Xunchang Fei

Nanyang Technological University | ntu · School of Civil and Environmental Engineering

This study presents a two-stage process to recover phosphorus (P) from sewage sludge (SS) hydrochar, aimed at reducing trace element (TE) contamination. SS, mixed with Al-rich alum sludge (AS), underwent acidic HTC to convert Ca-P to Al-P. Alkaline extraction of hydrochar produced a P-rich, TE-deficient extract, as Al-P dissolves at high pH (>12),...

Landfill methane (CH4) emissions account for ~10% of all anthropogenic CH4 emissions globally, amounting to ~50 Tg per year. The current emission inventories utilize a first-order decay model as recommended by the Intergovernmental Panel on Climate Change. In contrast to recent top-down atmospheric inversion results, the mainstream bottom-up invent...

Phosphorus (P) recovery from sewage sludge (SS) (or its ash/char) is challenging due to the presence of heavy metals (HMs) in SS. This study proposed the integration of SS, alum sludge (AS), sequential wet extraction, and pyrolysis for P recovery without simultaneous HM extraction. SS + AS mixture (P:Al molar ratio = 3:1) was first acid pretreated...

The predominant management approach for municipal solid waste (MSW) remains disposal, given significant increases in generation and disposal rates of MSW in recent decades. In addition to the well-documented carbon emissions from disposal sites, these sites accumulate numerous elements, the masses of which are substantial globally yet inadequately...

Effective waste management is a major challenge for Small Island Developing States (SIDS) like Maldives due to limited land availability. Maldives exemplifies these issues as one of the most geographically dispersed countries, with a population unevenly distributed across numerous islands varying greatly in size and population density. This study p...

Landfill methane (CH 4 ) emissions account for ~ 10% of all anthropogenic CH 4 emissions globally, amounting to ~ 50 Tg/year. Contrasted by “top-down” atmospheric inversion results, the mainstream “bottom-up” emission inventories, which use the Intergovernmental Panel on Climate Change’s (IPCC) model, exhibit significant bias due to inaccurate a pr...

Various combined processes with pre-coagulation have been developed for biologically treated landfill leachate, but the microscopic-level processes occurring during coagulation remain largely unknown. Herein, dissolved organic matter (DOM) fate using fluorescence excitation emission matrix spectroscopy combined with parallel factor analysis and ele...

Phosphorus recovery from sewage sludge using synergetic application of alum sludge, sequential wet extraction, and pyrolysis.

This study evaluated the hydrolysis and acidogenesis of food waste at different operating pHs (uncontrolled, 5.5, 6.5, 7.5, 8.5) in a leachate bed reactor (LBR) at room temperature. LBR operation at pH 6.5–8.5 resulted in a hydrolysis yield of 718–729 g SCOD/kg VSadded, which was statistically (p ≤ 0.05) higher than that obtained at pH 5.5 (577 g S...

Cr(VI) contamination of soil threatens the environment and reduces soil strength. Therefore, both Cr(VI) stabilization and soil reinforcement should be considered in site remediation for future construction. This study investigated a biochemical treatment process using magnesium ascorbyl phosphate (MAP) and phytase. MAP was hydrolyzed via phytase c...

Identification of environmental pollutants with harmful effects is commonly conducted by non-targeted analysis (NTA) using liquid chromatography coupled with high-resolution mass spectrometry. Prioritization of possible candidates is important yet challenging because of the large number of candidates from MS acquisitions. We aimed to prioritize can...

Global greenhouse gas (GHG) emissions from food loss and waste (FLW) are not well characterized from cradle to grave. Here GHG emissions due to FLW in supply chain and waste management systems are quantified, followed by an assessment of the GHG emission reductions that could be achieved by policy and technological interventions. Global FLW emitted...

Much work remains to understand the sources, fates, and transport processes of microplastics (MPs) in terrestrial and water environments. Specifically, the transport of MPs in soils and sediments in various locations is underexamined. The transport mechanisms of MPs in soil are complex due to possible blocking, ripening, and straining phenomena. In...

Compressibility is one of the important engineering properties of municipal solid waste (MSW) affecting the stability and functionality of a landfill. Although the correlations between MSW properties and compression parameters have been established, they either have low accuracy and small datasets or are only limited to a few specific landfills in...

High hydrophilicity and soil fixation collectively hamper the delivery of phosphorus (P) released from conventional chemical phosphorus fertilizers (CPFs) to plant rhizosphere for efficient uptake. Here, a phosphorus nutrient nanocarrier (PNC) based on morphology‐tailored nanohydroxyapatite (HAP) is constructed. By virtue of kinetic control of buil...

Landfills contain significant amounts of plastic waste (PW) and microplastics (MPs). However, the contributions of various PW fragmentation processes to the quality and quantity of MPs in landfills are unclear. In this study, LDPE and EPS pieces were mixed with sand to simulate landfilled solid waste, which experienced one-dimensional abiotic compr...

Metal-containing solid wastes can induce serious environmental pollution if managed improperly, but contain considerable resources. The detoxification and resource recoveries of these wastes are of both environmental and economic significances, being indispensable for circular economy. In the past decades, attempts have been made worldwide to treat...

With the rising demands on supply chain transparency and food security, the rapid outspread of the Internet of Things (IoT) to improve logistical efficiency, and the rising penetration of sensor technology into daily life, the extensive integration of the IoT in the food sector is well anticipated. A perspective on potential life cycle trade-offs i...

The revitalisation of the global economy after the Covid-19 era presents environmental geotechnics with the opportunity to reinforce the need for a change in paradigm towards a green, circular economy and to promote aggressively the use and development of sustainable technologies and management practices. This paper aims to assist in this effort by...

Sanitary landfills and uncontrolled dumpsites are plastic wastes (PWs) reservoirs containing ∼60% of all the plastics ever made, amounting to 5,000 × 10⁶ tons as of 2017. The distribution, long-term behavior, and release of macro- and microplastics (MPs) from disposal sites are critical to global plastics pollution, but are poorly understood and la...

The cumulative amount of plastic waste (PW) produced worldwide is staggering, and approximately 38% is disposed of in landfills. Currently, there is little information about the properties of landfilled PW to support proper recovery and management, nor to prevent secondary pollution, e.g., microplastics. In this study, the municipal solid waste (MS...

Modern regulated landfills are designed to protect the environment by containing and isolating municipal solid waste (MSW) from the environment. Instead of treating MSW as a hazard to be contained, next generation landfills, here termed Sustainable Energy Reactor Facilities (SERFs) are envisioned to be designed and operated with a main focus on ene...

Bisphenol A diglycidyl ether (BADGE)-based epoxy resin is one of the most widely used epoxy resins with an annual production amount of several million tons. Compared with all other legacy or emerging organic compounds, BADGE is special due to its toxicity and high reactivity in the environment. More and more studies are available on its analytical...

Ni(II) and chelated Ni(II) in wastewater are of environmental concern. This study explores the sequestration potential of structural Fe(II) in solid phase (≡Fe(II)) on Ni(II) and EDTA-Ni(II) using freshly prepared ferrous hydroxyl complex (FHC) as the Fe(II)-bearing mineral. The 1 mM Ni(II) could be completely sequestrated in 20 min by 3 mM FHC, al...

The global massive consumption of disposable face masks driven by the ongoing COVID-19 pandemic has emerged as a blooming disaster to both the land and marine environment that might last for generations. Growing public concerns have been raised over the management and control of this new form of plastic pollution, and one of the proposed sustainabl...

The recovery of valuable metals from the LiNi0·5Mn0·3Co0·2O2 in spent batteries deserves more attention. We report a series of feasible procedures to selectively recover the four metals (Li, Ni, Mn, and Co) using a combination of hydrometallurgical and pyrometallurgyical processes. Firstly, oxalic acid is used to dissolve Li and precipitate the oth...

The outbreak of the coronavirus disease 2019 (COVID-19) pandemic not only has created a health crisis across the world but is also expected to impact negatively the global economy and societies at a scale that is maybe larger than that of the 2008 financial crisis. Simultaneously, it has inevitably exerted many negative consequences on the geoenvir...

Metal oxide nanoparticles (NPs) dissolution in water environment is an important issue with regard to their environmental behaviors. The metal ion dissolves from surface defective site, but the effect of defect abundance remains largely unknown. This study aims to reveal this effect using ZnO NPs and O vacancy as the model system. The abundance of...

Microplastics (MPs) are emerging persistent contaminants in the terrestrial subsurface, and evidence has emerged for significant effects of MPs on soils’ biological and ecosystem functions. Main MPs sources include land spreading of sewage sludge and biowaste composts, plastic mulching film used in horticultural fields, wastewater irrigation, and l...

Aeration is one mainstream technique to accelerate municipal solid waste (MSW) degradation in landfills. The determination of an appropriate aeration rate is critical to the design and operation of a landfill aeration system. In this study, we analyze 132 waste degradation tests reported in forty one studies in the literature. We use L min⁻¹ kg⁻¹ d...

Prediction of methane (CH4) generation and settlement of biodegrading municipal solid waste (MSW) is of primary interest to landfills aiming at biogas recovery for energy generation and MSW stabilization. We investigate these two concurring processes using datasets from 35 laboratory column tests and 8 pilot- and full-scale landfill cells available...

Heterogeneous Fenton dominated by ·OH is limited in its application, as pre-acidification is required to maximize the generation amount and redox potential of ·OH. It is thus featured to consume resources and generate pollutants. In this study, both CuS/H2O2 and Cu2S/H2O2 are found to show better performances under close-to-neutral condition (pH 5....

Old landfills require pre‐aeration before excavation to reduce the emissions of volatile organic compounds and methane. Variation and distribution of gas species during landfill aeration is important in designing an aeration system and evaluating aeration progress. Limited research is conducted on the variation of gas concentration in aerobic landf...

The effects and mechanism of high-temperature annealing, a frequently-used strategy to modulate the properties of nanoparticles (NPs), on the dissolution of zinc oxide (ZnO) NPs are investigated in this study. The results show that annealing increases the ZnO NPs dissolution magnitude via increasing O vacancy abundance on the surface and in the bul...

The shear behavior of rock mass along its structural plane, i.e., joint, bedding plane, and foliation plane, plays a key role in determining rock strength which is highly anisotropic. The shear behavior along the foliation plane is rarely addressed from engineering geology point of view in the effect of anisotropy of on the shear behavior along fol...

The time-dependent behavior of rock joints, specifically creep and stress relaxation, govern the long-term stability of underground structures, but have not been fully understood. The effect of asperity degradation on the time-dependent behavior of rock joints is investigated in this test. Triangular synthetic rock joints with four asperity angles...

This study presents a systematic experimental investigation on the effects of joint roughness on the steady stage creep of rock joints. Multi-stage creep tests were conducted on synthetic rock joints with different roughness characterised by joint roughness coefficient (JRC, 0-2, 6-8 and 18-20) under different normal stress levels (10-30% of the un...

For municipal solid waste (MSW) landfills that are situated in seismically active regions, the response of MSW under dynamic loading is critical to landfill design. In this study, a large-size simple shear device is utilized to perform cyclic testing on MSW under constant load (CL) and constant volume (CV) conditions which are considered equivalent...

Municipal solid waste (MSW) is biodegradable in landfills under anaerobic conditions. The evolution of the hydrobiochemical-mechanical (HBM) processes during degradation is investigated first through experiments and subsequently through modelling. Three well-characterised MSW specimens from US landfill sites with significantly different waste compo...

Direct simple shear (DSS) testing, despite its limitations, is one of the most common laboratory element tests in geotechnical engineering practice. The development and validation of a 300-mm diameter DSS device as well as test data generated for two materials with oversized particles, specifically pea gravel and municipal solid waste, are presente...

Seven municipal solid waste (MSW) specimens with variable initial waste compositions were biodegraded in large (d = 300 mm, h = 600 mm) laboratory landfill simulators under leachate-recirculation-enhanced anaerobic biodegradation conditions to investigate changes in the biochemical and physical characteristics of solid waste, leachate and biogas du...

Although large-size simple shear (SS) testing of municipal solid waste (MSW) may arguably provide a more realistic estimate of the shear strength (r) of MSW than the most commonly used direct shear (DS) testing, a systematic comparison between the shear responses of MSW obtained from the two testing methods is lacking. In this study, a large-size s...

The degradation process of a municipal solid waste (MSW) sample from a landfill in Texas (TX), USA, was monitored in a large-scale laboratory landfill simulator for 1136 days. Simple shear testing was performed on reconstituted fresh and degraded waste specimens and an “undisturbed” degraded specimen. Shear resistance at 10% shear strain was define...

Constant load and constant volume simple shear testing was conducted on relatively fresh municipal solid waste (MSW) from two landfills in the United States, one in Michigan and a second in Texas, at respective natural moisture content below field capacity. The results were assessed in terms of two failure strain criteria, at 10% and 30% shear stra...

The compressibility of municipal solid waste (MSW) is of engineering interest as it affects the short-term and long-term performance of landfills, as well as their expansion, closure, and postclosure development. An assessment of the field settlement behavior of MSW can be reliably executed only when the various mechanisms contributing to the settl...

Biodegradation of municipal solid waste (MSW) is enhanced in bioreactor landfills via active leachate recirculation. Biogas consisting primarily of methane and carbon dioxide is generated during this process and can be recovered as an energy source. The physical, chemical, geotechnical and hydraulic characteristics of the waste are altered during a...

In-situ and laboratory tests were performed on lime sludge generated from a drinking water-softening process and disposed of in a sedimentation lagoon. The sludge consists predominantly of calcite. It is poorly graded, low-plasticity silt with in-situ w c around 70%, γ t around 15 kN/m³ and e between 1·5 and 2·5. The optimum w c for standard and mo...

Proper management and disposal of municipal solid waste (MSW) remains an unresolved global problem. One solution to handle existing and future MSW is to move away from modern landfills that focus on containment and move towards bioreactor landfills that promote MSW biodegradation and enhance methane (CH4) generation and its collection as an alterna...

The energy conversion potential of municipal solid waste (MSW) disposed of in landfills remains largely untapped because of the slow and variable rate of biogas generation, delayed and inefficient biogas collection, leakage of biogas, and landfill practices and infrastructure that are not geared toward energy recovery. A database consisting of meth...