Incinerated Sewage Sludge Ash Research Articles

Recycling of incinerated sewage sludge ash and waste glass powder in alkali-activated slag for sewer rehabilitation

A new era has dawned in the manufacturing of cement-free binders with appropriate mechanical strengths and durability to combat CO2 emissions. However, the assessment of their performance in extreme conditions is ongoing. Here, we attempted to use incinerated sewage sludge ash (ISSA), a waste product of sewage sludge incineration that contains limited amounts of heavy metals, along with waste glass powder (GP) and ground granulated blast furnace slag (GGBS), as precursors to produce cement-free binders through alkali-activation. The alkali-activated materials (AAMs) were then subjected to an intensified sewage corrosion test for 6 months. The aim was to utilize the heavy metals in the ISSA as biocides to resist the biogenic acid attack on the AAMs. The experimental results indicated that superior performance was achieved by using a ternary binder prepared with ISSA, GP, and GGBS under biogenic acid simulation. Such enhanced durability can be attributed to the low Ca content in the resulting alkali-activated gels, which also reduced the grain size of gypsum formed and prevented expansion deterioration. Furthermore, the slow release of heavy metals from the AAMs prepared with the ISSA, evidenced by the leaching test results, was able to inhibit microbial growth.

Recovery of phosphate from incineration ash of sewage sludge by chlorination and carbo-chlorination

In this study, the volatilization behavior of the constituent elements of sewage sludge incineration ash (SSA) with and without carbon during the chlorination was investigated for recovering P. For chlorination of SSA, Fe and K volatilized from 700 to 800 °C, no volatilization of P was observed. For chlorination of SSA with carbon, Fe, P, and Si volatilized from low temperatures, reaching volatility rates of 80, 55, and 35 %, respectively, at 1000 °C. When chlorinated SSA/C (sample with carbon added to chlorination residue prepared at 1000 °C for 30 min holding), P volatilized from 800 °C (10 %), reaching a volatilization rate of 75 % at 1000 °C. P volatilization increased from 10 to 55 % until 60 min holding at 800 °C without volatilization of Si, Mg, and K. Although P volatilization progressed at 900–1000 °C holding, Al, Mg, and Si also volatilized. These results indicate that combination of chlorination/carbo-chlorination is suitable for selective volatilization of P.

Effect of surface-modified incinerated sewage sludge ash as a reinforcing filler on the mechanical and thermal properties of polylactic acid composites

Biodegradable thermoplastic polylactic acid (PLA) has recently been limited in its broader development and application due to its high cost. Therefore, it is crucial to develop low-cost and high-performance PLA-based composites by adding fillers. In this study, surface-modified incinerated sewage sludge ash (M-OH-ISSA) was employed as a reinforcing filler in PLA to prepare PLA/M-OH-ISSA thermoplastic composites with varying M-OH-ISSA ratios (10–30 wt%), and the mold mechanism for the PLA/M-OH-ISSA composites was explored. The surface of incinerated sewage sludge ash (ISSA) was modified to improve interfacial adhesion by NaOH alkali treatment and KH570 silane grafting, which successfully grafted silane groups onto the surface of the ISSA and converted the surface from hydrophilic to hydrophobic, strengthening the compatibility between the ISSA and PLA. The effects of the M-OH-ISSA content on the mechanical and thermal properties of the PLA composites were investigated. The mechanical test results showed that the tensile and flexural properties of the 15 wt% M-OH-ISSA-filled PLA composites were excellent compared to those of pure PLA, with strengths of 33.67 MPa and 73.70 MPa, respectively, which are all 1.6 times greater than those of pure PLA. Morphological analysis via SEM indicated that the composites with 15 wt% M-OH-ISSA exhibited good adhesion between the M-OH-ISSA and the matrix. The thermal performance of the composites was determined by using differential scanning calorimetry (DSC) and thermogravimetric analysis (TG/DTG). The results showed that the crystallinity of the composites increased with increasing M-OH-ISSA content and that the thermal stability between 290°C and 400°C decreased slightly with increasing M-OH-ISSA. However, the composites have good thermal stability near 200°C and do not undergo thermal degradation if processed at this temperature. As a filler in composites, M-OH-ISSA can reduce PLA usage and improve polymer properties, applying PLA/M-OH-ISSA composites in packaging and 3D printing applications.

Preparation and characterization of biomass-ash composites derived from incinerated sewage sludge fly ash after hydrothermal treatment

With the increasing prominence of global environmental issues and the growing demand for sustainable development, biomass composites have attracted widespread attention as candidates for environmentally friendly and renewable construction materials. In this study, environmentally friendly biomass-ash composites (BACs) were fabricated using hydrothermally activated incinerated sewage sludge ash (HT-ISSA) as filler and straw powder with waste sawdust as the biomass matrix for hot pressing. An investigation was conducted into the effect of HT-ISSA on the physical properties of the composite, including the bending strength, compressive strength, and thermal conductivity. The composite prepared with 15 wt% HT-ISSA demonstrated an exceptionally high bending strength (30.60 MPa), compressive strength (44.76 MPa), and low thermal conductivity (0.2380 W/m·K). The enhanced physical properties of the BAC material are attributable to the change caused by hydrothermal treatment of the filler phase. Due to the introduction of hydrated calcium silicate, the cohesion performance of the filler significantly improved, thus leading to strong adhesion and penetration within the matrix. The obtained BAC is applicable for packaging and insulation materials, thus providing an effective solution for the economical and environmentally friendly recycling of incinerated sewage sludge ash and other bulk solid waste. Additionally, it contributes novel insights into alleviating the current shortage of forest resources.

Selective recovery of high purity aluminium phosphate from incinerated sewage sludge ash with Zr-modified biochar

Phosphorus recovery from incinerated sewage sludge ash (ISSA) is critical for the sustainable development of phosphorus resources due to its non-renewable nature. An innovative strategy based on a Zr-modified rice-husk biochar (Zr-RB) adsorbent has been proposed for the selective recovery of high-purity AlPO4 products from ISSA. 0.1 mol/L H2SO4 was chosen to extract phosphorus from ISSA with a phosphorus extraction of 54.5 ± 1.6 mg/g. Phosphorus was selectively adsorbed by the Zr-RB adsorbent with a maximum adsorption capacity of 53.1 ± 0.6 mg/g according to the Langmuir isotherm model. The adsorption kinetics of phosphorus in the leachate followed the pseudo-second order model, suggesting phosphorus adsorption by chemisorption processes. After 5 phosphorus adsorption-desorption cycles, the Zr-RB adsorbent still showed good adsorption performance for phosphorus, indicating its high stability. Electrostatic attraction and ligand exchange on the Zr-RB adsorbent were mainly responsible for the adsorption of phosphorus from the leachate. The simulation and experimental results demonstrated the production of high-purity AlPO4 products at the pH = 3.0 without the addition of exogenous substances, indicating the application potential of recovering high-value AlPO4 products from ISSA based on the Zr-RB adsorbent.

Upcycling municipal solid wastes to self-foaming glass-ceramics by chemical additive-free and rapid low-temperature sintering

Incinerated sewage sludge ash (ISSA) and waste glass (WG) produced in large quantities from municipal solid wastes are either not recycled or are used in relatively low-value applications. Here, we reported a scalable strategy to rapidly convert them, along with waste paper (WP), into novel foamed glass-ceramics (FGCs) by low-temperature sintering, considerably reducing environmental impact and manufacturing cost. The Fe2O3 in ISSA and cellulose in WP were used as precursors to trigger the self-foaming process at low temperatures by carbon-enhanced ferric reduction when WG formed the softened matrix without chemical additives. This study analyzed the foaming mechanism, physical properties of FGCs, and variable importance assisted by thermodynamics and machine learning. The resulting FGCs with 20 wt% ISSA content and 10 wt% WP addition exhibited the excellent properties of a geometric density of 0.76 ± 0.02 g/cm3, volume water absorption of 14.35 ± 2.48%, and compressive strengths of 7.15 ± 0.88 MPa by a short holding (5 min) at a low firing temperature of 850 °C. The successful synthesis and mechanistic study provide new insights into the development of waste-derived high-performance FGCs.

Micro and macro properties of silico-aluminophosphate geopolymer: Role of incinerated sewage sludge ash (ISSA)

The mechanistic insights into silico-aluminophosphate (SAP) geopolymer formation remain an enigma. Here, we aim to elucidate this process and improve the early-age performance of SAP geopolymers by utilizing incinerated sewage sludge ash (ISSA). Interestingly, phosphoric acid-ISSA interaction released Ca2+ and Al3+ ions from ISSA faster than the dealumination of metakaolin. These ions agglutinated with the active soluble (PO4)3- units, evidenced by transmission electron microscopy (TEM), enhancing the early-age compressive strength of ISSA-incorporated SAP geopolymer binders. In contrast, the later strengths were relatively similar to the reference. Such binders had primary silico-alumino-phosphate (S-A-P) gels, possibly intimate with calcium-phosphate (C-P) and alumino-phosphate (A-P) gels, improving the micromechanical properties of the binder. The elastic moduli of these gels lay between 23–25 GPa, higher than conventional N-A-S-H gels. Furthermore, ISSA switched the chemistry of reaction products by favoring AlIV-OP units over AlVI-OP units in SAP geopolymers, even though the Si environment remained unchanged, as confirmed by NMR.

Bioavailability transition path of phosphorus species during the sewage sludge incineration process

Sewage sludge incineration ash (SSIA) is rich in phosphorus (P), thus being considered as a reliable source of phosphorus recovery. Different P species behaved significant bioavailability. Based on this, a comprehensive investigation into the bioavailability transition path of P species during sewage sludge (SS) incineration was conducted. P predominantly existed in the form of inorganic phosphorus (IP) in SS with a higher concentration of non-apatite inorganic phosphorus (NAIP) and less concentration of apatite inorganic phosphorus (AP). During the SS incineration process, OP existed in the flocs and cell structures of SS underwent destruction, the released P then combined with metal elements such as Ca, Mg, Fe, and Al to form AP species (Ca/Mg–P) and NAIP species (Fe/Al/Mn–P), and the NAIP decomposition to release into gas phase. This was the initial step for enhancing the bioavailability of P species. As temperature increased and the incineration process progressed, the low-temperature-resistant NAIP dissociated, and the metal-binding sites of Al, Fe and Mn in NAIP species were gradually replaced by the Ca and Mg thus forming thermal stability AP species (Ca/Mg–P, such as CaHPO4, Ca2PO4Cl, and Mg3(PO4)2 et al.). This step was crucial for the bioavailability improvement of P species during the incineration process. Therefore, the IP proportions in TP were extremely high (＞98%), and this value gradually increased as incineration temperature raised. The higher incineration temperature, the lower NAIP concentration and higher AP concentration. Besides, additives such as coal/rice husk/eggshell played a significant affect. Additives wither higher Ca content were inclined to react with P to form Ca/Mg–P (AP), while the presence of SO2 would react with Ca metals to form CaSO4 thus inhibiting the formation of AP species (such as CaHPO4 and CaPO4Cl). This results could provide theoretical support for the efficient and directional migration of P during sewage sludge incineration.

Physicochemical properties of clayey deposits slurry treated by lime-activated ISSA and GGBS considering seawater salinity effect

This study sheds light on the engineering and environmental performance of lime-activated incinerated sewage sludge ash (ISSA) and ground granulated blast furnace slag (GGBS) treated Hong Kong marine deposits (HKMD) slurry by stabilisation/solidification (S/S) technology, which is proposed using as fill materials in reclamation projects. The S/S performance of the treated HKMD with distilled water and seawater under different salinities was investigated. The results show that seawater could help S/S treated HKMD gain strength by using activated industrial wastes (ISSA and GGBS). The hydration and pozzolanic reactions between ISSA, GGBS, CaO and clayey compositions in HKMD make contributions to the strength development, porosity decrease and heavy metals stabilisation, which is supported by the characterization analysis including thermo-gravimetric (TG) analysis, mercury intrusion porosimetry (MIP) tests, nitrogen adsorption/desorption isotherms (NAI), scanning electron microscopy coupled with energy-dispersive spectrometry (SEM-EDS) and the leaching test of toxicity characteristic leaching procedure (TCLP). Seawater of 1.8% salinity (18 g/kg) is better than the distilled water and seawater of 3.6% salinity as a substrate solution in the S/S treated HKMD, because of the highest unconfined compressive strength and lowest porosity in the treated samples. The highest pH may account for its highest strength under the 1.8% salinity conditions. The S/S process could effectively stabilize the contaminants regardless of the curing time and the salinity of the mixing solution, and the leachates from the stabilized HKMD are environmentally safe and meet the requirement of standard in Hong Kong on the recycling treated soil. Therefore, recycling wastes—ISSA and GGBS with lime can be used as an appealing binder to stabilize/solidify marine deposits as environmental-friendly reusable materials in reclamation projects.

Recycling of waste glass and incinerated sewage sludge ash in glass-ceramics

Disposal of waste glass and incinerated sewage sludge ash (ISSA) in landfills is a waste of resources and poses significant environmental risks. This work aims to recycle waste glass and ISSA together to form value-added glass-ceramics. The physical and mechanical properties, leaching behaviour, and microstructure of the glass-ceramics produced with different proportions of waste glass powder (WGP) and ISSA were investigated. Thermodynamic calculations were performed to predict the formation of crystalline phases and the phase transformation involved. The results showed the potential of WGP and ISSA as raw materials in glass-ceramics production. WGP effectively densified the microstructure of the glass-ceramics by forming a viscous phase. As WGP content increased, the total porosity of glass-ceramics decreased whereas the density increased, accompanied by the formed anorthite transforming into wollastonite. The incorporation of WGP densified and refined the pore structure of the glass-ceramics, thereby improving the mechanical properties and reducing the water absorption. The glass-ceramics produced with a 50:50 blend of WGP and ISSA exhibited the highest compressive strength of 43.7 MPa and the lowest water absorption of 0.3 %. All fabricated glass-ceramics exhibited innocuous heavy metal leaching. The co-sintering of ISSA and WGP can produce additive-free glass-ceramics, characterized by reduced energy consumption and notable heavy metal immobilization capacity. These materials hold promise for utilization in construction as building materials.

Selective recovery of phosphorus from the leachate of incinerated sewage sludge ash using the Zr-modified acid-leaching residue as adsorbent for two-fold resource utilization

Phosphorus, as an essential nutrient for plant growth, is crucial for the development of agriculture. In this study, a novel strategy using a zirconium-modified acid-leaching residue adsorbent (Zr-AR adsorbent) was proposed for the efficient and selective recovery of phosphorus from incinerated sewage sludge ash (ISSA). 0.2 mol/L HCl were optimized for the phosphorus extraction from ISSA. The acid-leaching residue with large pore structure and high specific surface area was first reused as a support to prepare Zr-AR adsorbent for a twofold resource utilization of ISSA. Without removing impurities from the leachate, the Zr-AR adsorbent could selectively adsorb phosphorus with a maximum phosphorus adsorption capacity of 53.1 ± 0.8 mg/g in the HCl system. During 5 phosphorus adsorption–desorption processes, the adsorption and desorption ratios of phosphorus remained stable at over 90 %, indicating the high stability of the Zr-AR adsorbent for selective phosphorus recovery. Without adjusting the pH, hydroxyapatite was produced from the phosphorus-rich solution with a phosphorus content of 33.4 ± 1.3 % P2O5, which could significantly promote the growth of ryegrass as a phosphorus fertilizer. The cost of the phosphorus recovery from ISSA was also preliminarily evaluated ($3.76 kg-P product), demonstrating the application potential of this strategy.

Efficient anaerobic digestate valorization: Nutrient recovery strategy for enhancing soil fertility in arid agricultural regions

Efficient nutrient cycling in agroecosystems is essential for sustainable agriculture, and the utilization of waste products from various industries can contribute to this process. In this study, we investigated the potential of using anaerobic digestate from food industry waste (sugar beets and food waste) as a nutrient source for fertilizer production. Digestates were sanitized using a mixture of inorganic acids (H2SO4 and H3PO4) or alkaline (KOH), with acidic hydrolysate yielding a higher concentration of amino acids (1981 mg/L) compared to alkaline (186 mg/L). The acidic hydrolysate was centrifuged, and the liquid fraction was used to create a foliar fertilizer. The solid fraction, acidic hydrolysate, sewage sludge incineration ash, and additives (ammonium nitrate, urea with urease inhibitor) were employed to formulate three granular fertilizers. Nitrogen balances were analyzed using Sankey charts for each fertilizer formulation. The highest nitrogen losses (45.90 kg N/1 kg formulation) were recorded in the production of fertilizer containing ammonium nitrate. The fertilizers' effectiveness was evaluated through preliminary wheat germination tests. The highest yields observed for the foliar fertilizer (1% dose) and granular with the addition of urea with a urease inhibitor (20% dose) groups, where fresh sprout mass was approximately 18% and 23% higher than the control, respectively. These findings demonstrate the potential of using anaerobic digestate from food industry waste for nutrient recycling in agroecosystems, contributing to sustainable agriculture.

Effect of seawater on solidification/stabilisation treatment of marine soft soil slurry by lime-activated ISSA and GGBS

It is proposed to use dredged marine sediments as fill material in marine reclamation engineering by stabilisation/solidification (S/S) technology with sustainable binding materials, which can help the soft soil gain strength to solve the engineering geological problem of its insufficient bearing capacity. In this work, lime and two types of industrial wastes, i.e., incinerated sewage sludge ash (ISSA) and ground granulated blast-furnace slag (GGBS), were selected as the binding materials. Hong Kong marine deposits (HKMD) slurry with a high initial water content of 110% was mixed with 30% binders (30% lime and 70% (ISSA+GGBS) with ISSA: GGBS = 3). The seawater (SW) with salinity of 3.6% was employed as mixing solution in S/S treatment of HKMD. To detect the effect of each main composition in SW on the performance of S/S HKMD, the pure solutions of NaCl, MgCl2 and Na2SO4 were adopted in this study.The results show that the use of SW in the lime-activated ISSA and GGBS treated dredged HKMD slurry is effective in improving its strength. The X-ray diffraction, thermo-gravimetric analysis and scanning electron microscopy observations present the formation of calcium/magnesium silicate hydrate (C/M-S-H), Friedel's salt and ettringite, which fill into the pores and interlock the particles in the mixture increasing the strength of the treated HKMD. The chemical compositions of SW have significant and different impacts on the performance of treated HKMD samples. Na+ can help the samples gain higher strength and result in the cracking development in the S/S samples. Mg2+ will lead to the formation of M-S-H, which reduces the porosity of treated HKMD samples. However, the contribution of M-S-H to the soil strength is less than that of C-S-H. Cl− in the mixture would slow down the reaction speed and show slight impacts on the modulus. SO42− accelerates the reactions in the treated samples and has a more significant effect on nano-size porosity of bulk sample. Consequently, the seawater has positive effect on the S/S performance of HKMD slurry, suggesting potential application in the practical projects.

Efficient and selective recovery of iron phosphate from the leachate of incinerated sewage sludge ash by thermally induced precipitation

Phosphorus recovery from incinerated sewage sludge ash (ISSA) is important but hindered by low selectivity. Here, a novel strategy of acid leaching followed by thermally induced precipitation was proposed for the efficient and selective recovery of FePO4 from ISSA samples. A high phosphorus leaching efficiency of ∼ 99.6% was achieved with 0.2 mol/L H2SO4 and liquid to solid (L/S) ratio of 50 mL/g. Without removing various co-existing ions (Al3+, Ca2+, SO42–, etc.), high-purity FePO4 of ∼ 92.9% could be facilely produced from this highly acidic H2SO4 leachate (pH = 1.2) by simple addition of Fe(III) at a molar ratio of 1:1 to the phosphorus and reacted at 80 °C for thermally induced precipitation. The remained acid leachate could be further reused for five times to continue leaching phosphorus from the ISSA samples and produce the FePO4 precipitates with a high phosphorus recovery efficiency of 81.1 ± 1.8%. The selective recovery of FePO4 from the acid leachate was demonstrated more thermodynamically favorable compared to other precipitates at this acidic pH of 1.2, and elevated temperature of 80 °C towards thermally induced precipitation. The estimated cost of this strategy was ∼$26.9/kg-P and lower than that of other existing technologies. The recovered FePO4 precipitates could be used as a phosphate fertilizer to promote the growth of ryegrass, and also as a precursor to synthesize high-value LiFePO4 battery material, demonstrating the high-value application potential of the phosphorus from the ISSA.

Phosphorus recovery from incinerated sewage sludge ash using electrodialysis coupled with plant extractant enhancement technology

Phosphorus (P) is an integral mineral nutrient for the growth of plants and animals. As the increasing population worldwide, the demand for P resources keeps increasing. Therefore, it is necessary to recover P from secondary resources. Unlike conventional P recovery processes, this work focused on the recovery of P from incinerated sewage sludge ash (ISSA) using electrodialysis as the main technology coupled with plant extractants. In this study, Amaranthus and hydrolyzed polymaleic anhydride (HPMA) were used as P extractants, investigating the effects of HPMA concentration and pH of the compound agent on the migration of P and heavy metals from ISSA. The results showed that the concentration of HPMA and pH of the compound agent had a significant influence on the mobility of P and heavy metals. Meanwhile, the impacts of eggshell additions and voltage on the recovery efficiency of P was also studied by using waste eggshells as calcium sources. We found that when eggshells were added at 10 g/L and the voltage was 10 V, the recovery efficiency of P reached 96.05%. Moreover, XRD patterns revealed that the mineral phase of recovered P-containing products was predominantly hydroxyapatite, which had good environmental benefits. Generally, the favorable results have been achieved in the recovery efficiency of P and has practical implications for P recovery from ISSA.

Efficiency comparison of mixture formulations in the stabilisation/solidification of the loess silt contaminated with zinc in terms of mechanical properties

The effectiveness of various types of binders in stabilizing/solidifying (S/S) contaminated soils is strongly dependent on the type of soil and contaminants present. The literature abounds with studies of stabilisation/solidification of clayey soils, which provides a background for initial assumptions in design of the method application for contamination of this type of soil. However, studies on the stabilisation/solidification of loess silt contaminated with heavy metals are not available. Filling this deficiency is important in order to ensure the rapid adoption of the most effective remedies in case of contamination and their immediate implementation in the subsoil. This paper has enabled the determination of the most effective mixture among the examined for the remediation of loess silt contaminated with zinc in terms of compressive strength. Strengths were determined with the implementation of 30% Portland cement (2.63 MPa), 30% of fly ash-cement mixture (2.21 MPa), an incinerated sewage sludge ash-cement mixture (0.93 MPa) and mixtures in which cement was replaced by an MgO activator (0.18 MPa for fly ash and 0.63 MPa for incinerated sewage sludge ash). In addition, the determination of strength was carried out for samples containing a mixture of fly ash, activator and cement (0.26 MPa) and incinerated sewage sludge ash, activator and cement (0.26 MPa), with weight ratios of 5:4:1 respectively. In summary, fly ash and cement in a 2:1 ratio can be considered the most effective binding mix in terms of unconfined compressive strength increase.

Chemical and Microbiological Techniques for Recovery and/or Removal of Elements from Incinerated Sewage Sludge Ash—A Review of Basic Methods

In the face of material shortages, growing environmental awareness, and technical advancement, incinerated waste materials are being considered secondary resources. Especially incinerated sewage sludge ash is of interest due to its massive and increasing production and relatively stable composition with a satisfying concentration of elements of value. This paper revises the basic methods for recovery of valuable components from incineration sewage sludge and simultaneous removal or stabilization of elements that may negatively influence the environment with further ash usage or storage. The presented work focuses on collating and analysing the efficiency of currently used approaches as well as their limitations and perspectives for future development. Chemical methods analysed include acidic and alkaline leaching, chelating, and sequential leaching. Due to scarce examples from literature, the exploration of a microbiological approach focuses on the mechanisms and potential for application of different microorganisms for element extraction. The methods described are relatively efficient and affordable, yet still need further development. Specifically, microbiological approaches are rarely used for incineration sewage sludge treatment regardless of their potential advantages over other approaches. Constant mineral and chemical composition within one incineration plant can vary among plants due to many factors, so a well-established range of techniques and an individual approach are important.

Solidification/stabilization treatment of Hong Kong marine deposits slurry at high water content by ISSA and GGBS

Soft soils have been adopted as a conventional fill material in land reclamation projects, which is quite promising in Hong Kong with a huge mass of dredged marine sediments produced per year. It is proposed to use Hong Kong marine deposits (HKMD) as fill material treated by stabilisation/solidification (S/S) technology with sustainable binding material. In this work, lime, incinerated sewage sludge ash (ISSA) and ground granulated blast furnace slag (GGBS) were selected as the binding materials. The S/S performance of the binders on HKMD slurry was investigated. The results showed that the use of ISSA and GGBS as part of the binder is effective in promoting the strength of HKMD slurry with a high initial water content of 200%. The HKMD slurry treated by 30% binders (30% lime and 70% (ISSA + GGBS) with ISSA: GGBS = 3) gains strength, which became higher with increasing curing time. The results from X-ray diffraction (XRD), thermo-gravimetric (TG) analysis and scanning electron microscopy-energy dispersive spectrometer (SEM-EDS) presented the formations of calcium (aluminium) silicate hydrate (C-(A)-S-H), Friedel’s salt, and ettringite, which are mainly responsible for the strength increase of treated HKMD with their phases filling into the pores, interlocking and reinforcing the particles in the mixture. The porosity of the treated HKMD in bulk and powder state was determined by mercury intrusion porosimetry technique (MIP) and nitrogen adsorption/desorption isotherms (NAI), it is found that the bulk porosity of treated HKMD samples reduces with curing time due to the neoformations, especially the ettringite crystal by SEM results. This work indicates the potential application of lime-activated recycling wastes (i.e., ISSA and GGBS) for S/S treatment of HKMD slurry.

Phosphorus Recovery and Simultaneous Heavy Metal Removal from ISSA in a Two-Compartment Cell

Traditional acid extraction or electrodialytic remediation (EDR) is inefficient to recover phosphorus (P) from incinerated sewage sludge ash (ISSA). This study used a hybrid process including acid extraction and EDR to extract P from ISSA and remove heavy metals/metals from the P extract sequentially. Specifically, the P extract was obtained by extracting ISSA with 0.2 M H2SO4 and a two-compartment cell was applied in the following EDR process. Constant currents of 15 mA, 35 mA and 50 mA were applied for the electromigration of the heavy metals/metals. Results showed that the efficiency of heavy metals/metals removal fluctuated and was relatively low (approximately 20%) under a current of 15 mA. Increasing the current to 35 mA significantly increased the removal efficiency and that of 50 mA was conspicuous, except Fe, Al and As (<50%). Meanwhile, P gradually immigrated to the catholyte after an EDR duration of 96 h. Consistent with heavy metal/metal immigration results, the pH change and 50 mA voltage drop were dramatic (the pH change was 12 and the voltage drop was 11 V). In addition, flocculent precipitates, which were predominantly Ca, P, Al, Mg and Fe, were found in the catholyte.

Production of sorptive granules from incinerated sewage sludge ash and upcycling in cement mortar

This paper describes a method to produce sorptive granules solely from solid waste. The produced granules can remove multi-toxic heavy metal(loid)s from wastewaters and be upcycled as lightweight aggregates in cement mortars. Specifically, kilogram-scale production of millimeter-sized granules was obtained via the thermal treatment of green bodies prepared from phosphorus-stripped incinerated sewage sludge ash (ISSA), peanut shell and waste bentonite at a mass ratio of 1:1:2 at 1050 °C under a N2 atmosphere. The synthesized granules with good mechanical strength (4.9 MPa) exhibited excellent adsorption capacities towards As(V), Cr(VI), Cu(II) and Pb(II) at respectively 14.11, 5.79, 14.12 and 23.52 mg/g at an initial solution pH of 3.0 via mechanisms including redox reactions, complexation, (co)precipitation, and cation exchange. Moreover, the potentially hazardous spent granules could be environmental safely reused as a partial river sand replacement in cement mortars based on the Toxicity Characteristics Leaching Procedure.