfredo

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      Alternative approaches to wastewater management including urine source separation have the potential to simultaneously improve multiple aspects of wastewater treatment, including reduced use of potable water for waste conveyance and improved contaminant removal, especially nutrients. In order to pursue such radical changes, system-level evaluations of urine source separation in community contexts are required. The focus of this life cycle assessment (LCA) is managing nutrients from urine produced in a residential setting with urine source separation and struvite precipitation, as compared with a centralized wastewater treatment approach. The life cycle impacts evaluated in this study pertain to construction of the urine source separation system and operation of drinking water treatment, decentralized urine treatment, and centralized wastewater treatment. System boundaries include fertilizer offsets resulting from the production of urine based struvite fertilizer. As calculated by the Tool for the Reduction and Assessment of Chemical and Other Environmental Impacts (TRACI), urine source separation with MgO addition for subsequent struvite precipitation with high P recovery (Scenario B) has the smallest environmental cost relative to existing centralized wastewater treatment (Scenario A) and urine source separation with MgO and Na3PO4 addition for subsequent struvite precipitation with concurrent high P and N recovery (Scenario C). Preliminary economic evaluations show that the three urine management scenarios are relatively equal on a monetary basis (<13% difference). The impacts of each urine management scenario are most sensitive to the assumed urine composition, the selected urine storage time, and the assumed electricity required to treat influent urine and toilet water used to convey urine at the centralized wastewater treatment plant. The importance of full nutrient recovery from urine in combination with the substantial chemical inputs required for N recovery via struvite precipitation indicate the need for alternative methods of N recovery.

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      The incorporation of Pb2+ during struvite precipitation: Quantitative, morphological and structural analysis

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      Struvite precipitated from wastewaters is an important fertilizer. However, struvite derived from wastewater usually contains toxic Pb, which can bring contamination to soil and even plants. Thus, understanding the incorporation mechanisms of Pb2+ during struvite precipitation is critical to its safe application. Here the influence of Pb concentration on struvite precipitation was assessed. When the initial Pb concentrations were at the range of 0.1–1mg/L, the formation of pitting and roughening on struvite crystal surfaces was observed by scanning electron microscopy (SEM), indicating a surface interaction between Pb and struvite. Combined with X-ray photoelectron spectra (XPS), the results confirmed that the formed Pb-enriched layer with Pb–OH and Pb-PO4 bonds was absorbed on struvite surface during precipitation. When Pb concentrations were increased to 10–100mg/L, the precipitation of dominating Pb phase, crystalline Pb10(PO4)6(OH)2, was confirmed by X-ray diffraction (XRD). Combined with XPS, the amorphous Pb hydroxide/phosphate and Mg phosphate were also detected in struvite solids. Our findings revealed that at low concentrations (0.1–1mg/L), Pb can affect the mineral surface by surface absorption, whereas Pb precipitated as separated phase(s) (e.g. Pb10(PO4)6(OH)2, Pb hydroxide and/or phosphate) at high Pb concentrations (10–100mg/L). Thus, the initial Pb2+ concentrations in wastewater will dictate final struvite contents and Pb-bearing phases in recovered solids.

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      Recovery of phosphorus and nitrogen from human urine by struvite precipitation, air stripping and acid scrubbing: A pilot study

      Chemosphere, Volume 212, 2018, pp. 1030-1037

      Sustainable and closed-loop nutrient cycling require the recovery of valuable resources from wastewater. Resource recovery from diluted wastewater streams is limited by diluted concentrations and unfavorable reaction kinetics. In comparison, source separated urine allows resource recovery from a highly concentrated nutrient stream, resulting in a more sustainable and efficient recovery practice. Different nutrient recovery methods from urine have been studied in lab-scale, but pilot or full-scale process evaluations remain sparse. In this study, recovery of struvite and ammonium sulfate from urine of pregnant women was demonstrated at a pilot-scale treatment facility by means of precipitation and air stripping/acid scrubbing. The system achieved 94% struvite precipitation efficiency but merely 55% of the crystals were removed and recovered. The low phosphorus recovery was due to the washout of small crystals that escaped the sieve and settling tank, hence requiring an improved method for crystals capture. The removal and recovery efficiencies for nitrogen were 93% and 85%, respectively. Composition analysis of the produced fertilizers indicated that struvite was the dominated precipitate and quality of the ammonium sulfate met European standards. Carbamazepine and diclofenac were added in the urine to measure the fate of pharmaceuticals in the treatment system. Very little of the spiked pharmaceuticals (<0.01%) accumulated in the produced struvite and ammonium sulfate. The overall energy demand of the pilot system was 1066 MJ per m3 urine processed or 198 MJ per kg N removed. Energy efficiency was not optimized and can be improved in many ways.

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      Characterization of induced struvite formation from source-separated urine using seawater and brine as magnesium sources

      Chemosphere, Volume 93, Issue 11, 2013, pp. 2738-2747

      Struvite (MgNH4PO4·6H2O) precipitation is widely used for nutrient recovery from source-separated urine in view of limited natural resources. Spontaneous struvite formation depletes the magnesium in hydrolyzed urine so that additional magnesium source is required to produce induced struvite for P-recovery. The present study investigated the morphology and purity of induced struvite crystals obtained from hydrolyzed urine by using seawater and desalination brine as low cost magnesium sources. The results demonstrated that both seawater and brine were effective magnesium sources to recover phosphorus from hydrolyzed urine. Crystals obtained from synthetic and real urine were revealed that the morphology was feather and coffin shape, respectively. Structural characterization of the precipitates confirmed that crystallized struvite was the main product. However, co-precipitates magnesium calcite and calcite were observed when seawater was added into synthetic and real urine, respectively. It was found that the presence of calcium in the magnesium sources could compromise struvite purity. Higher struvite purity could be obtained with higher Mg/Ca ratio in the magnesium source. Comparative analysis indicated that seawater and brine had similar effect on the crystallized struvite purity.

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      Nutrient recovery from anaerobically digested chicken slurry via struvite: Performance optimization and interactions with heavy metals and pathogens

      Science of The Total Environment, Volume 635, 2018, pp. 1-9

      The aim of this study was to assess the potential of struvite precipitation to recover nutrients from anaerobically-processed poultry slurry and struvite's interactions with heavy metals (Zn, Cu, Pb, Cr, and Ni) and pathogens (total coliforms and Escherichia coli). The impacts of pH, Mg, N, and P molar proportion, reaction time, and mixing rate and duration were explored to determine the optimal conditions for nutrient recovery through struvite precipitation. A pH range of 9.5 to 10.5, was ideal for P and N removal and recovery, with a molar ratio of 1:1:1 for Mg:N:P. A mixing rate of 150rpm for 10min could allow nutrient recovery with little loss (3.32%) of NH₃ through volatilization, and also achieve an optimal struvite crystal size (50–60μm). The results of X-ray diffractometry and scanning electron microscopy confirmed that the precipitates generated at pH9 and 10 were orthorhombic struvite. Moreover, along with the recovery of nutrients, 40, 45, 66, 30, and 20% of Zn, Cu, Pb, Cr, and Ni, respectively, and 70% total coliforms and E. coli were removed by struvite precipitation from poultry slurry. This was observed despite that the levels of contaminants (heavy metals) detected in struvite were well below the permissible limits and free of pathogens. Consequently, it was inferred that the struvite quality was reasonable by virtue of its heavy metal and pathogen content, and therefore appropriate for application in the field. Similarly, struvite precipitation has multiple benefits as it can effectively recover nutrients as well as reducing pathogenic populations.

    • Research article

      Quantification and mitigation of the negative impact of calcium on struvite purity

      Advanced Powder Technology, Volume 27, Issue 6, 2016, pp. 2354-2362

      The dairy industry is a major economic sector in New Zealand with a large amount of wastewater being produced annually. These wastewaters are rich in phosphorus (P), and can be used as a potential source for struvite crystallisation for fertilizer production and environmental pollution abatement. However, this technique is hindered by the presence of foreign ions, especially calcium, which is present in high concentrations in dairy waste. This work aims to resolve the negative extent of the effect of calcium on struvite crystallisation to establish quantitative recommendations around where P recovery using this method is feasible. The impact of calcium concentration on the purity, morphology and particle size was assessed using laboratory experiments, mimicking the composition of typical dairy wastewaters, at a pH of 9 and room temperature. The results indicate that only at high Ca:Mg concentration ratios of more than one did the calcium adversely affect the product morphology and the fraction of struvite in the final product. There was negligible effect when the calcium concentration was low. Furthermore, a high ammoniac nitrogen concentration mitigated the negative impact, and therefore has to be taken into consideration when wastewaters with both high calcium and nitrogen content are considered as feedstock.

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