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•Biochar provided microbial habitat in AD system and enhanced biogas production.•Excellent buffer capacity and accelerated electron transferring was observed.•Biochar applications for ...biogas generation and purification were analyzed.•Economic and environmental feasibilities of biochar addition in AD were evaluated.
Anaerobic digestion (AD) technology still faces some challenges including low methane productivity, instable operation efficiency and undesired refractory substances degradation. Biochar has recently been recognized as a promising alternative addition in AD process to enhance methane production. Based on VOSviewer analysis, this review presents a comprehensive summarizing of the applications, performances, and economies of biochar strategies in AD system. Firstly, typical production processes of biochar and its main characteristics including adsorption and immobilization ability, buffering ability and electron transfer ability were evaluated. Then, the applications of biochar in AD and its improving effects on biogas production/purification were summarized. Accordingly, the corresponding mechanisms of biochar addition in AD for digestion efficiency improvement were elucidated. Finally, the economic and environmental feasibilities of application biochar in AD, as well as prospective future studies were summarized. Through an overview of biochar in AD system, this paper aims to promote its widely practical applications.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•Sludge production in China in 2019 was 39.0 million tons, average 28.1 kg/y per capita.•Higher reginal urbanization rate and GDP led to a higher per capita sludge ...production.•Spatial/temporal trends of sludge treatment/disposal techniques were investigated.•Incineration in East China accounted 31.3% of GHG emission of sludge disposal in 2019.•Discrepancy, challenges and future perspectives of sludge disposal in China was analyzed.
This study statistically reported the current state of sludge treatment/disposal in China from the aspects of sources, technical routes, geographical distribution, and development by using observational data after 1978. By the end of 2019, 5476 municipal wastewater treatment plants were operating in China, leading to an annual sludge productivity of 39.04 million tons (80% water content). Overall, 29.3% of the sludge in China was disposed via land application, followed by incineration (26.7%) and sanitary landfills (20.1%). Incineration, compost, thermal hydrolysis and anerobic digestion were the mainstream technologies for sludge treatment in China, with capacities of 27,122, 11,250, 8342 and 6944 t/d in 2019, respectively. Incineration and drying were preferentially constructed in East China. In contrast, sludge compost was most frequently used in Northeast China (46.5%), East China (22.4%) and Central China (12.8%), while anaerobic digestion in East China, North China and Central China. The capacities of sludge facilities exhibited a sharp increase in 2009–2019, with an overall greenhouse gas emissions in China in 2019 reached 108.18 × 108 kg CO2-equivaient emissions, and the four main technical routes contributed as: incineration (45.11%) > sanitary landfills (23.04%) > land utilization (17.64%) > building materials (14.21%). Challenges and existing problems of sludge disposal in China, including high CO2 emissions, unbalanced regional development, low stabilization and land utilization levels, were discussed. Finally, suggestions regarding potential technical and administrative measures in China, and sustainable sludge management for developing countries, were also given.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•Environmental impacts and benefits of twelve current sludge treatment and disposal routes in China are evaluated.•Co-incineration has the negative toxicity impacts and carbon ...emissions due to the offset of energy recovery.•Carbon emissions of co-incineration, anaerobic digestion, and anaerobic digestion with thermal hydrolysis are −27.26, −572.44, and −474.92 kg CO2 eq/t DS, respectively.•Controlling heavy metals is the priority of digested sludge land application.
The management and utilization of sludge in a sustainable approach require a systematic analysis of the environmental impacts generated from diverse sludge treatment and disposal processes. This study systematically assessed 12 common sludge treatment and disposal routes based on the existing operating and construction conditions of representative sludge disposal projects in China. We evaluated their environmental impacts using a life cycle assessment following the International Organization for Standardization (ISO 14040 and ISO 14044), and found that the routes of co-incineration, mono-incineration, and anaerobic digestion with or without thermal hydrolysis may be useful in terms of simultaneously controlling environmental pollution and carbon emissions in China. Therein, the route of co-incineration was recommended as the best one because its human toxicity potential (−152.31 kg dichlorobenzene (1,4-DB) eq/ton dry solid (t DS)), freshwater ecotoxicity potential (FEP, −127.40 kg 1,4-DB eq/t DS), terrestrial ecotoxicity potential (TEP, −0.81 kg 1,4-DB eq/t DS), and global warming potential (−27.26 kg CO2 eq/t DS) were all negative (environmental benefits). Furthermore, the toxicity impacts of the mono-incineration route were also negative, but it still needed to further enhance energy recovery to reduce carbon emissions. Despite the routes of anaerobic digestion and thermal hydrolysis in combination with anaerobic digestion had the excellent negative carbon emission attributes (-572.44 kg CO2 eq/t DS, −474.92 kg CO2 eq/t DS), they showed serious FEP and TEP owing to the heavy metals pollution caused by subsequent land use of anaerobic digested sludge. Overall, this study selected the most suitable sludge treatment and disposal routes to simultaneously satisfy the requirements of carbon emission reduction and pollution control in China and proposed optimizing suggestions for future technical improvement and development.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
To clarify the potential carcinogenic/noncarcinogenic risk posed by particulate matter (PM) in Harbin, a city in China with the typical heat supply, the concentrations of PM
and PM
were analyzed from ...Nov. 2014 to Nov. 2015, and the compositions of heavy metals and water-soluble ions (WSIs) were determined. The continuous heat supply from October to April led to serious air pollution in Harbin, thus leading to a significant increase in particle numbers (especially for PM
). Specifically, coal combustion under heat supply conditions led to significant emissions of PM
and PM
, especially heavy metals and secondary atmospheric pollutants, including SO
, NO
, and NH
. Natural occurrences such as dust storms in April and May, as well as straw combustion in October, also contributed to the increase in WSIs and heavy metals. The exposure risk assessment results demonstrated that Zn was the main contributor to the average daily dose through ingestion and inhalation, ADD
and ADD
, respectively, among the 8 heavy metals, accounting for 51.7-52.5% of the ADD
values and 52.5% of the ADD
values. The contribution of Zn was followed by those of Pb, Cr, Cu and Mn, while those of Ni, Cd, and Co were quite low (<2.2%).
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
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•Protein/humic acid were more efficient in Zn2+ and Cd2+ sorption than polysaccharides.•Noticeable electrostatic interaction occurred for proteins/humic acid adsorption.•Freundlich ...model for Cu2+/Cd2+ sorption while Langmuir for Zn2+ on polysaccharide/HA.•Metals sorption on EPS was exothermic process, especially for humic acid and proteins.
To clarify the adsorption behaviors of typical heavy metals onto sludge extracellular polymeric substances (EPS), the adsorption capacities and mechanisms, as well as the contributions of the different EPS components (proteins, humic acids and polysaccharides), to the adsorption of Zn2+, Cu2+ and Cd2+ were separately explored. Overall, proteins exhibited a relatively high adsorption capacity for the three metals ions, followed by humic acid, whereas least for polysaccharides. The adsorption of Cu2+ and Cd2+ onto proteins, humic acid and polysaccharides fit well to the Freundlich isotherm, whereas Langmuir model was the best fit for Zn2+ bindings onto polysaccharides/humic acid. The binding of Cu2+, Zn2+ and Cd2+ onto the three EPS components was exothermically favorable, and significant electrostatic interactions were observed for the heavy metals sorption onto humic acid and proteins. In addition, the effect of metal ions sorption on the spectrum of the proteins, polysaccharides and humic acid was also explored.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
High levels of toxic organic pollutants commonly detected during domestic/industrial wastewater treatment have been attracting research attention globally because they seriously threaten human ...health. Sulfate-radical-based advanced oxidation processes (SR-AOPs) have been successfully used in wastewater treatment, such as that containing antibiotics, pesticides, and persistent organic pollutants, for refractory contaminant degradation. This review summarizes activation methods, including physical, chemical, and other coupling approaches, for efficient generation of sulfate radicals and evaluates their applications and economic feasibility. The degradation behavior as well as the efficiency of the generated sulfate radicals of typical domestic and industrial wastewater treatment is investigated. The categories and characteristics of the intermediates are also evaluated. The role of sulfate radicals, their kinetic characteristics, and possible mechanisms for organic elimination are assessed. In the last section, current difficulties and future perspectives of SR-AOPs for wastewater treatment are summarized.
The aim of this study was to evaluate the efficiency and optimization of co-digestion using sewage sludge (SS), maize straw (MS) and cow manure (CM) as feeds, and the effects of the mixing ratio and ...C/N ratio of the substrates were analyzed in detail. Among the three substrates tested, CM/MS exhibited better digestion than CM/SS and SS/MS in terms of all measures, including total daily biogas and net methane volume production, due to the hydrophilic characteristics and high level of biodegradability of CM, as well as its higher C/N ratio. The average biogas production was 613.8 mL/g VS for the co-digestion of CM/MS at a feed concentration of 15 g VS/L and using a 1:1 mixing ratio (C/N ratio of 28.3). The co-digestion of SS/CM/MS performed better than the individual digestion of the components because of the balanced C/N ratios and supply of carbon. The optimum conditions for maximizing methane potential were an SS:CM:MS ratio of 30:35:35 and a bulk VS concentration of 15.0 g VS/L, which led to a maximum methane production of 8047.31 mL (C/N ratio of 12.7). The high-throughput sequencing analysis showed clear differences in microbial communities during the entire co-digestion process.
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•Quasi-columnar (Gd0.9Yb0.1)2Zr2O7 (GYbZ)/yttria-stabilized zirconia (YSZ) coating experiences delamination failure under burner rig test.•Delamination initiates at particle-embedded ...regions beneath taller GYbZ column tips, followed by lower regions affected by shorter tapered columns.•The discontinuities of the strain tolerance lead to multiple out-of-plane stress concentration spots in the quasi-columnar coating.•Various strain energy release rate trends at different stress concentration spots reveal delamination mechanisms of quasi-columnar GYbZ/YSZ coatings.
A double-ceramic-layer (DCL) thermal barrier coating consisting of quasi-columnar structured (Gd0.9Yb0.1)2Zr2O7 (GYbZ) on top and yttria-stabilized zirconia (YSZ) beneath was deposited by plasma spray-physical vapor deposition (PS-PVD). The as-deposited GYbZ/YSZ coating is composed of a dense continuous layer at the bottom and a columnar layer growing on it. The columnar layer comprises taller coarse columns, shorter tapered columns, and particles filling in the gaps between the columns. The thermal shock behavior of the coating is evaluated in a burner rig at 1300 °C, during which the coating mainly fails in the form of delamination. The coating initially delaminates in the regions where the particles are embedded beneath the taller GYbZ columns tips. Subsequently, delamination occurs in the lower region of GYbZ coating and eventually fails at the TGO/YSZ interface. A finite element model tailored to the microstructural characteristics of the DCL coating was established. Stress distributions of the coating indicate that the discontinuities of the strain tolerance caused by abrupt microstructural or componential changes lead to multiple out-of-plane stress (σ22) concentration spots. The position and procedure of the delamination of GYbZ coating obtained based on the energy release rate of each σ22 concentration spot are consistent with experimental results.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Plasma spray physical vapor deposition (PS-PVD) was used to deposit yttria stabilized zirconia (YSZ) coatings with different columnar morphologies by varying the spray distance. Although similar ...quasi-columnar structures were formed at the spray distances of 600mm and 1400mm, the formation mechanisms of particles in the coatings were different. Besides, an electron beam physical vapor deposition (EB-PVD) like columnar coating out of pure vapor was deposited at a spray distance of 1000mm and the columnar consisted of elongated nano-sized secondary columns. The hardness and Young׳s modulus of the coatings were investigated. Compared to the other two quasi-columnar structures, the EB-PVD like columnar coating exhibited higher hardness (~9.0GPa ) and Young׳s modulus (~110.9GPa), mainly due to its low porosity and defect.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Antibiotics, the most frequently prescribed drugs, have been widely applied to prevent or cure human and veterinary diseases and have undoubtedly led to massive releases into sewer networks and ...wastewater treatment systems, a hotspot where the occurrence and transformation of antibiotic resistance take place. Extracellular polymeric substances (EPS), biopolymers secreted via microbial activity, play an important role in cell adhesion, nutrient retention, and toxicity resistance. However, the potential roles of sludge EPS related to the resistance and removal of antibiotics are still unclear. This work summarizes the composition and physicochemical characteristics of state-of-the-art microbial EPS, highlights the critical role of EPS in antibiotics removal, evaluates their defense performances under different antibiotics exposures, and analyzes the typical factors that could affect the sorption and biotransformation behavior of antibiotics. Next, interactions between microbial EPS and antibiotic resistance genes are analyzed. Future perspectives, especially the engineering application of microbial EPS for antibiotics toxicity detection and defense, are also emphatically stressed.
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•Sludge EPS are essential to antibiotics adsorption, binding, and transformation.•Substrate characteristics and operation conditions affected antibiotics interactions.•EPS retained ARGs entered the intercellular cell and weakened ARGs transformation.•Extensive studies are needed to explore the engineering applications of sludge EPS.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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