Abstract
Population and development megatrends will drive growth in cement production, which is already one of the most challenging-to-mitigate sources of CO
2
emissions. However, availabilities of ...conventional secondary cementitious materials (CMs) like fly ash are declining. Here, we present detailed generation rates of secondary CMs worldwide between 2002 and 2018, showing the potential for 3.5 Gt to be generated in 2018. Maximal substitution of Portland cement clinker with these materials could have avoided up to 1.3 Gt CO
2
-eq. emissions (~44% of cement production and ~2.8% of anthropogenic CO
2
-eq. emissions) in 2018. We also show that nearly all of the highest cement producing nations can locally generate and use secondary CMs to substitute up to 50% domestic Portland cement clinker, with many countries able to potentially substitute 100% Portland cement clinker. Our results highlight the importance of pursuing regionally optimized CM mix designs and systemic approaches to decarbonizing the global CMs cycle.
The recent discovery of complete ammonia oxidation (comammox) process in a single organism challenged the division of labor between two functional groups in the classical two-step nitrification ...model. However, the distribution and activity of comammox bacteria in various environments remain largely unknown. This study presented a large-scale investigation of the geographical distribution, phylogenetic diversity, and activity of comammox Nitrospira in typical agricultural soils. Among the 23 samples harvested across China, comammox Nitrospira clade A was ubiquitously detected at 4.14 × 104–1.65 × 107amoA gene copies/g dry soil, with 90% belonging to the subclade A2. The abundance of comammox Nitrospira clade B was two orders of magnitude lower than clade A. In all samples, comammox Nitrospira were 1–2 orders of magnitude less abundant than canonical nitrifiers, and soils with slightly high pH and C/N tended to enrich more comammox Nitrospira. Unlike canonical nitrifiers, comammox Nitrospira had sustained amoA gene transcription regardless of external ammonia supply, indicating their competitive advantage over other nitrifiers under low-ammonia conditions. When fed with 1 mM ammonium for 15 days, comammox Nitrospira in tested soils were enriched 2.36 times higher than those enriched by the same amount of nitrite, indicating their preference to utilizing ammonia as the substrate. DNA-SIP further confirmed the in situ nitrification activity of comammox Nitrospira. This study provided new insights into the broad distribution and diversity of comammox Nitrospira in agricultural soils, which could potentially play an important role in the microbial nitrogen cycle in soils.
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•Comammox Nitrospira are ubiquitous in soils but less abundant than canonical nitrifiers.•Most comammox Nitrospira in agricultural soils belong to clade A2.•Comammox Nitrospira favor growth in slightly alkaline soils with relatively high C/N.•Comammox Nitrospira prefer to use ammonia as the substrate rather than nitrite.•Comammox Nitrospira are important nitrifiers under low ammonia conditions.
As an emerging biotechnology capable of removing contaminants and producing electricity, microbial fuel cells (MFCs) hold a promising future in wastewater treatment. However, several main problems, ...including the high internal resistance (
R
in), low power output, expensive material, and complicated configuration have severely hindered the large-scale application of MFCs. The study targeted these challenges by developing a novel MFC system, granular activated carbon single-chamber MFC, termed as GAC-SCMFC. The batch tests showed that GAC was a good substitute for carbon cloth and GAC-SCMFCs generated high and stable power outputs compared with the traditional two-chamber MFCs (2CMFCs). Critical operational parameters (i.e. wastewater substrate concentrations, GAC amount, electrode distance) affecting the performance of GAC-SCMFCs were examined at different levels. The results showed that the
R
in gradually decreased from 60
Ω to 45
Ω and the power output increased from 0.2
W/m
3 to 1.2
W/m
3 when the substrate concentrations increased from 100
mg/L to 850
mg/L. However, at high concentrations of 1000–1500
mg/L, the power output leveled off. The
R
in of MFCs decreased 50% when the electrode distance was reduced from 7.5
cm to 1
cm. The highest power was achieved at the electrode distance of 2
cm. The power generation increased with more GAC being added in MFCs due to the higher amount of biomass attached. Finally, the multi-anode GAC-SCMFCs were developed to effectively collect the electrons generated in the GAC bed. The results showed that the current was split among the multiple anodes, and the cathode was the limiting factor in the power production of GAC-SCMFCs.
Summary
We explore the population‐scaling and gross domestic product (GDP)‐scaling relationships of material and energy flow (MEF) parameters in different city types based on economic structure. ...Using migration‐corrected population data, we classify 233 Chinese city propers (Shiqu) as “highly industrial” (share of secondary GDP exceeds 63.9%), “highly commercial” (share of tertiary GDP exceeds 52.6%), and “mixed‐economy” (the remaining cities). We find that, first, the GDP population‐scaling factors differ in the different city types. Highly commercial and mixed‐economy cities exhibit superlinear GDP population‐scaling factors greater than 1, whereas highly industrial cities are sublinear. Second, GDP scaling better correlates with city‐wide MEF parameters in Chinese cities; these scaling relationships also show differences by city typology. Third, highly commercial cities are significantly different from others in demonstrating greater average per capita household income creation relative to per capita GDP. Further, highly industrial cities show an apparent cap in population. This also translates to lower densities in highly industrial cities compared to other types, showing a size effect on urban population density. Finally, a multiple variable regression of total household electricity showed significant and positive correlation with population, income effect, and urban form effect. With such multivariate modeling, the apparent superlinearity of household electricity use with respect to population is no longer observed. Our study enhances understanding of MEFs associated with Chinese cities and provides new insights into the patterns of scaling observed in different city types by economic structure. Results recommend dual scaling by GDP and by population for MEF parameters and suggest caution in applying universal scaling factors to all cities in a country.
A new type of microbial fuel cell (MFC), multi-anode/cathode MFC (termed as MAC MFC) containing 12 anodes/cathodes were developed to harvest electric power treating domestic wastewater. The power ...density of MAC MFCs increased from 300 to 380 mW/m
2 at the range of the organic loading rates (0.19–0.66 kg/m
3/day). MAC MFCs achieved 80% of contaminant removal at the hydraulic retention time (HRT) of 20 h but the contaminant removal deceased to 66% at the HRT of 5 h. In addition, metal-doped manganese dioxide (MnO
2) cathodes were developed to replace the costly platinum cathodes, and exhibited high power density. Cu–MnO
2 cathodes produced 465 mW/m
2 and Co–MnO
2 cathodes produced 500 mW/m
2. Due to the cathode fouling of the precipitation of calcium and sodium, a decrease in the power density (from 400 to 150 mW/m
2) and an increase in internal resistance (R
in) (from 175 to 225
Ω) were observed in MAC MFCs.
There is a lack of field data on the water withdrawal and consumption intensity of thermoelectric power plants in China. With China's ambitious electricity capacity expansion and ever-growing water ...deficit, the overlooked water dimension of thermoelectric power generation could soon have significant water sustainability implications, and field data on water intensity of thermoelectric power plants will be essential to further our understanding of China's water-electricity nexus. To address this knowledge gap, this paper presents field data on the water withdrawal intensity and water balance of 19 coal-fired power plants in Shandong, China, categorized by different generator capacities (<100 MW ∼ >600 MW) and boiler technologies (subcritical, supercritical and ultra supercritical). This paper suggests that the annual average water withdrawal intensity of coal-fired power plants in Shandong (1.50-3.75 L kWh−1) is within the range of values reported for other countries, and that the distinction between water withdrawal and water consumption effectively vanishes since very little water is returned from withdrawal. This paper also suggests that there is quite significant seasonality in power plants' water intensity whereby the water intensity in July can be approximately 15-28% higher than the annual average. The seasonality is on a similar scale across all generator capacities, except for a small co-generation plant (<100 MW), which had substantially lower water intensity in January when a heat exchanger was used to provide heating.
Bisphenol A (BPA), a widely used petrochemical compound, has become an emerging global environmental management challenge because its leakage is associated with potential environmental and human ...health impacts. Until now, available BPA statistics have been limited to the products that directly use BPA. In this study, we delineate direct and indirect BPA flows for the 2012 Chinese economy. We find that construction, production of educational and recreational products, and automobile manufacturing are the most BPA-intensive sectors in terms of total BPA flows (300, 157, and 130 Gg total BPA flows, respectively). The public management and health sectors, however, incur significant indirect BPA flows, defined as embedded and inter-sectoral BPA placed into use, even though direct BPA use by these sectors is limited. By revealing the currently overlooked indirect BPA flows, this study reveals data gaps that are highly relevant to improving the accuracy of estimated BPA flows and losses. The method used herein is transferrable to other emerging and environmentally relevant materials, thereby providing the holistic understanding needed for cities, regions, or nations to design effective policy interventions.
Multi-anode/cathode microbial fuel cells (MFCs) incorporate multiple MFCs into a single unit, which maintain high power generation at a low cost and small space occupation for the scale-up MFC ...systems. The power production of multi-anode/cathode MFCs was similar to the total power production of multiple single-anode/cathode MFCs. The power density of a 4-anode/cathode MFC was 1184 mW/m
3, which was 3.2 times as that of a single-anode/cathode MFC (350 mW/m
3). The effect of chemical oxygen demand (COD) was studied as the preliminary factor affecting the MFC performance. The power density of MFCs increased with COD concentrations. Multi-anode/cathode MFCs exhibited higher power generation efficiencies than single-anode/cathode MFCs at high CODs. The power output of the 4-anode/cathode MFCs kept increasing from 200 mW/m
3 to 1200 mW/m
3 as COD increased from 500 mg/L to 3000 mg/L, while the single-anode/cathode MFC showed no increase in the power output at CODs above 1000 mg/L. In addition, the internal resistance (
R
in) exhibited strong dependence on COD and electrode distance. The
R
in decreased at high CODs and short electrode distances. The tests indicated that the multi-anode/cathode configuration efficiently enhanced the power generation.
China's import bans on solid wastes starting from 2017 have challenged the global trade system of plastic wastes, which remains poorly characterized. This study chooses polyethylene (PE) as a case ...and aims to map out the global trade networks of PE waste (GPETN) from 1976 to 2017.
We find that the size and complexity of the GPETN had been growing until 2016. After the mid-1990s, PE waste basically flowed from developed economies, mainly the EU and the US, to developing economies such as China. Since 2001 when admitted into the WTO, China's PE waste import surged until 2014 when it absorbed over 60% of global export. Regulations on solid waste import following the Green Fence campaign in 2013 resulted in substantial reductions in China's import as well as the global export of PE waste after 2014. Several other developing economies, such as Malaysia, Turkey, and Vietnam, had transitioned to net importers, but their imports were insufficient to replace China as new recycling bases for PE waste.
The results highlight the urgent need of a joint effort for developed and developing countries to build a stronger global circular economy system with sufficient capacity to treat PE waste locally.
Dissolved organic matter (DOM) in the sediment matrix affects contaminant remediation through consumption of oxidants and binding with contaminants. Yet the change in DOM during remediation ...processes, particularly during electrokinetic remediation (EKR), remains under-investigated. In this work, we elucidated the fate of sediment DOM in EKR using multiple spectroscopic tools under abiotic and biotic conditions. We found that EKR led to significant electromigration of the alkaline-extractable DOM (AEOM) toward the anode, followed by transformation of the aromatics and mineralization of the polysaccharides. The AEOM remaining in the cathode (largely polysaccharides) was resistant to reductive transformation. Limited difference was noted between abiotic and biotic conditions, indicating the dominance of electrochemical processes when relatively high voltages were applied (1–2 V/cm). The water-extractable organic matter (WEOM), in contrast, showed an increase at both electrodes, which was likely attributable to pH-driven dissociations of humic substances and amino acid-type constituents at the cathode and the anode, respectively. Nitrogen migrated with the AEOM toward the anode, but phosphorus remained immobilized. Understanding the redistribution and transformation of DOM could inform studies on contaminant degradation, carbon and nutrient availability, and sediment structural changes in EKR.
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•Significant electromigration of alkaline-extractable DOM (AEOM) toward anode•Concurrent migration of nitrogen with DOM and immobilization of phosphorus•pH-driven dissociation of water-extractable DOM (WEOM) at both anode and cathode•Significant electrochemical oxidation of aromatics and polysaccharides in AEOM•Significant biological oxidation of WEOM
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