Aerated Fluidized Bed Treatment for Phosphate Recovery from Dairy

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Aerated Fluidized Bed Treatment for Phosphate Recovery from Dairy and Swine Wastewater Alon Rabinovich, Ashaki A. Rouff, Beni Lew, and Marlon Ramlogan ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b02990 • Publication Date (Web): 16 Nov 2017 Downloaded from http://pubs.acs.org on November 21, 2017

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ACS Sustainable Chemistry & Engineering

Aerated Fluidized Bed Treatment for Phosphate Recovery from Dairy and Swine Wastewater Alon Rabinovich1, Ashaki A. Rouff,1* Beni Lew2, Marlon V. Ramlogan1. 1

Department of Earth and Environmental Sciences, Rutgers University, 101 Warren Street, Newark, New Jersey 07102, USA

2

Institute of Agricultural Engineering, ARO Volcani Center, P.O Box 6, Bet Dagan 50250, Israel

*Corresponding author contact information: Address: Department of Earth and Environmental Sciences, Rutgers University, 101 Warren Street, Newark, NJ 07102, USA. Email: [email protected] Phone: (973) 353-2511 Fax: (973) 353-1965

1 ACS Paragon Plus Environment


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Abstract An aerated fluidized bed reactor (aerated-FBR) was used for recovery of orthophosphate (PO4-P) from dairy (D-WW) and swine (S-WW) wastewater by struvite (MgNH4PO4·6H2O) precipitation. Model wastewater solutions (S-model, D-model) free of organic material were also treated. The maximum PO4-P recovery for treated livestock wastes was 94% for S-WW and 63% for D-WW. The PO4-P recovery did not improve for S-model compared to S-WW, but increased to 81% for D-model relative to D-WW, suggesting the high organic content of D-WW may hinder the recovery process. X-ray diffraction (XRD) analysis of recovered solids revealed that treated S-WW produced mostly struvite (95-98%) while D-WW yielded a mixture of struvite (28-33%), calcite (CaCO3) (17-55%) and monohydrocalcite (CaCO3·H2O) (13-42%). The Fourier transform infrared (FTIR) spectra of the solids confirm the presence of vibrational bands associated with these minerals. Simultaneous thermal analysis (STA) indicated that all solids, except for D-WW, show thermogravimetric (TG) trends consistent with the struvite and calcium carbonate content. The D-WW solids had additional TG steps, possibly due to high organic and colloidal content, and slightly improved ammonium stability. The aerated-FBR treatment is an effective method to reduce PO4-P from livestock wastewater through precipitation of pure struvite and struvite/calcium carbonate mixtures.

Keywords: struvite, livestock wastewater, nutrient recycling, aerated fluidized bed, XRD, FTIR, STA-EGA


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Introduction Livestock wastewater is nutrient-rich with high concentrations of orthophosphate (PO4-P) and ammonium (NH4-N), both extensively used by agronomic crop producers.1,2 The phosphorus (P) is present as PO4-P and organic P, such as phytic acids, that eventually degrade into PO4-P.3 The NH4-N is mostly from excess proteins in feed that are excreted as urea in urine.4 The United States (U.S.) livestock population consists mostly of poultry, hogs, and cattle. The hog and cattle industries with ~70-90 million animals per year contribute ~40% of nitrogen (N) and P emitted through livestock waste.5,6 The majority of livestock in the U.S are raised in concentrated animal feeding operations, which are regulated as contaminant point sources.1 Thus, all of their liquid wastes are contained in lagoons or storage/settling tanks, and are commonly discharged to topsoil as fertilizer through spraying.7,8 Wastewater discharged in this manner, as part of a nutrition management plan, has limited benefit as fertilizer because application is imprecise and the nutrients are not in slow release form.9 Effluent spraying also results in unnecessary water losses and contributes to greenhouse gas emissions.10,11 In some soil types such application may result in a reduction in crop yield due to excess PO4-P, salinity, and micronutrient accumulation over time.12,13 Excess nutrients in soils degrade water quality through eutrophication of surface waters via runoff, and leaching into groundwater by nitrification.14,15 Agricultural wastewater can be treated for nutrient recovery by an aerated fluidized bed reactor (aerated-FBR) method that precipitates PO4-P and NH4-N as struvite (MgNH4PO4·6H2O), a viable slow release fertilizer.16-18 Struvite precipitation is predicted from its saturation index (SI), which is influenced by Mg2+, NH4-N and PO4-P concentrations (eq. S1-S2), and is optimized at pH 9-1019-21 (Figure S1). For aerated-FBR treatment, struvite precipitation can be



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induced by raising the wastewater pH from a typical value of pH 6-8 to pH 8-9 by carbon dioxide (CO2(g)) stripping with aeration and sodium hydroxide (NaOH) titration.22 In this pH range other PO4-P salts, such as hydroxyapatite (Ca5(PO4)3OH; HAP) can also be supersaturated.23 Addition of struvite seeding can promote rapid mineralization around nucleation sites, increasing the rate of struvite formation relative to other PO4-P minerals.24 Although struvite components are required at an equimolar ratio (eq. S1), raising the Mg2+:PO4-P molar ratio to ~2:1 by Mg2+ addition further reduces the precipitation of competing PO4-P minerals.25 At high dissolved potassium (K) concentrations, isomorphic substitution for NH4+ may form K-struvite (KMgPO4·6H2O).26, 27 Struvite recovery can be hindered by dissolved organic carbon (DOC), and high Ca2+ content that lowers the Mg2+:Ca2+ ratio and oversaturates HAP.28 Calcite (CaCO3) and monohydrocalcite (CaCO3⋅H2O) are other Ca-bearing minerals that can form at high carbonate concentrations. Monohydrocalcite forms at Mg2+:Ca2+ ratios >1:1.2, a common condition in wastewaters.29 Complexation of Ca2+ with PO4-P, and calcite formation reduces the struvite growth rate, and produces poorly crystalline struvite.30 Similarly, high DOC concentration slows struvite growth and creates amorphous solids with PO4-P polymers.31 Smaller crystals and/or amorphous, flake-like particles are difficult to separate from wastewaters due to low density and higher buoyancy, and have poor aerated-FBR recovery. Struvite production from swine wastewater (S-WW) is well described,32 but few studies have investigated dairy wastewater (D-WW).33-36 The objectives of this study are to evaluate aerated-FBR treatment, using a unique small-scale design, for treatment for P recovery as struvite from S-WW and D-WW; optimize recovery by adjusting the hydraulic retention time (HRT); and assess the role of both HRT and wastewater constituents, such as Ca and organics,


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on the mineralogical, chemical and physical and properties of the recovered solids using geochemical techniques. Model solutions with similar inorganic compositions to the wastewaters (S-model, D-model) are analyzed in parallel to evaluate the effect of organics and Ca. Results elucidate the viability of the aerated-FBR method for treatment of different types of livestock wastewaters, predicts the expected P recovery contingent upon source, and the impact of wastewater type on the solids recovered. Ultimately, treatment of livestock wastewater for struvite fertilizer production can be an alternative to direct discharge of wastewaters to soils, and promotes sustainable use of nutrient resources.

Materials and Methods Wastewater and model solutions Dairy and swine wastewater were collected from Fulper Farm, Lambertville New Jersey, and the Rutgers New Brunswick New Jersey Agricultural Experiment Station, respectively. Liquid wastes were collected from a treatment lagoon on the dairy farm, and from a settling pool on the swine farm. The wastewaters were characterized for total P (as PO4-P mg/L by acid persulfate digestion), NH4-N, NO3-N, alkalinity (as CaCO3), Cl and DOC using colorimetry (Hach, DR-3900), and for trace and major elements by inductively coupled plasma optical emission spectroscopy (ICP-OES; Agilent, 5110 SVDV). Colorimetry and elemental analyses were conducted in duplicate and triplicate, respectively. Visual MINTEQ software37 was used for equilibrium modeling of wastewater composition to determine ionic strength, speciation and struvite saturation (Figure S1). The complexation of Ca with DOC was estimated using a Gaussian model, assuming normal distribution of ligand sites38 (Table S1, Figure S2). The organic molecular weight was input as 1500 Da, based on the 1-3000 Da range observed for organics in livestock waste.39 Model dairy and swine wastewaters were prepared



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with similar concentrations of major ions at the wastewater ionic strength (Table 1). Solutions were prepared in deionized water (DI) using KCl, MgCl2·6H2O, (NH4)2HPO4, NH4HCO3, NaNO3, NH4Cl and CaCl2·2H2O reagents (ACS grade, Thermo Fisher; Arcos Organics).

Aerated fluidized bed reactor A 14 L polyvinyl carbonate aerated-FBR was constructed with two chambers: a continuous flow stirred-tank reactor (CSTR) and a fluidized bed (FB) canal, connected by a 0.5” gap at the base of their shared wall (Figure 1). Most struvite reactors are either plug-flow or CSTR with separate FBRs.16,32,35 Thus, the combination of the CSTR and FBR into a single compact unit is a novel design.22 For CO2(g) purging, air flow is applied to the CSTR at 42 L air L-1 reactor volume hr-1 to maximize CO2(g) stripping while minimizing NH4-N volatilization,22 and a vacuum tube removes foam formed by aeration. Loss of NH4-N as NH3(g) was negligible, with no effect on struvite SI (Figure S3a). Influent solutions are added to the reactor using peristaltic metering pumps (Masterflex, Cole Parmer; Peristaltic, Fisher). Air flow and influent stirring (400 rpm) generates sufficient agitation for homogenization, and to prevent solid settling. The FB chamber has an inverted trapezoid profile that expands at its top, where an outflow tube is placed. The upward expansion of the FB canal reduces the effluent flow velocity, forcing free fall of larger suspended solids, thereby separating the effluent leaving the reactor from the solids formed in the CSTR.

Phosphate recovery Aerated-FBR treatment of wastewaters and model solutions was performed in batch then steady state flow-through mode. In batch mode, wastewater or model solution influent was added to the reactor and aerated for the duration of one HRT: HRT= [total reactor volume (14 L)]/ [influent flow rate (L/min)] (eq.1)


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Aeration raised pH to 8-8.5 (Figure S3b), and NaOH was used to titrate to pH 9. In flow-through mode, magnesium chloride (Mg2+) was added to the influent, and struvite seed at 0.1g/L reactor volume applied. Influent pumping rates were 880, 400 or 200 mL/min wastewater or model solution plus 28, 12 or 6 mL/min Mg2+ solution, for 15, 35 or 68 min HRT. A 35 min HRT was effective for struvite recovery from municipal wastewater,22 and was doubled or halved to optimize P recovery for the wastewaters studied here. A small volume of 2.5 N NaOH was titrated continuously to maintain pH at 9. Six samples were collected for each treatment: influent wastewater/model (S0), aerated batch mode effluent (S0a), and four flow-through effluent samples (S1-S4). To ensure steady state conditions in flow-through mode, the treatment was carried out for three HRTs (three reactor volumes of 14 L) before collecting the first sample (S1). Treatment was continued for three additional HRTs, with samples taken at the end of each HRT (S2-S4). All samples were collected from the FB chamber outlet, filtered through a 0.45 µm membrane and analyzed for P (as PO4-P) and NH4-N by colorimetric analysis. For statistical evaluation, the software module JMP 12.0 (SAS) was used to compare P removal between aerated-FBR experiments (Table S2). The percent P removal was calculated as: [1-(Si/S0)]×100

(eq. 2)

where Si is the mean P concentration of S1-S4 and S0 is the influent P concentration. To compare multiple treatments, an analysis of variance (ANOVA) was applied together with a TukeyKramer comparison of means40 at a 0.95 confidence level (eq. S3).

Solid characterization. Solid samples were collected from the reactor and air-dried. A mass of 50 ± 0.1 mg solid was dissolved in 10-15 mL 5% HCl, and filtered through a 0.45 µm membrane to separate the insoluble solid fraction. The filter residue was air-dried and weighed to determine



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recovered mass. The filtrate was analyzed by ICP-OES and colorimetry for elemental composition, P and NH4-N. Solids were analyzed by X-ray diffraction (XRD; D8 Advance, Bruker) from 5-60 °2θ at 0.016 °2θ resolution. TOPAS 4.2 software (Bruker) was used to estimate the mineral phase distribution by semi-quantitative analysis of the XRD patterns using a convolution based profile fitting fundamental parameters approach),41 combined with phase analysis (see Supporting Information). Degree of crystallinity was estimated using EVA software (Bruker). Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR; Perkin Elmer, Spectrum 100) scans were collected from 650-4000 cm-1 at 4 cm-1 resolution for additional mineralogical characterization and evaluation of functional groups. Simultaneous thermal analysis (STA) and evolved gas analysis (EGA) (Netzsch, Perseus STA 449 F3, Bruker Alpha FTIR) was performed from 28-1060 °C at a 20°C min-1 heating rate in a nitrogen (N2(g)) atmosphere. FTIR spectra for EGA were collected from 600-4000 cm-1 at 8 cm-1 resolution. Temperature ranges for ammonia (NH3(g)), water vapor (H2O(g)) and CO2(g) evolution were determined from the corresponding gas absorption peaks at 966, 1510 and 2360 cm-1, respectively. A Gram-Schmidt (GS) process of orthonormalizing was used to relate the total FTIR scan to the gas signal intensity. This data was compared to differential scanning calorimetry (DSC) results to determine the enthalpies of decomposition for gas release.

Results and Discussion Aerated-FBR P recovery The percent P recovery was compared for wastewater and model solutions (Figure 2a), and the significance of observed trends confirmed by Tukey Kramer


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statistical analysis (Figure 2b). More P removal was observed for S-WW (92-94%) than D-WW (46-64%); with no effect of HRT on removal from S-WW, and ~18% improvement for D-WW68 compared to D-WW-35. Since D-WW has higher DOC (800 mg/L) and Ca (5 mM) than SWW (200 mg/L and 1mM respectively) (Table 1), and these are known to inhibit struvite formation, both the amount of P and the rate of removal are lower. Comparing S-WW and Smodel, similar P removal was observed for S-model-35 and S-WW samples. However, S-model15 had the lowest P removal of all treated samples (44%). In S-WW, the Ca concentration is low, so complexation with DOC may sufficiently reduce free Ca2+ (Table S1), limiting any inhibitory effect on struvite formation. For S-model, in the absence of complexing organic ligands, Ca effectively reduces the rate of removal, requiring a longer HRT for recovery commensurate with S-WW. The D-model solutions showed no effect of HRT on P removal. However, P removal is enhanced for D-model-35 relative to D-WW-35, but is comparable for D-model-68 and D-WW68. Therefore, either higher DOC concentration, or its composition in D-WW,31 lowers the rate of P removal. These results provide some insight into the influence of DOC and Ca on struvite precipitation. When the Ca and DOC concentration is low, as in S-WW, complexation between the two appears to mitigate inhibitory effects of both components on the P removal rate. However, for D-WW, higher DOC may inhibit P removal, as the presence of Ca alone in Dmodel does not have an effect. Though these findings allow inferences to be made regarding the role of DOC on the observed processes, additional research is required to confirm the precise mechanisms.

Composition of aerated-FBR solids Approximately 12-24% of solids collected from D-WW treatment were in the insoluble fraction, consisting of wastewater suspended solids, compared to



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2% of S-WW solids (Table 2). In the soluble fraction, D-WW solids had higher DOC content (729% w/w) than S-WW solids (2-5% w/w). This is consistent with the higher DOC content in DWW (Table 1), precipitation of which may impact the P recovery process. The highest P content was observed for S-WW and S-model solids, in keeping with the P removal trend. The potassium (K) content was used as an indicator for K-struvite formation, with significant K only observed in D-WW solids, due to higher wastewater K concentrations.27 Similarly, higher carbonate concentration yielded higher calcite content for D-WW solids. The presence of trace elements in the solids is attributed to their build up through sorption by struvite42-45 and/or calcite. This process increased the trace element concentrations of the solids, even from the model solutions which had initial concentrations below ICP-OES detection limits.

Mineralogy and crystallinity of aerated-FBR solids The XRD patterns of the solids were used to confirm the mineralogy and determine crystallinity (Figure 3, Table S3). The mineral phase distributions, as calculated by mineralogical analysis of the XRD diffraction patterns (Figure S4), were compared to results from the solid elemental analysis. Results showed a poor match between struvite and K-struvite estimates from the mineralogical analysis and measured K content in solids. This occurs due to significant overlap between the XRD patterns of struvite and K-struvite. The K-struvite content was therefore estimated from the K:P molar ratio. Calcite and monohydrocalcite cannot be distinguished based on the total Ca content, however their XRD diffraction patterns are distinct, resulting in good quantification of these minerals. Results of the semi-quantitative analysis show differences in precipitated minerals contingent upon wastewater type. The S-WW and S-model solids yielded almost pure struvite (93-98%), consistent with the highest P removal and lower influent Ca concentration. The S-


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model-15 solid had the lowest fraction of struvite (78%), also in keeping with the P removal trend. This solid also had the highest fraction of calcite (21%), correlated with the highest elemental Ca concentration. Therefore the presence of Ca reduces struvite formation through precipitation of Ca-bearing minerals. The D-WW solids were a mixture of struvite (28-33%), Kstruvite (3-8%), calcite (17-55%) and monohydrocalcite (13-42%). The low fraction of struvite correlates with less effective P removal compared to S-WW samples. The D-model solids had higher struvite content (50-58%) and a lower fraction of Ca-bearing minerals (41-44%) though the initial Ca content in D-WW and D-model influents were the same. Therefore, the high Ca content of D-WW and D-model inhibits struvite formation, but Ca alone cannot account for reduced struvite precipitation from D-WW. As DOC is also present in D-WW, is detected in the solids, and is known to impact struvite formation, this likely accounts for a further reduction in the fraction of struvite. However, the exact mechanism(s) by which this occurs is unclear. Thus, when both influent Ca and DOC concentrations are high, conditions for struvite precipitation are most unfavorable. Crystallinity evaluation showed that S-WW and S-model solids were highly crystalline (94%), while D-WW solids were less crystalline (75-87%) and D-model solids most amorphous (43-60% crystallinity). Comparing S-WW to D-WW it is clear that the higher DOC and Ca concentrations promote poor mineral structure (Figure S5). The lower crystallinity of D-model solids suggests that higher Ca concentration may have a greater impact on mineralization from these solutions. Better P removal for D-model compared to D-WW, even though its solids are poorly crystalline, is due to rapid precipitation of amorphous P polymers, a known problem for struvite recovery.18



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Speciation of IR sensitive functional groups Qualitative evaluation of FTIR spectra of aeratedFBR solids (Figure 4) supports findings from P removal experiments and XRD analysis. Struvite has characteristic vibrations centered at 992 and 1432 cm-1 associated with the ν3 PO43-, and ν4 NH4+ bands.43-45 Calcite bands are located at 712, 875 and 1382 cm-1, for the ν4, ν2 and ν3 CO32vibrations.46 The S-WW and S-model-35 FTIR spectra were similar to the struvite standard spectrum, consistent with the >90% struvite content detected by XRD. The S-model-15 solid with 78% struvite and 21% calcite has spectral features dominated by struvite, but calcite peaks for the ν2 and ν4 CO32- bands are also evident. The D-WW and D-model solids are primarily a mixture of struvite, calcite and monohydrocalcite, with all spectra exhibiting ν2 CO32-, ν3 CO32and ν3 PO43- vibrations. The struvite ν4 NH4+ band overlaps with the ν3 CO32- band for these samples, so is not distinguishable. The D-WW solids with lowest struvite content (28-33%) are dominated by carbonate minerals (59-68%), and therefore exhibit the sharpest carbonate features. The D-WW-35 solid with the highest monohydrocalcite content (42%) also exhibits a distinct split in the ν3 CO32- peak at 1300-1500 cm-1, in addition to the appearance of a structural ν2 H2O peak at 1600-1700 cm-1.47 The D-model solids have higher struvite content (50-58%), and are also the least crystalline (43-60%), which may account for broadening of all bands in the spectra. The D-model-68 solid has no detected calcite, but does exhibit the ν2 CO32- peak at 875 cm-1, splitting in the ν3 CO32- band, and a broad ν2 H2O band at 1600 cm-1 due to the presence of 41% monohydrocalcite. The D-model-35 and D-WW-68 solids with lower monohydrocalcite content (5-13%) also have these features present in their spectra to some extent. For all dairy solids there is an observed shift in the ν3 PO43- band from 992 cm-1 for the struvite standard to 1002 cm-1 for D-WW, and to 1041 cm-1 for D-model solids. This shift is likely a result of structural deformation of the PO43- tetrahedron due to sorption of Ca and/or


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metal cations, such as Ni and Mn, present in these wastewaters (Table 1). Such deformation is caused by changes in symmetry of the PO43- tetrahedron through elongation or compression of the P-O bond, resulting in a change of the IR vibration absorption energy.43 Shifts in the ν3 PO43band has been observed for cation sorption to struvite,43,44,48 though this has not been observed for Ca2+. There is an increase in the ν3 PO43- bandwidth shift for D-model solids, with no DOC, compared to D-WW. The shift to higher wavenumber for the ν3 PO43- band in the absence of DOC suggests that DOC may reduce interactions between Ca2+ and struvite PO43- groups due to Ca-DOC complexation. Though the effect of Ca on the struvite structure is evident for D-model solids, the impact on both the percent P removed from solution and the percent struvite in the solids is less pronounced than that of DOC, as observed for D-WW.

Thermal analysis The thermal stability of the aerated-FBR solids measured by STA-EGA was consistent with the mineral compositions (Figure 5, Figure S6-S7, Table S4). For all solids, the TG mass loss was associated with the evolution of NH3(g), H2O(g) and/or CO2(g). Solids that were mostly struvite had a single mass loss step at 50-400 °C, and a maximum NH3(g) emission at 140-160 °C;49 and those with calcite or monohydrocalcite displayed a mass loss step at 500600 °C associated with CO2(g) and H2O(g), typical for calcite minerals47 (Figure S6). The S-WW and S-model solids had a TG mass loss typical for struvite,45 49 except for Smodel-15 that displayed the additional mass loss step for calcite (Figure 5a, Figure S6). The DWW and D-model solids have a two-step mass loss at 120-180 °C and 250-500 °C. The first mass loss is associated with evolution of NH3(g) and H2O(g) from struvite, and the second is due to release of CO2(g) and H2O(g) from carbonate minerals. The D-WW solids also release CO2(g) from organic material in the first, and additional NH3(g) in the second mass loss step. The release



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of NH3(g) at two distinct temperatures, is evidenced by two peaks in the GS curve at 140 °C and at 320 °C (Figure 5b). This indicates a higher fraction of NH4-N in the D-WW struvite structure that is more thermodynamically stable compared to other solids (Figure 5c). Total enthalpy of mass loss was calculated for all solids within the 50-400°C NH3(g) release temperature range (Figure 5d). Both S-WW treatments and S-model-35, which were mostly pure struvite, had the highest enthalpies of 1400-1600 J/g. The S-model-15 solid, with 78% struvite had an enthalpy of 1000 J/g. For dairy samples, D-WW-35 and D-model-35 had 720 J/g enthalpy (33-50% struvite), while both D-WW-68 and D-model-68 had 350-420 J/g enthalpy (28-58% struvite). For dairy samples, there was no difference between model and wastewater solids, and the sole difference seems to be the struvite content. Overall, higher struvite content resulted in higher enthalpy, as NH3(g) release has a relatively high heat capacity compared to release of H2O(g) and CO2(g) from organic matter. When comparing dairy samples, a slight decrease in enthalpy to struvite content is observed, but overall there is a linear relation between struvite content and enthalpy (Figure S8).

Implications for nutrient reclamation from livestock wastewater Direct discharge of livestock wastewaters introduces nutrients to soils in an uncontrolled manner, resulting in P accumulation, and/or leaching of dissolved P (9). The aerated-FBR treatment is an efficient method to reclaim P nutrients from these wastewaters. Aeration effectively raises the pH, and lowers the operation costs associated with lye (NaOH) addition.50 The price of lye is ~$330 per ton,51 making it the most expensive component in FBR treatments compared to Mg2+ addition and energy costs. Treatment to remove P was most effective for S-WW (93-94%) and slightly less effective for D-WW (46-63%). In previous works, aeration and Mg2+ addition in a single


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chamber reactor achieved only 92% P recovery from swine wastewater after a 4h HRT;52 and for dairy wastewater, treatment in four parallel FBRs yielded 24-28% P recovery over a 2h reaction time.34 Therefore the aerated-FBR process used here is faster and achieves better recovery for both wastewater types. Results from organic-free model wastewaters suggested that higher concentrations of either DOC or Ca may hinder P recovery, and is reflected in the Ca and DOC content of these solids. The mechanism(s) by which this inhibition occurs is unclear, except to say that Ca-DOC complexation may play a role in this process. Additional research, including types and speciation of organics in both the wastewaters and derived solids is required. The mineralogy of the solids was mostly struvite (S-WW) or a mixture of struvite, calcite and monohydrocalcite (D-WW). Higher struvite content was observed for S-WW (95-98%) compared to D-WW (28-33%) solids. The application of carbonate minerals together with struvite fertilizer has no known negative impact for soils; and struvite fertilizer is effective both in alkaline and acidic soils,53 with similar performance to traditional fertilizers.52,54 Thermal analysis showed a slight benefit for D-WW solids, with higher release temperatures (320 °C) for some of its NH4-N, and release temperatures that are similar to pure struvite (130-160 °C) for other volatiles. Higher thermal stability of struvite from D-WW fertilizer may reduce NH3(g) emissions, posing a great environmental and economic benefit. The aerated-FBR process is overall a viable means of nutrient recovery and fertilizer production from livestock wastewater for sustainable reuse.

Supporting Information



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Tables S1-S4, Figures S1-S8 and accompanying text: struvite saturation; Ca-DOC complexation; aeration impact on struvite saturation, pH and NH3(g) volatilization; statistical analysis; mineralogical analysis; scanning electron microscopy; simultaneous thermal analysis.

Acknowledgments Support was provided by National Science Foundation Grants EAR1506653, EAR-1337450 (XRD), EAR-1530582 (ICP-OES). Special thanks to Clint Burgher, Rutgers New Brunswick New Jersey Agricultural Experiment Station and Robert Fulper, Fulper Farm, for technical support, and to E.J. Elzinga for use of the FTIR.


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Tables Table 1. Chemical composition and other chemical properties of livestock wastewater and model solutions. Table 2. Composition of aerated-FBR solids.

Figures Figure 1. Schematic of aerated-FBR with solid arrows indicating direction of fluid flow: a. CSTR 11 L reaction chamber; b. overhead mixer (A20, Fisher) with PTFE coated 2.5 inch shaft set at 400 rpm; c. effluent level; d. PVC air frit with 10 L min-1 air flow regulator (Key instrument); e. wall mounted pH meter (PT100, Cole-Parmer); f. narrow 0.5 inch slit passage from CSTR to FB chamber; g. solid collection drain valve; h. effluent flow direction;

i.

depiction of solid crystals (dots) forming a fluidized bed; j. effluent exit tube; k. vacuum tube for foam removal (dashed arrow) for livestock wastewater samples; l. peristaltic pump (Masterflex I/P, Fisher). Figure 2. a) P removal with aerated-FBR treatment. The span of the diamonds represents the 95% confidence interval range for the one way analysis of variance (ANOVA), the central line is the mean for each treatment, closed symbols are livestock samples, and open symbols are model solutions; b) Comparison of mean dissolved P removal (%) by influent type, based on TukeyKramer analysis using an arcsine transformation for fraction values and the associated mean P removal value (%). Levels with the same assigned letters are statistically similar; n=4, α=0.05. Figure 3. Mineral phase analysis of aerated-FBR solids. a) Weight precent of each mineral phase based on mineralogical analysis of XRD patterns, and elemental analysis of solids (Table S3); b)



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Statistical output of analysis, where Rwp is the cumulative model error estimate and GOF is the ratio between calculated Rwp and an estimated minimum cumulative error for each solid sample. Figure 4. FTIR absorption spectra of aerated-FBR solids, struvite and calcite standards. Dashed lines indicate absorbance at bandwidths associated with different functional groups present in struvite and calcite. In order of decreasing wavenumber: a. H2O ν2, 1600 cm-1; b. NH4 ν4,1432 cm-1 c. CO3 ν3, 1382 cm-1; d. PO4 ν3+ν1, 992 cm-1 ; e. CO3 ν2 , 875 cm-1; f. CO3 ν4, 712 cm-1. Figure 5. STA-EGA analysis of aerated-FBR solids: a) TG % mass (Table S4); b) GS curve for total absorbance in the IR; c) Intensity of NH3(g) IR absorption at 966 cm-1 bandwidth; d) Integrated enthalpy (J/g) over the 50-400 °C temperature range at which NH3(g) is released.


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Table 1. Chemical composition and other chemical properties of livestock wastewater and model solutions. Influent D-WW S-WW D-model S-model Major constituents (mM) NH4-N 37 21 45 26 P 0.3 0.6 0.3 0.6 Mg 5 1 15 11 Cl 29 7 63 40 2CO3 41 13 41 13 NO3 1 3 1 3 K 19 5 20 5 Na 14 6 3 1 Ca 5 1 5 1 Trace elements (µM) 0.71 2.85 Si 909 142 0.00 0.18 Fe 34 3 1.11 1.11 Al 12 3 0.07 0.07 Ba 8 1 d DL DLd Mn 5 5 0.15 0.15 Zn 4 1 d d DL DLd DL Cu 2 DLd DLd DLd Ni 1 Organics (mg/L)a DOC 800 200 0 0 Total organics 1500 230 0 0 Other chemical properties pHb 7.9 6.8 8 8 c I (mM) 45 107 62 106 c Struvite SI at pH 9 1.40 1.72 1.40 1.65 c 2.52 1.59 2.51 1.54 Calcite SI at pH 9 a

As TOC mg/L, b initial pH, ccalculated using Visual MINTEQ d below detection limit (DL).



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Table 2. Composition of aerated-FBR solids.

Elements (mM/kg) Ca K Mg P Al Fe Mn Zn Insoluble (% w/w) DOC (% w/w)

D-WW 35

D-WW 68

D-model 35

D-model 68

S-WW 15

S-WW 35

S-model 15

S-model 35

1900 177 897 819 389 392 136 90

3067 105 1021 927 399 336 142 59

4275 41 2113 2186 65 97 11 47

3703 26 1106 1343 67 31 10 15

69 84 3815 3519 32 32 57 17

57 86 3872 3615 29 24 74 10

443 51 3888 3774 6 6 2 14

56 80 4331 4216 0 25 2 13

24

12

2

2

7

29

5

2


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Figure 1. Schematic of aerated-FBR with solid arrows indicating direction of fluid flow: a. CSTR 11 L reaction chamber; b. overhead mixer (A20, Fisher) with PTFE coated 2.5 inch shaft set at 400 rpm; c. effluent level; d. PVC air frit with 10 L min-1 air flow regulator (Key instrument); e. wall mounted pH meter (PT100, Cole-Parmer); f. narrow 0.5 inch slit passage from CSTR to FB chamber; g. solid collection drain valve; h. effluent flow direction;

i.

depiction of solid crystals (dots) forming a fluidized bed; j. effluent exit tube; k. vacuum tube for foam removal (dashed arrow) for livestock wastewater samples; l. peristaltic pump (Masterflex I/P, Fisher).



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Figure 2. a) P removal with aerated-FBR treatment. The span of the diamonds represents the 95% confidence interval range for the one way analysis of variance (ANOVA), the central line is the mean for each treatment, closed symbols are livestock samples, and open symbols are model solutions; b) Comparison of mean dissolved P removal (%) by influent type, based on TukeyKramer analysis using an arcsine transformation for fraction values and the associated mean P removal value (%). Levels with the same assigned letters are statistically similar; n=4, α=0.05.


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Figure 3. Mineral phase analysis of aerated-FBR solids. a) Weight precent of each mineral phase based on mineralogical analysis of XRD patterns, and elemental analysis of solids (Table S3); b) Statistical output of analysis, where Rwp is the cumulative model error estimate and GOF is the ratio between calculated Rwp and an estimated minimum cumulative error for each solid sample.



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Figure 4. FTIR absorption spectra of aerated-FBR solids, struvite and calcite standards. Dashed lines indicate absorbance at bandwidths associated with different functional groups present in struvite and calcite. In order of decreasing wavenumber: a. H2O ν2, 1600 cm-1; b. NH4 ν4,1432 cm-1 c. CO3 ν3, 1382 cm-1; d. PO4 ν3+ν1, 992 cm-1 ; e. CO3 ν2 , 875 cm-1; f. CO3 ν4, 712 cm-1.


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Figure 5. STA-EGA analysis of aerated-FBR solids: a) TG % mass (Table S4); b) GS curve for total absorbance in the IR; c) Intensity of NH3(g) IR absorption at 966 cm-1 bandwidth; d) Integrated enthalpy (J/g) over the 50-400 °C temperature range at which NH3(g) is released.



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TOC/Abstract Graphic

Synopsis Phosphorus is reclaimed from livestock wastewater by struvite precipitation in an aerated fluidized-bed reactor for sustainable use of nutrient resources.


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Aerated Fluidized Bed Treatment for Phosphate Recovery from Dairy

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