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Modification of biochar by low-cost iron sources has gained increasing attention to improve pollutants removal performance and reduce production costs compared to conventional chemical modifications. While such iron sources generally have complex compositions, their effects on properties of the iron-biochar composite are not well investigated. This study produced an iron-biochar (RBC) composite from co-pyrolysis of incinerated sewage sludge ash (ISSA) and peanut shell, and examined the role of silica with widespread existence in ISSA and other low-cost iron sources on properties of the iron-biochar composite relevant to As(III)/As(V) removal. Silica was found to react with iron during the pyrolysis process at 850 °C and formed iron silicon at the expense of producing zero valent iron and Fe

The particle packing of cementitious materials is of essential importance to the performance of paste which constitutes the most uncertain part of mortar/concrete. Such importance is arising from the fact that the design of cementitious particle system inevitably involves the packing design, particularly for the emerging materials of 3D printable concrete and ultra-high performance concrete (UHPC). So far, scientific understanding of the particle packing in these emerging materials remains inadequate. In this regard, wet packing method (WPM) was used to measure the wet packing density (WPD) of ternary particle systems consisting of cement, pulverized fuel ash (PFA) and micro-silica (MS). The optimum ternary particle system in terms of WPD was determined. Comparison between the experimental results and Andreasen and Andersen (A&A) model revealed the limitations of A&A model. The design approach based on WPD contour shall advance particle packing-oriented cement and concrete science towards sustainable concrete design.

Efficient depolymerization of lignocellulosic biomass is a prerequisite for sugar production and its subsequent upgradation to fuels and chemicals. Organic carbonate solvents, i.e., propylene carbonate (PC), ethylene carbonate (EC), and dimethyl carbonate (DMC), which are low in toxicity and biodegradable, were investigated as "green"co-solvents (PC/H2O, EC/H2O, DMC/H2O, solvent ratio 1:1) for depolymerization of cellulosic paper towel waste. PC/H2O and EC/H2O enhanced the depolymerization of paper towel waste and improved the total sugar yield (up to ∼25 C mol %) compared to H2O only (up to ∼11 C mol %) under mild reaction conditions (130 °C, 20 min). The higher performance of PC/H2O and EC/H2O can be attributed to higher availability of reactive protons in the catalytic system that facilitates efficient acid hydrolysis of recalcitrant cellulosic fibers. Moreover, a substantial buildup of in-vessel pressure by CO2 release during the microwave-assisted reaction because of decomposition of PC or EC might have accelerated the conversion of paper towel wastes. PC and EC are prospective solvents for lignocellulosic biomass conversion considering their green features and notable catalytic performance, which have a good potential for substituting conventional organic solvents such as dimethyl sulfoxide (DMSO) and tetrahydrofuran (THF) that are often considered hazardous in terms of health, safety, and environmental implications.

The management of large quantities of incinerated sewage sludge ash (ISSA) is problematic. Environmental and economic benefits can be achieved by using ISSA as an adsorbent for heavy metals removal due to its exceptionally porous structure and active components. In this study, the feasibility of using ISSA to treat heavy metals (Cd(II), Cu(II) and Zn(II)) contaminated waters from both single- and binary-metal systems were investigated. The results showed that the pH of the solution played a pivotal role in the adsorption of heavy metals by ISSA and the optimal pH for the adsorption of these metals was around 6.00. The adsorption process of Cu(II), Cd(II), and Zn(II) in a single-metal system was similar and fast. The equilibrium data followed the Freundlich isotherm model and the corresponding adsorption capacity was 0.13, 0.11 and 0.06 mmol/g, respectively. However, the presence of other competitive metal ions had adverse effects on both the adsorption rate and the adsorption capacity for the target metal ions. The affinity of ISSA towards the metals followed the order of Cu(II) > Cd(II) > Zn(II). The difference in pH value and Ca or Na concentration of the solution after adsorption revealed that cation exchange played a fundamental role in the adsorption of the target metals, while electrostatic attraction and precipitation were insignificant. Over all, the application of ISSA as an adsorbent would be a promising option to both relieve the waste disposal pressure and mitigate the complex heavy metals pollution.

This study designed an eco-friendly pervious concrete (PC) product using waste glass cullet (WGC) and recycled concrete aggregate (RCA) by dry-mixed compaction technique. The mechanical properties, water permeability behavior and related pore structure characteristics, thermal conductivity of the PCs were determined. The experimental results showed that the use of silica fume in the cement paste was effective to compensate for the low compressive strength of the PCs due to the use of narrowed graded aggregates without the incorporation of fine particles (less than 2.36 mm). Although the incorporation of recycled aggregates (i.e. WGC and RCA) into the PCs led to reductions in compressive strength, the water permeability of the PCs was improved, especially for the PCs prepared with WGC, as the use of WGC was conducive to improving the water permeability due to the negligible water absorption nature and smooth surface of glass cullet. Another encouraging result indicated that the PCs comprising 50% WGC as the fine aggregate and 50% RCA as the coarse aggregates could achieve satisfactory strength and permeability, which could largely meet the requirement of the standard (JIS A 5371) for permeable pedestrian pavers. The appropriate blending of the selected size of WGC (2.36–5 mm) and RCA (5–10 mm) to produce a desirable pore structure in the PCs were responsible for the good performance. In addition, the low thermal conductivity of the produced PCs provided an opportunity to use the PC as partition block materials for saving energy consumption of buildings.

The growing global demand for non-ferrous metals has led to serious environmental issues involving uncovered mine site slag dumps that threaten the surrounding soils, surface waters, groundwater, and the atmosphere. Remediation of these slags using substitute cement materials for ordinary Portland cement (OPC) and precursors for alkali-activated materials (AAMs) can convert hazardous solid wastes into valuable construction materials, as well as to attain the desired solidification and stabilization (S/S) of heavy metal(loid)s (HM). This review discusses the current research on the effect of non-ferrous slags on the reaction mechanisms of the OPC and AAM. The S/S of HM from the non-ferrous slags in AAM and OPC is also reviewed. HM can be stabilized in these materials based on the complex salt effect and isomorphic effects. The major challenges faced in AAMs and OPC for HM stabilization include the long-term durability of the matrix (e.g., sulfate attack, stability of volume). The existing knowledge gaps and future trends for the sustainable application of non-ferrous slags are also discussed.

Phosphorus (P) recovery from incinerated sewage sludge ash (ISSA) has been extensively investigated, and various recovered phosphate fertilizers (RPFs) have been produced. In this study, three RPFs (calcium phosphate compounds (CaP), struvite (SP), and P-loaded biochar (BP)) produced from ISSA were characterized and their agronomic effectiveness were verified by pot experiments with the cultivation of choy sum (Brassica campestris L. ssp. Chinensis var. utillis Tsen et Lee) and ryegrass (Lolium perenne L.). The SP has the highest P purity while the BP has the most complex P species. And the plant growth results showed that the RPFs greatly facilitated plant growth and demonstrated superior/comparable effects to those of MP/CoF. In general, choy sum fertilized with SP showed the best effect due to the Mg involved and the high P purity of SP, while ryegrass fertilized with BP performed the best among all of the groups because of the additional nutritional elements and the high P availability of BP. Additionally, the accumulation of heavy metals in the plants under all conditions did not exceed the limits stipulated in the regulations. These results indicate that recovering P from ISSA is an attractive technology to produce P fertilizers, which can alleviate both the scarcity of phosphate resources and the burden of ISSA management.

Optimization of pretreatment and various gas-solid interaction conditions is necessary for effective carbonation of recycled coarse aggregates derived from concrete wastes (RCA). This study demonstrated the use of linear weighted sum method to simultaneously optimize the pretreatment and carbonation test conditions. The optimization of the test conditions produced simplified, and eco-friendly pretreatments and drastically reduced the carbonation duration of RCA from 72 h to 3 weeks in previous studies to 18 h in this study. In addition, the optimum experimental conditions were validated by casting concrete using the carbonated RCAs. The optimized pretreatment and carbonation conditions were spraying Ca2+-rich wastewater at a level of 60% of the 24 h water absorption of RCA, 12 h air drying and 6 h carbonation at 60 °C. This study also demonstrated that wastewater derived from ready-mix concrete batching plants can be utilized for spraying the RCAs to improve carbonation efficiency. Also, the mechanical and durability properties of concrete prepared with RCAs produced from the optimized conventional carbonation and pressurized carbonation were similar. Therefore, optimized conventional carbonation can be utilized as an alternative to pressurized carbonation. The improved mechanical and durability properties of concrete prepared with carbonated RCAs were attributed to the improved physical properties of carbonated RCAs and improved microhardness of the interfacial transition zone of the new mortar. The simplified, faster, ecofriendly, optimized pretreatment and carbonation conditions opens a new vista for industrial carbonation applications and optimization of gas-solid interactions.

In this work, the influence of a naphthalene sulfonate–based superplasticizer on the initial corrosion of galvanized steel bars in the simulated concrete pore solution was studied. The init...

Five recycled coarse aggregate (RCA) treatment techniques including flow-through carbonation, pressurized carbonation, wet carbonation, nano silica (NS) pre-spraying and combined pressurized carbonation with NS pre-spraying, were utilized to improve the performance of recycled aggregate concrete (RAC). The characteristics of the stress–strain curves of RACs including peak stress, peak strain, elastic modulus, ultimate strain and toughness were evaluated after using the above RCA treatment techniques. A theoretical model for natural aggregate concrete was used to analyse the stress–strain curve of RAC. Additionally, the carbonation resistance of RAC after using different RCA treatment techniques were investigated. The results showed that the calculated stress–strain curve of RAC based on the theoretical model matched well with the experimental results. Among the three types of carbonation techniques, pressurized carbonation caused the highest improvement in peak stress and elastic modulus of RAC, followed by flow-through carbonation, the last was wet carbonation. The NS pre-spraying method contributed to even higher improvement in peak stress and elastic modulus of RAC than the pressurized carbonation method. The combined pressurized carbonation with NS pre-spraying exhibited the highest enhancement of RAC because both the RCA and the new interface transition zone (ITZ) were improved. The carbonation resistance of RAC was improved after using all the studied RCA treatment techniques.

Hong Kong is a densely populated city with high-rise developments, and as in other metropolitan cities, the amount of waste generated from construction projects in the city is increasing annually. The capacity of existing landfills is expected to be saturated by the 2020s. Construction waste management has been implemented for years but the performance is still not satisfactory. The aim of this research paper is to explore and formulate strategies and measures for effective construction waste management and reduction in highly urbanized cities such as Hong Kong. A desktop study on construction waste management practices was carried out for a preliminary understanding of the current situation in Hong Kong. Semistructured interviews and focus group meetings were further conducted to shed light on how to improve construction waste reduction and management in Hong Kong. The main contributions of this research study are the potential short-term, medium-term, and long-term strategies, which are related to the design stage, tender stage, construction stage, and government support. The five major strategies recommended are financial benefits to stakeholders, public policies in facilitating waste sorting, government supports for the green building industry, development of a mature recycling market, and education and research in construction waste minimization and management.

Turning waste-to-resources is one of the key scientific interests in recent years, especially within industrial symbiosis networks in order to reduce the waste management problem and associated environmental consequences, improve materials efficiency and conserve natural resources. Considering global concern over fossil fuel burning and CO2 emission, engineered fuels are increasingly used in cement production. The techno-environmental feasibility of using post-consumer wood derived fuel (WDF) in practical application is rarely reported. This study comprehensively evaluated the process feasibility and environmental compliances of utilizing WDF as an alternative fuel in the co-combustion process. The results revealed that physical parameters of WDF met the required fuel standards, and the air emissions by continuous emission measurements also met the specified limits and comparable to the baseline. The stack emission parameters monitored including particulates, dioxin, mercury, cadmium and thallium, and other heavy metals were about 60%, 2%, 21%, 6% and 7% of the specified limits. In addition to significantly reducing CO2 emission (16% for using 20% WDF as co-fuel), the characteristics, of the flue gas as monitored by continuous emission monitoring and periodic stack emission at the cement plant, and the produced clinker quality were also not affected by the use of WDF. These have demonstrated the suitability of WDF as co-fuel for cement production.

Construction waste includes waste arising from construction works such as new build, renovation, demolition and road works. Through waste sorting and separation, inert material can be used to fill in reclamation sites; however, the non-inert portion of the construction waste still goes to landfills. However, Hong Kong is running out of landfill space. When determining reduction and management strategies for construction waste, the Government's objectives are to reduce waste generation, maximize reusing and recycling and reduce the intake of mixed construction waste at landfills. In order to develop and implement the waste reduction and management strategies at project level, proper quantification of construction waste generation is a prerequisite. Our research reveals that limited information is currently available for understanding the magnitude and composition of construction waste and for preparing an appropriate construction waste management plan for a project on new or existing facilities. To bridge the gap, the aim of this research is to present a comprehensive and practical approach for estimating the construction waste for building projects once detail design is carried out for new build or major retrofitting works. The estimation of waste quantities is based on the actual design information available from tender or contract documentation for a project at the upstream stage (a full set of bills of quantities classified under standard format). The proposed methodology of aggregating wastages accruing to quantified elements for a complete building has its advantages over a ball park figure established through indexing or other methods as proposed in existing literature, in terms of ensuring accuracy and maximizing the use of available design information whilst the workflow is uninterrupted. Three representative case studies with different formwork and facade systems are depicted to highlight the significant effects on waste generation in otherwise similar construction projects.

A substantial amount of ash is produced after the incineration of sewage sludge which is difficult to manage. Its potential use as a cost-effective adsorbent for heavy metals is beneficial to both waste management and wastewater treatment. In this study, the adsorption kinetics, isotherms as well as the factors influencing the adsorption performance were assessed through batch sorption experiments. The results show that incinerated sewage sludge ash (ISSA) was effective in adsorbing Pb(II) from aqueous solution in a wide pH range (3.00–6.00) due to the combined contributions of ion exchange, precipitation and complexation, which was confirmed by systematic investigation through XRD, SEM-EDX, FTIR, XPS and a sequential extraction procedure (SEP) for Pb(II). Nonetheless, the adsorption of Pb(II) by ISSA would be adversely affected by high ionic strength. The sorption process was fast, and the equilibrium data could be well described by the Langmuir model, the maximum uptake capacity for Pb(II) increased with temperature and the calculated adsorption capacities at 298, 308 and 318 K for Pb(II) were 58.28, 60.06 and 62.42 mg/g, respectively. These findings indicate the ISSA can be recognized as a high-performance adsorbent for Pb(II) removal in wastewater treatment applications.

Waste composition analysis is essential for implementing appropriate management strategies. In Hong Kong, on-site waste quantification is often not practical due to site space limitation at construction sites. In addition, as the construction waste problem urgently needs addressing, reliable waste generation rates need to be derived over a short time. To address these two issues, this study presents an off-site snapshot methodology for estimating construction waste composition. Three construction sites, at the initial stage, mid-stage, and end stage respectively, are selected for illustrating the proposed snapshot methodology. It is found that the composition of inert and non-inert waste varies significantly at different construction stages. Non-inert waste is an important component of building construction waste, of which wood & timber waste contributes the largest proportion. Following wood & timber waste, metal waste is the second largest source of non-inert waste. Results show that the proposed off-site snapshot methodology can sufficiently solve the problem of limited on-site sorting space and derive reliable detailed waste generation information over a certain short time.

Municipal solid waste incinerator fly ash (IFA) is categorized as a hazardous waste, which requires proper treatment prior to landfilling due to its high concentrations of toxic elements. This study developed an innovative and cleaner method for stabilization/solidification (S/S) of IFA by the incorporation of supplementary cementitious materials (SCMs) and green stabilizers. Quantitative X-ray diffraction and thermogravimetric analyses indicated that toxic elements in IFA inhibited the cement hydration. Therefore, the single use of cement (10 wt%) was not efficient for the immobilization of toxic elements, especially for Pb. The incorporation of SCMs (20 wt% of binder) such as silica fume facilitated the formation of additional cement hydrates and reduced Pb leachability by 36.3%. The addition of green stabilizers such as potassium dihydrogen phosphate (KDP) and wood waste-derived biochar also improved the immobilization of toxic elements. KDP directly combined with Pb2+ to form a precipitate of Pb3(PO4)2, whereas biochar promoted the generation of cement hydrates for S/S via the effect of internal curing. The incorporation of silica fume (40 wt%) in the binder was the most effective. Overall, this study demonstrated that the selected green binders can serve as low-carbon and high-efficient material for S/S of hazardous ash residue such as IFA.

Stabilization/solidification (S/S) is a low-cost and high-efficiency remediation method for contaminated soils, however, conventional cement-based S/S method has environmental constraints and sustainability concerns. This study proposes a low-carbon, cement-free, clay-based approach for simultaneous S/S of As and Pb in the contaminated soil, and accordingly elucidates the chemical interactions between alkali-activated clay binders and potentially toxic elements. Quantitative X-ray diffraction and 27Al nuclear magnetic resonance analyses indicated that the addition of lime effectively activated the hydration of kaolinite clay, and the presence of limestone further enhanced the polymerization of hydrates. X-ray photoelectron spectroscopy showed that approximately 19% of As[III] was oxidized to As[V] in the alkali-activated clay system, which reduced toxicity and facilitated immobilization of As. During the cement-free S/S process, As and Pb consumed Ca(OH)2 and precipitated as Ca3(AsO4)2·4H2O and Pb3(NO3)(OH)5, respectively, accounting for the low leachability of As (7.0%) and Pb (5.4%). However, the reduced amount of Ca(OH)2 decreased the degree of hydration of clay minerals, and the pH buffering capacity of the contaminated soil hindered the pH increase. Sufficient dosage of lime was required for ensuring satisfactory solidification and contaminant immobilization of the clay-based S/S products. The leachability of As and Pb in high-Ca S/S treated soil samples was reduced by 96.2% and 98.8%, respectively. This is the first study developing a green and cement-free S/S of As- and Pb-contaminated soil using clay minerals as an environmentally compatible binding material. Keywords: Green/sustainable remediation, Low-carbon contaminant immobilization, Calcined clay, Alkali-activated materials, Waste valorization/recycling, Arsenic/lead leachability

The use of waste glasses as aggregates in cementitious materials provides a viable recycling option to alleviate the burden on landfills in Hong Kong. More interestingly, the light-transmitting properties of glass are beneficial to augment the TiO2-mediated photocatalytic activity. This study attempted to take full advantage of glass aggregate (GA) by attaching nano TiO2 particles on its surface. NaOH etching was employed to pre-treat the surface of GA in order to increase its surface area before TiO2 particles were attached. The experimental results showed that the treatment of NaOH etching effectively induced cracks and pores on the initially smooth surface of GA. As a result, a higher amount of nano TiO2 particles (0.0434 g per 50 g of GA) were attached/absorbed on the surface of the treated GA compared to the untreated analogue (0.0224 g per 50 g of GA) when immersed in 10 g L−1 TiO2 solutions. More importantly, the higher TiO2 absorption ability of the treated GA translated into a higher photocatalytic NOx removal activity. Compared with the untreated GA-TiO2 composites, the NaOH etched GA-TiO2 composites (immersed in 1 g L−1 TiO2 solutions) experienced an approximately 60% increase in the photocatalytic NOx removal efficiency. The overall findings revealed that compared with the sand-TiO2 composites, the NaOH etching treated GA-TiO2 composites not only garnered the beneficial effect from the light-transmitting of glass but also had the beneficial etching effect of NaOH treatment. Therefore, the developed NaOH etched GA-TiO2 composites hold great potential for applications in cementitious photocatalytic materials.

Waste timber formwork from construction sites was used as fibre to prepare wood-magnesium oxychloride cement (MOC) board. The effect of wood fibre content, pulverized fly ash (PFA) and incinerated sewage sludge ash (ISSA) on the mechanical and durability properties of wood-MOC board was investigated. Greenhouse gases (GHGs) emission, one of the representative and most globally concerned environmental impacts, for the production of different types of composite boards was assessed and compared by using lifecycle assessment (LCA) technique. The ‘cradle-to-gate’ system boundary with 1 kg of board production was considered as the functional unit in this assessment. The result showed that the wood-MOC composites prepared with a higher content of wood fibre had a lower thermal conductivity, higher flexural strength, higher residual flexural strength after exposure to high temperatures and water immersion, and better noise reduction effect. Even though the water absorption was increased with the increase of wood fibre content, it can still be considered to be low. The wood -MOC composites incorporating ISSA showed higher flexural strength, better high temperature resistance and better water resistance than other composites. In addition, the production of the wood MOC board induces lower GHGs emission than plywood and lower human toxicity than conventional resin-based particleboard.

Immense global generation of food waste calls for advanced technologies to maximize the use of such renewable carbon-based resources. In this study, corn, taro, lettuce, and bean sprout, were valorized for the production of value-added chemicals via sequential supercritical CO2 (scCO2) extraction and thermochemical conversion. The scCO2 extraction was performed at 350 bar and 50 °C for 60 min. The extracts of the lettuce contained sterols (764 μg g–1) that have potential anticancer properties. While bean sprout extracts had a higher content of saturated fatty acids (641 μg g–1), corn extracts comprised polyunsaturated fatty acids (405 μg g–1) as one of the major compounds, which are beneficial to cholesterol control. There were also notable amounts of wax esters (75–774 μg g–1) in these food waste extracts. Taro extracts were rich in both saturated (2313 μg g–1) and unsaturated fatty acids (1605 μg g–1) and, in particular, contained difatty acids that exhibit pharmaceutical activities. Moreover, the solid residues after scCO2 extraction served as the substrates for platform chemical production. The starch-rich substrates, i.e., taro and corn, resulted in 11–20% hydroxymethylfurfural (HMF) after microwave heating at 140 °C for 5–10 min using SnCl4 catalyst. In comparison, due to the high fiber content, lettuce and bean sprout required a higher temperature of 170–190 °C for chemical decomposition over H2SO4, generating a levulinic acid yield of ∼7%, in company with glucose and fructose as the coproducts. This study on the combined technologies suggested good compatibility between scCO2 extraction and subsequent thermochemical conversion, producing a wide spectrum of value-added chemicals from biomass waste. We herein highlight the vast potential of integrated technologies for food waste valorization in achieving sustainable and carbon-efficient biorefineries.

In recent years, the government and community have focused extensive attention on food waste recycling to achieve sustainable waste management. However, the motivation of stakeholders from the commercial and industrial sector to change recycling behaviour has not received enough attention. This study aimed to identify, prioritise, and quantify the relationships between key latent variables that affect the food waste recycling behaviour of relevant industries in Hong Kong (i.e. representatives from the hotel, food and beverages, and property management industries). This study integrated semi-structured interviews and a survey questionnaire on the basis of the Theory of Planned Behaviour, setting it apart from conventional studies on food waste behavioural factors. Qualitative content analysis and quantitative structural equation modelling were performed to analyse the interview and questionnaire responses, followed by correlation analysis to quantify the relationships between variables. The results demonstrate that food waste recycling behaviour is determined by three latent variables—administrative incentives and corporate support, logistics and management incentives, and economic incentives. Administrative incentives and corporate support demonstrate significant effects on recycling behaviour. Moral attitudes show a strong positive correlation with administrative incentives and corporate support. Similarly, there is a significant positive correlation between moral attitudes and logistics and management incentives. Administrative incentives and corporate support is the determining variable for the hotel and food and beverages industries, whereas logistics and management incentives are of the highest concern to property management representatives. These findings can facilitate the development of stakeholder-oriented policy to encourage corporate behavioural change towards food waste recycling for sustainable resource circulation.

Prefabrication is considered an important solution to tackle the issues of construction waste generation, and the high-risk and labour-intensive activities associated with conventional construction methods. This study assesses the key hindrances of adopting prefabrication and provides recommendations for promoting prefabrication in Hong Kong. Twenty-two hindrances were identified in the literature and classified in six groups. A questionnaire survey and face-to-face interviews were conducted to examine the level of importance of the barriers, and to provide comprehensive analyses of each hindrance. The most significant hindrances were “Inflexible for design change”, “Lack storage space on site”, “Long lead-in time”, “Long design time”, “High initial cost” and “High total cost”. Based on the findings of the survey and interviews, six recommendations were proposed to promote the usage of prefabrication in Hong Kong such as “Just-In-Time management”, “BIM technology”, “Legislation for refabrication”, “Potential government measures”, “Encouragement of design and building procure” and “Increase the consumer's confidence”.

Stabilization/solidification (S/S) is a low-cost and time-efficient method for soil remediation, however, delayed hydration reactions and high carbon footprint are major limitations for the treatment of high-Pb contaminated soil. This study develops a novel and low-carbon approach that combines ground granulated blast furnace slag (GGBS) and ordinary Portland cement (PC) with phosphate-/sulphate-rich byproducts to produce low-alkalinity, high-compatibility, high-strength binary cement (BC) for S/S process. Results show that contaminated soil with a large fraction of exchangeable and soluble Pb (e.g., shooting range sites) severely disturbed the formation of hydration products in conventional S/S treatment, whereas BC system could mitigate the Pb interference via precipitation and sorption evenly distributed on the BC hydrates as shown by elemental mapping. Thus, BC presented superior environmental performance in terms of toxicity characteristic leaching procedure (TCLP) and semi-dynamic leaching tests, which were substantiated by quantitative X-ray diffraction and thermogravimetric analyses. The addition of potassium dihydrogen phosphate reduced TCLP leachability of Pb by 86.9% and Pb diffusion coefficients by 69.4% due to the formation of insoluble Pb3(PO4)2. Similarly, incinerated sewage sludge ash enhanced Pb stabilization, whereas waste phosphogypsum increased early strength via precipitation of PbSO4, although the effectiveness of physical encapsulation was compromised due to reduction in hydration products. Therefore, the proposed binary binders with selected additives present a new and low-carbon S/S treatment for high-Pb shooting range soil remediation.

In this work, glucose isomerization to fructose was conducted via a solid base biochar catalyst derived from spent coffee grounds and melamine. The X-ray photoelectron spectroscopy spectra identified the majority of pyridinic nitrogen on the biochar surface, which imparted the strong base character of the catalyst. Activity of the catalyst was evidenced by fast conversion of glucose (12%) and high selectivity to fructose (84%) in 20 min at a moderate temperature (120 °C) compared to recently reported immobilized tertiary amines at comparable N concentrations (10–15 mol % relative to glucose). By increasing the reaction temperature to 160 °C, fructose yield achieved 14% in 5 min. The base biochar catalyst showed superior selectivity (>80%) to commonly used homogeneous base catalysts, such as aqueous hydroxides and amines (50–80%) and comparable catalytic activity (∼20 mol % conversion within 20 min). Moreover, cosolvent of acetone in the reaction system may increase the overall basicity by stabilizing prot...

Management of dredged sediment has been a worldwide challenge. Conventional off-site marine disposal of contaminated sediment incurs substantial cost implications and secondary pollution risks. This study developed value-added and time-effective approaches that transform contaminated sediment into construction materials to be used as fill materials, partition blocks, and paving blocks. The technical viability and economic feasibility of different binder/mixture designs and production methods were assessed. Thermogravimetric and X-ray diffraction analyses showed that contaminated sediment hindered hydrates formation and adversely influenced the properties of sediment-based products. Samples with 5 wt% binder could only fulfil strength requirements of fill materials. Tailored mixture designs with dry-mix/press method improved the precipitation reactions and densified the porous structure, which enhanced the performance and conformed to the requirements of partition blocks and even paving blocks. The leaching concentrations of potentially toxic elements and organic contaminants from the dredged sediment were substantially reduced by stabilization/solidification, which satisfied the leachability acceptance criteria for its on-site reuse. Moreover, cost and benefit assessment illustrated that the production of all three studied sediment-based products was potentially profitable, of which the scenario recycling sediment into paving blocks showed the highest profit. This novel solution can effectively mitigate burden of dredged sediment disposal and produce green construction materials in a sustainable way.

Management of incinerated sewage sludge ash (ISSA) and dredged contaminated marine sediments (CMSs) is a great challenge for Hong Kong and other coastal cities due to limited landfilling capacity. The present study investigates the use of high content (20% of sediment by mass) of ISSA in combination with cement/lime for solidification/stabilization (S/S) treatment of CMSs to provide a way to reuse the wastes as construction materials. The results showed that ISSA being a porous material was able to absorb a large amount of water rendering a more efficient solidification process of the marine sediment which normally had a very high water content (∼80%). The S/S treatment improved the engineering properties of the sediment, but reduced the workability, especially for the lime-treated samples. Lime can be used to replace ordinary Portland cement (OPC) for better heavy metal immobilization and carbon emission reduction. The hardened sediment samples prepared with 10% of lime and 20% of ISSA could attain a strength of 1.6 MPa after 28 d of curing. In addition, leaching tests confirmed that there was no environmental risk induced by these stabilized materials. The formation of hydrated cementitious compounds including calcium silicate hydrate (C–S–H)/calcium aluminate silicate hydrate (C-A-S-H)/hydrocalumite/calcite was mainly responsible for the strength development in the ISSA/lime-treated sediments.

Exploring effective uses of waste concrete powder (WCP), produced from recycling of construction & demolition waste is beneficial to the environment and sustainable development. In this study, WCP was first treated thermally to enhance the ability to remove Pb (II) from aqueous solutions. The experimental results revealed that the thermal treatment could enhance adsorption capacity due to modification of calcium bonding and pore structure of WCP. Preparation parameters such as temperature, particle size, and water-cement ratio were investigated to obtain the optimal operational conditions. Batch adsorption experiments were performed to explore influence factors of pH (1.00–6.00), ionic strength (0.05–2 mol/L), dosage (2–50 g/L), and temperature (25–45 °C). The pseudo-second-order kinetics model could adequately describe the adsorption process, and the Langmuir model was capable to predict the isotherm data well in the low concentration region (C0

With rapid economic growth and urbanisation, the reuse and recycling of solid wastes has become a high priority for the sustainable development of modern cities. In this study, two typical solid wastes, incinerated sewage sludge ash (ISSA) and waste bentonite, were co-valorised to produce granular adsorbents through a simple and energy-saving pelletisation/sintering process. A mixture of ISSA and bentonite at a weight ratio of 3:1 was pelletised and sintered at 700 °C. The resultant ceramsite, with good mechanical strength, could effectively remove Pb(Ⅱ) from aqueous solutions. The adsorption kinetics can be described by the pseudo-first-order (PFO) model. The results indicated that the Pb(Ⅱ) adsorption process was dominated by electrostatic attraction, precipitation, and complexation. The isothermal data exhibited a good correlation with the Freundlich model, indicating that the adsorption process was non-ideal and spontaneous. The maximum adsorption capacity was approximately 21.6 ± 0.35 mg/g at 318 K. After 5 cycles of regeneration, the adsorbent maintained good adsorption performance. Moreover, the removal rate was not greatly affected by ionic strength. These findings demonstrate that the granular adsorbent prepared with ISSA and waste bentonite can be recognised as a promising adsorbent for Pb-containing wastewater treatment.

The accumulation of heavy metal tailings has caused serious environmental and geological concerns. Therefore, treatment and recycling of heavy metal tailings have become urgent and vital. To this end, this paper proposes a biological solidification and stabilization (S/S) method, which applies enzymatically induced phosphate precipitation (EIPP) to strengthen Pb-Zn tailings and reduce the hazard of the heavy metals. The effectiveness and mechanism of EIPP-S/S have been systematically explored, including the effect of enzyme and reactant concentration, and tailings density on the treatment efficiency. The results showed that MgHPO4(H2O)3 (newberyite) and Pb9(PO4)6 were the main products of EIPP. The newberyite strengthened the tailings through connecting tailing particles and filling the pores, and the solidification effect was positively related to the reactant content and tailing compactness. The strength of the treated tailing sample could reach 2.7 MPa at a relative density of 90% with a reactant concentration of 1.5 M. After treatment, about 40% of Pb in the tailings changed from an acid-soluble state to oxidation state and residual state, as a result of the precipitation of Pb9(PO4)6. The concentration of leached Pb from the treated tailings under an acid rain environment was reduced from 0.86 mg/L before treatment to less than 0.02 mg/L, well below the limit of 0.1 mg/L in China’s ground/surface water. This study provides new insights into the treatment and reuse of tailings by applying an innovative EIPP-S/S method, which can flexibly treat tailings in an environmentally friendly manner.

Finding suitable disposal sites for dredged marine sediments and incinerated sewage sludge ash (ISSA) is a challenge. Stabilisation/solidification (S/S) has become an increasingly popular remediation technology. This study sheds light on the possible beneficial use of ISSA together with traditional binders to stabilise/solidify marine sediments. The performance of the binders on S/S of sediment 1 (clean) and sediment 2 (contaminated) was also compared. The results showed that the use of ISSA as part of the binder was effective in promoting the strength of the sediment with a high initial moisture content due to ISSA porous and high water absorption characteristics. The sediments treated with 10% cement and 20% ISSA attained the highest strength. Also, cement hydration as well as pozzolanic reactions between ISSA and Ca(OH)2 made contributions to the strength development. This was supported by the microstructural analysis, in particular the porosity results. In terms of environmental impacts, two leaching tests (toxicity characteristic leaching procedure and synthetic precipitation leaching procedure) found that all the S/S treated sediment by 10% lime and 20% ISSA resulted in the lowest leachate concentrations under the on-site reuse scenario or under simulative acidic rainfall conditions. Therefore, recycling waste ISSA with lime can be used as an appealing binder to replace cement to stabilise/solidify dredged marine sediments for producing fill materials.

Mortar made from concrete slurry waste (CSW) and municipal solid waste incineration bottom ash (MSWIBA) could be recycled into cold bonded lightweight aggregates (CBLA). However, the mechanism by which the CSW-MSWIBA mortar hardened and developed strength remains unexplored. Furthermore, the investigation in the previous study was limited to using the CBLA for wet precast lightweight concrete (LWC). Understanding the characteristic of CSW-MSWIBA mortar and exploring a new application of CBLA can promote the larger-scale recycling of CSW and MSWIBA. Herein, an investigation was performed on assessing the multi-component characteristics of CSW-MSWIBA mortar. The results showed that using MSWIBA (i.e., as compared to river sand) in CSW was advantageous for lower density and higher compressive strength of the mortar. The strength development of hardening CSW-MSWIBA mortar could largely be ascribed to the continuous cement hydration of CSW and the pozzolanic reaction between MSWIBA and CSW providing a better bonding at the CSW-MSWIBA interface. Following a pelletization process, the CSW-MSWIBA mortar was turned into cold bonded lightweight aggregates (CBLA). Through a trial of industrial-scale production, the CBLA were then used to fabricate semi-dry precast LWC, which met the LWC and masonry unit requirements as per BS EN 206 or JGJ/T 12 and BS 8103, respectively.

The disposal of sewage sludge ash (SSA) has become an environmental issue due to the limited available landfill space. This study aims at applying the finely-ground sewage sludge ash (FSSA) with quicklime and hydrated lime to develop a new type of lime-pozzolan system and study the effects of different types of lime on the mechanical properties of the systems. A traditional pozzolanic material (i.e. coal fly ash (FA)) was also used to compare with the FSSA. Multiple techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) were used to assess the hydration kinetics and microscopic characteristics of the lime-pozzolan systems. The results showed that the quicklime system exhibited lower strength than the hydrated lime system, which was due to its lower reaction degree with the FSSA and the higher porosity caused by the expansion during the vigorous hydration reaction of quicklime. Compared to FA, the FSSA attained higher strength for the whole curing period (up to 90 d) in the lime system due to the highly porous nature of FSSA leading to a lower effective water to binder ratio. However, in the hydrated lime system, due to the higher overall pozzolanic activity of FA, its long-term strength values gradually improved. Besides, calcium phosphate hydrate crystals were detected by XRD in the FSSA; while some clinotobermorite was found in the FA both from XRD and SEM, which might govern the strength gain in the lime-FA system. Overall, the application of FSSA as a pozzolan in the lime-pozzolan system could be a promising option to both relieve the waste disposal pressure and provide a potential sustainable construction material.