Search

AbstractThe development of novel adsorbents for water treatment has become a significant branch of materials science and environmental engineering, with annual research output growing exponentially. New adsorbents, however, are typically not developed beyond the laboratory scale, creating a discrepancy between research volume and commercial adoption. This study analyzes the development of adsorbents using a productization framework. Three types of companies (adsorbent manufacturers/dealers, consultants/process designers, and treatment plant operators) were interviewed to understand the challenges for up-scaling and ultimately commercializing new adsorbents, and the requirements for treatment processes and the expectations of customers (adsorbent users), adsorbent producers, and service providers were determined. A framework for developing optimal business models, strategies, and approaches for productizing adsorbents was also created. The main challenges for commercializing adsorbents include their properties (such as quality, availability, lifespan, and adaptability), profitability issues (regeneration, disposal, and logistics cost), and activities related to environmental legislation, testing, and verification.

Porous alkali-activated materials are synthetic aluminosilicates that should be often produced as granules for practical applications. In the present study, municipal solid waste incineration fly ash with ~1.2 wt% of metallic aluminium was used as a novel blowing agent for metakaolin (their ratio ranged from 0% to 100%) with an aqueous sodium silicate solution as the alkali-activator and granulation fluid in high-shear granulation. The compressive strength of all granules was sufficient (≥2 MPa). Water absorption indicated an increase in porosity as the fly ash content increased. However, X-ray microtomography imaging showed no clear correlation between the fly ash content and porosity. The granules exceeded the leaching limits for earth construction materials for antimony, vanadium, chloride and sulphate. Of those, antimony, chloride and sulphate could be controlled by decreasing the ash content, but the source of vanadium was identified as metakaolin. The increase in the fly ash content decreased the cation exchange capacity of the granules. In conclusion, the recommended fly ash content is equivalent to 0.3 wt% of Al0 and the developed granules could be best suited as light-weight artificial aggregates in concrete where the additional binder would provide stabilization to decrease the leaching.

In this study, porous hydroxyapatite-metakaolin geopolymer (HAP-MK-GP) granules were prepared with a novel method for adsorption of organic pollutants from aqueous solutions, using brilliant green dye as a model compound. The preparation involved combining finely powdered hydroxyapatite, metakaolin, and solid sodium metasilicate in a high-shear granulator. Then, hydrogen peroxide (H2O2) was added at different concentrations (0.0, 5.0, 7.5, or 10.0%) as a combined granulation fluid and blowing agent. In the resulting granules, metakaolin geopolymer bound the powdered hydroxyapatite as granules and contributed to the adsorption capacity. To determine their structural, morphological, and mechanical properties, the granules were characterized with infrared spectroscopy, X-ray fluorescence, scanning electron microscopy, specific surface area and porosity analysis, and compressive strength tests. The granules had a high porosity and promising compressive strength and Young's modulus of 0.8 and 10 MPa, respectively, potentially enabling their use in large-scale adsorption columns. The monolayer adsorption mechanism of brilliant green dye onto HAP-MK-GP granules was confirmed by fitting the obtained batch adsorption data to the Langmuir isotherm model which showed that the adsorption capacity was approximately 41 mg/g. The optimum conditions were: pH of 7, initial dye concentration of 100 mg/L, adsorbent dose of 3 g/L, agitation speed of 250 rpm, contact time of 30 min, and temperature of 298 K. The adsorption kinetic data indicated that the adsorption followed the pseudo-second-order kinetic model. The thermodynamic parameters, including Gibbs free energy, enthalpy, entropy, and activation energy, indicated that adsorption was spontaneous, endothermic, and was based on physisorption. The rate-limiting step was film diffusion. Based on the results, HAP-MK-GP granules could be a feasible adsorbent for the removal of dyes from industrial wastewater. Moreover, the facile granulation method presented here could be applied to other powdered adsorbents as well to prepare adsorbent granules.

Wastewater aeration is an important unit operation that provides dissolved oxygen for microorganisms in wastewater treatment. In this study, the impact of peracetic acid (PAA) dosing on wastewater aeration was assessed in terms of oxygen transfer, visual observation of bubble size changes, and evolution of dissolved oxygen from PAA (and H2O2) decomposition. Oxygen transfer coefficients improved with PAA concentrations of up to 7 mg/L, which was probably due to the smaller bubbles being formed from the aeration diffuser and evolution of small bubbles from PAA (and H2O2) decomposition. At a PAA concentration higher than 7 mg/L, the accumulation of acetate molecules to the gas–liquid interface of bubbles likely began to counteract the positive impact of bubble size decrease by increasing the mass transfer resistance of oxygen from bubbles to water. Finally, a continuous bench-scale primary effluent aeration experiment demonstrated that at a continuous PAA dosing of 1 mg/L, the air input by a compressor could be decreased by 54%, while keeping the oxygen level constant at approximately 1.5 mg/L. PAA dosing could be combined, for example, with aerated grit removal to enhance the primary effluent aeration together with additional benefits of partial disinfection and odor formation prevention. HIGHLIGHTS Peracetic acid (PAA) dosing was studied in combination with diffused fine bubble aeration of raw wastewater.; Moderate doses (≤7 mg/L) improved oxygen transfer from air bubbles to water.; PAA dosing increased the number of bubbles from the diffuser.; Decomposition of PAA provides directly dissolved oxygen.;

Background Stone wool is commonly used as a plant substrate in soilless cultivation and discarded after one growing season. Stone wool waste is difficult to recycle, and thus it is typically landfilled. Alkali-activation of stone wool (i.e., milling and mixing with an alkaline solution) has been shown to be a feasible way to upcycle this waste fraction into, for example, construction products. In this study, the aim was to develop recycled plant substrate from stone wool waste from greenhouses via alkali activation. Methods Waste stone wool from greenhouses was characterized by X-ray fluorescence (XRF) and mixed with sodium silicate solution either directly or after ball milling. The alkali-activation process was combined with the addition of H2O2, pre-made foam, or granulation to obtain suitable porous material for the plant substrate application. Preliminary greenhouse cultivation experiments of pea (Pisum sativum) were conducted with alkali-activated stone wool mixed with peat (a weight ratio of 1:1) and fertility analysis of the mixture were conducted. Results The results indicated that the most feasible production method was to use ball-milled stone wool and to combine alkali activation with granulation. The obtained granules could reach 2.7 MPa as compressive strength while the other methods resulted in very fragile material. The preliminary greenhouse cultivation experiments revealed that there were significant levels of nutrients (Ca, P, K, and S) and alkalinity leached from the granules which hindered the growth of pea. The high P and S amounts were also confirmed by the XRF results of stone wool. Conclusions It can be concluded that the developed granules did not function well as a plant substrate for pea but could enable the re-utilization of the nutrients contained in the greenhouse stone wool waste. Moreover, their application to acidic sulfate soils could be feasible as it would utilize the alkalinity of granules.

High-value applications, such as adsorbents, have drawn attention to geopolymers. In several of those applications, having the geopolymer as porous spherical particles is beneficial. This study presents a novel process for fabricating porous metakaolin-based geopolymer granules using a combination of direct foaming, one-part alkali activation, and granulation. In short, the precursor (e.g., metakaolin) and solid activator (e.g., sodium silicate) are loaded in a granulator, in which an aqueous blowing agent (e.g., H2O2) is added while the granulator is running, and the obtained granules are cured at 60 °C. Characterization of the granules for physico-chemical and morphological properties indicated an increase in overall porosity, especially in the µm-scale pores. Also specific surface area (+50%) and nanoscale pore volume (+102%) increased when using more concentrated H2O2 (20 or 30%) compared to nonporous granules. The use of porous granules was also demonstrated in dynamic adsorption experiments for ammonium (NH4+) uptake, which showed up to ∼126% increase in cumulative adsorption amount compared to nonporous granules. The highest NH4+ uptake was obtained with 10% H2O2 solution as the granulation fluid. The results confirmed the feasibility of the method for introducing porosity to geopolymer granules, which enhances the adsorption properties of the granules.

Alkali-activated materials (AAMs) are actively studied as adsorbents in wastewater treatment. They are frequently classified as low-, medium-, or high-calcium content since the gel nanostructure of AAMs changes upon the introduction of network-modifying cations (e.g., Ca2+). Furthermore, AAMs undergo changes in the phase composition and pore structure upon aging. In the present study, these two aspects were assessed for the first time in the context of adsorption: three typical mix designs involving metakaolin, blast furnace slag, or their mixture were prepared and studied for ammonium (NH4+) uptake at 7-, 28-, or 90-day age. The adsorption capacity of the “zeolite-like” metakaolin-based geopolymer increased from 34 to 87 mg/g when material was cured up to 90 days at room temperature. However, the adsorption capacity increase appears to be also depending on the metakaolin structure as approx. 1-month and 8-year old samples prepared with another metakaolin grade indicated almost similar adsorption capacity. Adsorption was clearly hindered when blast furnace slag was introduced in the mix designs, which turns the gel into “tobermorite-like” chain structures. Thus, this study demonstrated that using the Ca-content of precursors and material age are significant parameters for the interpretation of the adsorption results and practical development of AAM-based adsorbents.

Abstract 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.

This study investigated the effect of organic resin contained in glass wool on synthesis of alkali-activated binders. The study was performed on glass wool containing sugar or phenolic resin, comparing it with glass wool that did not contain resin, as a reference. The results showed that the organic resin could be qualitatively identified using Fourier-transform infrared spectroscopy (FTIR) and thermo gravimetry-mass spectrometer (TG-MS), with gradual decomposition occurring between 200 °C and 550 °C. The presence of organic resin reduced the milling efficiency of glass wool, modified the rheology by increasing the liquid demand, and slowed the strength development at room temperature. However, interestingly, the effect of the resin on the strength of the paste was less obvious at an age of 28 days. Curing for 24 h at 40 °C was beneficial for one-day strength development, in comparison to 20 °C and 60 °C, independent of the presence of the resin. All the cured paste samples, with and without resin, achieved a compressive strength of more than 40 MPa at 28 days, satisfying the requirement for many structural applications. Nevertheless, water immersion affected the materials’ strength, suggesting their suitability for dry environments or the need for suitable co-binders to increase their durability and water resistance.

In this study, tannin-furanic-based foams enforced with H3BO3 and ZnCl2 are investigated, as well as their properties such as mechanical strength, specific surface area, and pore size distribution. From an industrial point of view, the aforementioned properties of these foams play a key role when used as catalyst, adsorbent, or gas storing materials. Therefore, this study aims to prove that such enforced tannin-furanic foams are promising materials for these types of applications. According to the results, materials that are up to five times stronger can be achieved by carbonizing the foams in comparison to maturing them. With physical activation, it was possible to obtain a specific surface area as high as 845 m2/g with a pore volume of up to 0.35 cm3/g. Chemical activation, using ZnCl2 as the activating agent, produced a specific surface area and pore volume of 737 m2/g and 0.31 cm3/g. However, the pore sizes were mostly microporous, independently of activation procedure used.

Porous ceramics were generated by direct foaming the alkali-activated unprocessed kaolin (impure kaolin, iK) with the addition of hydrogen peroxide (H2O2) and calcining at a low temperature of 400 ​°C. Hydrogen peroxide, a blowing agent, decomposes producing oxygen gas bubbles forming the porous structure in the fresh alkali-activated iK paste. In the present study, three different molarity of alkali activator (5, 10, or 15 ​M NaOH) were employed. The dosage of blowing agent (H2O2) was varied between 0 and 2% with a constant dosage of 0.5% (wt. of binder) of surfactant. The gas bubbles in fresh-state geopolymer slurry are unstable with a tendency to coalesce. In such cases, surfactants are introduced to improve the stability of the gas-liquid interface. Two different surfactants: non-ionic and cationic ones were used to study the properties of alkali-activated porous material. Fresh properties such as viscosity, yield stress, foaming rate, and fresh density were compared between reference iK samples without surfactants and those with surfactants. The mechanical and microstructural properties of alkali-activated (AA) low-temperature porous iK ceramics were determined after calcination. Pore structures were characterized with electron microscope to understand the interaction of different parameters during fresh/hardened state and their relevance with the changes in the mechanical properties. Surfactants, irrespective of the type, highly influenced the fresh properties of the AA-iK samples, which in turn reflected on the compressive strength of the porous ceramics.

Geopolymers have been recently explored as sorbents for wastewater treatment, thanks to their mechanical and chemical stability and to their low-energy manufacturing process. One specific application could be the removal of ammonium (NH4+) through exchange with Na+ ions. Additive manufacturing (AM) represents an especially interesting option for fabrication, as it allows to tailor the size, distribution, shape, and interconnectivity of pores, and therefore the access to charge-bearing sites. The present study provides a proof of concept for NH4+ removal from wastewater using porous geopolymer components fabricated via direct ink writing (DIW) AM approach. A metakaolin-based ink was employed for the fabrication of a log-pile structure with 45° rotation between layers, producing continuous yet tortuous macropores which are responsible for the high permeability of the sorbents. The ink consolidates in an amorphous, mesoporous network, with the mesopores acting as preferential sites for ion exchange. The printed sorbents were characterized for their physicochemical and mechanical properties and the NH4+ removal capacity in continuous-flow column experiments by using a model effluent. The lattices present high permeability and high cation exchange capacity and maintained a high amount of active ions after four cycles, allowing to reuse them multiple times.

Concrete production is globally a major water consumer, and in general, drinking-quality water is mixed in the binder. In the present study, simulated sea water and reverse osmosis reject water were used as batching water for one-part (dry-mix) alkali-activated blast furnace slag mortar. Alkali-activated materials are low-CO2 alternative binders gaining world-wide acceptance in construction. However, their production requires approximately similar amount of water as regular Portland cement concrete. The results of the present study revealed that the use of saline water did not hinder strength development, increased setting time, and did not affect workability. The salts incorporated in the binder decreased the total porosity of mortar, but they did not form separate phases detectable with X-ray diffraction or scanning electron microscopy. Leaching tests for monolithic materials revealed only minimal leaching. Furthermore, results for crushed mortars (by a standard two-stage leaching test) were within the limits of non-hazardous waste. Thus, the results indicated that high-salinity waters can be used safely in one-part alkali-activated slag to prepare high-strength mortars. Moreover, alkali-activation technology could be used as a novel stabilization/solidification method for reverse osmosis reject waters, which frequently pose disposal problems.

Worldwide, tons of lignin is produced annually in pulping plants and it is mainly considered as a waste material. Usually lignin is burned to produce energy for the pulping reactors. The production of value-added materials from renewable materials like lignin, has proved to be challenging. In this study, the effects of addition of three different types of lignin in the production of tannin/furanic foams is investigated. The foams were matured, first at 373 K and finally carbonized at 1073 K and the properties of them including mechanical strength, specific surface area and pore development are investigated before and after thermal treatment. According to the results, higher mechanical strength is obtained if samples are carbonized at 1073K compared to matured ones at 373K. Up to 10 times stronger materials are achieved this way, which makes them promising as insulating or constructive materials. With physical activation, it is possible to obtain specific surface areas and pore volumes close to 1200 m2/g and 0,55 cm3/g respectively. Mainly micropores are developed during the steam activation which makes these foams more suitable and selective to be used as catalyst support materials in the catalytic conversion of small molecules or in adsorption or gas storage application.

Mineral wools—a general term for stone wool and glass wool—are the most common insulation materials in the world. Consequently, 2.5 million tons of mineral wool waste is generated globally which is mainly landfilled. Recently, it was found that mineral wool waste can be used as cementitious material by alkali activation. In alkali activation, dissolution is the primary process as it involves the breakage of bonds and release of ionic species from the surface of the material upon interaction with the reacting solution. Dissolution plays a significant role in the strength development and micro/nano-structural morphology of the final cementitious material. Here, we study the dissolution of stone wool (depicting chemistry of Al-Ca-Mg-Fe silicate glass) and glass wool (depicting chemistry of soda lime silicate glass) in sodium hydroxide solution to provide a better understanding of their reactivity under alkali activation.Experimental studies were carried out at two different liquid to solid ratio (L/S) conditions: high L/S (1000) and low L/S (50) in an N2 glove box. High L/S conditions give information on the early stages of the dissolution whereas low L/S provides later stages of the process.The ICP results show that under both L/S conditions glass wool releases increasing amount of Si, Al and B reaching 39−45 wt.%, 23−26 wt.% and 34−44 wt.% extent of dissolution with time respectively. However, in stone wool the release rate of Si and Al increases initially but becomes constant after certain time period. In both mineral wools, release rate of Ca and Mg varied with time. These changes in the release rate was observed to be due to precipitation of dissolved species. XRD results revealed that three crystalline phases-hydrotalcite, calcite, and calcium silicate were present on both glass and stone wool fibers after 25 days of dissolution. SEM results revealed that the morphology varies at different dissolution times and experimental conditions for both the mineral wools depicting the change in the reaction path. From these studies, we conclude that the dissolution rate and mechanism are controlled by both chemical composition of the fiber and the reacting solution conditions.

This article was produced based on a workshop on Coagulation and flocculation in water treatment, held at National Days of Chemical Education 13 to 14 April 2012. The workshop dealt with the central unit operation of surface water treatment, coagulation/flocculation. There are interesting chemical phenomena related to coagulation and flocculation, and it is possible to demonstrate them with relatively simple equipment. Demonstration, suitable for classroom environment, is presented in the section discussing surface water treatment. Water treatment is for the most part based on chemical phenomena and acknowledging the significance of them will become increasingly important as the supply of clean water decreases globally. This article provides a general view on the sufficiency of water supply in Finland and internationally, and examines the central chemical phenomena in the treatment processes of surface, ground and wastewater.