Low-carbon Sources Research Articles

Riboflavin enhanced denitrification of artificial wastewater under low C/N condition in cold season

Nitrogen removal under low C/N ratio in cold season is an arduous task. In this study, riboflavin was used as an eco-friendly electron mediator to improve the denitrification process in an SBR reactor under conditions of low temperature (10 °C to 15 °C) and limited carbon source (C/N ratio = 4.0). The results indicated that riboflavin created a suitable pH in the system for denitrification. Under water temperature of 10 °C to 15 °C, riboflavin (10 mg/L) stimulated the NO3–N and TN removal rate by 16.5%, and 51%, respectively. Riboflavin promoted the utilization efficiency of limited carbon source, driving the denitrification process with low residual acetate as electron donor. The rising cost of riboflavin supplement (10 mg/L) was 0.025 USD per m3 of wastewater. To satisfy the efficient nitrogen removal from municipal wastewater, the optimum C/N ratio and the selection of solid/immobilized redox mediators should be developed in future work.

Rescuing responsible hydropower projects

Given the still-growing use of coal and natural gas in generating electricity in many developing countries, it is necessary to put far more effort into promoting responsible large-scale hydropower projects. In contrast to hydro, solar and wind power face physical constraints that greatly limit their potential to replace fossil-fuel sources of power generation. Because designing hydro projects to reduce their socio-economic and environmental damage typically entails greater costs and/or lower capacity, subsidies are needed to increase the number of responsible, economically viable projects. Despite the past abuses, hydro offers low-carbon energy generation, low-cost power generation, and important potential for energy storage and peaking supply to supplement intermittent low-carbon sources such as wind and solar. The promotion of responsible hydropower requires greater awareness of the possibilities for responsible projects, greater overall climate funding, better provision for local participation and compensation, changes in the doctrines of additionality, and stronger institutions to identify, design, and broker these projects.

Interrelationship simulations among Brazilian electric matrix sources

Electricity in Brazil is mainly supplied by renewable sources. However, thermal sources are necessary to meet the demand in periods of climatic adversity. The research aimed to identify the existing relationships among Brazilian generating sources and to examine the effects of these relationships for each source, using a system of dynamic equation with VAR modeling and parameters estimated by SUR. The variable analyzed was electricity amount generated (GWh), divided by: biomass; coal; fuels; hydropower; natural gas; nuclear; and wind power. Monthly values ​​were collected at the National Electric Energy Agency website from January 2000 to June 2019. The dynamic equations parameters were estimated by SUR, which provided more functional equations and efficient predictions. The scenario simulations made it possible to verify hydropower generation and its dependence on thermal sources. The adjusted system exposed the reverse effects to this dependence, which suggest an increase in the use of non-conventional renewable sources, such as biomass and solar energy. As another alternative to reduce the matrix thermal dependency, the possibility of encouraging thermal generation from natural gas was identified, as it is a low carbon source, and the development of energy storage solutions, such as batteries, to maintain the electricity supply stability.

Feasibility of improving nitrogen removal by integrating the rice straw and zeolite with drainage ditches for farmland runoff control

Natural zeolite and rice straw have been widely used for removing nitrogen (N) from wastewater due to their different N removal mechanisms. In this study, the N removal performances of three substrate systems composed of zeolite (Z), rice straw (R) and their combination (ZR) were assessed for decontaminating farmland runoff characterized by high loads of ammonium - N or nitrate - N besides of a low carbon content. The N-cycling functional genes were also investigated. The results showed that ZR achieved significantly higher ammonium (48.9%–77.7%) and TN (39.7%–65.9%) removal rates than Z and R ( P < 0.05). ZR also exhibited the highest removal rates of nitrate (67.6%–82.7%) and TN (45.5%–62.1%) in nitrate wastewater treatment. The abundances of 16S rRNA and denitrifying genes (including nirK , nirS , narG and napA ) were significantly enhanced in ZR, which partly explained the higher N removal in the ZR than in the Z and R systems. These findings suggest that it is feasible to combine rice straw with zeolite as a substrate of drainage ditches for considerable N removal enhancement in the control of agricultural runoff. • ZR showed the highest nitrogen (N) removal rate when both NH 4 + -N and NO 3 − -N wastewaters were treated. • TN and NO 3 − -N removal in Z was limited by insufficient denitrification due to low organic carbon source. • The combination of zeolite and rice straw significantly increased the abundances of 16S rRNA and denitrifying genes.

Flexible CCS Technologies To Reduce the Cost of Net-Zero Carbon Electricity Systems

Studies have shown that firm, low-carbon sources of power such as fossil-fueled power plants with carbon capture and storage (CCS) can reduce the cost of net-zero carbon electricity systems. But other developments on the path to decarbonization, particularly the proliferation of variable renewable energy (VRE) such as wind and solar, complicate the design of CCS-equipped plants, which must operate with reduced capacity factors and increased cycling. An increasing number of jurisdictions are committing to net-zero carbon electricity systems with high penetration of VRE. This paper considers the implications for CCS- equipped power plants via examination of grid capacity expansion and production cost modelling. The need to reconsider the optimal design and operations of CCS plants is presented, with focus on tradeoffs between capital cost, efficiency, and CO2 capture rate. Approaches to economic optimization via minimizing cost and maximizing operational profits are discussed. Finally, the case will be made that future CCS plants must either enable maximum power plant flexibility or change the operating paradigm so that plants can operate under more steady-state conditions and shift their electrical output to the grid via storage or provide another service such as removing CO2 from the air.

Re-examining the role of nuclear fusion in a renewables-based energy mix

Fusion energy is often regarded as a long-term solution to the world's energy needs. However, even after solving the critical research challenges, engineering and materials science will still impose significant constraints on the characteristics of a fusion power plant. Meanwhile, the global energy grid must transition to low-carbon sources by 2050 to prevent the worst effects of climate change. We review three factors affecting fusion's future trajectory: (1) the significant drop in the price of renewable energy, (2) the intermittency of renewable sources and implications for future energy grids, and (3) the recent proposition of intermediate-level nuclear waste as a product of fusion. Within the scenario assumed by our premises, we find that while there remains a clear motivation to develop fusion power plants, this motivation is likely weakened by the time they become available. We also conclude that most current fusion reactor designs do not take these factors into account and, to increase market penetration, fusion research should consider relaxed nuclear waste design criteria, raw material availability constraints and load-following designs with pulsed operation.

Evaluation of Energy Transition Pathways to Phase out Coal for District Heating in Berlin

As Germany struggles to meet its near-term emissions reduction targets in lagging sectors like heating or transport, the need to identify energy transition pathways beyond power generation is urgent. This paper presents an investigation of tangible and climate-friendly transformation paths to replace the existing coal-fired units used for heat and power generation in Berlin with a largely CO2-free innovative technology mix. Although the literature has extensively covered the decarbonization of the power generation sector on different geographic scales, few studies have focused on the decarbonization of the heat sector in cities with large district heating networks, like Berlin. This paper aims to fill this gap. The proposed methodology combines three key elements: (1) scenario analysis including high-fidelity models of the European power market and the heat demand in Berlin, (2) evaluation of energy potential from low-carbon alternative sources, and (3) a techno-economic portfolio optimization. The results suggest that a coal phase-out by 2030 is feasible without any discontinuities in the provision of heat. Although low-carbon sources could partially substitute coal-based heat, they would not be sufficient to replace it completely. Thus, a gas-based hydrogen-ready combined heat and power plant linked with a power-to-heat plant would be required to fill the gap.

A machine learning approach on the relationship among solar and wind energy production, coal consumption, GDP, and CO2 emissions

China, India, and the USA are the world’s biggest energy consumers and CO2 emitters. Being the leading contributors to climate change, these economies are also at the core of environmental solutions. This paper investigates the causal relationship among solar and wind energy production, coal consumption, economic growth, and CO2 emissions for these three countries. To do so, we use an advanced methodology in Machine Learning to verify the predictive causal linkages among variables. The Causal Direction from Dependency (D2C) algorithm set CO2 emissions as the target variable. The obtained results were disaggregated and estimated in a supervised prediction model. The findings, confirmed by three different Machine Learning procedures, showed an interesting output. While a reduction in overall carbon emissions is predicted in China and the US (resulting from the intensive use of renewable sources of energy), India displays critical predictions of a rise in CO2 emissions. This indicates that curbing CO2 emissions cannot be achieved without conducting a comprehensive shift from fossil to renewable resources, although China and the U.S. present a more promising path to sustainability than India. Being an emerging renewable energy leader, India should further enhance the use of low-carbon sources in its power supply and limit its dependence on coal.

Using national environmental objectives in green public procurement: Method development and application on transport procurement in Sweden

Green public procurement can play an important role in reducing the environmental impact of societies. While its uptake is continuously growing, barriers to its use still remain. One barrier previously identified in literature is related to the lack of accessible and easy to use tools that help standardize the development of criteria in green tenders. In this paper, to help overcome this barrier, a method is presented that can be used to develop green public procurement tools that follow previous studies recommendations about including life-cycle assessment-based data and basing procurement criteria on national environmental objectives. The method was then applied to develop a procurement tool for green procurement of public transport services in Sweden based on the Swedish environmental quality objectives. Results from the assessment of 18 pre-defined fuel systems are shown together with an illustrative example of how the tool can be used in the process leading up to procurements to set relevant criteria and during the procurement to adjust incoming tender prices. The results showed that waste-based biomethane and hydrogenated vegetable oil systems were well aligned with the Swedish environmental quality objectives due to being able to contribute positively to several objectives. Crop-based biofuels, on the other hand, performed worse due to negative effects from agricultural practices. The performance of the electric vehicle systems depended in large on how the electricity was generated, where renewable sources and low carbon sources performed better than non-renewable alternatives.

The Paris Agreement on Climate Is Coming into Force: Will the Great Energy Transition Take Place?

The Paris Agreement within the UN Framework Convention on Climate Change to keep global warming within 1.5–2°С has been effective since November 4, 2016, and will come into force in 2020. According to the calculations of the Intergovernmental Panel on Climate Change, to achieve the above goal, it is necessary to reduce atmospheric greenhouse gas emissions by three times, to the level of 2019, when they amounted to 33.3 Gt, which will allow limiting the temperature rise to 1.5°C by 2050 or to 2°C by 2070. According to the International Renewable Energy Agency, this can be achieved only if by 2040–2050 the so-called Great Energy Transition takes place—a transition from the use of currently dominant fossil hydrocarbon fuels (coal, oil, and natural gas) to renewable energy sources, when their share in the total energy balance reaches 40% or more. Mathematical modeling is shown to help attain the Great Energy Transition and, hence, the goals of the Paris Agreement. However, to create a stable and sustainable energy system of the future, it is necessary not only to expand renewable energy sources rapidly but also to develop nuclear power as a low-carbon source of baseload electricity generation. Only the symbiosis of renewable energy sources and nuclear power plants with highly secure small and medium reactors of the latest generation will make it possible to oust and replace hydrocarbon fuels and solve the problem of climate security without prejudice against economic development.

Optimal Electricity Trading with Carbon Emissions Pinch Analysis

Many countries face the challenge of cutting greenhouse gas (GHG) emissions from electricity generation while coping with increasing demand. This problem is especially pronounced in developing countries with growing energy consumption. Commitments to cut GHG emissions can be met by increasing the share of low-carbon sources such as renewable and nuclear energy, but rapidly scaling up the capacity of such sources can be difficult. In a region of contiguous countries with heterogeneous levels of GHG intensity, electricity trading can be used to reduce the need for new power generation capacity. A country with a low-carbon power mix can export to its neighbours and thus reduce the need for new generation capacity in those countries. In this work, a variant of Carbon Emissions Pinch Analysis (CEPA) is developed for optimizing regional electricity trading to meet GHG emissions cuts. The method is demonstrated with the case of the Association of Southeast Asian Nations (ASEAN).

Cost-effective production of dextran using Saccharum officinarum juice (SOJ) as a potential feedstock: downstream processing and characterization

Dextrans are exo-polysaccharides prominently used as biomaterial on the grounds of their biodegradability and biocompatibility characteristics. There is an increasing interest and need to identify alternative cost-effective and renewable carbon source for dextran to reduce the production cost and to improve the overall economy of dextran production. In this work, dextran was produced using Saccharum officinarum juice (SOJ) as a low-carbon source by Leuconostoc mesenteroides MTCC 7337. The suitable condition/parameter for the production of dextran was found to be medium pH, 7; shaking speed, 150 rpm; inoculum size, 5% v/v; and nitrogen source, yeast extract. The different downstream factors including screening of solvent, supernatant to solvent ratio and precipitation time on the recovery of dextran, were studied. The organic solvent, ethanol with volume ratio of 1:4 (supernatant to solvent ratio), and precipitation time of 16 h were selected based on the maximum recovery of dextran from SOJ medium. The purified dextran was characterized by proton nuclear magnetic resonance spectroscopy (1H-NMR), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA) analysis. The results of rheological studies indicate that dextran solution behaves like a pseudoplastic fluid at higher concentrations of dextran solution. Based on the results, it was found that SOJ could be used as an alternate substrate for the production of dextran.

Quantifying urban wastewater treatment sector's greenhouse gas emissions using a hybrid life cycle analysis method – An application on Shenzhen city in China

Substantial amounts of greenhouse gas (GHG) emissions generated at urban wastewater treatment plants (WWTP) are gaining increasing appreciation. Improving upon the commonly used Process-Based Life-Cycle Analysis (PLCA) and Environmentally-Extended Life-Cycle Analysis (EIO-LCA) models, we construct a Hybrid Life Cycle Analysis (HLCA) model and quantify both direct and indirect GHG emissions at the operational stage of WWTPs in Shenzhen, one of the fastest urbanizing cities in the world. Data are collected from 26 wastewater treatment plants in Shenzhen, out of all 32, covering 5 commonly used wastewater treatment technologies in China, i.e. Sequencing Batch Reactor, Oxidation Ditch, Biological Filter, AAO-MBR and AAO. The results show that WWTPs using AAO-MBR technology have the highest GHG emission intensity, averaging 0.79 tons per m3, primarily due to its large electricity intensity required. WWTPs using other technologies emit 0.27 to 0.39 tons of GHGs per m3 of wastewater treated. GHG emissions associated with electricity use occupy the largest share, ranging from 65 to 75%. Therefore, transforming the energy structure of the electric power sector to low-carbon sources can reduce WWTPs operational GHG emissions. In total, GHG emissions from Shenzhen's urban wastewater sector have increased from below 0.5 million tons in 2012 to over 0.6 million tons in 2017. Inter-model comparison shows that EIO-LCA substantially underestimates the urban wastewater sector's GHG emissions using the water sector's average parameters while PLCA also results in minor underestimations due the omission of indirect emissions in the production stage of chemicals and other material inputs.

Nitrogen Removal Efficiency and Microbial Community Analysis of a High-Efficiency Honeycomb Fixed-Bed Bioreactor

Based on the concept of microbial community multi-processing in integrated spatial bacterial succession (ISBS), this study constructs a highly efficient cellular fixed-bed bioreactor that follows the growth of biological flora in the wastewater treatment process. The reactor is organically partitioned based on synergistic laws and in accordance with environmental and microbial metabolic changes, and sewage is subjected to unitized and specialized biological treatment under direct current conditions. The results show that the ISBS reactor exhibits stable nitrogen removal performance under a low-carbon source. Compared with traditional sewage biochemical treatment technology, the microbial concentration is increased by 2–3 times and even up to 12 times, and the ammonia nitrogen removal rate is maintained at 99%. The removal rate reaches 90% (hydraulic retention time of 14 h). High-throughput sequencing analysis based on 16S rDNA reveals the microbial community structure succession at different depths of the same section of the reactor. The microbial community is rich under the influence of environmental factors and exhibits different responses. The intervals vary. An analysis of the microbial community function explains why the ISBS reactor has high nitrogen removal efficiency.

Study of pyrite based autotrophic denitrification system for low-carbon source stormwater treatment

Improving the nitrogen removal capacity of stormwater runoff has been the main research direction of bioretention systems in recent years. Heterotrophic denitrification in traditional bioretention systems was often used, but insufficient carbon sources in the runoff limit it. In this study, two bioretention systems using natural pyrite and zeolite as substrates were constructed to explore the feasibility of pyrite-based autotrophic denitrification in bioretention for nitrogen removal. During eight months of operation at natural conditions, the results showed that pyrite had no negative effects on the removal of NH4+—N, but enhanced denitrification in the bioretention system with no or low carbon source in the influent. Pyrite based bioretention system (PBS) can adapt to low temperature and irregular wet and dry alternation. The average NH4+—N, TN, and TP removal efficiency of PBS during eight months were 87.6 %, 89.3 %, and 81.6 %. The average NH4+—N, TN, and TP removal efficiency of zeolite-based bioretention system (ZBS) were 98.7 %, 47.1 %, and 47.5 %. By-products (SO42- and Total iron) of PBS were all at an acceptable level. The dominant genera in PBS were Denitratisoma (3.6 %), Ellin6067 (2.7 %), Thiobacillus (2.6 %), Thauera (2.1 %), CL500−29 marine group (1.8 %), Sulfuritalea (1.7 %), Subgroup 10 (1.4 %). Genera Thiobacillus, Thauera, and Sulfuritalea were highly related to autotrophic denitrification. Moreover, genera Denitratisoma was highly related to heterotrophic denitrification. This study shows that pyrite could be a promising eco-friendly substrate in the bioretention system for nutrient removal.

Multiobjective component sizing of a hybrid ethanol-electric vehicle propulsion system

Concerns over energy efficiency and greenhouse gas (GHG) emissions are driving research investments into advanced propulsion technologies. Plug-in hybrid electric vehicles (PHEVs) can provide a bridge that connects transport electrification to renewable bioenergy sources such as ethanol. However, it remains unclear how this pathway can simultaneously address economic, energy and environmental goals. To tackle this challenge, the present study explores, for the first time, the multiobjective optimal sizing of PHEVs powered by low-carbon sources of electricity and ethanol-gasoline blend. The empirical ethanol-gasoline blend model is incorporated into the PHEV simulation whose relevant parameters are validated using laboratory data from the European Commission – Joint Research Centre. We develop a full picture of the use-phase well-to-wheel (WTW) GHG emissions from ethanol, gasoline and grid electricity and their energy consumptions. Consequently, market-oriented PHEV sizing solutions are provided as per the power utility generation portfolio and automobile fuel properties of the target region. The results indicate that better performances of the PHEV, regarding GHG emissions and energy consumption, are associated with larger battery size and smaller engine displacement but result in a higher cost-to-power ratio. Specifically, for E25-fuelled PHEVs in markets with world average electricity carbon intensity, every 1.0 USD/kW increase in cost-to-power ratio leads to savings of 1.6 MJ energy consumption and 1.7 g CO2-eq/km WTW GHG emissions. Moreover, a clear benefit of using E25 in the hybrid propulsion system is identified, where the energy consumption and GHG emissions can be reduced by 5.9% and 12.3%, respectively.

Trump’s “America first” energy policy, contingency and the reconfiguration of the global energy order

The global energy system is in transition to a new energy order characterized by the emergence of the United States as a net oil exporter, the shale revolution and the gradual shift towards low-carbon sources and renewables. The shale boom in the US was a game changer, as was the election of Donald Trump as US president. Trump pushed an ambitious “America first” agenda aimed at transforming the US into a global energy superpower. The purpose of this article is two-fold: first, it outlines the key pillars of the emerging global energy order. Second, it underscores the role of contingent events, a factor neglected by some previous studies because of their reliance on what A.O.Hirschman (1970) termed “paradigmatic thinking”. The recent transition in the international energy order is an outcome of two paramount, yet largely unanticipated events: the shale revolution in the US and Trump’s neomercantilist and unilateralist economic policies. While contingencies are an inherent feature of social reality, the scenario approach can be a useful heuristic for dealing with uncertainties. The article concludes by discussing the implications of these developments for global energy governance.

Advanced Nitrogen Removal Characteristics of Low Carbon Source Municipal Wastewater Treatment via Partial-denitrification Coupled with ANAMMOX

Partial-denitrification coupled with ANAMMOX is a novel biological nitrogen removal technology, which is expected to significantly reduce the external carbon source dosage for advanced nitrogen removal from municipal wastewater. In this study, ANAMMOX sludge was inoculated to investigate advanced nitrogen removal performance and sludge characteristics in a partial-denitrification/ANAMMOX reactor. The results showed that inoculation of ANAMMOX sludge could quickly start the partial-denitrification/ANAMMOX reactor. The effluent total nitrogen concentrations were (4.82±1.84) mg·L-1 with a chemical oxygen demand of 2.19±0.08. Sludge particles larger than 0.20 mm accounted for 86.16% in the reactor. This meant that granular sludge was formed, which was conducive to good retention of ANAMMOX bacteria in the reactor. The external carbon source dosage and the oxygen requirement for nitrification can be reduced by applying partial-denitrification coupled with ANAMMOX to advanced nitrogen removal from the effluent of secondary clarifier in municipal wastewater treatment plants.

The 2019 report of the MJA-Lancet Countdown on health and climate change: a turbulent year with mixed progress.

The MJA-Lancet Countdown on health and climate change was established in 2017 and produced its first Australian national assessment in 2018. It examined 41 indicators across five broad domains: climate change impacts, exposures and vulnerability; adaptation, planning and resilience for health; mitigation actions and health co-benefits; economics and finance; and public and political engagement. It found that, overall, Australia is vulnerable to the impacts of climate change on health, and that policy inaction in this regard threatens Australian lives. In this report we present the 2019 update. We track progress on health and climate change in Australia across the same five broad domains and many of the same indicators as in 2018. A number of new indicators are introduced this year, including one focused on wildfire exposure, and another on engagement in health and climate change in the corporate sector. Several of the previously reported indicators are not included this year, either due to their discontinuation by the parent project, the Lancet Countdown, or because insufficient new data were available for us to meaningfully provide an update to the indicator. In a year marked by an Australian federal election in which climate change featured prominently, we find mixed progress on health and climate change in this country. There has been progress in renewable energy generation, including substantial employment increases in this sector. There has also been some progress at state and local government level. However, there continues to be no engagement on health and climate change in the Australian federal Parliament, and Australia performs poorly across many of the indicators in comparison to other developed countries; for example, it is one of the world's largest net exporters of coal and its electricity generation from low carbon sources is low. We also find significantly increasing exposure of Australians to heatwaves and, in most states and territories, continuing elevated suicide rates at higher temperatures. We conclude that Australia remains at significant risk of declines in health due to climate change, and that substantial and sustained national action is urgently required in order to prevent this.

Effects of Temperature on the Characteristics of Nitrogen Removal and Microbial Community in Post Solid-Phase Denitrification Biofilter Process.

In order to solve the problems of high energy consumption, complex process and low nitrogen removal efficiency in the currently available low carbon source wastewater treatment processes, a novel coagulation sedimentation/post-solid-phase denitrification biofilter process (CS-BAF-SPDB) was proposed. The effect of temperature on the nitrogen removal performance of BAF-SPDB was intensively studied, and the mechanism of the effect of temperature on nitrogen removal performance was analyzed from the perspective of microbial community structure by using the polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE). The results showed that, to realize favorable nitrifying and denitrifying performance simultaneously in the BAF-SPDB unit, the operation temperature should be set above 18 °C. In addition, the influence of the macro operation parameters on the performance of the BAF and SPDB has a direct relationship with the dynamic changes of the micro microbial community. The influence of temperature on nitrification performance in BAF was mainly embodied in the change of composition, amount and activity of ammonia oxidizing bacteria Candidatus Nitrospira defluvii and nitrite oxidizing bacteria Nitrosomonas sp. Nm47, while that on denitrification performance in SPDB is mainly embodied in the change of composition and amount of solid carbon substrate degrading denitrifying bacteria Pseudomonas sp., Myxobacterium AT3-03 and heterotrophic denitrifying bacteria Dechloromonas agitate, Thauera aminoaromatica, Comamonas granuli and Rubrivivax gelatinosus.