Corn and Soybean Growth as Affected by Wastewater-Derived Struvite-Phosphorus Sources and Irrigation Water Types

Struvite (MgNH4PO4·6H2O) produced synthetically from a stock solution of known phosphorus (P) and nitrogen (N) concentrations has been shown to be an effective, alternative fertilizer-P source for various crops, but little is known about the potential agronomic effectiveness of struvite created from an actual municipal wastewater source. The objective of this study was to evaluate the effects of soil [i.e., Creldon silt loam (Oxyaquic Fragiudalf) and Calloway silt loam (Aquic Fraglossudalf) series], fertilizer-P source [i.e., synthetically produced electrochemically precipitated struvite (ECSTsyn), real-wastewater-derived ECST (ECSTreal), chemically precipitated struvite (CPST), monoammonium phosphate (MAP), and an unamended control (UC)], and irrigation water type (i.e., tapwater and struvite-removed wastewater) on corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] growth and N, P, and magnesium (Mg) uptake in a 60-day, greenhouse potted-plant study. Crop growth and N, P, and Mg uptakes for the struvite treatments (i.e., CPST, ECSTsyn, and ECSTreal) were generally similar to or at least 1.2 times greater than MAP. The ECSTsyn material commonly had up to five times greater N, P, and Mg uptake in corn and soybean than any other fertilizer-P source. Struvite-removed wastewater resulted in at least 1.3 times lower dry matter and N, P, and Mg uptake than tapwater. Similar corn and soybean results from the struvite fertilizers among the various soil-water type combinations compared to MAP suggest that struvite generates similar crop responses as at least one widely used, commercially available, multi-nutrient fertilizer-P source.

Soil Chemical Property Changes over Time from Struvite Compared to Other Fertilizer-Phosphorus Sources in Multiple Soils

Studies have shown that phosphorus (P) recovered from wastewater as the mineral struvite [MgNH4PO4·6(H2O)] may be a viable alternative fertilizer-P source. This study aimed to compare the effectiveness of electrochemically precipitated struvite (ECST), reclaimed from synthetic wastewater, to other commercial fertilizer-P sources in cultivated soils from Arkansas [AR;silt loam (SiL) and loam (L)], Missouri (MO;SiL), and Nebraska [NE;SiL and sandy loam (SL)]. A plant-less, moist-soil incubation experiment, including ECST, chemically precipitated struvite (CPST), monoammonium phosphate (MAP), triple superphosphate (TSP), and an unamended control (UC), was conducted to quantify soil pH, nitrate (NO3-N), ammonium (NH4-N), and Mehlich-3 (M3)-P, -Ca, -Mg, and -Fe concentrations at 0.5, 1, 2, 4, and 6 months. All measured soil properties differed (P ·kg-1 for AR-L-TSP after 1 month and NE-SiL-MAP after 6 months, respectively. Soil M3-P ranged from -29.6 mg·kg-1 in the AR-L-UC after 1 month to 429 mg·kg-1 AR-SiL-TSP after 0.5 months. Results showed that, over time, ECST had comparable pH and soil NO3-N, NH4-N, and M3-P, -Ca, -Mg, and -Fe behavior compared to CPST, MAP, and TSP across various soil textures.

Effects of heavy metal ions Cu^(2+)/Pb^(2+)/Zn^(2+)on kinetic rate constants of struvite crystallization

Struvite(MAP)crystallization technology is widely used to treat ammonia nitrogen in waste effluents of its simple operation and good removal efficiency.However,the presence of heavy metal ions in the waste effluents causes problems such as slow crystallization rate and small crystal size,limiting the recovery rate and economic value of the MAP.The present study was conducted to investigate the effects of concentrations of three heavy metal ions(Cu^(2+),Zn^(2+),and Pb^(2+))on the crystal morphology,crystal size,average growth rate,and crystallization kinetics of MAP.A relationship was established between the kinetic rate constant Ktcalculated by the chemical gradient model and the concentrations of heavy metal ions.The results showed that low concentrations of heavy metal ions in the solution created pits on the MAP surface,and high level of heavy metal ions generated flocs on the MAP surface,which were composed of metal hydroxides,thus inhibiting crystal growth.The crystal size,average growth rate,MAP crystallization rate,and kinetic rate constant Ktdecreased with the increase in heavy metal ion concentration.Moreover,the Ktdemonstrated a linear relationship with the heavy metal concentration ln(C/C~*),which provided a reference for the optimization of the MAP crystallization process in the presence of heavy metal ions.

Runoff-Water Properties from Various Soils as Affected by Struvite-Phosphorus Source and Water Type

Struvite (MgNH4PO4?6H2O) can be produced from municipal wastewater and has been shown to be an alternative fertilizer-phosphorus (P) source for various crops, but little is known about the runoff-water-quality implications from soil-applied struvite. The objective of this study was to evaluate the effects of soil [Creldon (Oxyaquic Fragiudalfs), Dapue (Fluventic Hapludolls), Roxana (Typic Udifluvents), and Calloway (Aquic Fraglossudalfs) series], fertilizer-P source [synthetically produced electrochemically precipitated struvite (ECSTsyn), real-wastewater-derived ECST (ECSTreal), chemically precipitated struvite (CPST), and monoammonium phosphate (MAP)], and water source (rainwater, groundwater, and struvite-removed real wastewater) over time on runoff-water-quality parameters from laboratory-conducted, rainfall-runoff simulations. Mesh tea bags containing each soil-fertilizer treatment combination were rained on with each water source (Trial 1), incubated for 6 months, and rained on again (Trial 2) to evaluate runoff-water quality. Struvite fertilizers had similar runoff-water-quality properties to those from MAP. In Trial 1, runoff total P (TP) concentration differences (i.e., soil-fertilizer-water-type response minus control response minus blank response) from ECSTsyn or ECSTreal were 1 to 5 times larger than MAP and CPST for all water-soil-fertilizer-P source treatment combinations, except for the Creldon-groundwater and Roxana-wastewater combinations. In both trials, runoff TP decreased over time in all water-soil and soil-fertilizer-P source treatment combinations, except for the Roxana-CPST combination where TP increased over time by 46%. The similar water-quality responses from the struvite fertilizers among the various soils and water types compared to MAP suggest that struvite has similar runoff-water-quality implications as at least one widely used, commercially available fertilizer-P source.

Struvite Effects on Rice Growth and Productivity under Flood-Irrigation in the Greenhouse

In recent years, electrochemical precipitation has gained interest as an alternative method for the synthesis of various minerals, including struvite, from waste streams that can serve as an alternative fertilizer. Studies in lowland cultivations, specifically rice (Oryza sativa) under flood-irrigated conditions, evaluating struvite as a possible alternative phosphorus (P) fertilizer source have been limited. The objective of this study was to evaluate rice response to electrochemically precipitated struvite (ECST) compared to triple superphosphate (TSP), diammonium phosphate (DAP), a chemically precipitated struvite (CPST), and an unamended control (UC), grown under flooded-soil conditions in the greenhouse. Aboveground vegetative dry matter (DM) P concentration was greatest from the UC (0.18%) and was lowest from DAP (0.08%). Root DM Mg concentration was greatest from ECST (0.13%) and was lowest from TSP (0.10%). Grain yield was greatest from DAP (11.2 Mg•ha−1) and was lowest from the UC (4.0 Mg•ha−1). Grain N, P, K, and Mg uptake were consistently greatest from DAP and consistently lowest from the UC. Grain N concentration was 1.1 times greater from CPST than from ECST, while all other measured rice properties did not differ between the struvite-P sources. The many similar rice responses between struvite materials (ECST and CPST) and TSP and DAP demonstrate that struvite, particularly ECST, is a valid alternative fertilizer-P source for rice-production systems. Further studies should evaluate potential environmental implications (i.e., runoff water quality and greenhouse gas emissions) from struvite use that could affect agricultural sustainability.

Effect of Copper (II) Ions on Quality of Struvite Produced in Continuous Reaction Crystallization Process at the Magnesium Ions Excess

The research results concerning continuous removal of phosphate (V) ions from solutions containing 1.0 or 0.20 mass % of phosphate (V) ions and 0.2 or 0.5 mg/kg of copper (II) ions using magnesium and ammonium ions addition are presented. Continuous reaction crystallization of struvite MgNH4PO4 × 6H2O ran both under stoichiometric conditions and at 20% excess of magnesium ions (pH 9, t 900 s). It was concluded, that presence of copper (II) ions in a process system influenced product quality moderately advantageously. Mean size of struvite crystals enlarged by ca. 6% only. Lower concentration of phosphate (V) ions and excess of magnesium ions caused, that products of ca. 9% - 13% larger crystal mean size (up to ca.40mm) were removed from the crystallizer. Presence of struvite crystals and copper (II) hydroxide were detected analytically in the products (Cu in a product varied from 6 to 90 mg/kg). Presence of copper (II) ions favored crystallization of struvite in the form of tubular crystals.

The Struvite Precipitation Index:A Practical Framework for Predicting Struvite Supersaturation in Water and Wastewater

In wastewater facilities, struvite (MgNH4PO4·6H2O) precipitation and subsequent accumulation within sludge processing can be an expensive nuisance or a pathway to orthophosphate reclamation and beneficial reuse. Predictive solubility models developed in the past have been computationally intensive, highly conservative, and have employed uncertain equilibrium constants for the evaluation of solution saturation. The StrPI (Struvite Precipitation Index) developed in this study is a new, computationally light framework for predicting struvite precipitation based on saturation pH. The model permits process-specific calibration (i.e. StrPI plus a correction pH) to deal with the highly variable characteristics of wastewater streams and to eliminate the pH-independent overprediction inherent in existing solubility models. Verification of this model was performed across a range of waste compositions, ionic strengths, and root-mean-square velocity gradients using data from both synthetic laboratory experiments and field tests. The StrPI framework was found to be an effective and uncomplicated predictor of struvite precipitation in both environments.

Agrotechnical Assessment of Struvite Application

Agrotechnical assessment of struvite produced by a lab-scale sedimentation unit is performed. As a source of phosphates and ammonia, liquor obtained through dewatering of Мunicipal wastewater treatment plant sludge was in use. The range of phosphates and ammonia was in the range of 130 - 250 and 380 - 560 mg/L, respectively. Seawater brine with a magnesium concentration of around 60 g Mg2+/L was applied as a source of magnesium. The agrotechnical characteristics of struvite obtained were compared to ammonium nitrate and carbamide in regards to the productivity effects on maize hybrid P9241. The results show that the effectiveness of struvite and some commercial fertilizers is quite close. The highest yield in the experiment was achieved with the application of carbamide plus ammonium nitrate (56.64 kg/ha), while in applying struvite solely it is 54.60 kg/ha. The highest protein content of maize (9.7%) was observed in the case of struvite/ammonium nitrate application.

Chemically Precipitated Struvite Dissolution Dynamics over Time in Various Soil Textures

Phosphorus (P) is a fundamental nutrient in agricultural production and is one of three major components in common fertilizers. The majority of fertilizer-P sources are derived from phosphorus rock (PR), which has finite abundance;thus a sustainable source of P is imperative for future agricultural productivity. A potential sustainable P source may be the recovery of the mineral struvite (MgNH4PO4·6H2O) from wastewater treatment plant effluent, but struvite behavior in soils of varying texture is not well characterized. The objective of this study was to assess the dissolution dynamics of a commercially available, wastewater-recovered struvite product over time in a plant-less, moist-soil incubation experiment with multiple soil textures. Chemically precipitated struvite (Crystal Green;CG) from municipal wastewater in pelletized and finely ground forms were added to soil cups at a rate of 24.5 kg∙P∙ha−1 containing soils of varying texture (i.e. loam, silty clay loam, and two different silt loams) from agricultural field sites in Arkansas. Soil cups were destructively sampled five times over a 6-month period to examine the change in water-soluble (WS) and weak-acid-extractable (WAE) P, K, Ca, Mg, and Fe concentrations from their initial concentration. After 0.5 months, both WS-P and WAE-P concentrations increased (P < 0.05) more from initial concentrations of the finely ground CG in all soils, which averaged 76.2 and 158 mg∙kg−1, respectively, than in the pelletized CG treatment, which averaged 14.0 and 12.2 mg∙kg−1, respectively, across all soils. Over the course of the 6-month incubation, WS- and WAE-P concentrations generally increased over time in the pelletized and decreased over time in the finely ground treatment, confirming the slow-release property of pelletized CG that has been previously reported. The results of this study provide valuable insight regarding struvite-P behavior in various soils and provide further supporting evidence for the utilization of struvite as a potential alternative, sustainable fertilizer-P source.

Continuous Reaction Crystallization of Struvite in a DTM Type Crystallizer With Jet Pump of Ascending Suspension Flow in a Mixing Chamber–Kinetic Approach of the Process

Reaction crystallization of struvite in water solutions containing 0.20 mass % of phosphate(V) ions by magnesium and ammonium ions addition was investigated experimentally. Process was carried out in DTM type crystallizer with liquid jet pump device in 298 K assuming stoichiometric conditions. Struvite crystals of mean size Lm 5.2-23.0 μm were produced depending on pH (9-11) and mean residence time of suspension in a crystallizer τ (900-3600 s). Under these conditions linear growth rate of struvite crystals (SIG MSMPR kinetic model) decreased 2-time with the increase in pH and 3-time with the elongation of mean residence time of crystal suspension from 7.11×10-9 m/s (pH 9, τ900 s) to 1.65×10-9 m/s (pH 11, τ3600 s). Nucleation rate varied within the 7.9×108-1.8×1010 1/(sm3) limits. Struvite product of maximal linear size exceeded 100 μm with 10 vol. % of < 3 μm fraction corresponded to pH 9 and τ3600 s.

Precipitation and Crystallization of Struvite from Synthetic Wastewater under Stoichiometric Conditions

Phosphate (V) ions were continuously removed from synthetic wastewater containing inorganic impurities using magnesium and ammonium ions. The product was magnesium ammonium phosphate (V) hexahydrate, struvite, MgNH4PO4 × 6H2O. Research ran in stoichiometric conditions in DT MSMPR type crystallizer with internal circulation of suspension. Increase in process environment pH from 9 to 11 resulted in 3-time decrease of mean struvite crystals size (from 40.1 to12.6mm). Elongation of mean residence time of suspension in a crystallizer up to 3600 s resulted in improvement of the product quality. Mean size of struvite crystals enlarged up to50.2mm. Based on kinetic calculations results (SIG MSMPR model) it was concluded, that linear struvite crystal growth rate varied within 5.04 × 10–9 – 1.69 × 10–8 m/s range, whereas nucleation rate within 1.4 × 107 – 1.7 × 1010 1/(s m3) limits. In solid product, besides struvite, also all impurities present in wastewater were identified analytically as hydroxides, phosphates and other salts.

Molecular Modeling of Chemicals Products Inhibitors of Growth Struvite Crystal

Struvite (MgNH4PO46H2O) crystals were produced by infection associated with urea generating organ- isms.The aim of this study is to examine the interactions between the enzyme urease and two inhibitors, the first is an inhibitor monoatomic: Aluminum and the second is a polyatomic: Citrate by the methods of molecular modeling: molecular mechanics, molecular dynamics (MM+, AMBER) and molecular docking (FleX). Supersaturated solutions induce crystallization by nucleation and subsequent crystal growth .The mechanisms for the formation of calcium phosphate urinary stones are still not understood. Chemicals prod- uct has been studied extensively as inhibitors and has been observed in the attachment of crystals to in vitro study. As a complement we have using an electron microscope Hitachi TM1000, we examined specimens of crystals struvite. The various figures show a set of grains of sizes of the order of 20 μm. The majority of these particles present regular forms. This suggests the crystal growing. This result to an alteration in the expression of these faces and the development of a characteristic architectural struvite morphology. Similar changes were observed in the presence of identical concentrations of citrate acid, and Alluminuium, emphasizing the unique interaction of phosphocitrate with the struvite crystal.

Selection of cost-effective magnesium sources for fluidized struvite crystallization

Struvite crystallization has been considered a promising approach to recover phosphorus from wastewater. However, its practical application is limited, probably because of the high cost of magnesium(Mg). In this study, a comprehensive economic analysis was conducted using five Mg sources(MgCl_2, MgSO_4, MgO, Mg(OH)_2, and bittern) during the operation of a pilot-scale fluidized bed reactor(FBR), using swine wastewater as the case matrix. First, the economic operating conditions were investigated, and subsequently, the performance and the costs of the five Mg sources were compared. The results indicated that the FBR could be operated most economically at pH of 8.5 and Mg to phosphorus(Mg/P) molar ratio of 1.5. Under these conditions, no significant differences in phosphorus removal and product quality could be found between the five Mg sources. Selecting the most economical Mg source was thus highly dependent on the prices of the reagents and Mg sources. Low-solubility Mg sources were preferable when NaOH was priced higher, while high-solubility Mg sources proved more economical when HNO_3 was expensive. The bittern was the most economical choice only when the distances for total inorganic orthophosphate removal and struvite recovery were shorter than 40 and 270 km, respectively. The current study provides an overview of the economic selection of an Mg source, which can help reduce the cost of struvite crystallization.

Effect of Ca:Mg ratio and high ammoniacal nitrogen on characteristics of struvite precipitated from waste activated sludge digester effluent

This study revealed the relationship between the presence of calcium impurities and ammoniacal nitrogen concentration upon crystallization of struvite.The research hypothesis was that the presence of both calcium and high concentrations of ammoniacal nitrogen(328–1000 mg/L)in waste activated sludge may influence the struvite quality and acid stability.Hence,we studied the impact of Ca:Mg ratio upon morphology,particle size,purity and dissolution of struvite,in the presence of varying levels of excess ammoniacal nitrogen.X-ray diffraction revealed that up to 31.4%amorphous material was made which was assigned to hydroxyapatite.Increasing the ammoniacal nitrogen concentration and elevation of the Mg:Ca ratio maximized the presence of struvite.Struvite particle size was also increased by ammoniacal nitrogen as was twinning of the crystals.Tests with dilute solutions of organic acid revealed the sensitivity of struvite dissolution to the physical characteristics of the struvite.Smaller particles(21.2μm)dissolved at higher rates than larger particles(35.86μm).However,struvite dissolved rapidly as the p H was further reduced irrespective of the physical characteristics.Therefore,addition of struvite to low p H soils was not viewed as beneficial in terms of controlled nutrient release.Overall,this study revealed that waste activated sludge effluent with high ammoniacal nitrogen was prospective for synthesis of high quality struvite material.

Bioelectrochemical acidolysis of magnesia to induce struvite crystallization for recovering phosphorus from aqueous solution

A novel struvite crystallization method induced by bioelectrochemical acidolysis of magnesia (MgO) was investigated to recover phosphorus (P) from aqueous solution using a dual-chamber microbial electrolysis cell (DMEC).Magnesium ion (Mg2+) in the anolyte was firstly confirmed to automatically migrate from the anode chamber to the cathode chamber,and then react with ammonium (NH4+) and phosphate (PO34-) in the catholyte to form struvite.Recovery efficiency of 17.8%-60.2% was obtained with the various N/P ratios in the catholyte.When MgO (low solubility under alkali conditions) was added into the anolyte,the bioelectrochemical acidolysis of MgO naturally took place and the released Mg2+ induced struvite crystallization in the cathode chamber for P recovery likewise.Besides,there was a strong linear positive correlation between the recovery efficiency and the MgO dosage (R2 =0.935),applied voltage (R2 =0.969) and N/P ratio (R2 =0.905).Increasing the applied voltage was found to enhance the P recovery via promoting the MgO acidolysis and the released Mg2+ migration,while increasing the N/P ratio in the catholyte enhanced the P recovery via promoting the struvite crystallization.Moreover,the electrochemical performance of the system was promoted due to more stable anolyte pH and lower pH gradient between the two chambers.Current density was promoted by 10%,while the COD removal efficiency was improved from 78.2% to 91.8% in the anode chamber.

Effect of struvite and organic acids on immobilization of copper and zinc in contaminated bio-retention filter media

Few studies have been carried out to connect nutrient recovery as struvite from wastewater and sustainable utilization of the recovered struvite for copper and zinc immobilization in contaminated soil.This study revealed the effect of struvite on Cu and Zn immobilization in contaminated bio-retention soil in the presence of commonly exuded plant organic acids.The research hypothesis was that the presence of both struvite and organic acids may influence the immobilization of Cu and Zn in soil.The outcome of this research confirmed that more than 99%of Cu and Zn was immobilized in bio-retention filter media by struvite application.Water-soluble Cu and Zn concentrations of struvite treated soil were less than 1.83 and 0.86 mg/kg respectively,and these concentrations were significantly lower compared to the total Cu and Zn content of 747.05 mg/kg in the contaminated soil.Application of struvite to Cu-and Zn-contaminated soil resulted in formation of compounds similar to zinc phosphate tetrahydrate(Zn3(PO4)2·4H2O)and amorphous Cu and Zn phases.Struvite was effective in heavy metal remediation in acidic soil regardless of the presence of Ca impurities in struvite and the presence of plant organic acids in soil.Overall,this study revealed that struvite recovered from wastewater treatment plants has potential for use as an amendment for heavy metal remediation in contaminated bio-retention soil.

Ammonia removal from low-strength municipal wastewater by powdered resin combined with simultaneous recovery as struvite

Low-strength municipal wastewater is considered to be a recoverable nutrient resource with economic and environmental benefits.Thus,various technologies for nutrient removal and recovery have been developed.In this paper,powdered ion exchange resin was employed for ammonia removal and recovery from imitated low-strength municipal wastewater.The effects of various working conditions(powdered resin dosage,initial concentration,and pH value)were studied in batch experiments to investigate the feasibility of the approach and to achieve performance optimization.The maximum adsorption capacity determined by the Langmuir model was 44.39 mg/g,which is comparable to traditional ion exchange resin.Further,the effects of co-existing cations(Ca^(2+),Mg^(2+),K^(+))were studied.Based on the above experiments,recovery of ammonia as struvite was successfully achieved by a proposed two-stage crystallization process coupled with a powdered resin ion exchange process.Scanning electron microscopy(SEM)and X-ray diffractometry(XRD)results revealed that struvite crystals were successfully gained in alkaline conditions(pH=10).This research demonstrates that a powdered resin and two-stage crystallization process provide an innovative and promising means for highly efficient and easy recovery from low-strength municipal wastewater.

Enhanced microalgae cultivation using digested kitchen waste sewage treated with struvite precipitation

This study demonstrated the feasibility of using struvite for nutrient management in algae cultivation on sewage wastewater.The results showed that struvite precipitation treatment dramatically reduced the ammonia in the digested kitchen waste sewage.The untreated sewage was unable to sustain continuous growth of algae,while the algae growth on the treated sewage was comparable with that on an artificial algae culture medium(BG11).The rapid growth on the treated sewage was accompanied by substantial removal of nutrients.The struvite precipitate recovered from the treated sewage was proven to be an alternative source of nitrogen,phosphorus and magnesium.The struvite precipitate was evidenced that it could substitute culture media in algae growth.This study showed that struvite treatment is viable for nutrient management of algae cultivation on sewage wastewaters which do not have suitable nutrient profiles.

Phosphorus Fertilizer Effects on Near-Surface Soil Aggregation in Furrow-Irrigated Rice on a Silt-Loam Soil

Well-aggregated soil has been shown to improve soil infiltration and reduce runoff and soil erosion, making well-aggregated soil important for productive, sustainable agriculture. One factor that may influence near-surface soil aggregate stability is fertilizer application. Rapid dissolution of fertilizers, which are mostly salts, can potentially disperse clays and destabilize aggregates. The objective of this study was to evaluate the potential effect of various fertilizer-phosphorus (P) and -nitrogen (N) sources [i.e., triple superphosphate (TSP), monoammonium phosphate (MAP), chemically precipitated struvite (CPST), electrochemically precipitated struvite (ECST), environmentally smart nitrogen (ESN)] and soil depth on water-stable aggregates (WSA) in furrow-irrigated rice on a silt-loam soil (Typic Albaqualf). Total WSA (TWSA) concentration was unaffected (P > 0.05) by fertilizer treatment or soil depth, while WSA concentration was numerically largest (P ∙g-1), which did not differ from CPST, ECST, and ESN in the 0 - 5 cm depth or the unamended control in the 0 - 5 and 5 - 10 cm depths, and was at least 1.7 times larger than ESN in the 5 - 10 cm depth (0.03 g∙g-1). Results indicated that WSA concentration among non-struvite fertilizer-P sources was generally similar to that from the struvite fertilizer materials. Principal component analysis determined that 32% of the variation of TWSA was mainly explained by changes in soil bulk density, pH, and electrical conductivity. Long-term, continual annual application of fertilizer-P and N could negatively impact soil aggregate stability, soil structure, and potentially erosion.

Metabolic evaluation and medical management of staghorn calculi

Staghorn renal calculi are large renal calculi that occupy nearly the entirety of the renal collecting system.They may be composed of metabolic or infection stone types.They are often associated with specific metabolic defects.Infection stones are associated with urease-producing bacterial urinary tract infections.The ideal treatment for staghorn calculi is maximal surgical removal.However,some patients are either unwilling or unable to proceed with that modality of treatment,and therefore other management must be used.One such technique is the metabolic evaluation with directed medical management.Based on contemporary evidence that the majority of staghorn stones are metabolic in etiology,and furthermore that even infection stones are usually associated with metabolic abnormalities,metabolic evaluation with directed medical management is recommended for all staghorn stone formers.The scientific basis of this recommendation is reviewed in the present work.