Sludge Ash Research Articles

Enhancement of magnesium phosphate cement with sintered sludge ash

Magnesium phosphate cement (MPC) is a promising material known for its rapid hardening and high early-strength properties. However, its potential in engineering applications is hindered by its harden at an uncontrolled rate, considerable volumetric distortion and poor water resistance. To address the limitations, this study investigates the influence of sintered sludge ash (SSA) modification on the setting time, volume deformation, mechanical strength and water resistance of MPC composites. Experimental reveals that the setting time of MPC composites increase with higher SSA content, and the inclusion of SSA significantly mitigate volumetric deformation. Moreover, the mechanical strength exhibits improvement at all ages, and combine with water resistance analysis, 15% SSA content is the optimal level. Based on the XRD, TG, MIP and SEM, the enhanced properties of the MPC composites may be attributed to the reaction of SSA in the MPC system, leading to the resulting aluminum-containing gel phase acting as a binder along with guano to densify the microstructure.

Production and Characterization of Bricks from Bottom Ash and Textile Sludge Using Plastic Waste as Binding Agent

The production of traditional clay bricks consumes a large amount of energy and resources and can lead to the depletion of natural resources like clay. On the contrary, the improper disposal of waste materials such as bottom ash, textile sludge, and plastic waste can lead to environmental pollution and health hazards. Bricks and concrete blocks have been widely used in construction, but the continuous exploitation of raw materials can negatively impact the environment. This study aimed to produce bricks made from municipal solid waste, incinerated bottom ash, and textile sludge, using plastic waste as a binder. It assessed the potential use of these bricks as an alternative material for brick block production. The physical and chemical characteristics of the raw materials were determined using standard test methods. The crushed plastic waste was melted and mixed with dried textile sludge and bottom ash in various ratios, including 1 : 1 : 1, 2 : 1 : 1, 1 : 2 : 1, 1 : 1 : 2, and 1 : 2 : 2 for plastic, municipal incinerated bottom ash, and textile sludge, respectively. The mixed sample was then placed into molds until it dried, and the resulting bricks were tested for compressive strength, water absorption, efflorescence, and leachability. The results indicated that the bricks had suitable physical and chemical properties, with compressive strength ranging from 8.527 to 16.4 MPa and water absorption percentages ranging from 1.3 to 3.4%. Slight efflorescence was observed for the 1 : 2 : 2 ratios. The production of traditional clay bricks consumes a large amount of energy and resources and can lead to the depletion of natural resources like clay. On the other hand, the improper disposal of waste materials such as bottom ash, textile sludge, and plastic waste can lead to environmental pollution and health hazards.

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.

Enhancing Phosphorus Fertilizer Value of Sewage Sludge Ashes and Biochars Through Chemical Pre-treatments and Application Methods

PurposeThis study aimed to improve the phosphorus (P) fertilizer value of sewage sludge ashes and biochars through different pre-treatments and application methods.MethodsIn experiment 1, two sewage sludges, their respective ash, and biochar underwent three chemical pre-treatments (H2SO4, NaOH, and Ca(OH)2. These materials were utilized as P fertilizers in a maize plant trial), using two application methods (mixed and placed). In experiment 2, biochars sourced from four sewage sludges were pre-treated with H2SO4 and NaOH and then employed as P fertilizers in a barley plant trial.ResultsExperiment 1 revealed a significant impact of application method on shoot dry matter, with mixing outperforming placement. Acidification pre-treatment of the ash led to significantly higher shoot dry matter (2.7 ± 0.3 g) and P uptake (7.9 ± 0.9 mg per plant) compared to untreated ash (0.7 ± 0.1 g; 1.9 ± 0.2 mg per plant). Similarly, NaOH-treated biochar caused elevated shoot dry matter (2.6 ± 0.4 g) and P uptake (6.9 ± 0.4 mg per plant) compared to untreated biochar (0.7 ± 0.2 g; 1.9 ± 0.1 mg per plant). These outcomes highlight the dependence of pre-treatment efficacy on biomaterial composition. Experiment 2 demonstrated that despite differing elemental compositions of the biochars, NaOH treatment led to significantly greater shoot dry matter and P uptake compared to untreated and acidified treatments.ConclusionsChemical pre-treatments have the potential to enhance the short-term P fertilizer value of ashes and biochar. However, further studies are essential to assess the economic feasibility and potential environmental risks, including increased heavy metal solubility.Graphical

Co-disposal kinetics and characteristics of sewage sludge and municipal solid waste incineration fly ash

Sewage sludge (SS) and municipal solid waste incineration fly ash (MSWIFA) have characteristics of high yield, scattered distribution, and strong harm. Co-disposal of SS and MSWIFA in the existing cement kilns is a prospective way to deal with these two types of solid waste. In this study, the pyrolysis kinetic, thermogravimetric analysis, heat and mass transfer characteristics and pollutant release during SS and MSWIFA co-disposal were investigated through a series of experiments and simulations. In the experiment, pulverized coal (PC) was used as fuel to imitate the real environment of a cement kiln. According to the results, the interaction of the two solid wastes was observed mainly during the devolatilization and combustion periods. At an average blending ratio (60%) and 25 ℃/min heating rate, the blend actual mass loss rate has the largest difference compared to the linearly calculated mass loss rate (0.74%/min), with higher comprehensive combustion characteristic index (3.54), and the blends have better overall heat transfer, internally converging to 350 K. Meanwhile, when SS proportion in PC-SS-MSWIFA is between 20% and 30%, the emission concentration of SO2 and NO was low, and it has good environmental benefits. This research aims to offer theoretical support for the co-disposal of SS and MSWIFA.

Life Cycle Assessment (LCA) of the integrated technology for the phosphorus recovery from sewage sludge ash (SSA) and fertilizers production

Life Cycle Assessment (LCA) of the integrated technology for the phosphorus recovery from sewage sludge ash (SSA) and fertilizers production

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.

Relationship between Chloride Migration, Bulk Electrical Conductivity and Formation Factor of Blended Cement Pastes

Abstract This study investigates the links between the non-steady-state chloride migration coefficient, the bulk electrical conductivity and the formation factor of blended cement paste specimens. 18 different binders were tested: two Portland cements (low- and high-alkali) in combination with limestone filler, fly ash, calcined clay, two biomass ashes, sewage sludge ash and crushed brick, as well as two Portland composite cements. In addition, the latter and the low-alkali Portland cement were tested in concrete as well for comparison. Mixes with high-alkali cement showed better resistance to chloride transport, and the effect of supplementary cementitious materials was found to be strongly linked with their reactivity. Moreover, the results showed a clear correlation of the migration coefficient with the bulk electrical conductivity and, to a lesser extent, with the formation factor. However, these relationships are strongly influenced by the methods used to determine conductivities and they need to be validated for higher maturities. Finally, the results suggested a fairly good correspondence between the results obtained on paste and concrete.

Insights into durability assessment for compacted soils treated with paper sludge ash-based stabilizers

To utilize industrial by-products in construction projects, soil stabilization using paper sludge ash-based stabilizers (PSASs) has recently been developed. PSASs can be manufactured by insolubilizing the heavy metals in original paper sludge (PS) ash, which is a waste product emitted from paper mills. This study assessed the durability of clays treated with PSASs in wet-dry or dry-wet environments through various evaluation tests. Initially, the particle size distributions (PSDs) in the clays that had undergone various pretreatments were assessed. Then, unconfined compression tests were performed on the treated clays that had undergone dry and wet curing cycles using demolded specimens. Finally, cone index tests were carried out on the treated clays that had undergone dry and wet curing cycles while the samples were constrained in molds. Based on the test results, the durability assessment of the clays treated with PSASs was discussed, considering the specifics of each evaluation test and contrasting the findings with those obtained for clays treated with cement. The generated PSDs were found to contain more fine particles as the time spent washing the samples prior to sieving was increased. The findings indicated that PSAS-treated clays will eventually become muddy, even though it is unlikely that these treated clays will ever be subjected to washing with water while being stirred after construction. The unconfined compression test results also demonstrated that, after several dry-wet cycles, the strength of the PSAS-treated specimens had decreased. It was revealed that clays treated with PSASs might be less resistant to dry-wet curing cycles than those treated with cement. However, PSAS-treated samples using unconfined compression test specimens are still being investigated and are a topic of debate because the strength development mechanisms of PSASs and cement are not similar. To address this issue, a series of cone index tests were conducted on samples treated with PSASsto examine the change in strength caused by the dry-wet curing process. The results of the cone index tests were different from those of the unconfined compression tests. The cone index test results revealed that the samples must be constrained during the assessment tests in order to assess the durability of PSAS-treated soils subjected to dry-wet curing. In addition, it was proposed in this study that the idea of maturity would be applicable to PSAS-treated soils with a range of curing temperatures and curing times as long as the soils were constrained during the assessment tests.

Viability of calcinated wastepaper sludge ash geopolymer in the treatment of road pavement subgrade materials

Problematic ground conditions constituted by weak or expansive clays are commonly encountered in construction projects and require some form of chemical treatment such as lime and cement to re-engineer their performance. However, in the light of the adverse effects of these traditional additives on the climate, alternative eco-friendlier materials are now sourced. In the current study, the viability of calcinated wastepaper sludge ash geopolymer in enhancing the engineering behaviour of a problematic site condition is evaluated. A highly expansive clay (HEC) constituted with a blend of kaolinite and bentonite clays is treated with calcinated wastepaper sludge ash (CPSA) geopolymer. Activation of the precursor is actualised at room temperature using a combination of NaOH and Na2SiO3 at various activator to soil + binder ratios (AL/P), and molarity (M). The mechanical, microstructural, and mineralogical characteristics of the treated clay were investigated through unconfined compressive strength (UCS), swell, water absorption, SEM, and EDX analysis. The performance of the stabilised samples was then compared with the requirements for road subgrade and subbase materials and that of OPC and lime-GGBS treatment. The results showed that CPSA-geopolymer enhanced the engineering properties of the treated clay better than traditional binders (OPC and Iime-GGBS). UCS improvement of 220 % was observed in the CPSA-stabilised soil over that of OPC-treated ones, while the swell potential and water absorption were drastically reduced by over 95 and 97 % respectively after 28-day soaking. The SEM and EDX results showed improved crystallisation of earth-metal-based cementitious flakes (NASH) with increasing CPSA, molarity, and AL/P ratios, which enhanced the inter-particle bonds with simultaneous reduction in porosity. The modified characteristics of the stabilised materials meet the requirements for pavement subgrades. Further, the equivalent carbon emission (CO2-e) from the stabilised materials were also evaluated and compared with that of traditional binders. The results also showed that CPSA-geopolymer had lower CO2-e at higher subgrade strengths than OPC, making it more eco-friendly. Therefore, wastepaper sludge, a common landfill waste from paper recycling is a viable geopolymer precursor that could be utilised in enhancing the engineering properties of subgrade and sub-base materials for road and foundation construction.

Increasing phosphorus plant availability from P-rich ashes and biochars by acidification with sulfuric acid

Biochars and ashes derived from thermal treatment of P-rich wastes could be used as bio-based fertilizers to improve P recycling. However, thermal treatments often result in low plant P availability. Acidification of these materials before soil application could potentially increase plant P availability. Based on the water-extractable P levels obtained in titration experiments, sulfuric acid concentrations between 2.5 M and 10 M were applied to digestate solids char and ash (DS-C, DS-A), poultry litter ash (PL-A), insect frass char (IF-C), sewage sludge char and ash (SS-C, SS-A) and meat and bone char (MB-C). Acidified and untreated materials were applied in a pot experiment with maize in 33P labeled soil to determine fertilizer P uptake. The acidification resulted in a significant increase in P solubility. The amount of acid required depended on the materials’ buffer capacity and P speciation. Based on XRD analysis, we assume that mainly Ca-associated P was solubilized. In the pot experiment, acidified materials outperformed untreated materials and the unfertilized control in terms of biomass and P uptake. The P recovery from the acidified materials ranked in the order DS-C > SS-A > PL-A > IF-C > DS-A > SS-C > MB-C. The acidification did not significantly decrease soil pH, nor was there an effect on plant heavy metal availability. In conclusion, acidification increased plant growth and P uptake without affecting plant heavy metal uptake and soil pH. Therefore, acidification to increase the P fertilizer value of ashes and chars is a promising approach to facilitate P recycling.

Study on the fate of phosphorus, fluorine and chlorine in sludge during incineration

Sludge is often incinerated to achieve complete harmlessness and maximum capacity reduction, but the utilization of P (phosphorus) and the environmental pollution of F (fluorine) and Cl (chlorine) released from sludge incineration are usually ignored. In this paper, a series of experiments were employed to inquire into the conversion of various forms of P and the release of various forms of F and Cl after sludge incineration at different temperatures; the agriculture application prospect of P in sludge incineration ash and the environmental pollution caused by the release of F and Cl were discussed. The results show that P in sludge mainly exists as NAIP (non-apatite inorganic P) which biological effect was small. In the process of sludge incineration, InorgP (inorganic P) began to volatilize at 900 ℃, and the remaining P in sludge ash was 30.96 % at 1100 ℃. The forms of P in sludge incinerated at different temperatures varied considerably: a small amount of OrgP (organic P) in the sludge was converted into InorgP at 400 ℃; with the increase of incineration temperature, AP (apatite P) increased gradually, with 3.00 × 103–7.98 × 103 g/t in sludge ash at 700–1100 ℃. At 900 ℃, the content of AP in incineration ash was the highest, accounting for 58.98 % of Total P, which was the most suitable for slow-release phosphate fertilizer. At 600–1100 ℃, more Cl release, with a release rate of 50.61–92.70 %, among which the Cl for HCl (ClHCl) was 1.64 × 103–1.95 × 103 g/t at 700–1100 ℃. The F release rate was 1.52–37.39 %, among which the InorgF (inorganic F: mainly refers to F in HF and SiF4) was 1.13–27.91 g/t at 300–1100 ℃, the release amount of OrgF (organic F) was 1.59–1.86 g/t at 600–800 ℃. It can be seen that after incineration above 700 ℃, the sludge incineration ash may be used as a slow-release phosphate fertilizer, the release of Cl has greater environmental pollution and instrument corrosion than that of F, and the exhaust gas from sludge incineration cannot be discharged directly into the atmosphere.

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.

Phosphorous extraction and heavy metal separation from sewage sludge ash by two-compartment electrodialysis in an upscaled tube reactor

Two-compartment electrodialytic extraction (2C-ED) is a one-step process for the simultaneous phosphorous extraction and separation of heavy metals from sewage sludge ash (SSA). The process is driven by an applied electric DC field, which can be supplied from renewable sources. The proof-of-concept of the method was conducted in small laboratory cells; however, upscaling to a continuous 2C-ED process, which additionally can treat SSA suspensions at a low liquid-to-solid (L:S) ratio, requires a new design. This paper presents such a new design. In principle, ED consists of two compartments separated by a cation exchange membrane. One compartment contains a suspension of SSA in water and the anode. A cathode is placed in the other compartment. Electrolysis at the anode acidifies the suspension causing the dissolution of phosphorous and heavy metals. The heavy metals are separated from the suspension by electromigration into the catholyte, whereas the dissolved phosphorous remains in the dispersion solution. In the new design, the SSA was suspended in a tube-shaped reactor with the cation exchange membrane covering the outside. The reactor was placed in a container with the catholyte. Periodically turning off the reactor kept SSA in suspension even at a low L:S ratio without corners and pockets where the SSA otherwise tends to settle. Five 2C-ED experiments were conducted with 1.5 to 3 kg SSA at varying currents and durations. Up to 89% P was extracted. The extracted P was concentrated in the dispersion solution of the SSA suspension, where the obtained P-related concentrations of heavy metals were far below the limiting values for spreading on agricultural land. The experiments underlined that treating the SSA in a suspension with a low L:S ratio is advantageous. A comparison to previous laboratory experiments in small cells treating 50 g SSA shows a significantly more efficient use of the applied current in the new reactor setup. Thus, the new reactor design for 2C-ED fulfilled the set criteria for the operation and did additionally result in a higher efficiency than the laboratory setups, i.e., the design can be the first step towards an upscaling.

Preparation and performance of non-sintered lightweight aggregates derived from textile sludge and coal fly ash

The feasibility of preparing non-sintered lightweight aggregate using textile sludge and coal fly ash as the main raw materials was investigated. Extensive experiments were conducted to analyze the effects of different coal fly ash/sludge ratio, sodium silicate addition and curing time on the performance of non-sintered lightweight aggregates (NSLWAs). The optimal preparation parameters were determined as follows: coal fly ash/cement ratio of 2.2, textile sludge addition of 20%, sodium silicate addition of 10%, and curing time of 28 days. Under these optimal preparation conditions, the cylindrical compressive strength of NSLWAs was relatively high. The test results of Zn leaching toxicity test and S content all met the relevant standards and environmental safety requirements. NSLWA has a dense internal structure with uniformly distributed grains. By analyzing the hydration reaction mechanism during the NSLWAs preparation, it can be obtained that part of Zn<sup>2+</sup> was stabilized by conversion into insoluble Ca(Zn(OH)<sub>3</sub>)<sub>2</sub>･2H<sub>2</sub>O, while the remaining part was solidified and stabilized through encapsulation and adsorption of hydration products. Furthermore, it was discovered that pozzolanic admixtures played a crucial role in the hydration and hardening process of NSLWAs, and the presence of C-S-H gel and Mullite contributed to the increase in cylinder compressive strength of NSLWAs.

Influence of wastepaper sludge ash as partial cement replacement on the properties of lightweight foamed concrete

This study focused on the effect of using wastepaper sludge ash (WPSA) as a partial substitute for cement in the production of lightweight foamed concrete (LFC). The LFC was produced with a constant dry density of 1350 kg/m3 by controlling the foam content. In this study, six mixtures of LFC were produced using WPSA as a partial substitute of 0%, 5%, 10%, 15%, 20% and 25% of the cement mass. Setting time, spreading ability and density tests were performed immediately after the mixing process to evaluate the fresh LFC properties. Meanwhile, the compressive strength, flexural strength, cleavage tensile strength and modulus of the elasticity tests were performed at test ages 7, 14 and 28 days to evaluate the mechanical properties. Water absorption, capillary absorption, gas permeability, porosity and pore distribution were performed to evaluate the transport properties. Furthermore, SEM evaluation was performed to evaluate the microstructure. The inclusion of WPSA as a 15% partial cement replacement achieved the highest mechanical properties. The compressive strength was 11.2 MPa, the flexural strength was 2.61 MPa, the tensile strength was 1.72 MPa, and the elastic modulus was 3.253 GPa. Inclusion of WPSA as a partial substitute for cement with 25% led to the best transport properties by having the lowest water absorption and porosity by 17.4% and 37.75%, respectively.

Enhancement of H2 and light oil production and CO2 emission mitigation during co-pyrolysis of oily sludge and incineration fly ash

The proper treatment and utilization of oily sludge (OS) and incineration fly ash (IFA) remains a significant challenge due to their hazardous nature. To attain effective recovery of petroleum hydrocarbons and synergistic disposal, this study investigated the co-pyrolysis of OS and IFA, resulting in successful energy recovery, CO2 mitigation, and heavy metal immobilization. Results revealed that the peak ratio of light oil to heavy oil fractions reached 179.42% with 20 wt% IFA addition, accompanied by the highest aromatic hydrocarbons selectivity of 30.72% and the lowest coke yield of 106.13 mg/g OS under the optimal temperature of 600 °C. In-depth analysis indicated that IFA inhibited the poly-condensation of macromolecular PAHs and promoted their cracking into light aromatic hydrocarbons. The addition of 50 wt% IFA significantly increased H2 yield (21.02 L/kg OS to 60.95 L/kg OS) and facilitated CO2 sequestration due to its higher content of Ca-bearing minerals. Moreover, high IFA ratios promoted the reduction of Fe species in OS to a low-valence state. Heavy metals in co-pyrolysis char were well immobilized into stable fractions with lower environmental risks. This work highlights the potential of co-pyrolysis as a viable approach for simultaneous disposal of multiple hazardous wastes and offers new insights for their utilization.

Onsite treatment of wastes in municipal waste incinerator: Co-sintering of fly ash and leachate sludge into value-added ceramic granule

The leachate sludge (LS) and fly ash (FA) are the foci of hazardous wastes which generated from the municipal solid waste incineration (MSWI). The current work developed a new way to use energy from MSWI process for the on-site sintering of LS and FA at a relatively low temperature. With the assistance of CaF2, granule of LS and MSWI FA were co-sintered. The influence of temperature, the mass of CaF2, and the mass ratio of LS/MSWI FA were investigated. As a result, heavy metals volatilization and leaching in the form of chlorinated salts were controlled. In addition, CaF2 improved the compressive strength of the granule under low-temperature sintering. Moreover, the scale-up co-sintering test was achieved in an MSWI chamber. The results showed that the optimum condition was sintering at 973K for 1 h. The compressive strength of sintered product reached 4.25 MPa, which met the standard of ceramic granule. Moreover, with the addition of CaF2, the volatilization rate of Pb, Zn, and Cd decreased by 6%, 7%, and 6%, respectively. This method can be a promising technique for the utilization of solid wastes.

Estimation of contribution rate derived soil component in sewage sludge ash using chemical mass balance of plagioclase by X-ray diffraction

Estimation of contribution rate derived soil component in sewage sludge ash using chemical mass balance of plagioclase by X-ray diffraction

Extraction of Phosphorus from Sewage Sludge Ash—Influence of Process Variables on the Electrodialytic Process

Phosphorus is a critical, irreplaceable raw material, and developing methods to recover P from secondary sources such as sewage sludge ash (SSA) is crucial. Two-compartment electrodialytic extraction (2C-ED) is one method where an electric DC field is applied to extract P and separate heavy metals simultaneously. Several process parameters influence 2C-ED, and they influence each other mutually. This paper explores chemometrics modeling to give insight into the 2C-ED process and, specifically, optimization of the experimental parameters towards 80% P extraction. A projections-to-latent-structures model was constructed based on new 2C-ED experiments conducted with one SSA type. The model was stable (high correlation factor and predictive power). Variable importance in the projection (VIP) plots showed that the influence of the variables was in the order: current > duration > L:S ratio > stirring velocity > dispersion solution (weak acid or distilled water). Contour plots were used for exploring different P extraction strategies. For example, more P mass per unit current was extracted at an L:S ratio of 7 compared to L:S 14. This shows that treating a thicker SSA suspension is preferable to optimize the current efficiency. The chemometric model proved valuable for optimizing the 2C-ED process and future scale-up.