A holistic framework of biochar-augmented cementitious products and general applications: Technical, environmental, and economic evaluation.

In the context of the circular economy, the development of innovative and low-carbon concrete that incorporates different kinds of waste materials is gaining attention among the research community, regulatory agencies, and policymakers. These materials can be incorporated into concrete mixtures as aggregates or as fillers for improvement of product properties. This study aims to identify reliable designs for biochar-augmented cementitious products and general applications through technical, environmental, and economic assessments. The outcomes demonstrate that 5 wt% biochar addition could enhance the compressive strength of the final products. Using biochar, together with other recycled materials, can enormously reduce the environmental impacts, especially for global warming, enabling biochar-augmented cementitious products and general application as carbon-negative resources. The highest GWP reduction reached -720 kg CO2/tonne, equal to a 200% saving. A high quantity of biochar could be included in several specific applications (up to 60 wt%). The economic assessment highlights that the proposed designs are cost-effective and carbon tax can be significantly reduced. Carbon credits can also be earned for some carbon-negative designs. These findings can serve to mitigate GHG emissions and provide decision-makers with a reliable and holistic framework towards the goal of carbon neutrality.

Recent advancements and challenges in emerging applications of biochar-based catalysts.

The sustainable utilization of biochar produced from biomass waste could substantially promote the development of carbon neutrality and a circular economy. Due to their cost-effectiveness, multiple functionalities, tailorable porous structure, and thermal stability, biochar-based catalysts play a vital role in sustainable biorefineries and environmental protection, contributing to a positive, planet-level impact. This review provides an overview of emerging synthesis routes for multifunctional biochar-based catalysts. It discusses recent advances in biorefinery and pollutant degradation in air, soil, and water, providing deeper and more comprehensive information of the catalysts, such as physicochemical properties and surface chemistry. The catalytic performance and deactivation mechanisms under different catalytic systems were critically reviewed, providing new insights into developing efficient and practical biochar-based catalysts for large-scale use in various applications. Machine learning (ML)-based predictions and inverse design have addressed the innovation of biochar-based catalysts with high-performance applications, as ML efficiently predicts the properties and performance of biochar, interprets the underlying mechanisms and complicated relationships, and guides biochar synthesis. Finally, environmental benefit and economic feasibility assessments are proposed for science-based guidelines for industries and policymakers. With concerted effort, upgrading biomass waste into high-performance catalysts for biorefinery and environmental protection could reduce environmental pollution, increase energy safety, and achieve sustainable biomass management, all of which are beneficial for attaining several of the United Nations Sustainable Development Goals (UN SDGs) and Environmental, Social and Governance (ESG).

Life-cycle assessment of pyrolysis processes for sustainable production of biochar from agro-residues.

Net carbon management of agro-residues has been an important pathway for reducing the environmental burdens of agricultural production. Converting agro-residues into biochar through pyrolysis is a prominent management strategy for achieving carbon neutrality in a circular economy, meeting both environmental and social concerns. Based on the latest studies, this study critically analyzes the life cycle assessment (LCA) of biochar production from different agro-residues and compares typical technologies for biochar production. Although a direct comparison of results is not always feasible due to different functional units and system boundaries, the net carbon sequestration potential of biochar technology is remarkably promising. By pyrolyzing agro-residues, biochar can be effectively produced and customized as: (i) alternative energy source, (ii) soil amendment, and (iii) activated carbon substitution. The combination of life cycle assessment and circular economy modelling is encouraged to achieve greener and sustainable biochar production.

GenX is not always a better fluorinated organic compound than PFOA: A critical review on aqueous phase treatability by adsorption and its associated cost.

Hexafluoropropylene oxide dimer acid (GenX) has been marketed as a substitute for perfluorooctanoic acid (PFOA) to reduce environmental and health risks. GenX and PFOA have been detected in various natural water sources, and adsorption is recognized as a typical treatment process for PFOA removal. In this paper, comparisons of GenX and PFOA adsorption are evaluated, including adsorption potential, adsorption mechanisms, and associated costs. A detailed literature review suggests that anion-exchange resins are more effective in removing GenX than activated carbon. GenX removal efficiency through activated carbon (30%) is lower than that of PFOA (80-95%), while GenX and PFOA removal efficiencies by anion exchange resins are similar (99%). Unconventional adsorbents, such as ionic fluorogels and covalent organic frameworks can effectively remove GenX from water. The review reveals that GenX adsorption is more challenging, requiring almost 4 times the treatment cost of its predecessor, PFOA. Annual operation and maintenance costs for GenX adsorption (initial concentration of GenX and PFOA = 0.2 µg.L-1) by GAC for treating 10,000 m3 per day is almost US$1,000,000 per year, but only around US$240,000 per year for PFOA. Desorption of GenX in the presence of PFOA highlights GenX's inferior treatability by adsorption. It is believed that GenX is a more environmentally friendly compound than PFOA, but this environmental friendliness comes with the price.

Environmental fate, toxicity and risk management strategies of nanoplastics in the environment: Current status and future perspectives.

Tiny plastic particles considered as emerging contaminants have attracted considerable interest in the last few years. Mechanical abrasion, photochemical oxidation and biological degradation of larger plastic debris result in the formation of microplastics (MPs, 1 µm to 5 mm) and nanoplastics (NPs, 1 nm to 1000 nm). Compared with MPs, the environmental fate, ecosystem toxicity and potential risks associated with NPs have so far been less explored. This review provides a state-of-the-art overview of current research on NPs with focus on currently less-investigated fields, such as the environmental fate in agroecosystems, migration in porous media, weathering, and toxic effects on plants. The co-transport of NPs with organic contaminants and heavy metals threaten human health and ecosystems. Furthermore, NPs may serve as a novel habitat for microbial colonization, and may act as carriers for pathogens (i.e., bacteria and viruses). An integrated framework is proposed to better understand the interrelationships between NPs, ecosystems and the human society. In order to fully understand the sources and sinks of NPs, more studies should focus on the total environment, including freshwater, ocean, groundwater, soil and air, and more attempts should be made to explore the aging and aggregation of NPs in environmentally relevant conditions. Considering the fact that naturally-weathered plastic debris may have distinct physicochemical characteristics, future studies should explore the environmental behavior of naturally-aged NPs rather than synthetic polystyrene nanobeads.

Biochar Aging: Mechanisms, Physicochemical Changes, Assessment, And Implications for Field Applications.

Biochar has triggered a black gold rush in environmental studies as a carbon-rich material with well-developed porous structure and tunable functionality. While much attention has been placed on its apparent ability to store carbon in the ground, immobilize soil pollutants, and improve soil fertility, its temporally evolving in situ performance in these roles must not be overlooked. After field application, various environmental factors, such as temperature variations, precipitation events and microbial activities, can lead to its fragmentation, dissolution, and oxidation, thus causing drastic changes to the physicochemical properties. Direct monitoring of biochar-amended soils can provide good evidence of its temporal evolution, but this requires long-term field trials. Various artificial aging methods, such as chemical oxidation, wet-dry cycling and mineral modification, have therefore been designed to mimic natural aging mechanisms. Here we evaluate the science of biochar aging, critically summarize aging-induced changes to biochar properties, and offer a state-of-the-art for artificial aging simulation approaches. In addition, the implications of biochar aging are also considered regarding its potential development and deployment as a soil amendment. We suggest that for improved simulation and prediction, artificial aging methods must shift from qualitative to quantitative approaches. Furthermore, artificial preaging may serve to synthesize engineered biochars for green and sustainable environmental applications.

Evaluating the environmental impacts of stabilization and solidification technologies for managing hazardous wastes through life cycle assessment: A case study of Hong Kong.

Proper management of hazardous materials arouses widespread environmental concerns due to its enormous ecological and health impacts. The development of green stabilization/solidification (S/S) technology for resourceful utilization of hazardous materials, as well as the immobilization of potentially toxic elements is of great scientific interests. Cement-based S/S is often considered a low-cost and highly efficient technology, but the environmental sustainability of a broad spectrum of S/S technologies has yet to be evaluated. Therefore, this study assessed the environmental sustainability of S/S technologies for managing two common types of hazardous wastes, i.e., contaminated marine sediment and municipal solid waste incineration fly ash (MIFA) by using life cycle assessment (LCA). A total of 17 scenarios under three strategies for sediment and two strategies for MIFA S/S technologies were comprehensively evaluated. The LCA results identified the most preferable S/S technology in each strategy. In particular, Scenario 1 (mixture of sediment with a small percentage of ordinary Portland cement and incinerated sewage sludge ash) of Strategy 1 (use as fill materials) would be the preferred option, as it reduces about 54% and 70% global warming potential compared to those of Scenarios 2 and 3, respectively. This is the first initiative for evaluating the environmental impacts of a wide range of recently developed S/S technologies using green/alternative binders for diverting hazardous wastes from disposal. The results can serve as a decision support for the practical application of the environmentally friendly S/S technology for sustainable remediation.

Thallium contamination, health risk assessment and source apportionment in common vegetables.

As an element with well-known toxicity, excessive thallium (Tl) in farmland soils, may threaten food security and induce extreme risks to human health. Identification of key contamination sources is prerequisite for remediation technologies. This study aims to examine the contamination level, health risks and source apportionment of Tl in common vegetables from typical farmlands distributed over a densely populated residential area in a pyrite mine city, which has been exploiting Tl-bearing pyrite minerals over 50 years. Results showed excessive Tl levels were exhibited in most of the vegetables (0.16-20.33 mg/kg) and alarming health risks may induce from the vegetables via the food chain. Source apportionment of Tl contamination in vegetables was then evaluated by using Pb isotope fingerprinting technique. Both vegetables and soils were characterized with overall low 206Pb/207Pb. This indicated that a significant contribution may be ascribed to the anthropogenic activities involving pyrite deposit exploitation, whose raw material and salgs were featured with lower 206Pb/207Pb. Further calculation by binary mixing model suggested that pyrite mining and smelting activities contributed 54-88% to the thallium contamination in vegetables. The results highlighted that Pb isotope tracing is a suitable technique for source apportionment of Tl contamination in vegetables and prime contamination from pyrite mining/smelting activities urges authorities to initiate proper practices of remediation.

Groundwater depletion and contamination: Spatial distribution of groundwater resources sustainability in China.

China is facing a groundwater depletion and deterioration crisis, culminating from long-term over-exploitation and groundwater contamination. Aggravating factors include population growth, unprecedented urbanization and climate change. Sustainable groundwater management is called for, however, a valid means for a national-scale assessment of groundwater resource sustainability does not currently exist. Here we present a drivers-pressures-states-impact-response (DPSIR) assessment framework. Based on this framework, groundwater sustainability indices for mainland China's 31 provinces and municipalities were derived, with an average score of 59.5 out of 100, ranging from 47.3 for Tianjin to 72.9 for Tibet. We found that due to fewer Drivers and better States, groundwater resources in southern China are far more sustainable than those in the northern and eastern areas. An appraisal of subcategories shed light on the importance of affording attention to externalities such as societal, economic and environmental factors, which are interrelated as complex systems. Based on the assessment findings, implications for policy and decision-making suggestions for sustainable management of China's groundwater resources are put forward.

Assessment of sources of heavy metals in soil and dust at children's playgrounds in Beijing using GIS and multivariate statistical analysis.

Potentially toxic elements such as heavy metals are ubiquitous in the environment. Risk-based environmental management relies upon identifying pollution sources, pathways, and the exposed population. In a Chinese urban setting, many residents live in high-rise buildings without private gardens. Therefore, the main residential risk of exposure to contaminated soils and dusts may be associated with public open spaces. As children are the most vulnerable receptor, playgrounds represent an important yet often overlooked exposure point. The present study assessed plausible sources of heavy metals at children's playgrounds in a representative metropolitan environment. Soil and equipment dust samples were collected from 71 playgrounds across Beijing, which were analyzed for 11 different heavy metals. Principal component analysis (PCA) was used to identify the latent constructs which control heavy metal variability and reflect potential sources. Cluster analysis (CA) was conducted to group sampled locations, which provided further insights on plausible sources. The main factors extracted from the PCA were then subject to geostatistical analysis. The systematic combination of GIS with multivariate statistical analysis proved valuable for elucidating anthropogenic and natural sources. Elevated Be, V, Cr, Mn, Co, Ni, As in playground soils were found to derive mainly from the natural background (spatial autocorrelation = 2 km), while elevated Cu and Pb was attributed to traffic activities (spatial autocorrelation = 17 km), especially along the routes of Beijing's inner ring-roads, the major roads toward the northwest and northeast, and the international airport. These results suggest that heavy metals in playground equipment dust may derive mainly from atmospheric deposition of air pollution of both natural and anthropogenic origin (spatial autocorrelation = 11-13 km). Among them, Be, V, Mn, Co, Cu, As, Pb were attributed to atmospheric pollution deriving from the north of Beijing, brought by the prevailing northern wind in the winter season; whereas, Cr and Ni may possibly be brought from the southeast by the summer season winds. Knowledge of anthropogenic vs. natural origins of heavy metals in playgrounds is critical in assessing health impact and designing policy instruments for metropolitan areas.

Multimedia modeling of the PAH concentration and distribution in the Yangtze River Delta and human health risk assessment.

Emissions of polycyclic aromatic hydrocarbons (PAHs) in China remain at a high level compared to those in developed countries. The Yangtze River Delta (YRD) is an economic and industrial center in China with an extremely large population. The potentially high emissions and excess cancer risk from human exposure in this region cannot be neglected. This study applied a multimedia model to estimate the concentrations of 16 US EPA priority PAHs in the environment in the YRD with a well-developed PAH-emission inventory for 2014. The model predicted that the average concentrations of ΣPAHs were 274 ng/m3 in the air, 255 ng/g in the soil, 15 ng/g in vegetation, 147 ng/L in freshwater and 144 ng/g in sediment, as well as 99 ng/L and 80 ng/g in seawater and sediment, respectively. Soil is the PAH sink in this region, and the net flux of the total PAHs is always from air to soil for each isomer. A deterministic assessment observed that the ELCR (excess lifetime cancer risk) ranged from 2.5 × 10-6 to 3.0 × 10-5 for exposure by air inhalation and from 3.5 × 10-7 to 7.9 × 10-6 for exposure by soil ingestion. The probabilistic results did not find any probability of ELCR >10-4 by exposure via soil ingestion in the YRD. The probabilistic ELCR induced by inhalation exposure varied from 8.1 × 10-7 to 3.1 × 10-4 in the YRD. This study provided a comprehensive overview of PAHs occurrence in natural environments and of the relevant human health risks. The information presented in this study could help authorities to enact a strategy regarding emission reduction and pollution control relevant to PAHs. CAPSULE: Multimedia modeling predicted distributions and compositions of PAHs in different environmental compartments, and deterministic and probabilistic ELCRs induced by air inhalation and soil ingestion were also provided.

Phthalate esters and organochlorine pesticides in agricultural soils and vegetables from fast-growing regions: a case study from eastern China.

The present study investigated phthalate esters (PAEs) and organochlorine pesticides (OCPs) in agricultural soils and vegetables from eastern China. The concentrations of PAEs ranged from 109 to 5560 ng/g in soils and 60.1 to 2390 ng/g in cabbages, with average concentrations of 946 and 601 ng/g, respectively. The concentrations of OCPs ranged from <0.1 to 662 ng/g in soils and <0.1 to 42.8 ng/g in cabbages, with average concentrations of 134 and 11.6 ng/g, respectively. OCPs were mainly in the 0-30 cm surface soil layers, while PAEs could infiltrate in deep soil profiles to 70-80 cm layer. Potential source analysis traced the occurrence of OCPs to both historical application and current usage, whereas building materials and agricultural plastic film were possible input sources of PAEs in the ambient environment. OCPs showed no apparent effect on soil microbial communities, whereas significant negative relationship was observed between PAEs and fungi in soils (R = -0.54, p < 0.01). Human health risk assessment data revealed marginal noncarcinogenic risks and low carcinogenic risks in these soils. Notably, PAEs posed a comparable or higher risk level compared with that of OCPs. This study suggests the need for better regulation on pollution control and management of PAE-elevated sites to protect soil quality and food safety.

Successful control of internal phosphorus loading after sediment dredging for 6years: A field assessment using high-resolution sampling techniques.

The effectiveness of sediment dredging for the control of internal phosphorus (P) loading, was investigated seasonally in the eutrophic Lake Taihu. The high-resolution dialysis (HR-Peeper) and diffusive gradients in thin films (DGT) techniques were used to measure the concentrations of soluble Fe(II) and soluble reactive P (SRP) as well as DGT-labile Fe/P in the non-dredging and post-dredging sediments. The P resupply kinetics from sediment solids were interpreted using DGT Induced Fluxes in Sediments (DIFS) modeling. The results showed no obvious improvement in water and sediment quality after dredging for 6years, due to their geographical proximity (a line distance of approximately 9km). However, dredging significantly decreased the concentrations of soluble Fe(II)/SRP and DGT-labile Fe/P in sediments, with effects varying at different depths below the sediment-water interface; More pronounced effects appeared in January and April. The diffusive flux of pore water SRP from sediments decreased from 0.746, 4.08 and 0.353mg/m2/d to 0.174, 1.58 and 0.048mg/m2/d in April, July and January, respectively. DIFS modeling indicated that the P retention capability of sediment solids was improved in April in post-dredging site. Positive correlations between pore water soluble Fe(II) and SRP as well as between DGT-labile Fe and P, reflect the key role of Fe redox cycling in regulating dredging effectiveness. This effect is especially important in winter and spring, while in summer and autumn, the decomposition of algae promoted the release of P from sediments and suppressed dredging effectiveness. Overall, the high-resolution HR-Peeper and DGT measurements indicated a successful control of internal P loading by dredging, and the post-dredging effectiveness was suppressed by algal bloom.

Sustainability likelihood of remediation options for metal-contaminated soil/sediment.

Multi-criteria analysis and detailed impact analysis were carried out to assess the sustainability of four remedial alternatives for metal-contaminated soil/sediment at former timber treatment sites and harbour sediment with different scales. The sustainability was evaluated in the aspects of human health and safety, environment, stakeholder concern, and land use, under four different scenarios with varying weighting factors. The Monte Carlo simulation was performed to reveal the likelihood of accomplishing sustainable remediation with different treatment options at different sites. The results showed that in-situ remedial technologies were more sustainable than ex-situ ones, where in-situ containment demonstrated both the most sustainable result and the highest probability to achieve sustainability amongst the four remedial alternatives in this study, reflecting the lesser extent of off-site and on-site impacts. Concerns associated with ex-situ options were adverse impacts tied to all four aspects and caused by excavation, extraction, and off-site disposal. The results of this study suggested the importance of considering the uncertainties resulting from the remedial options (i.e., stochastic analysis) in addition to the overall sustainability scores (i.e., deterministic analysis). The developed framework and model simulation could serve as an assessment for the sustainability likelihood of remedial options to ensure sustainable remediation of contaminated sites.

Integrating EDDS-enhanced washing with low-cost stabilization of metal-contaminated soil from an e-waste recycling site.

While chelant-enhanced soil washing has been widely studied for metal extraction from contaminated soils, there are concerns about destabilization and leaching of residual metals after remediation. This study integrated 2-h soil washing enhanced by biodegradable ethylenediaminedisuccinic acid (EDDS) and 2-month stabilization using agricultural waste product (soybean stover biochar pyrolyzed at 300 and 700 °C), industrial by-product (coal fly ash (CFA)), and their mixture. After integration with 2-month stabilization, the leachability and mobility of residual metals (Cu, Zn, and Pb) in the field-contaminated soil were significantly reduced, especially for Cu, in comparison with 2-h EDDS washing alone. This suggested that the metals destabilized by EDDS-washing could be immobilized by subsequent stabilization with biochar and CFA. Moreover, when the remediation performance was evaluated for phytoavailability and bioaccessibility, prior EDDS washing helped to achieve a greater reduction in the bioavailable fraction of metals than sole stabilization treatment. This was probably because the weakly-bound metals were first removed by EDDS washing before stabilization. Both individual and combined applications of biochar and CFA showed comparable effectiveness regardless of the difference in material properties, possibly due to the high level of amendments (150 ton ha(-1)). Based on the mobility and bioaccessibility results, the estimated human health risk (primarily resulting from Pb) could be mitigated to an acceptable level in water consumption pathway or reduced by half in soil ingestion pathway. These results suggest that an integration of EDDS washing with soil stabilization can alleviate post-remediation impacts of residual metals in the treated soil.

Green remediation and recycling of contaminated sediment by waste-incorporated stabilization/solidification.

Navigational/environmental dredging of contaminated sediment conventionally requires contained marine disposal and continuous monitoring. This study proposed a green remediation approach to treat and recycle the contaminated sediment by means of stabilization/solidification enhanced by the addition of selected solid wastes. With an increasing amount of contaminated sediment (20-70%), the 28-d compressive strength of sediment blocks decreased from greater than 10MPa to slightly above 1MPa. For augmenting the cement hydration, coal fly ash was more effective than lime and ground seashells, especially at low sediment content. The microscopic and spectroscopic analyses showed varying amounts of hydration products (primarily calcium hydroxide and calcium silicate hydrate) in the presence of coal fly ash, signifying the influence of pozzolanic reaction. To facilitate the waste utilization, cullet from beverage glass bottles and bottom ashes from coal combustion and waste incineration were found suitable to substitute coarse aggregate at 33% replacement ratio, beyond which the compressive strength decreased accordingly. The mercury intrusion porosimetry analysis indicated that the increase in the total pore area and average pore diameter were linearly correlated with the decrease of compressive strength due to waste replacement. All the sediment blocks complied with the acceptance criteria for reuse in terms of metal leachability. These results suggest that, with an appropriate mixture design, contaminated sediment and waste materials are useful resources for producing non-load-bearing masonry units or fill materials for construction uses.

Mixture design and treatment methods for recycling contaminated sediment.

Conventional marine disposal of contaminated sediment presents significant financial and environmental burden. This study aimed to recycle the contaminated sediment by assessing the roles and integration of binder formulation, sediment pretreatment, curing method, and waste inclusion in stabilization/solidification. The results demonstrated that the 28-d compressive strength of sediment blocks produced with coal fly ash and lime partially replacing cement at a binder-to-sediment ratio of 3:7 could be used as fill materials for construction. The X-ray diffraction analysis revealed that hydration products (calcium hydroxide) were difficult to form at high sediment content. Thermal pretreatment of sediment removed 90% of indigenous organic matter, significantly increased the compressive strength, and enabled reuse as non-load-bearing masonry units. Besides, 2-h CO2 curing accelerated early-stage carbonation inside the porous structure, sequestered 5.6% of CO2 (by weight) in the sediment blocks, and acquired strength comparable to 7-d curing. Thermogravimetric analysis indicated substantial weight loss corresponding to decomposition of poorly and well crystalline calcium carbonate. Moreover, partial replacement of contaminated sediment by various granular waste materials notably augmented the strength of sediment blocks. The metal leachability of sediment blocks was minimal and acceptable for reuse. These results suggest that contaminated sediment should be viewed as useful resources.

Effects of solution chemistry on arsenic(V) removal by low-cost adsorbents.

Natural and anthropogenic arsenic (As) contamination of water sources pose serious health concerns, especially for small communities in rural areas. This study assessed the applicability of three industrial byproducts (coal fly ash, lignite, and green waste compost) as the low-cost adsorbents for As(V) removal under various field-relevant conditions (dissolved oxygen, As(V)/Fe ratio, solution pH, and presence of competing species). The physico-chemical properties of the adsorbents were characterized by XRD, XRF, FT-IR, and NMR analysis. Batch experiments demonstrated that coal fly ash could provide effective As(V) removal (82.1%-95%) because it contained high content of amorphous iron/aluminium hydroxides for As(V) adsorption and dissolvable calcium minerals for calcium arsenate precipitation. However, the addition of lignite and green waste compost was found unfavourable since they hindered the As(V) removal by 10%-42% possibly due to dissolution of organic matter and ternary arsenate-iron-organic matter complexes. On the other hand, higher concentrations of dissolved iron (comparing As(V)/Fe ratios of 1:1 and 1:10) and dissolved oxygen (comparing 0.2 and 6 mg/L) only marginally enhanced the As(V) removal at pH 6 and 8. Thus, addition of dissolved iron, water aeration, or pH adjustment became unnecessary because coal fly ash was able to provide effective As(V) removal under the natural range of geochemical conditions. Moreover, the presence of low levels of background competing (0.8 or 8 mg/L of humic acid, phosphate, and silicate) imposed little influence on As(V) removal, possibly because the high adsorption capacity of coal fly ash was far from exhaustion. These results suggested that coal fly ash was a potentially promising adsorbent that warranted further investigation.