Metallic iron (Fe0)-based materials for aqueous phosphate removal: A critical review

Electrochemically mediated phosphorus and energy recovery from digested effluent

The growing global concern over the high phosphorus concentration in discharged wastewaters has driven the demand for exploring the means to recover it from wastewater. We previously demonstrated the possibility of phosphorus recovery by iron-air fuel cells from digested effluent. The present study focused on further optimizing the performance of the fuel cell by adjusting the wastewater properties (initial pH) and device parameters (anode/cathode area ratio, electrode spacing). Under neutral or slightly alkaline conditions, the HCO3- ions accelerated the formation of iron anode passivation layer, resulting in a decreased phosphate removal efficiency and vivianite yield. Additionally, the occurrence of oxygen crossover with small electrode spacing and anode/cathode area ratio significantly influenced the efficiency of fuel cells in terms of phosphate removal, vivianite production, and electricity generation. The results showed that an acidic pH (5.78), an adequate anode/cathode area ratio (1.3), and an appropriate electrode spacing (5 cm) were prone to increase vivianite yield. Furthermore, the fuel cell achieved the highest electric energy output with an initial pH of 5.78, an anode/cathode area ratio of 0.4, and an electrode spacing of 7.5 cm. As far as operational cost was concerned, the iron-air fuel cell system exhibited a potential cost-saving advantage of about 65.6% compared to the traditional electrochemical crystallization system.

Simultaneous nitrate and phosphorus removal in novel steel slag biofilters: Optimization and mechanism study

The simultaneous nitrate (NO3--N) and phosphorus (P) removal systems are considered to be an effective wastewater treatment technology. However, so far, there are few studies on system optimization to improve NO3--N and P removal. In this study, nine simultaneous NO3--N and P removal biofilters (SNPBs) were constructed to treat simulated wastewater. In order to optimize the NO3--N and P removal, different material loading positions were set: (1) red soil, steel slag, and rice straw (RSR), (2) steel slag, red soil, and rice straw (SRR), and (3) red soil, rice straw, and steel slag (RRS). Results showed that the above three treatments had mean removal efficiencies of 58%-91% for NO3--N and 55%-81% for TP, with the best N and P removal occurring in the SRR. The TN mass balance indicated that microbial removal was responsible for 78.2% of the influent TN in the SRR biofilter. The key microorganisms were Enterobacter, Klebsiella, Pseudomonas, Diaphorobacter, and unclassified_f_Enterobacteriaceae, which accounted for 61.9% of the total microorganisms. The main P-removal mechanism was the formation of Al-P, Fe-P, and Ca-P in red soil or steel slag layer. In addition, the decrease of SRR effluent pH from 11.86 in 1-7 days to 7.75 in 8-50 days indicated that red soil and rice straw had a synergistic effect on water pH reduction. These results suggest that a reasonable combination of steel slag with red soil and rice straw not only simultaneously removes NO3--N and P but also additionally solves the problem of high pH caused by steel slag.

Promoted iron corrosion and enhanced phosphate removal by micro-electric field driven zero-valent iron

Zero-valent iron (Fe0) is restricted in phosphate removal due to the formation of a passive P-Fe layer on its surface. A micro-electric field (0.20 mA cm-2) was employed in Fe0 column to facilitate iron corrosion for enhanced phosphate removal with a Fe0 column as the control. The performance of two columns was compared by batch experiment at a Fe0 filling rate of 10 vol% with quartz sand as dispersing media. The stability and reusability of micro-electric field driven Fe0 (MFD-Fe0) column was estimated by cyclic test. Solid phase analysis showed promoted iron corrosion, iron ion generation, and secondary mineral production such as lepidocrocite and magnetite in the MFD-Fe0 column. Since iron ions tended to precipitate with phosphate, and iron minerals provided reaction sites for phosphate adsorption, the MFD-Fe0 column achieved an enhanced phosphate removal of 94.1%, 2.8 times higher than that of the Fe0 column. The increase of current density from 0 to 0.20 mA cm-2 significantly improved phosphate removal from 24.5% to 94.1%, further demonstrating the promoting effect of micro-electric field on iron corrosion. The MFD-Fe0 column also possessed excellent stability and reusability. It only showed a slight decrease of phosphate removal from 94.1% to 89.7% in eight cycles. It restored a phosphate removal capacity of 97.4% as compared to the initial MFD-Fe0 column by eluting iron (hydro)oxides on Fe0 and quartz sand surfaces with sulfuric acid. This study indicated that MFD-Fe0 is a promising method to remove phosphate from water and an alternative strategy for overcoming Fe0 passivation.

Cross-linked quaternized polyethersulfone-amino crystalline nanocellulose composite membrane for enhanced phosphate removal from wastewater

Cross-linked quaternized polyethersulfone (QPES) hybrid mixed polymer membranes (MPMs) loading amino crystalline nanocellulose (ACNC) were successfully fabricated and applied for phosphate removal. The successful production of novel materials was validated by microscopic, spectral, and microanalytical methods. When compared to the native QPES membrane, the primary qualities of QPES hybrid membranes (hydrophilicity, porosity, permeability, antifouling) have been greatly improved overall. In addition, the surface zeta potential (SZP) and ion exchange capacity (IEC) measurements demonstrated the high positive surface charge densities of MPMs, which is beneficial for phosphate uptake. Phosphate adsorption by these membranes was studied at different temperatures, contact times, and initial phosphate concentrations using batch experiments, to investigate the optimal conditions for phosphate uptake. The MPMs showed excellent adsorption capacities with maximal removal capacities in the range of 68.8-87.95 %. Phosphate adsorption on MPMs was regulated primarily by the Sips isotherm model with multilayer adsorption capabilities and exhibited pseudo-second order kinetics (R² = 0.9951-0.9976). The positive ΔH° and ΔS° values are indicative of the endothermic nature of phosphate adsorption and randomness increase. The negative ΔG° value indicates the spontaneousity of phosphate adsorption. Phosphate removal effectiveness of the membranes was maintained following recovery and regeneration with NaOH.

The Effects of Nanoparticles- Zerovalent Iron on Sustainable Biomethane Production through Co-Digestion of Olive Mill Wastewater and Chicken Manure

The impacts of nanoparticles-zerovalent iron (NP-ZVI) on anaerobic co-digestion (AcoD) were assessed. The production of biogas and methane (CH4), as well as the removal efficiency of volatile solids (VS) and contaminants were investigated in the AcoD of chicken manure (CM) and olive mill wastewater (OMWW) with the addition of NP-ZVI at different concentrations (10–50 mg/g VS) and different sizes resulting from various mixing volume ratios (MVR) of NaBH4:FeSO4.7H2O. The results show that NP-ZVI ≤ 30 mg/g VS at MVR-2:1, MVR-4:1, and MVR-6:1 improves the AcoD. In contrast to 40–50 mg/g VS of NP-ZVI, which caused an inhibitory impact in all of the AcoD stages, as well as a decrease in the contaminant’s removal efficiency, the concentration of 10–30 mg NP-ZVI/g VS at MVR-4:1 achieved a maximum improvement of CH4 by 21.09%, 20.32%, and 22.87%, respectively, and improved the biogas by 48.14%, 55.0%, and 80.09%, respectively, vs. the 0 additives. Supplementing AcoD with NP-ZVI at a concentration of 30 mg/g VS at MVR-4:1 resulted in maximum enhancement of the contaminant removal efficiency, with a total oxygen demand (TCOD) of up to 73.99%, turbidity up to 79.07%, color up to 53.41%, total solid (TS) up to 59.57%, and volatile solid (VS) up to 74.42%. It also improved the hydrolysis and acidification percentages by up to 86.67% and 51.3%, respectively.

Condition optimization of iron-air fuel cell to treat phosphate-containing wastewater regarding sustainable development

Increasing use of phosphorus products and excessive exploitation of phosphorus resources become two major problems in perspective of phosphorus sustainable development. Phosphorus recovery is the shortcut to solve this dilemma. Combining electrochemistry, an iron-air fuel cell was adopted to recover phosphate and electricity from phosphate-containing wastewater in our previous studies. The present study focused on investigating the effects of catholyte/anolyte conductivity, external resistance, and anolyte pH on the performance of iron-air fuel cell, and obtaining the optimized conditions. Furthermore, the electrochemical methods of phosphate recovery were compared and assessed, and it is concluded that iron-air fuel cell has great potential for energy recovery. The phosphate removal efficiencies and vivianite yield roughly positively correlated with the catholyte conductivity and the anolyte pH, but negatively correlated with the external resistance and the anolyte conductivity. The electricity generation roughly positively correlated with the catholyte conductivity and anolyte conductivity, but showed limitations in the test range of anolyte pH and external resistance. To pursue high phosphate removal efficiencies and vivianite yield, the catholyte conductivity, external resistance, anolyte pH and anolyte conductivity were suggested to be 35 g-NaCl/L, 10 Ω, 8 and 0 g-NaCl/L. While if electricity generation was the primary goal, these parameters should be 35 g-NaCl/L, 220 Ω, 5 and 70 g-NaCl/L. The optimized conditions will help to improve the phosphate removal efficiency, vivianite yield and electricity generation, and to promote the development of iron-air fuel cell technology.

Using Iron Tailings for Phosphate Removal in Cemented Phosphogypsum (PG) Backfill

Compared with the post-treatment of pollutants, such as the removal of phosphate from wastewater, it is more important to develop effective emission control strategies to reduce phosphate pollution. Phosphogypsum (PG) is a typical solid waste byproduct of phosphate production and contains high amounts of residual phosphate. In order to control the phosphate emissions during the recycling of PG aggregates for cemented backfill, another solid waste product—iron tailings (ITs)—was added during the preparation of backfill slurry. The results showed that the ITs effectively accelerated the phosphate removal in cemented PG backfill, enabling the quick reduction in the phosphate concentration to the discharge standard (<0.5 mg/L) within 15 min. This means that the emissions of phosphate to bleeding water were effectively controlled. The adsorption experiment showed that phosphate was adsorbed by the ITs, and the adsorption data fitted well with the Langmuir adsorption model (R2 = 0.98) and pseudo-second-order kinetic model (R2 = 0.99), indicating that the phosphate adsorption of ITs was a monolayer chemical adsorption. Furthermore, an unconfined compressive strength (UCS) test was performed on the backfill with the addition of ITs. Compared to the control group (without ITs), the UCS of backfill with 20% ITs increased from 1.08 MPa to 1.33 MPa, indicating that the addition of solid waste could be beneficial to the strength development of the backfill by mitigating the interference of phosphate with the hydration process. The backfill cured for 28 d was selected for the toxic leaching test, and the phosphate concentration in the leachates was always below 0.02 mg/L, indicating that ITs can effectively immobilize phosphate in backfill for a long time.

Fe0-Supported Anaerobic Digestion for Organics and Nutrients Removal from Domestic Sewage

Results from different research suggest that metallic iron (Fe0) materials enhance anaerobic digestion (AD) systems to remove organics (chemical oxygen demand (COD)), phosphorus and nitrogen from polluted water. However, the available results are difficult to compare because they are derived from different experimental conditions. This research characterises the effects of Fe0 type and dosage in AD systems to simultaneously remove COD and nutrients (orthophosphate (PO43−), ammonium (NH4+), and nitrate (NO3− Lab-scale reactors containing domestic sewage (DS) were fed with various Fe0 dosages (0 to 30 g/L). Batch AD experiments were operated at 37 ± 0.5 °C for 76 days; the initial pH value was 7.5. Scrap iron (SI) and steel wool (SW) were used as Fe0 sources. Results show that: (i) SW performed better than SI on COD and PO43− removal (ii) optimum dosage for the organics and nutrients removal was 10 g/L SI (iii) (NO3− + NH4+) was the least removed pollutant (iv) maximum observed COD, PO43− and NO3− + NH4+ removal efficiencies were 88.0%, 98.0% and 40.0% for 10 g/L SI, 88.2%, 99.9%, 25.1% for 10 g/L SW, and 68.9%, 7.3% and 0.7% for the reference system. Fe0-supported AD significantly removed the organics and nutrients from DS.

Removal of Phosphates in Aqueous Solution by Adsorption on Calcium Oxide

The aim of this work is the removal of phosphates from an aqueous solution by adsorption on a new, inexpensive adsorbent, calcium oxide. We have also shown interest in the choice of removal method, which is adsorption. The kinetic study of the removal of phosphate ions by adsorption on calcium oxide allowed us to calculate the value of adsorption capacity as a function of the parameters affecting adsorption: Amount of adsorbent, initial concentration of phosphate ion solution, pH of the mixture and temperature. The study of adsorption isotherms showed that the Freundlich model is the most appropriate for the phenomenon of phosphate ion adsorption. Modeling of the kinetic data by the pseudo-first order and pseudo-second order equations shows that the adsorption process is best described by the second order equation. Thermodynamic parameters such as enthalpy ΔH°, entropy ΔS° and free enthalpy ΔG° were also evaluated to determine the nature of adsorption. The results show that the adsorption process is a spontaneous and endothermic physisorption.