Deyi Hou

Sustainable Waste and Materials Management: National Policy and Global Perspective

aste generation and resource shortages have long beenrecognized as two of the greatest challenges humansociety is facing. In the early 1970s, the Club of Rome, a groupof pioneering global thinkers, predicted in their milestone bookThe Limits to Growth that “if the present growth trends in worldpopulation...pollution ... and resource depletion continueunchanged, the limits to growth on this planet will be reachedsometime within the next one hundred years”. Since the 1970s,“sustainability” has become a key word in modern culture andhas drawn a massive increase of attention. Many countries nowconsider sustainability a top priority of their national policies onwaste and materials management. However, these policies tendto focus on each individual country and therefore may lack aglobal perspective.The United Kingdom (UK) Department for Environment,Food and Rural Affairs (Defra), in a White Paper entitled“Government Review of Waste Policy in England 2011”published June 14, 2011, sets out actions to achieve anambitious goal of “zero waste economy”. This commitmentmay be partly attributed to England’s recent success in boostingits waste recycling rate. In 2010/11, England’s household wasterecycling rate reached 40%, representing a significant increasefrom 11% in 2000/01. The commercial and industrial recyclingrate is 52%, up from 42% in 2002/03. This increase of recyclingrate is astonishing when compared to that in the United Stateswhere the municipal solid waste recycling rate only increased by5% over a decade, reaching 34% in 2010. A large portion ofUK’s recycled materials are exported to other countries,primarily countries in the Far East. Currently the UK exports15 million tonnes of recycled materials, which is equivalent toapproximately 32% of the total household and commercialwaste.While cheering for greatly improved recycling practice in theUK, we may ignore certain adverse effects associated with it, forinstance, waste and contamination transfer. The UK isexporting 80% of its low-grade mixed papers, but only 20%of its high grade paper.

Citric acid facilitated thermal treatment: An innovative method for the remediation of mercury contaminated soil

Thermal treatment is a promising technology for the remediation of mercury contaminated soils, but it often requires high energy input at heating temperatures above 600°C, and the treated soil is not suitable for agricultural reuse. The present study developed a novel method for the thermal treatment of mercury contaminated soils with the facilitation of citric acid (CA). A CA/Hg molar ratio of 15 was adopted as the optimum dosage. The mercury concentration in soils was successfully reduced from 134 mg/kg to 1.1mg/kg when treated at 400°C for 60 min and the treated soil retained most of its original soil physiochemical properties. During the treatment process, CA was found to provide an acidic environment which enhanced the volatilization of mercury. This method is expected to reduce energy input by 35% comparing to the traditional thermal treatment method, and lead to agricultural soil reuse, thus providing a greener and more sustainable remediation method for treating mercury contaminated soil in future engineering applications.

Biochar application for the remediation of heavy metal polluted land: A review of in situ field trials

Polluted land is a global issue, especially for developing countries. It has been reported that soil amendment with biochar may reduce the bioavailability of a wide range of contaminants, including heavy metal(loids), potentially reclaiming contaminated soils for agricultural use. However, there have been only limited reports on the in situ application of biochar at the field scale. This review was devoted to providing preliminary scientific evidence from these field trials, based on a review of 29 publications involving field applications of biochar in 8 different countries. The data show that biochars effectiveness in reducing the impacts of pollution depends on a myriad of factors in the field, including the application time period, site-specific factors (e.g. climate, biochar dosage rate, and mixing depth), biochar feedstock type, and biochar properties. The results of this review indicate that biochar application can potentially reduce contaminant bioavailability in the field; for instance, a significant decrease (control normalized mean value=0.55) in the Cd enrichment of rice crops was observed. It was found that the use of biochar may help increase crop yields on polluted land, and thus reduce the amount of mineral fertilizer used in the field. However, in order to maximize the benefits of biochar addition, farmers need to accept that the dosage rates of mineral fertilizers should be reduced. This review also revealed that the effectiveness of biochar in mitigating pollution may decrease with time due to ageing factors, such as leaching of biochar alkalinity.

Mercury removal from contaminated soil by thermal treatment with FeCl3 at reduced temperature

Thermal treatment has been used to remediate mercury-contaminated soils; however, existing thermal technologies use high temperatures (e.g., 600-800°C) and require high energy costs. Moreover, the treated soil is unfavorable for agricultural reuse. To address these issues, the present study developed a method for the thermal treatment of mercury-contaminated soils at a reduced temperature (400°C) by adding FeCl3. A FeCl3/Hg molar ratio of 100:1 in the soil was adopted as the optimum dosage of FeCl3 required to achieve maximum reduction of mercury. The mercury concentration in soils was successfully reduced to 0.8 mg kg(-)(1) when treated at 400°C for 60 min and the treated soil retained most of its original soil properties. FeCl3 addition during thermal treatment not only accelerated the volatilization of mercury in the easily removed fraction but also reduced the volatilization temperature of mercury in the hardly removed fraction. The adsorbable organic halogens and PCDD/Fs formed during thermal treatment with FeCl3 would not affect the soil reuse in agriculture. The thermal decontamination method reduces energy costs and leads to agricultural soil reuse, thus providing a greener and more sustainable remediation method for treating mercury-contaminated soil in future engineering applications.

Assessing effects of site characteristics on remediation secondary life cycle impact with a generalised framework

The ‘sustainable remediation’ concept has been broadly embraced by industry and governments in recent years in both the US and Europe. However, there is a strong need for more research to enhance its ‘practicability’. In an attempt to fill this research gap, this study developed a generalised framework for selecting the most environmentally sustainable remedial technology under various site conditions. Four remediation technologies were evaluated: pump and treat (P&T), enhanced in situ bioremediation (EIB), permeable reactive barrier (PRB), and in situ chemical reduction (ISCR). Within the developed framework and examined site condition ranges, our results indicate that site characteristics have a profound effect on the life cycle impact of various remedial alternatives, thus providing insights and valuable information for determining what is considered the most desired remedy from an environmental sustainability perspective.

High efficiency removal of methylene blue using SDS surface-modified ZnFe 2 O 4 nanoparticles

Recent studies have shown that hazardous organic dye substances can be removed from aqueous solutions by spinel ferrite nanomaterials. We found that Sodium Dodecyl Sulfonate (SDS) surface-modified mesoporous ZnFe2O4 nanoparticles (10-50nm) have a remarkably high maximum adsorptive capacity (∼699.30mg/g) for aqueous Methylene Blue (MB) removal at T of 288K and pH of 12. Unmodified ZnFe2O4 nanoparticles suffer from particle agglomeration, which reduces surface area, thus reducing their adsorptive capacity. Here it is shown that when modified with SDS, the specific surface area increased by ∼34%. It is also shown that the anionic SDS surfactant significantly increased the electrostatic attraction to the cationic MB compound. Moreover, it was found that adsorption of MB positively correlated with the aqueous solutions pH, which is attributed to a stronger negative charge on the SDS modified ZnFe2O4 surface at high pHs. The SDS-modified ZnFe2O4 adsorption of MB fitted well with the Langmuir adsorption isotherm model, and kinetic data fitted into a pseudo-second-order model. Thermodynamic parameters indicated that the adsorption was spontaneous and exothermic in nature, and physisorption dominated the adsorption of MB. The findings of this study demonstrate the potential for enhanced removal of MB contamination from aqueous solutions by SDS-modified ZnFe2O4 nanoparticles and, therefore, the potential for them to remove cationic organic dye from wastewater.

Stability of heavy metals in soil washing residue with and without biochar addition under accelerated ageing

Soil washing residue (SWR), which typically concentrates the washed toxic metals and is comprised of high contents of clay particles, may pose risks to the surrounding environment. This study aims to simulate accelerated ageing to assess the stability of selected metals (Cd2+ (132mg/kg), Cu2+ (248mg/kg) and Pb2+ (3470mg/kg)) in a SWR (89.68% of clay) with and without biochar treatment. The soil was incubated under constant moisture and wet-dry cycles (accelerated ageing), respectively, and the mobility and fractions of heavy metals in the soils with and without biochar treatment were examined. Under the constant moisture condition, biochar addition at 5% w/w reduced the leached Cd2+ (by 1.81%) and Cu2+ (by 8.70%) from SWR at day 1 and the leached Cu2+ (by 51.08%) and Pb2+ (by 25.36%) from SWR at day 14; however, the leached metals in the TCLP solution from the biochar-amended soils still exceed the regulatory limits (1mg/L for Cd2+, 5mg/L for Pb2+, no regulatory limits for Cu2+). Conversely, accelerated ageing (14days) significantly increased the fractions of exchangeable Cd2+ (from 3.63-3.94% to 6.21-6.29%) and Pb2+ (from 0.025-0.027% to 0.034-0.041%) as well as the TCLP leachabilities of Cd2+ (from 2.91-3.28% to 3.46-3.73%), Cu2+ (from 0.08-0.10% to 0.03-0.06%) and Pb2+ (from 0.25-0.35% to 0.52-0.57%) in the soils, as compared with those incubated under constant moisture, regardless of biochar addition. This study reveals challenges associated with stabilising SWR due to the presence of residual fine-grained particles.

Modeling aerobic biodegradation in the capillary fringe.

Vapor intrusion from volatile subsurface contaminants can be mitigated by aerobic biodegradation. Laboratory column studies with contaminant sources of chlorobenzene and a mixture of chlorobenzene, 1,2-dichlorobenzene, and 1,4-dichlorobenzene showed that contaminants were rapidly degraded in thin reactive zones with high biomass and low substrate concentrations in the vicinity of the capillary fringe. Such behavior was well characterized by a model that includes oxygen-, substrate-, and biomass-dependent biodegradation kinetics along with diffusive transport processes. An analytical solution was derived to provide theoretical support for the simplification of reaction kinetics and the approximation of reactive zone location and mass flux relationships at steady state. Results demonstrate the potential of aerobic natural attenuation in the capillary fringe for preventing contaminant migration in the unsaturated zone. The solution indicates that increasing contaminant mass flux into the column creates a thinner reactive zone and pushes it toward the oxygen boundary, resulting in a shorter distance to the oxygen source and a larger oxygen mass flux that balances the contaminant mass flux. As a consequence, the aerobic biodegradation can reduce high contaminant concentrations to low levels within the capillary fringe and unsaturated zone. The results are consistent with the observations of thin reactive layers at the interface in unsaturated zones. The model considers biomass while including biodegradation in the capillary fringe and unsaturated zone and clearly demonstrates that microbial communities capable of using the contaminants as electron donors may lead to instantaneous degradation kinetics in the capillary fringe and unsaturated zone.

Engineering practice of mechanical soil aeration for the remediation of volatile organic compound-contaminated sites in China: Advantages and challenges

In recent years, many industrial enterprises located in the urban centers of China have been relocated owing to the rapid increase in urban development. At the sites abandoned by these enterprises, volatile organic compounds have frequently been detected, sometimes at high concentrations, particularly at sites abandoned by chemical manufacturing enterprises. With the redevelopment of sites and changes in land-use type associated with these sites, substantial amounts of contaminated soils now require remediation. Since China is a developing country, soil remediation warrants the usage of techniques that are suitable for addressing the unique challenges faced in this country. Land shortage is a common problem in China; the large numbers of contaminated sites, tight development schedules, and limited financial resources necessitate the development of cost-effective methods for land reclamation. Mechanical soil aeration is a simple, effective, and low-cost soil remediation technique that is particularly suitable for the remediation of large volatile organic compound-contaminated sites. Its effectiveness has been confirmed by conducting laboratory studies, pilot tests, and full-scale projects. This study reviews current engineering practice and developmental trends of mechanical soil aeration and analyzes the advantages and disadvantages of this technology for application in China as an emerging soil remediation market. The findings of this study might aid technology development in China, as well as assist other developing countries in the assessment and implementation of costeffective hazardous waste site soil remediation programs.

Structural equation modeling of PAHs in ambient air, dust fall, soil, and cabbage in vegetable bases of Northern China

A series of field samples including ambient air (gaseous and particulate phases), dust fall, surface soil, rhizosphere soil and cabbage tissues (leaf, root and core), were collected in vegetable bases near a large coking manufacturer in Shanxi Province, Northern China, during a harvest season. A factor analysis was employed to apportion the emission sources of polycyclic aromatic hydrocarbons (PAHs), and the statistical results indicated coal combustion was the dominant emission source that accounted for different environmental media and cabbage tissues, while road traffic, biomass burning and the coking industry contributed to a lesser extent. A structural equation model was first developed to quantitatively explore the transport pathways of PAHs from surrounding media to cabbage tissues. The modeling results showed that PAHs in ambient air were positively associated with those in dust fall, and a close relationship was also true for PAHs in dust fall and in surface soil due to air-soil exchange process. Furthermore, PAHs in surface soil were correlated with those in rhizosphere soil and in the cabbage leaf with the path coefficients of 0.83 and 0.39, respectively. PAHs in the cabbage leaf may dominantly contribute to the accumulation of PAHs in the edible part of cabbages.