Crystallization and precipitation of phosphate from swine wastewater by magnesium metal corrosion

Siderophore mediated mineralization of struvite: A novel greener route of sustainable phosphate management

Efficient and sustainable removal of phosphate ions from an aqueous solution is of great challenge. Herein we demonstrated a greener route for phosphate recovery through struvite formation by using bacterial siderophore. This method was efficient for removal of phosphate as low as 1.3 mM with 99% recovery efficiency. The siderophore produced by Pseudomonas taiwanensis R-12-2 act as template for the nucleation of struvite crystals and was found sustainable for recycling the phosphorous efficiently after twenty cycles. The formation of struvite crystals is driven by surrounding pH (9.0) and presence of Mg²⁺ and NH₄⁺ ions along with PO₄^3- and siderophore which was further validated by computational studies. The morphology of struvite was characterized by scanning electron microscopy, followed by elemental analysis. Furthermore, our results revealed that the siderophore plays an important role in struvite biomineralization. We have successfully demonstrated the phosphate sequestration by using industrial waste samples, as possible application for environmental sustainability and phosphate conservation. For the first time electrochemical super-capacitance performance of the struvite was studied. The specific capacitance value for the struvite was found to be 320 F g^-1 at 1.87 A g^-1 and retained 92 % capacitance after 250 cycles. The study revealed the potential implications of siderophore for the phosphate recycling and the new mechanism for biomineralization by sequestering into struvite.

Advances in Struvite Precipitation Technologies for Nutrients Removal and Recovery from Aqueous Waste and Wastewater

The abatement of nutrient compounds from aqueous waste and wastewater is currently a priority issue. Indeed, the uncontrolled discharge of high levels of nutrients into water bodies causes serious deteriorations of environmental quality. On the other hand, the increasing request of nutrient compounds for agronomic utilizations makes it strictly necessary to identify technologies able to recover the nutrients from wastewater streams so as to avoid the consumption of natural resources. In this regard, the removal and recovery of nitrogen and phosphorus from aqueous waste and wastewater as struvite (MgNH4PO4·6H2O) represents an attractive approach. Indeed, through the struvite precipitation it is possible to effectively remove the ammonium and phosphate content of many types of wastewater and to produce a solid compound, with only a trace of impurities. This precipitate, due to its chemical characteristics, represents a valuable multi-nutrients slow release fertilizer for vegetables and plants growth. For these reasons, the struvite precipitation technology constantly progresses on several aspects of the process. This manuscript provides a comprehensive review on the recent developments in this technology for the removal and recovery of nutrients from aqueous waste and wastewater. The theoretical background, the parameters, and the operating conditions affecting the process evolution are initially presented. After that, the paper focuses on the reagents exploitable to promote the process performance, with particular regard to unconventional low-cost compounds. In addition, the development of reactors configurations, the main technologies implemented on field scale, as well as the recent works on the use of struvite in agronomic practices are presented.

The role of reagent adding sequence in the NH4+-N recovery by MAP method

Ammonium-nitrogen (NH₄⁺-N) recovery from high concentration of NH₄⁺-N-containing wastewater by struvite (MgNH₄PO₄·6H₂O, MAP) precipitation method has been realized, but whether NH₄⁺-N recovery under different reagent adding sequence of NaOH, solid Mg salt and P salt can generate different effects, remains ambiguous. In view of the problem, four modes to add reagents were investigated in detail on the formation of struvite. The results show that the Mode IV (M-IV, i.e. using 50% NH₄⁺-N wastewater to dissolve completely the Mg salt and the P salt, respectively and then simultaneously poured into a beaker to mix the solution evenly and adjust the pH to 9.5.) has the highest NH₄⁺-N recovery efficiency (90.80%) and the maximum mass of precipitates (896 mg) because of the more amount of alkali and initial seed formation. From the morphology of the obtained precipitates, it can be seen that sample M-IV is more loose and porous than the others. XRD patterns show that the four products under the different modes basically agree with the standard MAP.

Impact of Sequential Treatments with Natural and Na-Exchanged Chabazite Zeolite-Rich Tuff on Pig-Slurry Chemical Composition

Notwithstanding the widespread use of natural and pre-exchanged zeolites for zootechnical effluent treatment, little attention has been dedicated to the variation in the chemical composition of the treated slurries, besides the effects on their NH4+ content. This paper aimed at elucidating the compositional variations in terms of major and trace elements of a raw pig-slurry (PS) after three sequential treatment cycles (TC) with three different grain sizes of natural and Na-exchanged zeolite-rich volcanic tuffs (natural ZTs and NaZTs). A series of laboratory batch experiments revealed that all ZTs had profoundly influenced the final PS chemical composition. As expected, the NaZTs were more efficient in terms of NH4+ removal than the natural ZTs, reaching almost 60% reduction of the initial content after three TCs. A parallel effect of this efficient removal was the remarkable increase in Na+. The Na-forms of ZTs led also to stronger competition with K+ ions, resulting in adsorption of this macronutrient and hence in a reduction of the fertilization value of the PS. In terms of heavy metals and other trace elements, all the treatments with ZTs had significantly increased the Li, Ba, Rb, Sr, Ga, and U content in the PS.

Phosphate Recovery from Swine Wastewater by a Struvite Precipitation Electrolyzer

Struvite precipitation electrolyzers are interesting environmental electrochemical reactors with potential applications for efficient phosphate recovery from wastewater, such as swine wastewater. In this paper, effects of phosphate concentration and pH on the struvite precipitation reaction rate were investigated. When phosphate concentration decreased from 100 to 20 mg/L, the precipitation reaction rate decreased from 396.65 mg/L·h to 70.46 mg/L·h, indicating that the reaction rate of struvite crystallization can be controlled by adjusting pH according to the change of phosphate concentration. Numerical simulation of different currents and flow rates on pH in the electrolyzer was developed and validated, and pH in the electrolyzer was dynamically measured along the distribution point of the flow field. We aimed to test the treatment effect of the electrolyzer on actual swine wastewater. When the flow rate was 20 L/h and constant voltage was 4 V, the electrolyzer was run continuously for 5 hours with the volume of 50 L. The phosphate recovery efficiency reached 99.51%, and the time-space yield of the struvite precipitation electrolyzer was 0.0219 kg/m2·h. The harvested struvite particles were identified by XRD and SEM-EDS, which presented orthorhombic structure and high purity. Economic analysis demonstrated that the proposed electrolyzer was cost-effective and technologically convenient.

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 (MgCl₂, MgSO₄, 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 HNO₃ 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 270km, respectively. The current study provides an overview of the economic selection of an Mg source, which can help reduce the cost of struvite crystallization.

Application of Struvite Alters the Antibiotic Resistome in Soil, Rhizosphere, and Phyllosphere

Struvite recovered from wastewater is a renewable source of phosphorus and nitrogen and can be used as fertilizer for plant growth. However, antibiotics and resistome can be enriched in the struvite derived from wastewater. Robust understanding of the potential risks after struvite application to soils has remained elusive. Here, we profiled antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) in struvite, soil, rhizosphere and phyllosphere of Brassica using high-throughput quantitative PCR. A total of 165 ARGs and 10 MGEs were detected. Application of struvite was found to increase both the abundance and diversity of ARGs in soil, rhizosphere and phyllosphere. In addition, ARGs shared exclusively between Brassica phyllosphere and struvite were identified, indicating that struvite was an important source of ARGs found in phyllosphere. Furthermore, OTUs shared between rhizosphere and phyllosphere were found to significantly correlate with ARGs, suggesting that microbiota in leaf and root could interconnect and ARGs might transfer from struvite to the surface of plants via rhizosphere using bacteria as spreading medium. These findings demonstrated that struvite as an organic fertilizer can facilitate the spread of antibiotic resistance into human food chain and this environment-acquired antibiotic resistance should be put into human health risk assessment system.

Phosphate enhance recovery from wastewater by mechanism analysis and optimization of struvite settleability in fluidized bed reactor

Since phosphorus, a non-renewable and non-substitutable resource, has become the principal contributor and limiting factor to water eutrophication, achieving phosphorus removal and recovery from wastewater is pretty essential. Even though struvite crystallization process has been widely used for phosphate (P) recovery in wastewater treatment, its application is hampered by difficulties controlling small particle size and crystal growth. This study was conducted to control the settleability of struvite by calculating and predicting the struvite-settling percentage (Ps), which is always affected by the initial concentration of P (CP), solution pH (pH), reaction time (t), reaction temperature (T), agitation rate (Ar), and inlet flow velocity (vf) of the fluidized bed reactor. The results showed that the settleability of struvite could be enhanced by increasing T and decreasing pH, Ar, or vf, and would perform worse with overlong t or excessive CP. The dynamic variation process of the solution supersaturated index (SI) combined with the phase equilibrium theory and Ostwald ripening mechanism explained the above results sufficiently. The logistic model was chosen to predict the Ps under multi-factors, but the accuracy needs to be improved.