Adsorptive removal of phosphorus from aqueous solution using sponge iron and zeolite

Sulfoaluminate cement-modified loess as bioretention cell filler for nutrient removal from stormwater runoff

In order to reduce the consumption of sand and gravel resources, the use of loess can reduce transportation costs and realize the in-situ construction of spongy in areas with rich loess resources. But the collapsibility and low permeability of loess make it unable to be directly used as the filler of bioretention cells. In this study, sulfoaluminate cement (SAC) mixed with a small amount of basalt fiber was considered to be used for loess modification, and the physicochemical properties and nutrient removal effect of SAC-modified loess as filler in bioretention cells were comprehensively evaluated. The results showed that when the SAC dosage was 15% and the basalt fiber addition was 0% (S15B0) and 0.6% (S15B6) and the curing time was 14 days, the stability and appropriate permeability can be exhibited, which can preliminarily satisfy the requirements of bioretention cell. SAC made the maximum adsorption capacity of S15B0 and S15B6 for ammonia nitrogen (NH4+-N) and phosphate higher than that of sand by 10.96%-31.51% and 45.92%-76.72%, respectively. The hydration products in SAC modified loess can fill the internal pores of loess particles and provide structural support, and ultimately reduce the accumulated pores, mesoporous pore size (20%) and surface homogeneity. Both S15B0 and S15B6 showed good removal effects of NH4+-N and COD. The TP removal efficiency was stable at 95.43%∼99.95%. Both the antecedent drying days and the submerged zone have an effect on the nitrogen removal in the bioretention cells, where a longer antecedent drying days is detrimental to the nitrogen removal, and the installation of a submerged zone improves the nitrogen removal. The basalt fiber can enhance the transformation process from nitrate-nitrogen to nitrite-nitrogen in the bioretention cell. Therefore, the modification of SAC can provide a certain idea for the in-situ use of loess as the filler of the bioretention cell.

Effects of carrier surface hydrophilic modification on sludge granulation: From sludge characteristics, extracellular polymeric substances, and microbial community

Aerobic granular sludge (AGS) is a powerful biotechnological tool capable of treating multiple pollutants simultaneously. However, the granulation process and pollutant removal efficiency still need to be further improved. In this study, Fe2O3- and MnO2-surface-modified straw foam-based AGS (Fe2O3@SF-AGS and MnO2@SF-AGS), with an average particle size of 3 mm, were developed and evaluated. The results showed that surface modification reduced the hydrophobic groups of carriers, facilitating the attachment and proliferation of microorganisms. Notably, MnO2@SF-AGS showed excellent granulation performance, reaching a stable state about one week earlier than the unmodified SF-AGS. The polymeric substance content of MnO2@SF-AGS was found to be 1.28 times higher than that of the control group. Furthermore, the removal rates for NH4+-N, TN, and TP were enhanced by 27.28%, 12.8%, and 32.14%, respectively. The bacterial communities exhibited significant variations in response to different surface modifications of AGS, with genera such as Saprospiraceae, Terrimonas, and Ferruginibacter playing a crucial role in the formation of AGS and the removal of pollutants specifically in MnO2@SF-AGS. The charge transfer of metal ions of MnO2@SF promotes the granulation process and pollutant removal. These results highlight that MnO2@SF-AGS is an effective strategy for improving nitrogen and phosphorus removal efficiency from wastewater.

Performances and mechanisms of simultaneous removal of nitrate and phosphate by biofilter assembled with sponge iron/copper and corn cobs

Sponge iron (SI) is a potential material for removing nitrate and phosphate from water. We decorated the SI with copper (Cu) to enhance its removal performance. To gain insight into the nitrate and phosphate removal utilizing SI/Cu and microbial coupling systems, three biofilters filled with corn cob (CC), corn cob + sponge iron (CS) and corn cob + sponge iron/copper (CSCu) were constructed. The results showed that the effluent NO3--N and PO43--P concentrations of CSCu remained consistently below 1 and 0.1 mg/L. The introduction of SI/Cu led to the enrichment of the Dechloromonas genus, making it the dominant microbial group, occupying 42.65% of the effective sequences. Modification of SI with Cu increased nitrogen cycle-related functional genes abundance in CSCu, with a 634% increase in nirS compared to CS. These findings proved that SI/Cu was a promising material, providing an approach to concomitantly removing nitrate and phosphate.

State of the art and prospects of zeolites and metal organic frameworks (MOFs) for nitrogen and phosphorus removal in dairy wastewater

Water is an essential resource for humans, animals, and plants. Water is also necessary for the manufacture of many products such as milk, textiles, paper, and pharmaceutical composites. During manufacturing, some industries generate a large amount of wastewater containing numerous contaminants. In the dairy industry, for each litre of drinking milk produced, about 10 L of wastewater is generated. Despite this environmental footprint, the production of milk, butter, ice cream, baby formula, etc., are essential in many households. Common contaminants in dairy wastewater include high biological oxygen demand (BOD), chemical oxygen demand (COD), salts as well as nitrogen and phosphorus derivatives. Nitrogen and phosphorus discharges are one of the leading causes in the eutrophication of rivers and oceans. Porous materials have long held significant potential as a disruptive technology for wastewater treatment. However, thus far they have been understudied for use in dairy wastewater treatment. Ordered porous materials, such as zeolites and metal organic frameworks (MOFs), represent classes of porous materials with significant potential for the removal of nitrogen and phosphorus. This review explores the different zeolites and MOFs applied in the removal of nitrogen and phosphorus from wastewater and the prospect of their potential for use in wastewater management in the dairy industry.

Cycling of phosphorus from wastewater to fertilizer using wood ash after energy production

Quercus wood was used for thermal energy production, and wood bottom ash (WDBA) was used as a medium for water purification and soil fertilizer in accordance with the recently proposed food-water-energy nexus concept. The wood contained a gross calorific value of 14.83 MJ kg^-1, and the gas generated during thermal energy production has the advantage of not requiring a desulfurization unit due to its low sulfur content. Wood-fired boilers emit less CO2 and SOX than coal boilers. The WDBA had a Ca content of 66.0%, and Ca existed in the forms of CaCO3 and Ca(OH)2. WDBA absorbed P by reacting with Ca in the form of Ca5(PO4)3OH. Kinetic and isotherm models revealed that the results of the experimental work were in good agreement with the pseudo-second-order and Langmuir models, respectively. The maximum P adsorption capacity of WDBA was 76.8 mg g^-1, and 6.67 g L^-1 of WDBA dose could completely remove P in water. The toxic units of WDBA tested using Daphnia magna were 6.1, and P adsorbed WDBA (P-WDBA) showed no toxicity. P-WDBA was used as an alternative P fertilizer for rice growth. P-WDBA application resulted in significantly greater rice growth in terms of all agronomic values compared to N and K treatments without P. This study proposed the utilization of WDBA, obtained from thermal energy production, to remove P from wastewater and replenish P in the soil for rice growth.

Bio-assembled MgO-coated tea waste biochar efficiently decontaminates phosphate from water and kitchen waste fermentation liquid

Crystal morphology of metal oxides in engineered metal-biochar composites governs the removal of phosphorus (P) from aqueous solutions. Up to our best knowledge, preparation of bio-assembled MgO-coated biochar and its application for the removal of P from solutions and kitchen waste fermentation liquids have not yet been studied. Therefore, in this study, a needle-like MgO particle coated tea waste biochar composite (MTC) was prepared through a novel biological assembly and template elimination process. The produced MTC was used as an adsorbent for removing P from a synthetic solution and real kitchen waste fermentation liquid. The maximum P sorption capacities of the MTC, deduced from the Langmuir model, were 58.80 mg g−1 from the solution at pH 7 and 192.8 mg g−1 from the fermentation liquid at pH 9. The increase of ionic strength (0–0.1 mol L−1 NaNO3) reduced P removal efficiency from 98.53% to 93.01% in the synthetic solution but had no significant impact on P removal from the fermentation liquid. Precipitation of MgHPO4 and Mg(H2PO4)2 (76.5%), ligand exchange (18.0%), and electrostatic attraction (5.5%) were the potential mechanisms for P sorption from the synthetic solution, while struvite formation (57.6%) and ligand exchange (42.2%) governed the sorption of P from the kitchen waste fermentation liquid. Compared to previously reported MgO-biochar composites, MTC had a lower P sorption capacity in phosphate solution but a higher P sorption capacity in fermentation liquid. Therefore, the studied MTC could be used as an effective candidate for the removal of P from aqueous environments, and especially from the fermentation liquids. In the future, it will be necessary to systematically compare the performance of metal-biochar composites with different metal oxide crystal morphology for P removal from different types of wastewater.

Graphical Abstract

Catalytic activity and mechanism of typical iron-based catalysts for Fenton-like oxidation

Heterogeneous Fenton-like systems were exploited for the degradation of Reactive Red X-3B (RR X-3B) using iron-carbon composite, sponge iron, chalcopyrite and pyrite as catalysts. The effect of operational variables on the catalytic activity and metal leaching behavior of catalysts was evaluated and the catalytic mechanism was discussed. The experimental results showed that under the optimum conditions, chemical oxygen demand (COD) removals by Fenton-like systems could reach 89.91%, 86.84%, 80.11% and 60.02% with iron-carbon composite, sponge iron, chalcopyrite and pyrite, respectively. Micro-electrolysis of iron-carbon composite and sponge iron resulted in higher COD removal at acid pH range. Electron Paramagnetic Resonance (EPR) analysis and quenching tests showed that ^•OH was the main reactive oxygen species responsible for the degradation of RR X-3B. A large amount of Fe²⁺ leached from iron-carbon composite and sponge iron, which served as a homogeneous Fenton catalyst during the degradation of RR X-3B. In contrast, much lower amount of Fe²⁺ was leached from chalcopyrite and pyrite, and surface catalysis of the minerals played more important role in the generation of ^•OH. Surface characterization and density functional theory (DFT) calculation results illustrated that ≡Fe(II) was the primary surface catalytic site during the reaction. The reduction of ≡Fe(III) and ≡Cu(II) can be facilitated by sulfides on the mineral surface. The Fenton-like systems catalyzed by iron-based materials exhibited higher H₂O₂ utilization and COD removal than classical Fenton system. With the lower metal leaching concentration and stable surface property, chalcopyrite and pyrite may be more practical applicable from a long-term catalytic activity point of view.

Strengthen the purification of eutrophic water and improve the characteristics of sediment by functional ecological floating bed suspended calcium peroxide and sponge iron jointly

To overcome the shortcomings of conventional ecological floating bed (CEFB) in purifying landscape water, this study constructed a functional ecological floating bed (FEFB) through the suspension of calcium peroxide (CP) and sponge iron (SI) jointly below the CEFB. The purification effect of water quality and influence of sediment were compared in control check, CEFB, and FEFB systems, which were loaded the same sediment and reclaimed water in a field experiment. Results showed that the FEFB suspended with CP and SI had evident purification effect on the quality of landscape water supplied with reclaimed water and can maintain stably the nutrient status of the water body at mesotrophic levels and low turbidity. The FEFB promoted the degradation of humus, thus eliminating the chroma risk in water body caused by the decay of plants from the CEFB. Moreover, the FEFB can control the sediment mass produced, reduce the total nitrogen (TN) mass of sediment, and decrease the transformable TN (TTN) content in the sediment. The FEFB enhanced the stability of phosphorus (P) in the sediment, where the relative content of Ca-P and stable P reached 42.18% and 64.27%, respectively. To sum up, the FEFB suspended with SI and CP can not only effectively control the eutrophication and sensory index of landscape water but also change the TTN content and P forms in sediment, making the sediment more stable. Thus, the FEFB provides an innovative approach to reduce endogenous nutrient release for landscape water along with recharging with reclaimed water.

Preparation of Mn/Ti-modified zeolite and its performance for removing iron and manganese

Excessive iron and manganese presented in groundwater sources may cause harm to human health that needs to be solved urgently. This research aims to develop high-performance Mn/Ti-modified zeolites using sol-gel method and hydrothermal synthesis method to remove Fe2+ and Mn2+ simultaneously. The preparation parameters were optimized by response surface methodology, and the results confirmed that the optimal preparation conditions were as follows: mass ratio of MnO2-TiO2/zeolite = 1, hydrothermal temperature = 200°C, and calcination temperature = 500°C. The results of batch adsorption experiments showed that the best removal rate of Fe2+ and Mn2+ by modified zeolite materials which was prepared under the optimum conditions reached 96.8% and 94.4%, respectively, at which the saturated adsorption capacity was 2.80 mg/g and 1.86 mg/g. Through the adsorption kinetics, thermodynamics, internal diffusion, and isothermal adsorption analyses, it is confirmed that the adsorption process of Fe2+ and Mn2+ by the modified zeolite is mainly chemical adsorption. The results of the Weber-Morris internal diffusion model prove that internal diffusion is not the only step that controls the adsorption process. In addition, combined with the characterization of the composite-modified zeolite and the adsorption experimental study, it shows that there is an autocatalytic reaction in the adsorption process.

Removal of phosphate from synthetic wastewater: A comparative study between both activated clays using an experimental design methodology

Phosphate-loaded industrial wastewaters have resulted in numerous environmental issues that have hard hit the Gulf of Gabes-Tunisia, making the environmental protection one of the most compelling priorities. Consequently, this study aimed first to compare the amounts of phosphate adsorbed by two types of Tunisian activated clays. The second goal was to assess and optimize the phosphate removal efficiency of these clays, using Box-Behnken design (BBD) under response surface methodology. Results showed that the highest adsorption amounts of 130.16 mg g^-1 , 125.42 mg g^-1 were yielded for Jebel Haidoudi clay and Douiret clay, respectively. These values demanded an initial phosphate concentration of 300 mg L^-1 , a contact time of 5 h, and a pH of 2). Thus, kinetic and isotherm studies of phosphate elimination from synthetic solutions demonstrated that for both activated clays, the pseudo-second-order and Langmuir equation fitted very well the experimental data, respectively. These results indicate that phosphate adsorption might be mainly a chimisorption phenomenon and a monolayer process. All these findings confirmed that both activated clays could be considered as a competent, cost-effective, efficient and ecological alternative for the elimination of phosphate from industrial wastewaters. PRACTITIONER POINTS: Activated clay could be adopted as an efficient and cost-effective adsorbent. The optimum conditions were nominated as 300 mg L^-1 of initial phosphate concentration, 5 h contact times and pH = 2. The probable uptake mechanism of phosphate followed predominantly the acid-base interaction and hydrogen bond.

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

The discharge of excessive phosphate from wastewater sources into the aquatic environment has been identified as a major environmental threat responsible for eutrophication. It has become essential to develop efficient but affordable techniques to remove excess phosphate from wastewater before discharging into freshwater bodies. The use of metallic iron (Fe⁰) as a reactive agent for aqueous phosphate removal has received a wide attention. Fe⁰ in-situ generates positively charged iron corrosion products (FeCPs) at pH > 4.5, with high binding affinity for anionic phosphate. This study critically reviews the literature that focuses on the utilization of Fe⁰-based materials for aqueous phosphate removal. The fundamental science of aqueous iron corrosion and historical background of the application of Fe⁰ for phosphate removal are elucidated. The main mechanisms for phosphate removal are identified and extensively discussed based on the chemistry of the Fe⁰/H₂O system. This critical evaluation confirms that the removal process is highly influenced by several operational factors including contact time, Fe⁰ type, influent geochemistry, initial phosphate concentration, mixing conditions, and pH value. The difficulty in comparing independent results owing to diverse experimental conditions is highlighted. Moreover, contemporary research in progress including Fe⁰/oxidant systems, nano-Fe⁰ application, Fe⁰ material selection, desorption studies, and proper design of Fe⁰-based systems for improved phosphate removal have been discussed. Finally, potential strategies to close the loop in Fe⁰-based phosphate remediation systems are discussed. This review presents a science-based guide to optimize the efficient design of Fe⁰-based systems for phosphate removal.

Phosphorus Release and Speciation in Manganese(IV) Oxide and Zeolite-Amended Flooded Soils

Phosphorus (P) losses from flooded soils and subsequent transport to waterways contribute to eutrophication of surface waters. This study evaluated the effectiveness of MnO₂ and a zeolite Y amendment in reducing P release from flooded soils and explored the underlying mechanisms controlling P release. Unamended and amended (MnO₂ or zeolite, surface-amended at 5 Mg ha^-1) soil monoliths from four clayey-alkaline soils were flooded at 22 ± 2 °C for 56 days. Soil redox potential and dissolved reactive P (DRP), pH, and concentrations of major cations and anions in porewater and floodwater were analyzed periodically. Soil P speciation was simulated using Visual MINTEQ at 1, 28, and 56 days after flooding (DAF) and P K-edge X-ray absorption near-edge structure spectroscopy and sequential fractionation at 56 DAF. Porewater DRP increased with DAF and correlated negatively with pe+pH and positively with dissolved Fe. Reductive dissolution of Fe-associated P was the dominant mechanism of flooding-induced P release. The MnO₂ amendment reduced porewater DRP by 30%-50% by favoring calcium phosphates (Ca-P) precipitation and delaying the reductive dissolution reactions. In three soils, the zeolite amendment at some DAF increased porewater and/or floodwater DRP through dissolution of Ca-P and thus was not effective in reducing P release from flooded soils.

Effects of Recycled Sponge Iron on Phosphorus Recovery from Polluted Water

Phosphorus in water not only degrades water quality but also leads to a waste of resources. In this study, adsorption thermodynamics and kinetics were used to study the effect of sponge iron on phosphorus removal, and a filtration bed was used to simulate the phosphorus removal in polluted water. The results showed that the maximum theoretical adsorption capacity of the modified sponge iron was increased from 4.17 mg/g to 18.18 mg/g. After desorption with 18.18 mol/L of sodium hydroxide and reactivation with 6% (w%) sulfuric acid, the activation rate of modified sponge iron can reach 98%. In a continuous operation experiment run for approximately 200 days, the sponge iron phosphorus removal percolation bed showed a good phosphorus removal ability. Under the condition of TP = 10 mg/L, HRT = 1 H, the comprehensive phosphorus removal rate was 30–89%, and the accumulated phosphorus adsorption per unit volume was 6.95 kg/m3. Wastewater from the regeneration of the sponge iron base can be used to recover guano stone. The optimum conditions were pH = 10, n (Mg2+):n (PO43−):n (NH4+) = 1.3:1:1.1. Under the optimum conditions, the phosphorus recovery rate could reach 97.8%. The method provided in this study has theoretical and practical significance for the removal and recycling of phosphorus in polluted water.

Recent advances in developing innovative sorbents for phosphorus removal-perspective and opportunities

Phosphorus is an essential mineral for the growth of plants which is supplied in the form of fertilizers. Phosphorus remains an inseparable part of developing agrarian economics. Phosphorus enters waterways through three different sources: domestic, agricultural, and industrial sources. Rainfall is the main cause for washing away a large amount of phosphates from farm soils into nearby waterways. The surplus of phosphorus in the water sources cause eutrophication and degradation of the habitat with an adverse effect on aquatic life and plants. Phosphate elimination is necessary to control eutrophication in water sources. Among the different methods reported for the removal and recovery of phosphorus: ion exchange, precipitation, crystallization, and others, adsorption standout as a sustainable solution. The current review offers a comparative assessment of the literature on novel materials and techniques for the removal of phosphorus. Herein, different adsorbents, their behaviors, mechanisms, and capacity of materials are discussed in detail. The adsorbents are categorized under different heads: iron-based, silica-alumina-based, calcium-based, biochar-based wherein the metal and metal oxides are employed in phosphorus removal. The ideal attribute of adsorbent will be the utilization of spent adsorbents as a phosphate plant food and a soil conditioner in agriculture. The review provides the perspective on the current research with potential challenges and directives for possible research in the field.

The use of recycled materials in a biofilter to polish anammox wastewater treatment plant effluent

Anammox is gaining popularity for treating wastewater containing high-strength ammonia due to lower energy demand compared to conventional nitrification-denitrification processes; however, anammox is reported to increase nitrate loads in the effluent. The objective of this study was to assess the applicability of recycled materials [recycled concrete aggregate (RCA) and rice husks (RH)] as a polishing step to improve anammox reactor effluent quality. Anammox effluents were separately passed through two single-stage columns containing RCA and RH, and one two-stage column (50% RCA, 50% RH) to quantify total N, ammonia, nitrate, nitrite, and phosphate removal efficiencies. Langmuir isotherm experiments were conducted to quantify nitrate, nitrite, and phosphate sorption capacities in the columns. The RCA column exhibited the highest phosphate sorption capacity (0.074 mg/g), while the RH column exhibited higher nitrite and nitrate adsorption (0.063 mg/g and 0.023 mg/g respectively). We created a Hydrus-1D model to estimate pseudo-first-order reaction rates in the columns. Because RCA media can form metal-phosphate precipitates, the fastest phosphate reaction rate (1.58 min-1) occurred in the RCA column. The two-stage column demonstrated the greatest overall removals for all nutrients, and removal rates were consistent throughout the experimental period. The two-stage column achieved 15% total N, 94% ammonia-N, 38% nitrate-N, 75% nitrite-N, and 27% phosphate removal. The maximum nitrite, nitrate, and phosphate adsorption capacities in the two-stage column were 0.030 mg/g, 0.017 mg/g, and 0.014 mg/g respectively. This is the first study to demonstrate that recycled materials can successfully be integrated into a biofilter as an effluent polishing step to remove nutrients from anammox wastewater.

Use of sponge iron dosing in baffled subsurface-flow constructed wetlands for treatment of wastewater treatment plant effluents during autumn and winter

Sponge iron (SI) is widely used in water treatment. As effluents from wastewater treatment plant (WWTP) require advanced treatment methodology, three forms of constructed wetlands (CWs): wetlands with sponge iron (SI), copper sulfate modified sponge iron (Cu/SI), and sponge iron coupled with solid carbon sources (C/SI), have been investigated in this paper for the removal effects of organic matter and nutrients in WWTP effluents, and the corresponding mechanisms have been analyzed. The results showed the effect of baffled subsurface-flow constructed wetland (BSFCW) with SI dosing to purify the WWTP effluents after the stable operation. The water flow of this BSFCW is the repeated combination of upward flow and downward flow, which can provide a longer treatment pathway and microbial exposure time. The average removal rates of total inorganic nitrogen (TIN) were 27.80%, 30.17%, and 44.83%, and the average removal rates of chemical oxygen demand (COD) were 19.96%, 23.73%, and 18.38%. The average removal rates of total phosphorus (TP) were 85.94%, 82.14%, and 83.95%. Cu/SI improved the dissolution of iron, C/SI improved denitrification, and a winter indoor temperature retention measure was adopted to increase the effectiveness of wetland treatment during the winter months. After comprehensively analyzing X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and two-dimensional numerical simulation diagrams, a plausible conjecture that microbes use electrons from SI for autotrophic denitrification is presented. Moreover, the stress effect of wetlands dosed with SI on plants decreased stepwise along the course since C/SI used on wetlands had less impact on plant stress.

Ecological floating bed for decontamination of eutrophic water bodies: Using alum sludge ceramsite

In this study, a combined ecological floating bed (C-EFB) with alum sludge ceramsite (ASC) was designed to improve the water purification effect of traditional ecological floating beds (T-EFBs). During the ASC preparation stage, alum sludge was shaped into a ball, air-dried, and fired under 600 °C. The physical and chemical properties of the ASC meet the requirements of Artificial Ceramsite Filter Materials for Water Treatment (CJ/T229-2008). This study investigated the increased capability of this new-type artificial substrate (ASC) on the removal of chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), total phosphorus (TP), and total nitrogen (TN) from eutrophic landscape water. Compared with the T-EFB, the C-EFB owns a higher purification efficiency. The highest average efficiency of COD, NH4+-N, TN and TP removals during the four operating stages was 78.2%, 58.1%, 46.7% and 53.2%, respectively, in the C-EFB, which were all higher than those of 53.5%, 32.4%, 27.2% and 25.8%, respectively, for the T-EFB. Among them, the C-EFB showed a higher advantage in the removal of TP. The results showed that the potential benefits of utilizing ASC in seriously eutrophic bodies of water.

Glycine- and Alanine-Intercalated Layered Double Hydroxides as Highly Efficient Adsorbents for Phosphate with Kinetic Advantages

Phosphate is the main cause of eutrophication. Layered double hydroxides (LDH) are considered to be promising phosphate adsorbents due to their high affinity and large capacity. In this study, we partially intercalated zwitterionic glycine and alanine into Cl-LDH (corresponding to MgAl-LDH with interlayer anion Cl⁻) and synthesized efficient inorganic–organic nanohybrids for phosphate removal with kinetic advantages. Gly-Cl-LDH, Ala-Cl-LDH and Cl-LDH were characterized, and their phosphate adsorption performances under the influence of environment factors (e.g., solution pH, coexisting anions, contact time and phosphate concentration) were investigated. The results show that Gly-Cl-LDH and Ala-Cl-LDH had larger specific surface areas and larger interlayer spaces than Cl-LDH, and exhibited better adsorption performance at a lower pH and better adsorption selectivity against SO₄²⁻. Kinetic experiments indicated that Gly-Cl-LDH and Ala-Cl-LDH can reduce phosphate concentrations to a lower level in a shorter time. The pseudo-second-order kinetic constants of Gly-Cl-LDH and Ala-Cl-LDH were 1.27 times and 3.17 times of Cl-LDH, respectively (R² > 0.996). The maximum adsorption capacities derived from a Langmuir model of Cl-LDH, Gly-Cl-LDH and Ala-Cl-LDH are 63.2 mg-P/L, 55.8 mg-P/L and 58.2 mg-P/L, respectively, which showed superiority over the prevailing phosphate adsorbents. This research provides highly efficient adsorbents for removing phosphate from aqueous solutions.

Phosphorus recovery from waste activated sludge by sponge iron seeded crystallization of vivianite and process optimization with response surface methodology

As a novel phosphorus recovery product, vivianite (Fe₃(PO₄)₂·8H₂O) has attracted much attention due to its enormous recycling potential and foreseeable economic value. Taking sponge iron as seed material, the effect of different reaction conditions on the recovery of phosphorus in waste activated sludge by vivianite crystallization was studied. Through single factor tests, the optimal conditions for vivianite formation were in the pH range of 5.5-6.0 with Fe/P molar ratio of 1.5. Scanning electron microscopy (SEM), powder X-ray diffraction (XRD), and energy dispersive spectroscopy (EDS) were used to analyze the components of the crystals. The results showed that the vivianite produced by sponge iron as the seed crystal were larger and thicker (300-700 μm) than other seed (200-300 μm) and without seed (50-100 μm). Moreover, vivianite, which was synthesized with sponge iron as seed, was obviously magnetic and could be separated from the sludge by rubidium magnet. The Box-Behnken design of the response surface methodology was used to optimize the phosphorus-recovery process with sponge iron (maximum phosphorus recovery rate was 83.17%), and the interaction effect of parameters was also examined, pH had a significant effect on the formation of vivianite. In summary, this research verifies the feasibility of using sponge iron as the seed crystal to recover phosphorus in the form of vivianite from waste activated sludge, which is conducive to the subsequent separation and utilization of vivianite.

Optimization of nutrient removal performance of magnesia-containing constructed wetlands: a microcosm study

Recently, magnesia has drawn much attention for enhancing phosphorus (P) removal of constructed wetlands. However, the poor nitrogen (N) removal efficiency of magnesia-containing constructed wetlands (Mg-CWs) inherently caused by magnesia impedes its application. In this study, peat and intermittent aeration were applied to enhance N removal in a Mg-CW, identified as P-CW and A-CW, respectively. A high TP removal rate (around 90%) was achieved in all CW, and the TN removal rate in the P-CW was 91.05% higher than that in the Mg-CW, which was mainly because the carbon source provided by the peat directly promoted the growth and metabolism of microorganisms and plants. Higher fresh weight of plants was obtained in P-CW (64.94 ± 5.78 g), compared with A-CW (35.88 ± 15.25 g) and Mg-CW (46.25 ± 18.88 g), accomplished by stronger tolerance to high pH (>10). The microbial abundance (16S rRNA) in the P-CW was 15.6 and 8.12 times higher than that of Mg-CW and A-CW, respectively, resulting in lower global warming potential. Tanking all factors into consideration, addition of peat could be an effective method to optimize the nutrient removal performance of Mg-CW.

Comparing natural red soil and irons for removal of phosphorus from wastewater using the multi-soil-layering system and its economic analysis

The study uses an emerging soil treatment technology, the Multi-Soil Layering System (MSL), which is composed of the zeolite permeability layers (PL) and the soil mixture block layers (SMB). The experimental results show that the SMBs with iron particle (SMB-I) removed more than 83% of the total phosphorus (P) pollution in the water, and the outflow sewage concentration is 9.6 mg/L. In contrast, the SMBs with red clay (SMB-R) has 23% removal rate, and the outflow sewage concentration is 46.45 mg/L. Only 0.013 mg/L Fe concentration was detected in the SMB-R system and release of Fe from red soil is hardly achieved under neutral water environment. The SMB-R and SMB-I systems reduced 108.89 mg/g and 20.93 mg/g respectively and the SMB-R had higher removal efficiency of P per gram released Fe. The chromaticity problem of the effluent water in the SMB-I is up to 225 platinum cobalt, and that of the SMB-R is 172 platinum cobalt. Adding 10 g oyster shell (slice-only) and/or 0.65 g polyglutamic acid have effectively removed up to 99% 25-mg/L Fe in the effluent water; the chromaticity problem caused by Fe effluent was successfully solved. Furthermore, the iron particle has the highest unit cost among the materials in the SMBs (US$1.47/kg in lab and US$0.12/kg in field). Removal of 1 mg/L TP in the MSL system costs US$0.036 (by lab) in terms of removal TP rate in the laboratory was 83% and is economically feasible in field development.

Kinetics of Simultaneous Ammonium and Phosphate Recovery by Natural Zeolite

Nowadays, fertilizers containing nitrogen and phosphorus are indispensable for medium and large-scale industrial agriculture. To meet the growing demand of nutrients and reduce the accompanied ecological footprint of primary fertilizer production, processes and technologies for nutrient recovery are necessary and have to be developed. This study represents the basis of an extension of the ion-exchange-loop-stripping process (ILS), which is a combined stripping and ion exchange process using natural zeolite for nitrogen recovery. In batch experiments with a special zeolite filled stirrer, the mechanism and kinetics of simultaneous ammonium and phosphate recovery by natural zeolite were determined. Zeolite loadings of 6.78 mg PO43− g−1 were reached and after regeneration, phosphate recovery rates up to 75% of the initial concentration were achieved. The speed of phosphate precipitation is mostly controlled by the pH value of synthetic wastewater. Phosphate removal in simultaneous experiments does not affect ammonium sorption onto zeolite. These findings and the different removal mechanisms of ammonium and phosphate lead to versatile applications in wastewater treatment and reveal great potential of natural zeolite in simultaneous nutrient recovery processes.

Performances and mechanisms of simultaneous nitrate and phosphate removal in sponge iron biofilter

Sponge iron is a potential material for nitrogen and phosphate removal. To explore the performances and mechanisms of nitrogen and phosphate removal by sponge iron, a sponge iron biofilter was established. The results showed that nitrate was completely removed at HRT of 48 h without external carbon source and at HRT of 3 h with C/N ratio of 5. Furthermore, it was easy to achieve partial denitrification at HRT of 1 h with C/N ratio of 3. The mechanisms of nitrate removal were chemical reduction and nitrate dependent ferrous oxidation without external carbon source and heterotrophic denitrification with external carbon source. XPS result indicated that phosphate was removed by the formation of ferric phosphate precipitation. High throughput sequencing showed that iron-oxidizing bacteria Gallionellaceae was highly enriched in biofilter, accounting for 17.83%, which indicated that it was feasible to achieve autotrophic nitrate removal by sponge iron biofilter.

Preparation of Sorbents Containing Straetlingite Phase from Zeolitic By-Product and Their Performance for Ammonium Ion Removal

In this study, straetlingite-based sorbents were used for NH4+ ion removal from a synthetic aqueous solution and from the wastewater of an open recirculation African catfish farming system. This study was performed using column experiments with four different filtration rates (2, 5, 10, and 15 mL/min). It was determined that breakthrough points and sorption capacity could be affected by several parameters such as flow rate and mineral composition of sorption materials. In the synthetic aqueous solution, NH4+ removal reached the highest sorption capacity, i.e., 0.341 mg/g with the S30 sorbent at a filtration rate of 10 mL/min and an initial concentration of 10 mg/L of NH4+ ions. It is important to emphasize that, in this case, the Ce/C0 ratio of 0.9 was not reached after 420 min of sorption. It was also determined that the NH4+ sorption capacity was influenced by phosphorus. In the wastewater, the NH4+ sorption capacity was almost seven times lower than that in the synthetic aqueous solution. However, it should be highlighted that the P sorption capacity reached 0.512 mg/g. According to these results, it can be concluded that straetlingite-based sorbents can be used for NH4+ ion removal from a synthetic aqueous solution, as well as for both NH4+ and P removal from industrial wastewater. In the wastewater, a significantly higher sorption capacity of the investigated sorbents was detected for P than for NH4+.

Phosphorus Removal from Wastewater: The Potential Use of Biochar and the Key Controlling Factors

In recent years, a large volume of literature has been published regarding the removal of phosphorus (P) from wastewater. Various sorbing materials, such as metal oxides and hydroxides, carbonates and hydroxides of calcium (Ca) and magnesium (Mg), hydrotalcite, activated carbon, anion exchange resins, industrial solid wastes and organic solid wastes, have been suggested for P removal. Many of these sorbents are expensive and/or may cause some environmental problems. In contrast, biochar, as an economical and environmentally friendly sorbing material, has received much attention in recent years and has been used as a novel sorbent for the removal of different organic and inorganic pollutants. Biochar is a type of sustainable carbonaceous material that is produced from the thermal treatment of agricultural organic residues and other organic waste streams under oxygen free conditions. This paper reviews the potential use of biochar and the key controlling factors affecting P removal from wastewater. The ability of biochar to remove P from wastewater depends on its physical and chemical properties. Some of the most important physicochemical properties of biochar (structural characteristics, electrical conductivity (EC), mineral composition, pH, zeta potential, cation exchange capacity (CEC) and anion exchange capacity (AEC)) are affected by the feedstock type as well as temperature of pyrolysis and the P sorption capacity is highly dependent on these properties. The P removal is also affected by the water matrix chemistry, such as the presence of competing ions and bulk pH conditions. Finally, several recommendations for future research have been proposed to facilitate and enhance the environmental efficiency of biochar application.

Production of zeolitic materials in pilot scale based on coal ash for phosphate and potassium adsorption in order to obtain fertilizer

The use of different types of zeolites (X, Na-P1, and 4A) synthesized by different methods and scales were tested in this work to adsorb nutrients present in synthetic solutions and industrial effluents for later application as fertilizer. Modifications with calcium chloride were performed on the zeolite with the best performance to increase its adsorption capacity. The best performing zeolite was type X (ZXH) produced on a pilot scale by the hydrothermal process. Its adsorption capacity without modification was 149 mg P-PO₄/g zeolite and 349 mg K/g zeolite. With the change, there was a fourfold increase in these results, which were up to threefold higher than reported in the literature. The kinetic model that best characterized the adsorption process was the intraparticle diffusion model, and the equilibrium isotherm was that of Freundlich. The adsorption tests performed with industrial effluent showed high removal of the nutrients of interest (> 90% for PO₄^3- and > 95% for K⁺). The desorption tests with zeolites nutrient-loaded from synthetic solutions showed 13 to 24% PO₄^3- and 14 to 47% K⁺ release within 24 h, while for zeolite nutrient-loaded from effluent the release were 7 and 100% for PO₄^3- and K⁺, respectively. The results we obtained in this work indicated the potential use of zeolites in the treatment of effluent and its application as a fertilizer.

Characteristics and mechanisms of phosphorous adsorption by rape straw-derived biochar functionalized with calcium from eggshell

Biochar modified with calcium source is acted as an effective adsorbent for phosphorous recovery. In this research, eggshell is used as a low-cost and environmentally friendly calcium source to replace chemical reagents such as CaCO₃, Ca(OH)₂ and CaCl₂ used in the modified biochar production. Biochar derived from rape straw and modified with eggshell shows prominent phosphorous adsorption performance (e.g., equilibrium adsorption amount, 109.7 mg/g). The kinetic and isotherm analysis demonstrate that chemical adsorption process is performed as the main controlled step for the modified biochar adsorption, and the phosphate adsorption process is composed of both monolayer adsorption and multi-layer adsorption. Moreover, it is found from the physicochemical structures comparison before and after phosphate adsorption that Ca-P precipitation, hydrogen bonding and electrostatic attraction are identified as main adsorption mechanisms. In addition, the adsorbed phosphates are mainly distributed inside the space with pore sizes of 15-50 nm.

Positive effects of zeolite powder on aerobic granulation: Nitrogen and phosphorus removal and insights into the interaction mechanisms

Aerobic granular sludge is considered one of the most promising biological wastewater treatment technologies of the 21st century. However, the long granulation time and poor treatment effect on N and P have severely limited its popularity and large-scale application. In this study, we systematically examine the strengthening effects of zeolite powder on granulation, N and P removal, and their interaction mechanisms. The addition of zeolite powder decreased sludge granulation time to 18 d, and improved average N and P removal rates by 4.48% and 2.22%, respectively. The multi-pore and nutrient-rich environment of the zeolite powder is beneficial for maintaining microbial activity and granular stability. Moreover, its adsorption to N and P enriches their respective removal strains, improving their removal efficiency.

Na@La-modified zeolite particles for simultaneous removal of ammonia nitrogen and phosphate from rejected water: performance and mechanism

Rejected water from sludge processing in wastewater treatment plants (WWTPs) is very harmful due to its high concentration of ammonia nitrogen and phosphorus. It is therefore necessary to find a low-cost and convenient technique to simultaneously remove ammonia nitrogen and phosphorus from rejected water. In this study, natural granular zeolite was modified by NaCl and La(OH)₃ to obtain a new material (Na@La-MZP), with several advantages compared with powdered zeolite. Na@La-MZP could remove 92.61% ammonia nitrogen (50 mg/L) and 99.01% phosphate (60 mg/L) at the optimal conditions of dosage 12.5 g/L, initial pH 6.0 and reaction time 12 hours, which enabled the effluent to satisfy the discharge standard (GB 18918-2002) for municipal WWTPs in China. The maximum adsorption capacity of Na@La-MZP was determined as 17.92 mg NH₄⁺-N/g and 9.53 mg P/g by the Langmuir isotherm. Pseudo-second-order kinetics could well illustrate the adsorption process and show that the ammonia nitrogen and phosphate can be degraded by chemical reaction. The characterizations of Na@La-MZP confirmed the removal mechanism of ammonia nitrogen and phosphate. The Na@La-MZP still maintained more than 75% removal efficiency after five reuses. Furthermore, the estimated cost of this treatment method was 0.22 $/m³ rejected water.

Preparation of a New Iron-Carbon-Loaded Constructed Wetland Substrate and Enhanced Phosphorus Removal Performance

Iron-carbon substrates have attracted extensive attention in water treatment due to their excellent processing ability. The traditional iron-carbon substrate suffers from poor removal effects, separation of the cathode and anode, hardening, secondary pollution, etc. In this study, a new type of iron-carbon-loaded substrate (NICLS) was developed to solve the problems of traditional micro-electrolytic substrates. Through experimental research, a preparation method for the NICLS with Fe and C as the core, zeolite as the skeleton, and water-based polyurethane as the binder was proposed. The performance of the NICLS in phosphorus-containing wastewater was analyzed. The results are as follows: The optimal synthesis conditions of the NICLS are 1 g hydroxycellulose, wood activated carbon as the cathode, an activated carbon particle size of 200-60 mesh, and an Fe/C ratio of 1:1. Acidic conditions can promote the degradation of phosphorus by the NICLS. Through the characterization of the NICLS (scanning electron microscope (SEM), X-ray diffractometer (XRD), and energy-dispersive spectrometer (EDS), etc.), it is concluded that the mechanism of the NICLS phosphorus removal is a chemical reaction produced by micro-electrolysis. Using the NICLS to treat phosphorus-containing wastewater has the advantages of high efficiency and durability. Therefore, it can be considered that the NICLS is a promising material to remove phosphorus.

Novel talc encapsulated lanthanum alginate hydrogel for efficient phosphate adsorption and fixation

In the present work, talc (a low-cost clay) encapsulated salts alginate (TAL) beads were synthesized by cross-linking with lanthanum ion and tested for phosphate adsorption. Multiple methods were applied for the characterization of composites. The combined effect of talc and lanthanum improved phosphate removal performance of TAL beads. Factors such as talc content, La³⁺ concentration, adsorbent dosage, pH, co-existing ions (Cl^-, NO₃^- and SO₄^2-) were studied in batch experiments. The optimized TAL-7 beads exhibited satisfactory selectivity towards phosphate in the coexistence of competing anions and could remain efficient phosphate removal in the pH range of 4-6. The phosphate removal efficiency reached to 95% with a maximum uptake of 16.4 mg P/g obtained at the optimal pH 4. Further experiments suggested that Langmuir isotherm model and the pseudo-second-order kinetic model could well describe the phosphate adsorption process of TAL-7 beads. Moreover, TAL-7 beads exhibited superior phosphate fixation performance in the long-term experiment. The results from adsorption experiment and characterization analysis demonstrated that TAL-7 beads could be a cost-effective and promising biosorbent for phosphate adsorption and fixation in the aqueous environment.

Review: recent developments of substrates for nitrogen and phosphorus removal in CWs treating municipal wastewater

Substrates are the main factor influencing the performance of constructed wetlands (CWs), and especially play an important role in enhancing the removal of nitrogen and phosphorus from CWs. In the recent 10 years, based on the investigation of emerged substrates used in CWs, this paper summarizes the removal efficiency and mechanism of nitrogen and phosphorus by a single substrate in detail. The simultaneous removal efficiency of nitrogen and phosphorus by different combined substrates is emphatically analyzed. Among them, the reuse of industrial and agricultural wastes as water treatment substrates is recommended due to the efficient pollutant removal efficiency and the principle of waste minimization, also more studies on the environmental impact and risk assessment of the application, and the subsequent disposal of saturated substrates are needed. This work serves as a basis for future screening and development of substrates utilized in CWs, which is helpful to enhance the synchronous removal of nitrogen and phosphorus, as well as improve the sustainability of substrates and CWs. Moreover, further studies on the interaction between different types of substrates in the wetland system are desperately needed.

Advanced treatment of effluent from municipal wastewater treatment plant by strengthened ecological floating bed

The performance of eological floating bed (EFB) with novel carbon source (CS) and reed biochar substrate (RBS) derived from reed straw (RS) was evaluated for the advanced treatment of effluent from wastewater treatment plants (WWTPs). The average carbon releasing capacity of CS was 4.50 mg/g, and the P adsorption capacity of RBS was 0.39 mg/g. The additional CS and RBS increased the average removal efficiencies of total nitrogen (TN) and total phosphorus (TP) by 57.6% and 46.7%, respectively. Furthermore, the high-throughput sequencing results revealed significantly different microbial species richness and diversity due to the CS and RBS. Some genera related to nitrogen removal, such as Pseudomonas, Rhodobacter, Hydrogenophaga, Bradyrhizobium, Acinetobacter and Thiobacillus, were enriched in the EFB with CS and RBS. This study provided a suitable method for effectively treating low C/N wastewater such as WWTPs effluent using EFB strengthened by processed wetland plant.

Untangling the nitrate removal pathways for a constructed wetland- sponge iron coupled system and the impacts of sponge iron on a wetland ecosystem

Sponge iron (s-Fe⁰) is a potential alternative electron donor for nitrate reduction. To gain insight into the mechanism of denitrification in a constructed wetland- sponge iron coupled system (CW-Fe⁰ system), the removal performance and reduction characteristics of nitrate in constructed wetlands (CWs) with and without s-Fe⁰ application were compared. Results indicated that s-Fe⁰ intensified the removal of nitrate with a 6h-HRT. The nitrate removal efficiency was improved by 16-76 % with various influent NO₃^--N concentrations (10-30 mg L^-1) and at a chemical oxygen demand(COD)/N ratio of 5. The rates of chemical denitrification were positively correlated with the dosage of s-Fe⁰ and negatively correlated with the influent COD concentration. 16S rDNA sequencing revealed that hydrogen-utilizing autotrophic denitrifier of Hydrogenophaga was highly enriched (accounting for 10 % of the total OTUs) only in CW-Fe⁰ system. The micro-environment created by s-Fe⁰ was suitable for heterotrophic denitrifiers of Thauera, Tessaracoccus and Simplicispira. The determination of physiological indicators for plants showed that the application of s-Fe⁰ causes abiotic stress to wetland plants (Canna indica L.). Nevertheless, s-Fe⁰ can be used as a substrate for CWs, since it allows a high-efficiency removal of nitrate by mediating chemical denitrification and hydrogen-driven autotrophic denitrification.

Investigation of adsorption mechanism of phosphate(V) ions on the nanostructured Na-A zeolite surface modified with ionic polyacrylamide with regard to their removal from aqueous solution

The sorption properties of Na-A-type synthetic zeolite, obtained from fly ash with regard to the phosphate(V) ions, were determined. The Na-A zeolite was prepared using hydrothermal conversion of fly ash with aqueous sodium hydroxide. The effects of solution pH and zeolite surface modification by ionic polyacrylamide (PAM) were examined. Both anionic and cationic forms of PAM were applied. The adsorption and electrokinetic data were obtained by means of spectrophotometric measurements, potentiometric titrations and zeta potential determination. It was shown that the presence of ionic polyacrylamide adsorption layers modifies the surface properties of the solid. The resulting composite material (zeolite/polymer) can be applied for effective removal of phosphate(V) ions from the liquid medium. Its regeneration possibilities are also considerable. Additionally, the use of fly ash for zeolite preparation leads to management of hazardous waste material.

The bioaccessibility and fractionation of arsenic in anoxic soils as a function of stabilization using low-cost Fe/Al-based materials: A long-term experiment

Arsenic (As)-contaminated soils occur widely worldwide. In the present study, three low-cost Fe/Al-based materials, including red soil (RS), sponge iron filter (SIF) and Al-based water treatment sludge (WTS), were applied as amendments to remediate As-contaminated soils under anoxic conditions. After 180 d of incubation, the proportion of the sum of nonspecifically absorbed As (F1) and specifically absorbed As (F2) to the total As was reduced by 6%, 52% and 13% with 5% of RS, SIF and WTS addition, respectively, compared to the control soil (31%). The results showed that among the three amendments, SIF was the most effective at decreasing As bioaccessibility in soils. Compared with RS and WTS, SIF intensified the decrease of labile fractions and the increase of unlabile fractions, and the redistribution of the amorphous oxide-bound fraction (F3) and crystalline hydrous oxide-bound fraction (F4) occurred in the SIF-amended soil. Moreover, the As stabilization processes were divided into two stages in the control and RS-amended soil, while the processes were divided into three stages in both SIF- and WTS-treated soil. The As stabilization processes in all treated soils were characterized by the transformation of labile fractions into more immobilizable fractions, except for F4 transforming into F3 in the first stage in SIF-amended soil. Correspondingly, inner-surface complexation and occlusion within Fe/Al hydroxides were the common driving mechanisms for the transformation of As fractions. Therefore, taking into consideration the results of this study, SIF could be a more promising alternative than the other two materials to passivate As in anoxic soils.

Nitrogen doped char from anaerobically digested fiber for phosphate removal in aqueous solutions

This study explores the use of an engineered char produced from the pyrolysis of anaerobically digested fiber (ADF) to adsorb phosphate from aqueous solutions. Two series of engineered chars were produced. The first series was a CO₂ activated (CA) char produced via slow pyrolysis between 350 and 750 °C. The second series was a nitrogen doped (ND) char activated in the presence of ammonia at comparable temperatures. Proximate analysis, elemental composition, gas physisorption, Inductively coupled plasma mass spectrometry (ICP-MS), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier Transform Infrared Spectroscopy (FTIR) and X-ray powder diffraction (XRD) techniques were used to characterize properties of resulting products. The surface area of the carbon product increased after nitrogen doping through ammonization (166.6-463.1 m²/g) compared to CO₂ activated chars (156.5-413.1 m²/g). Phosphate adsorption isotherms for both CO₂ activated and nitrogen doped chars can be described by the Langmuir- Freundlich and Redlich Peterson adsorption models. Nitrogen doped carbon phosphate sorption capacity in aqueous solutions was twice compared to CO₂ activated carbons. As carbonization/activation temperature increased the sorption capacity increased from 3.4 to 33.3 mg g^-1 for CA char and 6.3-63.1 mg g^-1 for nitrogen doped char.

Comprehensive evaluation of substrate materials for contaminants removal in constructed wetlands

Considerable number of studies have been carried out to develop and apply various substrate materials for constructed wetlands (CWs), however, there is a lack of method and model for comprehensive evaluation of different types of CWs substrates. To this end, this article summarized nearly all the substrate materials of CWs available in the literatures, including natural materials, agricultural/industrial wastes and artificial materials. The sources and physicochemical properties of various substrate materials, as well as their removal capacities for main water contaminants including nutrients, heavy metals, surfactants, pesticides/herbicides, emerging contaminants and fecal indicator bacteria (FIB) were comprehensively described. Further, a scoring model for the substrate evaluation was constructed based on likely cost, availability, permeability, reuse and contaminant removal capacities, which can be used to select the most suitable substrate material for different considerations. The provided information and constructed model contribute to better understanding of CWs substrate for readers, and help solve practical problems on substrates selection and CWs construction.

Synthesis and adsorption performance of La@ZIF-8 composite metal–organic frameworks

In this study, ZIF-8 with a rhombic dodecahedron structure was prepared by a hydrothermal method. Then La(OH)₃, was successfully loaded onto the ZIF-8 by an immersion deposition method, to form a lanthanide-based metal–organic framework (La@ZIF-8) composites. The structure and properties of La@ZIF-8 were verified by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and zeta potential measurements. The optimum process conditions are discussed within the materials and methods. The effects of initial phosphorus concentration, dosage, pH and contact reaction time on the phosphorus removal performance of the nanomaterial were investigated. The results indicated that La@ZIF-8 exhibited an excellent adsorption capacity (147.63 mg g⁻¹) and its phosphorus removal efficiency could reach as high as 99.7%. Experimental data were interpreted using different adsorption kinetic and isotherm models. The kinetic behavior conformed to the pseudo-second-order kinetic model, which indicated the chemisorption of phosphorus by La@ZIF-8. The adsorption behavior of phosphorus by La@ZIF-8 fitted well to the Langmuir isotherm model, suggesting a monolayer chemical adsorption process. The majority of the adsorbed phosphate could be desorbed by NaOH (2 mol L⁻¹), and the removal efficiency of the recycled La@ZIF-8 reached 90%, even after the fifth cycle. The obtained results demonstrate the great application potential of the prepared La@ZIF-8 as a fascinating adsorbent for the removal of phosphate.

In this study, La(OH)₃ was successfully loaded on ZIF-8 by immersion deposition method, to form lanthanide-based metal–organic frameworks (La@ZIF-8) composites.

Preparation and evaluation of bis(diallyl alkyl tertiary ammonium salt) polymer as a promising adsorbent for phosphorus removal

Problems associated with water eutrophication due to high phosphorus concentrations and related environmentally safe solutions have attracted wide attention. A novel bis(diallyl alkyl tertiary ammonium salt) polymer, particularly poly(N¹,N¹,N⁶,N⁶-tetraallylhexane-1,6-diammonium dichloride) (PTAHDADC), was synthesized and characterized by Fourier transform infrared spectroscopy, nuclear magnetic resonance, scanning electron microscopy, mercury intrusion method, and thermogravimetric analysis. The adsorption characteristics in phosphorus were evaluated in dilute solution, and the recycling properties of PTAHDADC were investigated. Results showed that PTAHDADC possessed macropores with a size distribution ranging from 30 to 130 μm concentrating at 63 μm in diameter and had 46.52% of porosity, excellent thermal stability below 530K, and insolubility. PTAHDADC could effectively remove phosphorus at pH = 7-11 and had a removal efficiency exceeding 98.4% at pH = 10-11. The adsorption equilibrium data of PTAHDADC for phosphorus accorded well with the Langmuir and pseudo-second-order kinetic models. Maximum adsorption capacity was 52.82 mg/g at 293 K. PTAHDADC adsorbed phosphorus rapidly and reached equilibrium within 90 min. Calculated activation energy E_a was 15.18 kJ/mol. PTAHDADC presented an excellent recyclability with only 8.23% loss of removal efficiency after five adsorption-desorption cycles. The morphology and structure of PTAHDADC slightly changed as evidenced by the pre- and post-adsorption of phosphorus, but the process was accompanied by the partial deprotonation of the (-CH₂)₃NH⁺ group of PTAHDADC. The adsorption was a spontaneous exothermic process driven by entropy through physisorption, electrostatic attraction, and ion exchange. Survey results showed that PTAHDADC was a highly efficient and fast-adsorbing phosphorus-removal material prospective in treating wastewater.

Mechanistic Study of Phosphorus Adsorption onto Iron Z-A: Spectroscopic and Experimental Approach

Iron was incorporated into an LTA type zeolite using the sol-gel hydrothermal method to form Iron-zeolite-A (Iron-Z-A), and its phosphate adsorption-desorption efficiency were analyzed. Samples were characterized by EDS, SEM, XRD, EPR, FT-IR XPS, and Raman to ensure the apt synthesis of Iron-Z-A and to interpret the mechanism of adsorption-desorption of PO43− in an aqueous solution. EPR and XPS analysis confirmed that the iron was doped as Fe3+ in the LTA structure. The XPS peak shift (Fe-2p), FT-IR band shift, and intensity change (–OH) confirmed the existence of the ligand exchange mechanism. In the adsorption phase at pH 5, the derivative of phosphate (H2PO4−) acts as a ligand and interacts with OH of Fe on the zeolite surface to form “Iron-zeolite (oxy) hydroxide bound phosphate”. In the desorption phase at pH 10, phosphate ligand is detached and get mixed in the aqueous phase as HPO42−. The EDS data, Si–O–Al band shift and intensity change in FT-IR and XPS peak intensity change proved the contribution of Al in the process of adsorption. The data of adsorption fitted well with the Langmuir’s isotherm and pseudo-second-order kinetic model. The amount of PO43− adsorbed was a function of adsorbent’s surface area regardless of concentration. The amount of PO43− being adsorbed by the metal ions was found to be 382.296 mg PO43−/g Fe and 56.296 mg PO43−/g Al.

Adsorption of different forms of phosphorus on modified corn bracts

Excessive phosphorus discharged into the environment could result in the eutrophication, leading to water pollution. Hence, the efficient method for phosphorus removal is urgently in need. In this paper, an agricultural by-product, corn bract, modified by Zr was proposed to remove different forms of phosphorus. A comparison study about the adsorption performance of organic phosphorus (OP) and inorganic phosphorus (IP) was investigated. The results indicated that both the OP and IP reached the maximum adsorption amounts when the initial pH was 2. Compared with IP adsorption, the adsorbent showed higher adsorption rate but lower adsorption capacity for OP. The complexation and the electrostatic attraction were possibly the main adsorption mechanisms. PRACTITIONER POINTS: The agricultural waste, corn bract, was proposed to remove phosphorus. The adsorption performances of OP and IP were compared. The adsorbent showed higher adsorption rate but lower adsorption capacity for OP.

Critical Review: Biogeochemical Networking of Iron in Constructed Wetlands for Wastewater Treatment

Iron is present in all types of wastewater; however, besides acid mine drainage, where it is a major constituent of concern, it is usually neglected in other types of wastewaters. In all kinds of constructed wetlands, iron plays important role in removal of organics and phosphorus, and it has an impact on transformation of nitrogen, sulfur, and metals. The biogeochemistry of iron is well understood in natural wetlands, but knowledge about iron impact on microbiological and chemical transformations during wastewater treatment in constructed wetlands is very limited. So far, the sparse research in this area provides limited information on observed interactions with several varying parameters across the studies, making it difficult to draw fundamental and mechanistic conclusions. A critical review of the complex biogeochemical networking of iron in CWs is therefore necessary to fill the gap in knowledge on the role of iron and its biogeochemical multi-interactions in wastewater treatment processes of CWs. This review is the first with specific focus on iron, discussing its mitigation and retention in CWs with different configurations and operational strategies, and presenting both seasonal dynamics and the potential remobilization of Fe. It also comprehensively discusses the interactions of redox-controlled iron turnover with the biogeochemical processes of other elements, for example, carbon (C), nitrogen (N), phosphorus (P), sulfur (S), and heavy metals. The health response of wetland plants to both deficiency and toxicity of Fe in CWs designed with specific treatment targets has also been evaluated. Due to the complexity of various wastewater compositions and microredox gradients in the root rhizosphere in CWs, future research needs have also been identified.

Kinetics and Thermodynamics of Efficient Phosphorus Removal by a Composite Fiber

In the current study, we investigated the kinetics and thermodynamics of phosphorus removal by zeolite/steel slag/fly ash/basalt (ZSFB) composite fiber. Kinetic analysis indicated that the adsorption of phosphorus is best fitted with the pseudo-second-order model. The maximum adsorption capacity of the fiber calculated by the Langmuir model was found to be 4.18 mg/g and the partition coefficient was 1.49 mg/g/µM. Thermodynamics results revealed that the Gibbs free energy ΔG0 of the composite fiber was negative, indicating that the adsorption is a spontaneous process; the standard enthalpy of reaction ΔH0 was positive, indicating that the adsorption is endothermic. Adsorption under different influencing factors and desorption experiments were conducted to investigate the phosphorus removal characteristics of ZSFB composite fiber. Dynamic adsorption and the phosphorus removal experiment were also conducted in a fixed-bed reactor to study factors affecting the time of breakthrough. Results indicate that the performance of ZSFB composite fiber was not relatively outstanding compared with nanomaterials and magnetic composites. However, its performance has already met the class A demands of “discharge standard of pollutants for municipal wastewater treatment plant” (GB18918-2002) which means it can be applied to remove phosphorus from real wastewater in a cost-effective way with low-priced raw materials.

The Impact of Temperature on the Removal of Inorganic Contaminants Typical of Urban Stormwater

Appropriate management of urban stormwater requires consideration of both water quantity, resulting from flood control requirements, and water quality, being a consequence of contaminant distribution via runoff water. This article focuses on the impact of temperature on the efficiency of stormwater treatment processes in permeable infiltration systems. Studies of the removal capacity of activated carbon, diatomite, halloysite, limestone sand and zeolite for select heavy metals (Cu and Zn) and biogenes (NH4-N and PO4-P) were performed in batch conditions at 3, 6, 10, 15, 22, 30 and 40 °C at low initial concentrations, and maximum sorption capacities determined at 3, 10, 22 and 40 °C. A decrease in temperature to 3 °C reduced the maximum sorption capacities (Qmax) of the applied materials in the range of 10% for diatomite uptake of PO4-P, to 46% for halloysite uptake of Cu. Only the value of Qmax for halloysite, limestone sand and diatomite for NH4-N uptake decreased slightly with temperature increase. A positive correlation was also observed for the equilibrium sorption (Qe) of Cu and Zn for analyses performed at low concentrations (with the exception of Zn sorption on limestone sand). In turn, for biogenes a rising trend was observed only in the range of 3 °C to 22 °C, whereas further temperature increase caused a decrease of Qe. Temperature had the largest influence on the removal of copper and the smallest on the removal of phosphates. It was also observed that the impact of temperature on the process of phosphate removal on all materials and ammonium ions on all materials, with the exception of zeolite, was negligible.

Permeable Reactive Barriers for Preventing Water Bodies from a Phosphorus-Polluted Agricultural Runoff-Column Experiment

This paper aims to examine the potential of permeable reactive barriers (PRBs) as an in-situ removal approach for phosphate polluted agricultural runoff. Four different reactive materials (RMs) of: autoclaved aerated concrete (AAC), Polonite®, zeolite and limestone were tested. The study was conducted as a column experiment with a sandy loam soil type charging underlying RM layers with phosphorus (P) and a soil column without RM as a reference. The experiment was carried out over 90 days. During this time the P-PO4 load from the reference column equaled 6.393 mg and corresponds to 3.87 kg/ha. Tested RMs are characterized by high P-PO4 retention equaling 99, 98, 88 and 65% for Polonite®, AAC, zeolite and limestone, respectively. At common annual P loss rates of 1 kg/ha from intensively used agricultural soils, the PRB volume ranged from 48 to 67 m3 would reduce the load between 65 and 99% for the RMs tested in this study.

Developing an anaerobic digester with external Zeolite filled column for enhancing methane production from swine manure - A feasibility study

Development of digesters with an external zeolite column facilitates the convenient removal of the zeolite with TAN, without disturbing the continuous anaerobic digestion process. A digester with an inside zeolite bed (In-Zeo) and digester without adding zeolite (No-Zeo) were employed to compare the process performance with digester with external zeolite column (EX-Zeo). The cumulative, CH₄ yields were 5% and 15% greater in the EX-Zeo, and the In-Zeo digesters respectively compared to the No-Zeo digesters. Also, the % VS reduction was 49%, 55% and 41%, respectively in the Ex-Zeo, In-Zeo and No-Zeo digesters. The results indicated that treatment with 7% zeolite during anaerobic digestion has the potential to improve biodegradation of swine manure. The addition of zeolite appeared to reduce TAN from the digestate, thereby enhancing the CH₄ yield. Zeolite could be used either internally or externally to enhance CH₄ production through anaerobic digestion of swine manure.