Removal of ammonium from municipal wastewater with powdered and granulated metakaolin geopolymer

Ammonium removal and recovery from municipal wastewater by ion exchange using a metakaolin K-based geopolymer

Among the available technologies for ammonium removal from wastewater, ion exchange represents one of the most promising ones in the perspective to recover ammonium and produce a fertilizing product. However, the vast majority of previous studies on ammonium ion exchange did not evaluate the process robustness under real operational conditions nor optimized the desorption step. In this paper, tests of ammonium removal and recovery were conducted on a metakaolin K-based geopolymer, compared with a high-performing Italian natural zeolite in K-form. Real municipal and saline wastewater was treated in a continuous flow pilot plant equipped with a 60-cm adsorption bed (bed volume 203 mL, sorbent mass 145-173 g, empty bed contact time 10 min). Geopolymer granules showed higher performances in terms of selectivity towards ammonium, operating capacity (8.5 mg_N g^-1 dry adsorbent at an inlet concentration of 40 mg_N L^-1), bed volumes of wastewater treated at the selected breakpoint (149). Geopolymer resulted to be a cost-effective adsorbent for wastewater treatment capable to adsorb cations by ion exchange, allowing a fractionated desorption procedure that led to recover ammonium in a solution composed mainly by NH₄NO₃ (37%_wt) and KNO₃ (56%_wt), potentially usable as fertilizer. The geopolymer robustness was assessed after repeated adsorption/regeneration cycles showing that the geopolymer mechanical and morphological properties did not deteriorate. The results make the tested geopolymer a very promising material for the optimization and scale-up of the ammonium recovery process in a circular economy perspective.

Research and Application Progress of Geopolymers in Adsorption: A Review

Geopolymer is a porous inorganic material with a three-dimensional mesh structure, good mechanical properties, a simple preparation process (no sintering) and a low economic cost, and it is environmentally friendly. Geopolymer concrete has been widely used in the construction field, and many other studies have revealed that geopolymer will become one of the most promising inorganic materials with unique structure and properties. This paper provides a review of the development and current status of geopolymers and briefly explains the effects of material proportioning, experimental factors and activators on geopolymer performance. Because of the advantages of high specific surface area and high porosity, geopolymers could be used as adsorbent materials. This paper summarizes the research progresses of the adsorption of metal cations, anions, dyes, and gases by geopolymers, which emphasizes the geopolymer membranes in adsorption, and discusses the challenges and opportunities for the development of more efficient, sustainable and practical adsorption protocols.

A State-of-the-Art Review on Innovative Geopolymer Composites Designed for Water and Wastewater Treatment

There is nothing more fundamental than clean potable water for living beings next to air. On the other hand, wastewater management is cropping up as a challenging task day-by-day due to lots of new additions of novel pollutants as well as the development of infrastructures and regulations that could not maintain its pace with the burgeoning escalation of populace and urbanizations. Therefore, momentous approaches must be sought-after to reclaim fresh water from wastewaters in order to address this great societal challenge. One of the routes is to clean wastewater through treatment processes using diverse adsorbents. However, most of them are unsustainable and quite costly e.g. activated carbon adsorbents, etc. Quite recently, innovative, sustainable, durable, affordable, user and eco-benevolent Geopolymer composites have been brought into play to serve the purpose as a pretty novel subject matter since they can be manufactured by a simple process of Geopolymerization at low temperature, lower energy with mitigated carbon footprints and marvellously, exhibit outstanding properties of physical and chemical stability, ion-exchange, dielectric characteristics, etc., with a porous structure and of course lucrative too because of the incorporation of wastes with them, which is in harmony with the goal to transit from linear to circular economy, i.e., "one's waste is the treasure for another". For these reasons, nowadays, this ground-breaking inorganic class of amorphous alumina-silicate materials are drawing the attention of the world researchers for designing them as adsorbents for water and wastewater treatment where the chemical nature and structure of the materials have a great impact on their adsorption competence. The aim of the current most recent state-of-the-art and scientometric review is to comprehend and assess thoroughly the advancements in geo-synthesis, properties and applications of geopolymer composites designed for the elimination of hazardous contaminants viz., heavy metal ions, dyes, etc. The adsorption mechanisms and effects of various environmental conditions on adsorption efficiency are also taken into account for review of the importance of Geopolymers as most recent adsorbents to get rid of the death-defying and toxic pollutants from wastewater with a view to obtaining reclaimed potable and sparkling water for reuse offering to trim down the massive crisis of scarcity of water promoting sustainable water and wastewater treatment for greener environments. The appraisal is made on the performance estimation of Geopolymers for water and wastewater treatment along with the three-dimensional printed components are characterized for mechanical, physical and chemical attributes, permeability and Ammonium (NH4+) ion removal competence of Geopolymer composites as alternative adsorbents for sequestration of an assortment of contaminants during wastewater treatment.

Hydrothermal Synthesis of Sodalite-Type N-A-S-H from Fly Ash to Remove Ammonium and Phosphorus from Water

In this study, the hydrated sodium aluminosilicate material was synthesized by one-step hydrothermal alkaline desilication using fly ash (FA) as raw material. The synthesized materials were characterized by XRD, XRF, FT-IR and SEM. The characterization results showed that the alkali-soluble desilication successfully had synthesized the sodium aluminosilicate crystalline (N-A-S-H) phase of sodalite-type (SOD), and the modified material had good ionic affinity and adsorption capacity. In order to figure out the suitability of SOD as an adsorbent for the removal of ammonium and phosphorus from wastewater, the effects of material dosing, contact time, ambient pH and initial solute concentration on the simultaneous removal of ammonium and phosphorus are investigated by intermittent adsorption tests. Under the optimal adsorption conditions, the removal rate of ammonium was 73.3%, the removal rate of phosphate was 85.8% and the unit adsorption capacity reached 9.15 mg/L and 2.14 mg/L, respectively. Adsorption kinetic studies showed that the adsorption of ammonium and phosphorus by SOD was consistent with a quasi-secondary kinetic model. The adsorption isotherm analysis showed that the equilibrium data were in good agreement with the Langmuir and Freundlich model. According to thermodynamic calculations, the adsorption of ammonium and phosphorus was found to be a heat-absorbing and spontaneous process. Therefore, the preparation of SOD by modified FA has good adsorption properties as adsorbent and has excellent potential for application in the removal of contaminants from wastewater.

Compositional effects of clay-fly ash geopolymers on the sorption process of lead and zinc

Because long-term leachate penetration through a hydraulic barrier is unavoidable, active-passive liners are widely used to mitigate the migration of potential contaminants. Geopolymerization represents a viable method for metals removal, which simultaneously improves the properties of local clay to compensate for the lack of suitable soil in the design of active-passive liners. This study investigated how clay-fly ash geopolymers enhance the sorption of divalent lead [Pb(II)] and divalent zinc [Zn(II)] from leachate compared with an untreated clay. Two clay-fly ash geopolymers were synthesized from the mixtures containing 50 and 60% fly ash to the total solid mass and then activated by 10 M NaOH solutions. The influence of Na/fly ash ratios and activator content was also examined. The results indicate that a fly ash-based geopolymer could be a simple solution to increase the sorption capacity of local clay. A lower ratio of Na/fly ash and activator content, resulting in a higher porosity, led to a better performance for metal removal. According to the results of sorption isotherms and batch experiments, Pb(II) and Zn(II) exhibit different sorption behaviors affected by the compositions of synthesized clay-fly ash geopolymers, which could be adjusted to reach a proper sorption capacity. The results of the kinetic study also show that the heterogeneous matrix of the clay-fly ash geopolymers with different porosities led to mutual cooperation between reaction and diffusion-controlled steps for metal removal.

Synthesis and characterization of coal fly ash and palm oil fuel ash modified artisanal and small-scale gold mine (ASGM) tailings based geopolymer using sugar mill lime sludge as Ca-based activator

The continuous accumulation of artisanal and small-scale gold mining (ASGM) tailings in the Philippines without adequate storage and disposal facility could lead to human health and environmental disasters in the long run. In this study, ASGM tailings was simultaneously stabilized and repurposed as construction material via geopolymerization using coal fly ash, palm oil fuel ash and a powder-based alkali activator. Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) identified iron sulfides in the tailings containing arsenic (As), cadmium (Cd), copper (Cu), lead (Pb) and zinc (Zn), which could be released via weathering. The average unconfined compressive strengths (UCS) of tailings-based geopolymers at 14 days curing were 7.58 MPa and 7.7 MPa with fly ash and palm oil fuel ash, respectively. The tailings-based geopolymers with palm oil fuel ash had higher UCS most likely due to CASH reaction product formation that improved strength formation. The toxicity characteristic leaching procedure (TCLP) results showed very low leachabilities of As, Pb and Fe in the geopolymer materials suggesting ASGM tailings was effectively encapsulated within the geopolymer matrix. Overall, the geopolymerization of ASGM tailings is a viable and promising solution to simultaneously stabilize mining and industrial wastes and repurpose them into construction materials.

Alkali-Activated Adsorbents from Slags: Column Adsorption and Regeneration Study for Nickel(II) Removal

Alkali-activated adsorbents were synthesized by mixing three different slags from the steel industry: blast furnace slag (BFS), ladle slag (LS), and Lintz–Donawitz converter slag (LD). These powdered slag-based geopolymers (GP) were used to remove nickel(II) from aqueous solutions in fixed-bed column studies. The experiments were conducted in pH 6 using a phosphate buffer with initial nickel(II) concentration of 50 mg/L. Samples were taken at time intervals of between 5 and 90 min. Three adsorption–desorption cycles were implemented with a flow rate of 5 mL/min. The geopolymers were characterized by Fourier-Transform Infrared Spectroscopy (FTIR), X-ray powder diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), X-ray fluorescence (XRF), specific surface area measurements, and a leaching test. The data were found to describe the Thomas, Adams–Bohart, and Yoon–Nelson models well. For GP (BFS, LS), experimental adsorption capacity was 2.92 mg/g, and for GP (LD, BFS, LS), it was 1.34 mg/g. The results indicated that the produced adsorbents have the potential to be used as adsorbents for the removal of nickel(II).

Surface Modification of Cured Inorganic Foams with Cationic Cellulose Nanocrystals and Their Use as Reactive Filter Media for Anionic Dye Removal

In this work, a surface cationized inorganic-organic hybrid foam was produced from porous geopolymer (GP) and cellulose nanocrystals (CNCs). GPs were synthesized from alkali-activated metakaolin using H₂O₂ as a blowing agent and hexadecyltrimethylammonium bromide (CTAB) as a surfactant. These highly porous GPs were combined at pH 7.5 with cationic CNCs that had been synthesized from dissolving pulp through periodate oxidation followed by cationization in a deep eutectic solvent. The GP-CNC hybrid foams were employed as reactive filters in the removal of the anionic dye, methyl orange (MO; 5-10 mg/L, pH 7). The effects of a mild acid wash and thermal treatments on the structure, properties, and adsorption capacity of the GPs with CNCs and MO were investigated. The CNCs aligned as films and filaments on the surfaces of the neutralized GPs and the addition of CNCs improved MO removal by up to 84% compared with the reference sample. In addition, CTAB was found to disrupt the attachment of CNCs on the pores and improve adsorption of MO in the GPs with and without CNCs.

Ag- or Cu-modified geopolymer filters for water treatment manufactured by 3D printing, direct foaming, or granulation

In this work, we compared the main characteristics of highly porous geopolymer components for water treatment applications manufactured by 3D printing, direct foaming, or granulation. Furthermore, different approaches to impregnate the materials with Ag or Cu were evaluated to obtain filters with disinfecting or catalytic properties. The results revealed that all of the investigated manufacturing methods enabled the fabrication of components that possessed mesoporosity, suitable mechanical strength, and water permeability, even though their morphologies were completely different. Total porosity and compressive strength values were 28 vol% and 16 MPa for 3D-printed, 70–79 vol% and 1 MPa for direct-foamed, and 27 vol% and 10 MPa for granule samples. Both the filter preparation and the metal impregnation method affected the amount, oxidation state, and stability of Ag and Cu in the filters. However, it was possible to prepare filters with low metal leaching between a pH of 3–7, so that the released Ag and Cu concentrations were within drinking water standards.

The Use of Ca- and Mg-Rich Fly Ash as a Chemical Precipitant in the Simultaneous Removal of Nitrogen and Phosphorus—Recycling and Reuse

The European Union’s circular economy strategy aims to increase the recycling and re-use of products and waste materials. According to the strategy, the use of industry waste material should be more effective. A chemical precipitation method to simultaneously remove phosphorus and nitrogen from synthetic (NH4)2HPO4 solution and the liquid phase of anaerobic digestate using fly ash as a precipitant was tested. Fly ash is a waste material formed in the power plant process. It mainly contains calcium oxide (CaO) and magnesium oxide (MgO). Saturated precipitant solution was prepared from fly ash, which was added in small proportions to (NH4)2HPO4 solution during the experiment. Fly ash’s effectiveness as a precipitant was compared with that of commercial CaO and MgO salts, and it can be observed that fly ash removed as much ammonium and phosphate as commercial salts. Fly ash sufficiently removed ammonium nitrogen and phosphate from the liquid phase of anaerobic digestate, which led to the formation of ammonium magnesium hydrogen phosphate hydrate, struvite (NH4MgPO4·6H2O), and calcium hydroxide phosphate, monetite, CaPO3(OH). In this study, we have shown for the first time that fly ash can be used to manufacture recycled, slow-release fertilizers from anaerobic digestate.

Treatment of Sewage Using a Constructed Soil Rapid Infiltration System Combined with Pre-Denitrification

The activated sludge process of the anaerobic/oxic (A/O) process has a good denitrification performance because it can make full use of the carbon source in the original sewage, and the denitrification can provide alkalinity for aerobic nitrification. The traditional constructed soil rapid infiltration (CSRI) system, on the other hand, has a poor nitrogen removal effect. Dividing the traditional CSRI system into two sections, one performs denitrification as an anoxic section, while the other performs nitrification as an aerobic section and is placed after the anoxic section. The nitrification liquid of the effluent from the aerobic section is mixed with the original wastewater and enters the anoxic section for denitrification. We expected that this would be improved by combining CSRI with a pre-denitrification step that would make full use of the carbon source in the original sewage. In a small-scale experimental model, the removal efficiencies of nitrogen, in the form of ammonium, nitrate, and total nitrogen (TN), as well as chemical oxygen demand (COD), were determined. The hydraulic load was varied, while the backflow reflux capacity was kept constant, to determine the effect on the pre-denitrification process. An average removal rate of 95.4% for NH₄⁺-N and 96% for COD could be obtained when a hydraulic load of 80 cm³(cm²·d)⁻¹ and a reflux ratio of 75% were applied. Under these conditions, the average removal rate of TN was 77.4%, which is much higher than what can be typically achieved with conventional CSRI systems.

Removing Organic Matter and Nutrients from Pig Farm Wastewater with a Constructed Wetland System

Pollutants from pig farms in Mexico have caused problems in many surface water reservoirs. Growing concern has driven the search for low-cost wastewater treatment solutions. The objective of this research was to evaluate the potential of an in-series constructed wetland to remove nutrients from wastewater from a pig farm. The wetland system had a horizontal flow that consisted of three cells, the first a surface water wetland, the second a sedimentation cell, and the third a subsurface flow wetland. The vegetation used was Thypa sp. and Scirpus sp. A mix of soil with red volcanic rock (10–30 mm diameter) and yellow sand (2–8 mm diameter) was used as a substrate for the vegetation. The experiments were carried out in duplicate. Water samples were collected at the inflow and outflow of the cells. Two hydraulic retention times (HRT) (5 and 10 days) and three treatments were evaluated: 400, 800, and 1200 mg·L⁻¹ of chemical oxygen demand (COD) concentration. Data was collected in situ for temperature, pH, dissolved oxygen (DO), electrical conductivity (EC), and total dissolved solids (TDS). COD, total Kjeldahl nitrogen (TKN), ammonia nitrogen (NH₃–N), and total phosphorous (TP) were analyzed in the laboratory. The results showed that the in-series constructed wetland is a feasible system for nutrient pollutant removal, with COD removal efficiency of 76% and 80% mg·L⁻¹ for a 5- and 10-day HRT, respectively. The removal efficiency for TKN, NH₃–N, and TP reached about 70% with a 5-day HRT, while a removal of 85% was obtained with a 10-day HRT. The wetland reached the maximum removal efficiency with a 10-day HRT and an inflow load of 400 mg·L⁻¹ of organic matter. The results indicate that HRT positively affects removal efficiency of COD and TDS. On the other hand, the HRT was not the determining factor for TP removal. Treatment one, with an initial COD concentration of 400 mg·L⁻¹, had the highest removal of the assessed pollutants, allowing for the use of water for irrigation according to Mexican regulatory standards (NOM-001). The water quality resulting from treatments two and three (T2 = 800 mg·L⁻¹ of COD and T3 = 1200 mg·L⁻¹ of COD) did not comply with minimal requirements for irrigation water.