Struvite Precipitation Research Articles

Phosphorus and bioenergy recovery from anaerobic co-digestion of food waste and corn residues with digested sludge: effect of HRT and pre-treatment methods

AbstractOrganic wastes from the human ecosystem including food waste (FW), agricultural waste and digested sludge (DS) from wastewater treatment can be utilized as valuable materials in anaerobic co-digestion (AcoD) for the dual purpose of bioenergy production and phosphorus (P) recovery through a chemical precipitation process. In this study, AcoD using FW and corn residues (CS) with DS for simultaneous sustainable phosphate release and biogas production were investigated. Different hydraulic retention times (HRT) of 10, 20, and 30 days were investigated, and FW was grinded, while CS pre-treatment methods including physical (FWCS), chemical (FWCS-Chem), and thermal (FWCS-Temp) were considered. The substrates of FW and CS compositions were conducted with a total organic loading of 6 g volatile solids (VS)/L/d (5 FW/1 CS) with a carbon-to-nitrogen ratio (C/N) of 24. The results indicate that FWCS-Chem showed the highest cumulative biogas production simultaneously with P release at HRT 20 days with 7279 L/m3 and 29.67%, respectively. Moreover, the effluent from all digesters exhibited a Mg/P ratio above 1, suitable for struvite precipitation without an external Mg source. Accordingly, FW, FWCS, and FWCS-Chem achieved P recovery rates of 63.64%, 69.75%, and 70.19% at 20-day HRT, with corresponding P contents in solids of 9.45, 9.43, and 8.29%, respectively. These values are comparable to commercial phosphate fertilizer containing 8.80% P. Moreover, incinerating the precipitating solids offers high-quality P concentrations in solids of up to 15.52, 16.32, and 16.31%, respectively. Hence, 20-day HRT was found to be the optimal condition for FW, CS, and DS for anaerobic co-digestion, resulting in the highest biogas production, P release, and maximum financial return for P recovery. Graphical abstract Phosphorus and bioenergy recovery from anaerobic co-digestion of food waste and corn residues with digested sludge.

Phosphorus recovery potential from sewage sludge by struvite precipitation: remodelling policy framework in Rajasthan, India.

The manufacturing of fossil-based fertilizers by extraction of rock phosphate has contributed to carbon emissions and depleted the non-renewable phosphorus reserves. Sewage sludge, which is a waste product from Sewage Treatment Plants (STPs), is rich in phosphorus. The existing techniques for sludge management contribute to carbon emissions and ecological footprint. Struvite (raw fertilizer) and biochar recovery from sludge has emerged as viable methods to reduce carbon emission and ensure economic sustainability of STPs. In this work, the potential for phosphorus recovery and revenue generation is discussed for Rajasthan state in India. The fate of phosphorus and heavy metals in STPs is evaluated which indicates that about 70% of the phosphorus and trace amounts of metals end up in sewage sludge. Further, the power consumption is high in STPs due to industrial wastewater ingress. There is a need to bridge the gap between sewage treatment and generation in Rajasthan, improve STP performance before resource recovery inclusion at policy-level and scale-up. Mixing struvite with biochar can lead to safe application of struvite as raw fertilizer as heavy metals are sequestered by biochar. A business framework is developed to serve as a blueprint and potential model for linking technical and market viability.

An Integrated Process of Struvite Precipitation/Membrane Filtration Using Flat Ceramic Membranes Is an Effective Method for the Treatment of Liquid Fraction Digestate from a Municipal Biogas Plant

One method of processing municipal waste biogas plant digestate is to separate it into solid and liquid fractions. Since the digestate can be a potential source of water, it must undergo the appropriate treatment. Pressurised membrane processes preceded by struvite precipitation can be particularly useful in this regard. Experiments were conducted to determine the effectiveness of treating the digestate liquid fraction from a municipal waste biogas plant using an integrated process that combines struvite precipitation with membrane filtration, employing flat ceramic membranes with different cut-off values. The results confirm that this integrated process is effective for digestate treatment. A significantly increased improvement in the final quality of the test solution and a reduction in membrane fouling intensity were observed compared to those of these processes conducted separately. It is noteworthy that the purest solution was obtained when struvite precipitation and filtration through a flat ceramic membrane with a cut-off of 1 kDa were combined. This approach enabled the precipitation of struvite, a valuable fertiliser; the protection of the membranes from fouling; and a high degree of organic compound removal. The recovered water from the digestate (after dilution or removal of excess salts) can be used in agriculture or horticulture.

Investigation of optimum conditions for the recovery of magnesium ammonium phosphate from human urine using the Box–Behnken design

ABSTRACT Urine from domestic wastewater greatly increases the nutritional value of wastewater. Urine has a high concentration of nutrients and minerals that can be utilized as plant growth agents, according to a chemical analysis. Due to its high phosphate, nitrogen, and potassium content, human urine can serve as a sustainable substitute for chemical fertilizers. Struvite, also referred to as MAP, can be considered as a sustainable fertilizer and it is a magnesium ammonium phosphate crystal with the chemical formula of MgNH4PO4·6H2O. Struvite may be formed from many types of wastewater, one inexpensive and reliable source for struvite formation being human urine. However, struvite formation requires an external magnesium supply due to the extremely low concentration of magnesium in human urine. In this work, magnesium ammonium phosphate was precipitated from human urine by examining the effects of Mg2+ dose, temperature, and pH on struvite crystals. Several experiments for struvite precipitation were created using the Box–Behnken design. Struvite crystals formed upon the addition of a magnesium source at 20 °C, pH 10, and a mole ratio of 1:1. The results show that the large-scale application and nutrient recovery of struvite crystals from human urine are promising.

Integrated Struvite Precipitation and Fenton Oxidation for Nutrient Recovery and Refractory Organic Removal in Palm Oil Mill Effluent

Anaerobically treated palm oil mill effluent (AnT-POME), containing a high concentration of ammoniacal-nitrogen (NH4+-N) and soluble chemical oxygen demand (sCOD) was subjected to sequential processes of struvite precipitation to recover NH4+-N and Fenton oxidation for sCOD removal. The optimization of treatment was conducted through response surface methodology (RSM). Under optimized struvite precipitation conditions (Mg2+/NH4+, PO43−/NH4+ molar ratios: 1; pH 8.2 ± 0.1), NH4+-N concentration decreased to 41 ± 7.1 mg L−1 from an initial 298 ± 41 mg L−1 (78.8 ± 1.6 % removal). Field emission scanning electron microscopy (FESEM) coupled with energy-dispersive X-ray spectroscopy (EDX) confirmed NH4+-N was recovered as struvite. Subsequent Fenton oxidation under the optimized conditions (H2O2 dosage: 2680 mg L−1; molar ratio of Fe2+/H2O2: 0.8; reaction time: 56 min) reduced sCOD concentration to 308 ± 46 mg L−1 from an initial 1350 ± 336 mg L−1 (76.0 ± 1.0 % removal). The transparent appearance of treated AnT-POME validated the removal of sCOD responsible for the initial brownish appearance. Models derived from RSM demonstrated significance, with high coefficients of determination (R2 = 0.99). Overall, integrated struvite precipitation and Fenton oxidation effectively removed NH4+-N and sCOD from AnT-POME, contributing to nutrient recovery and environmental sustainability.

Kinetic study of magnesium dissolution using a magnesium oxide industrial by-product

Phosphorus recovery via struvite precipitation in wastewater treatment plants (WWTPs) is a key technology for nutrient recovery. This work investigates the dissolution kinetics of an industrial low-grade magnesium oxide (LG-MgO) by-product as an alternative to common magnesium sources for struvite precipitation. The main aims were to develop a parsimonious dissolution kinetic model capable of predicting the release of magnesium into the solution with accuracy and studying the influence of temperature on dissolution kinetics. The simultaneous fitting of all the experiments by non-linear regression rendered overall process values of the dissolution model’s frequency factor (498,606 L3.22 min−1 mmol−1.74), activation energy (37.51 kJ·mol−1), and reaction order (2.74). The goodness-of-fit for all experiments was evaluated by the total sum of squared residuals and R2 coefficients, being excellent under all conditions. The estimated kinetic coefficient values showed a temperature-dependent variation of the kinetic coefficient, increasing from 0.079 to 0.219 L3.22 min−1 mmol−1.74 when the temperature increased from 15 to 35 °C. The magnesium dissolution was fast in the first 5 min, where 40–78 % of magnesium dissolved with respect to the initial magnesium in the solid. Despite the assumptions made in the model derivation, the developed kinetic model provides a practical, reliable, and easy-to-use tool for WWTPs to estimate the LG-MgO dosage required to achieve targeted magnesium concentrations, thereby improving reagent use efficiency and phosphorus recovery.

Nutrient Recovery via Struvite Precipitation from Wastewater Treatment Plants: Influence of Operating Parameters, Coexisting Ions, and Seeding

Phosphorus (P) is a critical element for life, and wastewater treatment systems can be strategic points for its recovery, thereby avoiding eutrophication pollution in nature. The aim of this research was to investigate P recovery via struvite, namely in terms of the influence of operating parameters, coexisting interfering ions, and seeding. This paper focuses on synthetic solutions, although an assessment was performed on wastewater. The results of the assessment indicated that, in the synthetic solution, the minimum concentration for struvite precipitation is about 30 mg P/L, and that the Mg/P molar ratio of 1 promotes P removal efficiency with less contribution from other minerals. In order to assess the results in terms of real-world scenarios, the influence of coexisting ions (calcium and sodium) was investigated. Calcium was shown to have the greatest impact on the process, as 80% was removed for an initial concentration of 200 mg Ca/L. Indeed, these experiments generated an amorphous precipitate that did not contain struvite. The utilization of biomass ash (size < 63 µm) as seeding in crystallization increased the P removal efficiency compared to the sample without seed and helped to control the pH. The precipitation experiments with wastewater demonstrated good P removal efficiencies (over 90%) but indicated a reduction in the purity of the final product (struvite was a minor crystalline phase identified in XRD—15%wt).

Biorefinery of waste activated sludge: Nutrient recovery and microbial lipid production by Yarrowia lipolytica

The rising generation of waste activated sludge (WAS) demands a fundamental shift towards resource reuse and recovery. The conventional methodologies used to manage this by-product derived from wastewater treatment plants are increasingly constrained due to stringent regulatory measures aimed at mitigating its adverse impacts on the environment and public health. Therefore, this work evaluated a promising strategy for the efficient management of WAS, transforming it into a valuable renewable source to produce high-value-added compounds, such as lipids and a slow-release fertilizer (struvite). Wet oxidation (WO) was identified as a suitable technique for solubilising WAS while generating short-chain fatty acids (primarily acetic acid). It was found that conducting WO at 200 °C for 120 min resulted in a 65% reduction of the total suspended solids (TSS) content and 87% of the volatile suspended solids (VSS) content. Additionally, under these conditions, 4440 ± 105 mg/L and 593 ± 21 mg/L of acetic and propionic acid were obtained, respectively, which were assimilated by Yarrowia lipolytica to produce biolipids. Furthermore, the rupture of WAS flocs also led to the solubilisation of 980 ± 8 mg/L of ammonium. During the struvite precipitation stage, a NH4:PO4:Mg ratio of 1:1.5:1.5 was found to be the most effective for removing soluble ammonium (97.4 ± 0.8%), resulting in a high-purity struvite formation, and enhancing the carbon/nitrogen (C/N) ratio of the oxidised WAS from 3 to 105. This improvement in the C/N ratio raised the lipid content from 36 ± 1% to 49 ± 1% during the cultivation of Y. lipolytica. The application of the sequencing batch culture strategy further increased lipid content to 59 ± 1%, with 6.0 ± 0.3 g/L as the final concentration after the fifth cycle. The lipids produced, mainly monounsaturated fatty acids with 40% of oleic acid, offer potential as biodiesel feedstock. This lipid composition led to biodiesel properties, including cetane number, iodine value, kinematic viscosity and density that met international standards. Therefore, this research presents a promising alternative not only for WAS management but also for harnessing valuable resources, thereby establishing a basis for large-scale studies.

Magnesium Utilization in Dolomite Rocks by Struvite Precipitation in an Insulated Column Reactor

Dolomite is a natural mineral rock with the chemical formula CaMg(CO3)2. Pure dolomite contains 21.70% calcium and 13.04% magnesium. Dolomite has not been widely used in the industrial sector until now. One way to increase the economic value of dolomite rock is to utilize its magnesium content as a precursor to struvite mineral which is the raw material for slow release fertilizer. Under alkaline conditions, struvite minerals are formed at concentrations of Mg2+, NH4+, and PO43-. Struvite solution (MAP) can be prepared by reacting phosphoric acid, ammonium hydroxide, and dolomite as a magnesium source in a molar ratio of 1:1:1. In a continuously operated isolated column reactor, the pH ranged from 8 to 12, and the reactor inlet air velocity ranged from 0.25 to 1.25 L/min. The chemical elements of dried struvite were determined using XRF (X-Ray Fluorescence), and the morphology was analyzed using SEM (Scanning Electron Microscope). At the same time, the crystal phase composition was identified using the Rietveld XRD (X-Ray Diffraction) technique. Based on the results of XRF analysis, the highest magnesium content was found under operating conditions with pH 12, air rate 0.75 L/min, and magnesium content 15.5%.

Performance evaluation of a microbial fuel cell for resource recovery as struvite and bioelectricity generation from slaughterhouse wastewater

AbstractBACKGROUNDThe microbial fuel cell (MFC) is a potential cost‐effective technology for the energy‐neutral treatment of wastewater. However, the successful implementation of this technology in resource recovery is still limited. In this study, a microbial electrochemical cell was designed and operated for 30 days. Critical factors for removal and recovery of nitrogen and phosphorus as struvite from wastewater were assessed.RESULTSOptimization studies on critical factors such as the chemical oxygen demand (COD) of wastewater (500–2000 mg L−1) and cathode aeration rate (45–135 mL min−1) were conducted using a pure culture of Escherichia coli. The system yielded an average power density of 465 mW m−2, average current density of 915 mA m−2 and phosphorus recovery at an extent of 40% as struvite. Additionally, a maximum reduction in the COD of 90% with an average coulombic efficiency of about 82% was obtained at a short interval of 30 days. Solubility studies of the recovered struvite for 12 h at different pH values from 4.5 to 9 showed a maximum solubility of 80% at pH 4.5 and a minimum of 3.5% at pH 9.CONCLUSIONThis study moves one step closer to applying MFC technology for nitrogen‐ and phosphorus‐rich wastewater treatment with concurrent struvite precipitation and electricity production. In this way, Sustainable Development Goals 2, 6 and 7 can be achieved through resource recovery, clean water and bioenergy. © 2024 Society of Chemical Industry (SCI).

Evaluating hydrothermal liquefaction hydrochar from sewage sludge as a phosphorus resource through struvite production

Hydrothermal liquefaction (HTL) has attracted considerable attention for valorizing sewage sludge to biofuels while the solid residue, hydrochar, has received little attention for its final application. In the current work hydrochar recovered from hot separation in a pilot-scale HTL plant is evaluated for its nutrient value, in particular as a sustainable Phosphorus (P) resource. Following thorough characterization of the hydrochar, P recovery as struvite (NH4MgPO4·6H2O) is investigated to produce a fertilizer with a lower heavy metal content that could be used in current agricultural practices. P extraction using inorganic (hydrochloric and sulphuric) and organic (citric) acids is evaluated by applying 0.1–1 mol/L of acids for 1–12 h with a liquid/solid ratio of 10 mL/g. A second-order polynomial model was established by response surface methodology (RSM) to predict the P extraction with different acids. The optimum operating conditions for maximum P extraction (94 %) are suggested as 0.7 M of acid strength (H2SO4) and 6.5 h of extraction time. Addition of citric acid (CA) during the struvite precipitation from acid-leached P solution was found to improve the struvite purity from 36.6 % to 54 % with a reduction in heavy metal content. Furthermore, morphological analysis validated the formation of struvite. Upon comparison with the regulations, hydrochar was found to exceed some of the heavy metal limits but was low in polyaromatic hydrocarbons (PAHs), per- and polyfluorinated substances (PFAS) and showed low toxicity to Aliivibrio fischeri. P extraction and struvite precipitation are shown to reduce heavy metal contents below regulatory limits with P recoveries from 40 % to 67 %. Thus, as an alternative to direct land application of hydrochar, harvested struvite from hydrochar could be applied as a fertilizer with no apparent environmental risk.

Nutrient recovery from manure digestate by using waste magnesite powder and bone meal as sustainable substitutes for struvite precipitation

AbstractBACKGROUNDStruvite (MgNH4PO4.6H2O) precipitation is a sustainable approach that can offer simultaneous removal/recovery of nutrients from biogas plant effluents. However, most biogas plant effluents contain a higher molar concentration of nitrogen (N) than magnesium (Mg) and phosphorus (P). Therefore, the external addition of Mg2+ and phosphate (PO43‐) salts is needed to maximize the recovery. In this study, Mg‐rich waste magnesite powder and P‐rich bone meal were used as sustainable additives. The Box–Behnken design was applied to determine optimum conditions of process parameters (pH, Mg:N and P:N molar ratios) to maximize ammonium‐nitrogen (NH4‐N), PO4‐P and Mg2+recoveries.RESULTSNH4‐N, PO4‐P and Mg2+ recoveries were in the ranges 78.5%–96.9%, 69.2%–96.3% and 75.1%–99.9%, respectively. The actual and predicted values showed significant consistency, indicating that the model is satisfactory. Under optimum conditions (pH = 9.0, Mg:N = 2.2, P:N = 1.8), 97.8 ± 0.1% NH4‐N, 96.6 ± 0.31% PO4‐P and 84.4 ± 0.9% Mg2+ recovery were attained. The X‐ray diffraction results confirmed the sole presence of struvite crystals. Scanning electron microscopy images showed irregular prismatic orthorhombic crystals and amorphous material depositions on precipitates of ~25 μm crystal size. The product was 49% struvite with 15.2% P content. The heavy metal content was lower than regulatory limits.CONCLUSIONEven though waste material and industrial by‐products have been used as additives in this process, high NH4‐N and PO4‐P recoveries were recorded under optimum conditions. These results are promising and illustrate a powerful example of industrial symbiosis, and the precipitate containing struvite can serve as a valuable product. © 2024 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).

Comprehensive impacts of the presence of proton exchange membrane on the efficiency of Mg-air fuel cell to remove nutrients and recover struvite

Mg-air fuel cell (MAFC) can achieve simultaneous recovery of phosphorus and nitrogen from wastewater in the form of struvite while generating electricity. This article investigated the comprehensive impacts of the presence of proton exchange membrane (PEM) on the efficiency of MAFC in treating synthetic wastewater, including phosphate and ammonium removal, power generation, and struvite generation. The results showed that the PO43−-P was completely removed within 20 min in the dural-chamber (DC) cell and the removal rate was 6.30 mg-P·cm−2·h−1, which was 1.55 times that of the single-chamber (SC) cell. The removal rate of NH4+-N in the DC cell was 3.37 mg-P·cm−2·h−1, which was 2.70 times that of the SC cell. However, the SC cell produced 63.10 mW·h of electricity, which was 4.61 times that of the DC cell. The precipitates were confirmed to be struvite, with a purity of 99.31 %(DC) and 93.95 % (SC). The low corrosion potential of Mg leads to hydrogen evolution corrosion during the reaction, resulting in low current efficiency, but the current efficiency increased with reaction time. PEM accelerated the hydrogen evolution corrosion, aggravated the magnesium corrosion, increased the internal resistance, and impaired electrical generation capacity, but provided more Mg2+ and alkalinity for the precipitation of struvite. In conclusion, the DC cell had a great capacity for removing nutrients (PO43− and NH4+) and producing high-purity struvite, while the SC cell had a strong ability to generate electricity.

Applying Natural and K-Enriched Zeolite Before Struvite Precipitation Improved the Recovery of NH4+ from Liquid Digestate and the Reagent Use Efficiency

Applying Natural and K-Enriched Zeolite Before Struvite Precipitation Improved the Recovery of NH4+ from Liquid Digestate and the Reagent Use Efficiency

Process performance and precipitate quality of phosphorus recovery by struvite precipitation in a fluidized bed reactor using a MgO industrial by-product

Phosphorus recovery through struvite precipitation has gained interest due to the potential use of struvite as a fertiliser, with fluidised bed reactors being a popular technology for carrying out the process. Struvite precipitation requires a magnesium source and an alkaline reagent. This research uses a low-grade magnesium oxide (LG-MgO) industrial by-product with a 56 wt% of MgO as magnesium source and an alkaline reagent to lower operating costs and value-add an industrial by-product. LG-MgO is poorly soluble in water, but its solubility increases significantly when dissolved in anaerobic digestion supernatants due to its circumneutral pH and high buffer capacity. Phosphorus precipitation was carried out in a laboratory-scale fluidised bed reactor where three operating variables (i.e. P:Mg molar ratio, feed inlet position, and recirculation flow rate) were studied to determine the LG-MgO impact on precipitate struvite content. Experimental results showed a high struvite content in all precipitates, close to the values reported for pure magnesium sources. The P:Mg molar ratio influenced precipitate composition. The percentage of struvite in the precipitate were 75–82 wt%, 85–88 wt%, and 75–76 wt% for the P:Mg ratio of 1:0.5, 1:1 and 1:3, respectively. The feed inlet position (side or bottom) also had an impact on precipitate struvite content when the P:Mg molar ratio was 1:3, but not for the other molar ratios. The recirculation flow rate did not have a significant impact on precipitate struvite content.

Do investments in phosphorus recovery from dairy processing wastewater pay off?

While phosphorus fertilizers contribute to food security, part of the introduced phosphorus dissipates into water bodies leading to eutrophication. At the same time, conventional mineral phosphorus sources are increasingly scarce. Therefore, closing phosphorus cycles reduces pollution while decreasing trade dependence and increasing food security. A major part of the phosphorus loss occurs during food processing. In this article, we combine a systematic literature review with investment and efficiency analysis to investigate the financial feasibility of recovering phosphorus from dairy processing wastewater. This wastewater is particularly rich in phosphorus, but while recovery technologies are readily available, they are rarely adopted. We calculate the Net Present Value (NPV) of investing in phosphorus recycling technology for a representative European dairy processing company producing 100,000 tonnes of milk per year. We develop sensitivity scenarios and adjust the parameters accordingly. Applying struvite precipitation, the NPV can be positive in two scenarios. First, if the phosphorus price is high (1.51 million EUR) or second if phosphorus recovery is a substitute for mandatory waste disposal (1.48 million EUR). However, for a variety of methodological specifications, the NPV is negative, mainly because of high input costs for chemicals and energy. These trade-offs between off-setting pollution and reducing energy consumption imply, that policy makers and investors should consider the energy source for phosphorus recovery carefully.

Calibration of a sewage sludge anaerobic digestion model with multiple mineral precipitation for two case studies

Including multiple mineral precipitation in anaerobic digestion models is important to accurately assess the quantity of phosphates (PO4-P) in the liquid phase of digested sludge that can be recovered as a fertilizer in struvite precipitation reactors or by emerging processes such as ion exchange membranes. However, the performance of such processes is highly impacted by the presence of potassium (K+) or calcium (Ca2+) ions, which are most often neglected when validating precipitation models. The novelty of this work was to provide a calibration procedure of an anaerobic digestion model with multiple mineral precipitation that can be used for different case studies and do not focus only on PO4-P but also on K+, Ca2+ Mg2+. To draw this calibration procedure, data from two anaerobic digesters located near Lyon (France) and in the Navarra region (Spain), treating sludge with different biodegradability and concentration ranges of phosphorus (P), calcium (Ca), magnesium (Mg), potassium (K) and soluble inorganic carbon (SIC), have been used. This procedure includes the calibration of the inert COD fraction (fXI,COD) and kinetic precipitation constants (Kr) using Bayesian Monte Carlo techniques. However, a unique parameter set for both anaerobic digesters cannot be identified, leading to site-specific parameters for fXI,COD (0.30 and 0.43), Kr,MgCO3 (274 and 0.4), Kr,CaCO3 (21 and 0.12) and Kr,ACP (270 and 58). The calibrated model was able to estimate PO4-P, Ca2+, Mg2+ and K+ concentration in digested sludge with a relative error below 10 %.

Struvite recovery from microbial fuel cells treating different nutrient-rich wastewaters

Wastewater is an abundant renewable source of nutrients such as nitrogen and phosphorus. However, current recovery methods require substantial amounts of energy and chemicals, which pose various economic and environmental burdens. Microbial fuel cells (MFCs) represent a feasible alternative for nutrient recovery from wastewater as they reduce the cost of chemicals and energy input while producing electricity from treated organics. Despite the promising benefits of MFCs, there is limited knowledge of the effect of substrate type on their operation and nutrient recovery. Therefore, this study investigates the efficiency of struvite formation for nutrient recovery in 700-ml-volume dual-chamber MFCs using various wastewaters: urine, centrate, and greywater (laundry and dishwasher wastewater). The performance was assessed based on electricity output, organics removal in terms of soluble chemical oxygen demand (SCOD), and struvite recovery. The highest SCOD removal efficiency of over 95 % was achieved with the centrate-fed cell. Moreover, the highest maximum power densities generated from the urine, centrate, and greywater-fed MFCs were 1.7, 1.5, and 0.95 mW/cm2, respectively. In terms of struvite recovery, the urine-fed cell produced the highest struvite precipitate quantity (2.1 g/l), followed by the centrate (1.8 g/l) and the greywater (0.4 g/l). The phosphate recovery efficiencies were 55, 36, and 48 % for the MFCs treating urine, centrate, and greywater, respectively. Morphological and chemical analyses of the formed precipitates confirmed that the nutrients were recovered primarily as struvite. Overall, the results and conclusions of the present study support the potential for utilizing MFCs for nutrient recovery and energy generation.

Comparative evaluation of drying methods for struvite produced from electrocoagulated source-separated urine: Implications for quality, energy and cost-effectiveness

Struvite precipitation from source-separated urine is crucial for waste utilization and sustainability. However, after precipitation, the high moisture content of struvite necessitates an additional drying process that can be costly and inefficient. In the present study, the performance of different drying methods—open sun drying, air drying, conventional drying (20–100 °C), and microwave drying (180–720 W) on the quality of struvite obtained from source-separated urine through electrocoagulation using Mg–Mg electrodes were evaluated. It was found that higher temperatures and power in the convective oven and microwave resulted in higher diffusivity (10−9-10−7 m2s−1), leading to reduced drying times. Different models were employed to comprehend the drying mechanism, and the one with the highest correlation coefficient (R2 = 0.99) and the lowest statistical values was selected. The key findings indicated that higher power and temperature levels were more cost-effective. However, characterization of the dried struvite using X-ray diffraction and Fourier-transformed infrared spectroscopy, disintegration of struvite crystals at temperatures above 60 °C in the conventional oven and 180 W in the microwave oven was observed. Based on the results, we conclude that sun drying is a cost-effective and environmentally friendly alternative for drying struvite without compromising its quality.

Burgeoning innovation and scalability activities for phosphorus recovery from wastewater treatment facilities

Phosphorus has been described as life's bottleneck due to its finite source and indispensable role in sustaining living cell functionalities. The paradigm shift from recycling to linear phosphorus consumption that transpired after the Green Revolution brought about one of the most concerning recent environmental challenges-eutrophication. Many recovery technologies have been developed to reinstate phosphorous recycling in sophisticated and safe ways. This study critically reviewed the current state of global phosphorous natural reserves and pollution. It also discussed forecasted consumption trends and how the recovery could assist in meeting the increasing phosphorous demands. The current phosphorous recovery processes were reviewed. A multi-criteria comparison of the technologies within their technology redness levels (TRLs) groups was carried out using the PROMETHEE ranking approach. The comparison criteria focused on efficiency, product quality, and energy and chemicals consumption. The processes with the highest preference scores in their respective TRL groups employed chemical leaching and struvite precipitation. This study also presents patent analyses of P recovery technologies over the past 8 years. These analyses showed that China is at the forefront of patent production, while Europe leads in commercialization. Biochar modification and electrode materials development dominate recent innovations in P recovery.