Volume 41, Issue 9,
, 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.
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 (www.novaqatis.eawag.ch) 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
- K.M. Udert et al.
Urea Hydrolysis and Precipitation Dynamics in a Urine-Collecting System
- H. Sanderson et al.
Probabilistic hazard assessment of environmentally occurring pharmaceuticals toxicity to fish, daphnids and algae by ECOSAR screening
- M. Ronteltap et al.
Struvite precipitation thermodynamics in source-separated urine
- M. Maurer et al.
Treatment processes for source separated urine
- K.M. Lewis et al.
pKa values of estrone, 17 beta-estradiol and 2-methoxyestrone
- T.A. Larsen et al.
Separate management of anthropogenic nutrient solutions (human urine)
Water Sci. Technol.
- H. Jönsson et al.
Source-separated urine nutrient and heavy metal content, water saving and faecal contamination
Water Sci. Technol.
- B. Halling-Sorensen et al.
Occurrence, fate and effects of pharmaceutical substances in the environment—a review
- P. Chand et al.
Electron-paramagnetic resonance study of doped synthetic-crystals of struvite and its Zinc analog
Spectrochim. Acta A—Mol. Biomol. Spectrosc.
- F. Abbona et al.
Effect of ammonia excess on the crystal habit of NiNH4PO4·6H2O (Ni-Struvite)
J. Cryst. Growth
Crystal chemistry of struvite analogs of type MgMPO4·6H2O (M+=K+, Rb+, Cs+, Ti+, NH4+)
Micronutrient sources-metal ammonium phosphates as fertilizers
J. Agric. Food Chem.
Adsorption of pesticides onto quartz, calcite, kaolinite, and alpha-alumina
J. Environ. Quality
Urine Separation—Closing the Nutrient Cycle
Effectiveness of the water-insoluble component of triple superphosphate for yield and phosphorus uptake by plants
J. Agric. Sci.
Chemical composition and fertilizer use efficiency
Zukunftsweisende Sanitär und Abwassertechnik—erstes Pilotprojekt der Schweiz fur Urinseparierung, -speicherung und -steuerung im technischen Massstab
Re-engineering the toilet for sustainable waste water management
Environ. Sci. Technol.
Factors hindering the degradation of pharmaceuticals from human urine in an iron-activated persulfate system
2024, Journal of Environmental Sciences (China)
This study investigated the degradation of clofibric acid (CFA), bezafibrate (BZF), and sulfamethoxazole (SMX) in synthetic human urine using a novel mesoporous iron powder-activated persulfate system (mFe-PS system), and identified the factors limiting their degradation in synthetic human urine. A kinetic model was established to expose the radical production in various reaction conditions, and experiments were conducted to verify the modeling results. In the phosphate-containing mFe-PS system, the 120min removal efficiency of CFA decreased from 95.1% to 76.6% as the phosphate concentration increased from 0.32 to 6.45 mmol/L, but recovered to 90.5% when phosphate concentration increased to 16.10 mmol/L. Meanwhile, the increased concentration of phosphate from 0.32 to 16.10 mmol/L reduced the BZF degradation efficacy from 91.5% to 79.0%, whereas SMX removal improved from 37.3% to 62.9%. The mFe-PS system containing (bi)carbonate, from 4.20 to 166.70 mmol/L, reduced CFA and BZF removal efficiencies from 100% to 76.8% and 80.4%, respectively, and SMX from 83.5% to 56.7% within a 120-min reaction time. In addition, alkaline conditions (pH ≥ 8.0) inhibited CFA and BZF degradations, while nonacidic pH (pH ≥ 7.0) remarkably inhibited SMX degradation. Results of the kinetic model indicated the formation of phosphate (H2PO4·/HPO4·−) and/or carbonate radicals (CO3·−) could limit pharmaceutical removal. The transformation products (TPs) of the pharmaceuticals revealed more incompletely oxidized TPs occurred in the phosphate- and (bi)carbonate-containing mFe-PS systems, and indicated that H2PO4·/HPO4·− mainly degraded pharmaceuticals via a benzene ring-opening reaction while CO3·− preferentially oxidized pharmaceuticals via a hydroxylation reaction.
Dissolution rate and growth performance reveal struvite as a sustainable nutrient source to produce a diverse set of microbial protein
2023, Science of the Total Environment
To provide for the globally increasing demand for proteinaceous food, microbial protein (MP) has the potential to become an alternative food or feed source. Phosphorus (P), on the other hand, is a critical raw material whose global reserves are declining. Growing MP on recovered phosphorus, for instance, struvite obtained from wastewater treatment, is a promising MP production route that could supply protein-rich products while handling P scarcity. The aim of this study was to explore struvite dissolution kinetics in different MP media and characterize MP production with struvite as sole P-source. Different operational parameters, including pH, temperature, contact surface area, and ion concentrations were tested, and struvite dissolution rates were observed between 0.32 and 4.7 g P/L/d and a solubility between 0.23 and 2.22 g P-based struvite/L. Growth rates and protein production of the microalgae Chlorella vulgaris and Limnospira sp. (previously known as Arthrospira sp.), and the purple non‑sulfur bacterium Rhodopseudomonas palustris on struvite were equal to or higher than growth on conventional potassium phosphate. For aerobic heterotrophic bacteria, two slow-growing communities showed decreased growth on struvite, while the growth was increased for a third fast-growing one. Furthermore, MP protein content on struvite was always comparable to the one obtained when grown on standard media. Together with the low content in metals and micropollutants, these results demonstrate that struvite can be directly applied as an effective nutrient source to produce fast-growing MP, without any previous dissolution step. Combining a high purity recovered product with an efficient way of producing protein results in a strong environmental win-win.
Arsenic effects and behavior during the transformation of struvite to newberyite: Implications for applications of green fertilizers
2023, Chemical Engineering Journal
Struvite recovered from wastewaters is an increasingly popular green fertilizer but can sequester hazardous heavy metal(loid)s, including arsenic. The recycled struvite applied as fertilizers in soils often undergoes dissolution and subsequent transformation to newberyite over time, potentially resulting in arsenic contamination. Therefore, understanding the fate of arsenic during struvite transformation to newberyite is critical to its safe application. Herein, we have investigated the effects of arsenic on the transformation of struvite to newberyite and examined the associated consequences of this transformation for arsenic mobilization. Our results demonstrate that low arsenic contents have minor but detectable retardation on the struvite-newberyite transformation, and high arsenic loading can severely inhibit this transformation. However, the mechanisms of the struvite-newberyite transformation are independent of the arsenic concentrations. Most arsenic is retained in the solids during the struvite-newberyite transformation. Also, the arsenic contents in both struvite and newberyite increase with increasing the initial pH values. Moreover, spectroscopic analyses and first-principles calculations show that the dominant arsenic species incorporated is AsO43- in struvite but HAsO42- in newberyite. These results have important implications for understanding the roles of arsenic in struvite-based green fertilizers and developing optimal applications of these materials for the remediation of arsenic contamination in aqueous environments.
Donnan dialysis for phosphate recovery from diverted urine
2022, Water Research
There is a critical need to shift from existing linear phosphorous management practices to a more sustainable circular P economy. Closing the nutrient loop can reduce our reliance on phosphate mining, which has well-documented environmental impacts, while simultaneously alleviating P pollution of aquatic environments from wastewater discharges that are not completely treated. The high orthophosphate, , content in source-separated urine offers propitious opportunities for P recovery. This study examines the use of Donnan dialysis (DD), an ion-exchange membrane-based process, for the recovery of orthophosphates from fresh and hydrolyzed urine matrixes. transport against an orthophosphate concentration gradient was demonstrated and orthophosphate recovery yields up to 93% were achieved. By adopting higher feed to receiver volume ratios, DD enriched orthophosphate in the product stream as high as ≈2.5×the initial urine feed concentration. However, flux, selectivity, and yield of orthophosphate recovery were detrimentally impacted by the presence of SO42− and Cl− in fresh urine, and the large amount of HCO3− rendered hydrolyzed urine practically unsuitable for P recovery using DD. The detrimental effects of sulfate ions can be mitigated by utilizing a monovalent ion permselective membrane, improving selectivity for transport over SO42− by 3.1×relative to DD with a conventional membrane; but the enhancement was at the expense of reduced orthophosphate flux. Critically, widely available and low-cost/waste resources with sufficiently high Cl− content, such as seawater and waste water softening regenerant rinse, can be employed to improve the economic viability of orthophosphate recovery. This study shows the promising potential of DD for P recovery and enrichment from source-separated urine.
Urea hydrolysis and long-term storage of source-separated urine for reuse as fertiliser is insufficient for the removal of anthropogenic micropollutants
2022, Water Research
Human and animal source-separated urine, stored and allowed to naturally hydrolyse (the bio-catalysed transformation of urea to ammonia and bicarbonate), has been used for millennia as a fertiliser in agriculture. In a context of growing water scarcity and climate uncertainty, source-separation of urine is facing a strong revival thanks to the emergence of cost-effective waterless collection systems. Concomitantly, urine source-separation can be used as a method for nutrient recovery and subsequent reuse. In its simplest form, such recovery consists of collection followed by urea hydrolysis and storage as sole treatment. Numerous guidelines, including by the World Health Organisation, consider that this is sufficient to stabilise the nutrients and inactivate any potential pathogens in the urine. However, it is still unclear whether said urine is effectively free from other compounds of concern, such as anthropogenic micropollutants with known toxicological effects. Moreover, it is also currently unknown if the metabolites produced by human consumption of these products behave in similar way during short- and long-term storage i.e. whether any changes in chemical structure mean that these could be sorbed and/or precipitated in a different way, or if they can potentially be degraded by the biomass inherently present in urine collection systems. Finally, there is currently no knowledge of whether the observed concentrations of micropollutants in stored hydrolysed urine could potentially have toxicological effects if/when applied to soils and edible crops. To fill these research gaps, 20 commonly consumed compounds were selected in this study and their concentrations in the liquid and solid phases studied in the short- and long-term (up to ≥ 2 years). During the initial process of urea hydrolysis (≤ 5 days), ethyl-glucuronide was the sole compound effectively removed (by deconjugation), while only two other compounds, erythromycin and its metabolite, saw a reduction in their concentration (likely due to biomass sorption). Subsequently, during early storage (≤ 15 days), only three additional compounds were removed: paracetamol (> 99%), acesulfame (11.5%) and carbamazepine-10,11 epoxide (40.7%). Finally, long-term storage of up to 24 months did not result in any further significant removal for any of the measured compounds, indicating that the procedure of hydrolysis+storage is not effective for the removal of anthropogenic micropollutants. The results of this investigation raise strong concerns about the direct reuse of hydrolysed/stored human source-separated urine, and evidence the need for post-processing before implementation as fertiliser into edible crops due to the inherent toxicological risk, particularly to infants.
Effect of organics on Cu and Cr in recovered struvite from synthetic swine wastewater
2022, Journal of Cleaner Production
The fast development of struvite precipitation provides an excellent opportunity for cost-effective removal and recovery of nitrogen and phosphorus in swine wastewater. Meanwhile, swine wastewater is rich in heavy metals and organic matters, whose interaction might change heavy metals' distribution and toxicity in recovered struvite. This research investigates the effect of organic matter on heavy metals' speciation variation during phosphorus (P) recovery. The results demonstrate that when the concentration of citric acid, humic acid, and tetracycline increases from 0 to 500mg/L, the P recovery efficiency decreases from 95.14% to 85.39%, 81.76%, and 74.28%, respectively. When the concentration of ammonium citrate, tetrasodium iminodisuccinate, and ethylenediaminetetraacetic acid vary from 0 to 100mg/L, the P recovery efficiency decreases from 95.14 to 83.21, 85.97, and 81.32mg/L, respectively, while the Cr in recovered struvite is increased from 1.88 to 2.92mg/kg, 1.58–2.64mg/kg and 0.86–12.6mg/kg, respectively. It could be concluded that the pH increase promotes Cr and Cu's toxicity shifting to a stable state under the presence of citric acid, while Cr and Cu with humic acid or tetracycline shift to an active state. Besides, chelating agents can reduce heavy metal contents in the recovered struvite, but they also significantly inhibit the P recovery efficiency.
Life cycle comparison of centralized wastewater treatment and urine source separation with struvite precipitation: Focus on urine nutrient management
Water Research, Volume 79, 2015, pp. 88-103
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.
The incorporation of Pb2+ during struvite precipitation: Quantitative, morphological and structural analysis
Journal of Environmental Management, Volume 276, 2020, Article 111359
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.
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.
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.
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.
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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