Low Global Warming Potential Research Articles

Integrated production of methanol and biochar from bagasse and plastic waste: A three-in-one solution for carbon sequestration, bioenergy production, and waste valorization

The shift from fossil fuels to renewable energy is a crucial strategy to achieve carbon neutrality. However, the methanol industry relies heavily on fossil fuels. Alternative feedstocks, such as biomass and plastics, still face many challenges. Biomass is hydrogen-deficient and cannot achieve a high methanol yield, while plastic gasification consumes too much energy. Accordingly, this research proposed a new method to synergistically co-produce methanol and biochar from bagasse pyrolysis and plastic waste gasification. This innovative approach was assessed using techno-economic analysis and hybrid life-cycle assessment based on sugarcane bagasse resources in Guangxi province as a case study and compared with the other four scenarios. The results indicated that the novel method exhibits huger economic and environmental benefits with a low payback period of 6.32 years and a low global warming potential of −1875.41 kg CO2-eq/t. However, the high total capital cost is the primary potential obstacle to widespread promotion. Spatial-temporal analysis shows that Chongzuo and Laibin have the most tremendous methanol production potential and economic and environmental benefits due to their high bagasse production. This study contributes to biomass utilization and plastic waste management by proposing a synergistic process and offers multiple benefits for carbon sequestration, energy security, and waste valorization.

Solar powered cascade system for sustainable deep-freezing and power generation - exergoeconomic evaluation and multi-objective optimization for tropical regions

The global initiative to decarbonize the refrigeration sector aims to provide cooling energy while reducing CO2 emissions. In India, the majority of urban industrial refrigeration systems are powered by fossil fuel based electricity, which increases consumption of fossil fuel and it contributes to global warming. To address this issue, two unique solar thermal operated cooling configurations, the Simple Cascade System (SCS) and the Recuperative Cascade System (RCS), were designed to fulfil urban industrial cooling energy demands. The surplus electricity generated by these systems is transferred to the on-site grid. Ethane, n-butane, and R1233zd(E) were selected as working fluids due to their low global warming potential (GWP). Among them, the RCS system with R1233zd(E) demonstrated the highest energy and exergy performance, benefiting from its superior thermodynamic properties and effective utilization of internal heat. In New Delhi, the R1233zd(E) operated RCS system achieved the highest cooling and electricity outputs at 54 kW and 20 kW, respectively. Although the R1233zd(E) operated RCS system incurred higher costs, the performance improvement outweighed the increase in cost. To assess the system sustainability in terms of exergy utilisation, a new indicator sustainability index (SI) was developed and established with values of 1.1. Increasing the evaporator temperature enhanced the system performance but also raised total plant cost, while raising the system condenser temperature had the opposite effect. The multi-objective optimization assessment for RCS configuration indicated an optimal objective value of an energy utilization ratio (EUR) of 0.16, an exergy efficiency of 8.7 %, and a capital cost of 20 $/h.

Dual purpose ratooned rice improves agri-food production with reduced environmental cost

China is faced with the contemporaneous needs to improve resource-use efficiency, raise production and enhance environmental stewardship of status quo agrifood production systems. Dual purpose ratoon rice cropping systems comprise a promising innovation for addressing such challenges through production of forage and grain on the same land parcel. Here, we conducted life cycle assessments of forage-grain ratoon rice (FG-RR), contrasting sustainability indicators associated with FG-RR against those of traditional ratoon rice (productivity, environmental impact and economics) across four provinces in central China. Compared with conventional systems, we show that FG-RR systems had superior energy output (+37%) and energy use efficiency (+37%), but also lower global warming potential (−17%) and eutrophication potential (−13%). Such benefits were attributed to lower methane emissions and ammonia volatilization, together with enhanced nitrogen fertilizer management. We found that FG-RR systems had significantly higher productivity, with yields being 6%–152% greater than traditional production systems, particularly in the climatically challenged areas of Xinyang and Chizhou. We show that biophysical benefits translated to economic dividends, particularly in Chizhou, where net profits were as high as $716 ha−1. We conclude that FG-RR present a sustainable alternative to traditional rice farming methods, with substantial benefits in terms of production efficiency, environmental sustainability, and economic prosperity. We opine that adoption of FG-RR systems helps address challenges associated with suboptimal productivity, particularly in regions prone to environmental degradation and climatic challenges.

Seasonal performance assessment and experimental investigation of R32 drop-in and BPHX size in an R410A chiller when using two compressor modulation strategies

The decrease in fossil fuel reserves and high energy consumption by HVAC&R equipment require the use of compressors with better efficiencies and capacity modulation strategies. Usually, seasonal performance studies focus on compressor capacity modulation methods, however the current study explores the idea of improving the seasonal performance of two compressor modulation techniques: a two-stage and a variable speed compressor with different capacity modulation ranges by using larger condensers in an R410A water ethylene glycol chiller system. The analysis shows that oversizing the heat exchangers has larger benefits with the compressor modulation strategy with lower range. Additionally, the seasonal performance estimated according to AHRI 551/591 (2020) of a two-stage compressor with oversized condenser is higher than a basic single speed compressor with a better motor indicating that oversizing brazed plate heat exchanger (BPHX) might yield higher performance than improving the compressor motor efficiency. Due to the high global warming potential (GWP) of R410A, there is a focus on replacing it with low GWP refrigerants such as R32 to reduce CO2 emissions. This study would also compare the performance when using R32 as a drop-in refrigerant in the two different R410A compressor capacity modulation strategies with comparable cooling capacity. When the refrigerant was changed from R410A to R32, the integrated part load value (IPLV.SI), an efficiency metric for variable speed compressor remains relatively constant at 5.5 while it increases from 3.9 to 4.4 for the two-stage compressor. It is hypothesized that low refrigerant mass flow rate (m˙ref) provided by the variable speed compressor when matching the load at the lower part load conditions leads to refrigerant maldistribution in BPHX and reduced IPLV.SI.

Comprehensive carbon footprint analysis of wastewater treatment: A case study of modified cyclic activated sludge technology for low carbon source urban wastewater treatment

To reduce pollution and carbon emissions, a quantitative evaluation of the carbon footprint of the wastewater treatment processes is crucial. However, micro carbon element flow analysis is rarely focused considering treatment efficiency of different technology. In this research, a comprehensive carbon footprint analysis is established under the micro carbon element flow analysis and macro carbon footprint analysis based on life cycle assessment (LCA). Three wastewater treatment processes (i.e., anaerobic anoxic oxic, A2O; cyclic activated sludge technology, CAST; modified cyclic activated sludge technology, M-CAST) for low carbon source urban wastewater are selected. The micro key element flow analysis illustrated that carbon source mainly flows to the assimilation function to promote microorganism growth. The carbon footprint analysis illustrated that M-CAST as the optimal wastewater treatment process had the lowest global warming potential (GWP). The key to reduce carbon emissions is to limit electricity consumption in wastewater treatment processes. Under the comprehensive carbon footprint analysis, M-CAST has the lowest environmental impact with low carbon emissions. The sensitivity analysis results revealed that biotreatment section variables considerably reduced the environmental impact on the LCA and the GWP, followed by the sludge disposal section. With this research, the optimization scheme can guide wastewater treatment plants to optimize relevant treatment sections and reduce pollution and carbon emissions.

In tube condensation of low global warming potential refrigerants in an axial micro-fin aluminum tube

Environmental regulations have driven the development of refrigerants with low global warming potential (GWP). To design heat exchangers using these new refrigerants, data are needed concerning the heat transfer coefficient and pressure drop in two-phase flow. Another change is the increasing use of aluminum tubes rather than copper tubes to reduce heat exchanger cost. Hence, this study presents an experimental investigation of flow condensation using an expanded axial micro-fin aluminum tube with a fin-tip diameter of 5.96 mm. The experiments included single compounds R-32, R-1234yf, and R-1234ze(E), zeotropic mixtures with low glide (R-454B), and zeotropic mixtures with high-glide (R-454C and R-455A). Experiments were conducted at condensation temperatures ranging from 40 °C to 50 °C, reduced pressures ranging from 0.21 to 0.55, and mass fluxes ranging from 150 to 350 kg/(m2 s). Data obtained for these refrigerants constitute one of the first reports for high-glide refrigerants using axial micro-fin aluminum tubes. An evaluation of heat transfer degradation of zeotropic mixtures due to mass transfer resistance at the liquid/vapor interface is presented. This information can be used to design heat exchangers for next generation air conditioning and refrigeration systems.

Comparative analysis of cement-based bricks in India: a cradle-to-gate life cycle assessment

The main aim of this study is to quantify the environmental impact caused by different types of bricks used in the Indian construction field. This study considered four brick types: Autoclave Aerated Concrete, Fly ash, and Cellular Foam bricks. The prime objectives of the investigation are to evaluate and compare the embodied energy and resource depletion by modelling the environmental impact of the bricks by Global Warming Potential (GWP) with the LCA software SimaPro. The study’s use of a cradle-to-gate approach provides a comprehensive understanding of the environmental implications associated with four types of bricks. Moreover, the analysis conducted using SimaPro 8.1 software with the life cycle ReCiPe 2016 v1.1 and IMPACT 2002 + v2.15 demonstrates the rigour and accuracy of the findings. The results indicate that cement bricks have the lowest Global Warming Potential, specific heat, and cost, making them a more environmentally and economically friendly option than other bricks. Furthermore, weight, water absorption, density, thermal conductivity, and compressive strength were also analyzed and showed other better-performing bricks.

Enhancing indoor thermal comfort and sustainability: A solar-driven desiccant cooling and adsorption chiller system with environmental impact assessment

Addressing indoor thermal comfort in buildings located in hot and humid climates is a persistent challenge, demanding innovative cooling solutions that are both efficient and environmentally responsible. This paper introduces a new integration of a Phase Change Material (PCM)-based solar desiccant cooling system with an adsorption chiller, a setup designed to enhance indoor thermal comfort conditions while utilizing renewable energy sources. This research simultaneously leverages the heating and cooling capacities of the adsorption chiller, leading to an efficient system performance. The TRNSYS software is used to evaluate the system's behavior in a typical house with moderate cooling demand and characterized by high relative humidity. Two types of solar collectors, the evacuated tube and Wavy Direct Absorption Solar Collectors (WDASC), are evaluated to supply the required thermal energy, providing a comprehensive assessment of the system’s efficiency under different configurations. Additionally, the study conducts a comprehensive Life Cycle Assessment (LCA) to quantify the Global Warming Potential (GWP) of the systems. The results confirm the proposed system's capability to maintain indoor thermal comfort within acceptable Predicted Mean Vote (PMV) and Predicted Percentage of Dissatisfied (PPD) ranges. The evacuated tube collector showed marginally better performance (average PMV: 0.018, average PPD: 6.7 %) compared to the WDASC (average PMV: 0.075, average PPD: 7.3 %). Additionally, the evacuated tube collector demonstrates superior energy (75.68 %) and exergy (10.82 %) efficiencies compared to the WDASC. The system utilizing the evacuated tube collector surpasses the WDASC configuration, achieving a higher Coefficient of Performance (COP) of 0.47 compared to 0.41, and emitting lower GWP values of 0.0194 kg-CO2 per kWh of cooling capacity compared to 0.0201 kg-CO2. An analysis of Embodied Energy reveals that the adsorption chiller is the most significant contributor to lifecycle energy consumption, with a quicker Energy Payback Time (EPBT) for the evacuated tube system (2.75 years) compared to the WDASC system (3.94 years). This research thus contributes a highly efficient, sustainable, and environmentally friendly solution to the challenge of cooling in buildings, setting a new standard for future green building practices.

Ecological transition for the gas mixtures of the MRPC cosmic ray telescopes of the EEE Project

The Extreme Energy Events (EEE) Collaboration is fully involved in an ecological transition. The use of the standard gas mixture, C2H2F4 + SF6, has stopped in favor of an alternative green mixture based on C3H2F4 with the addition of He or CO2.The choise of these new mixtures is motivated by the significant lower Global Warming Potential (GWP) to reduce the emission of gases potentially contributing to the greenhouse effect.The EEE experiment consists of 61 muon telescopes based on Multigap Resistive Plate Chambers (MRPCs), each telescope composed of 3 chambers filled with gas.Several EEE detectors are today completely fluxed with the new ecological mixture. This contribution will report recent results about the telescope performance obtained from studies with the eco-friendly alternative mixture carried out in the last years.

An evaluation of energy and carbon budgets in diverse cropping systems for sustainable diversification of rainfed uplands in India's eastern hill and plateau region

With increasing cost and use of energy in agriculture, the traditional practice of mono-cropping of rice in upland is neither sustainable nor eco-friendly. It is necessary to identify crop diversification options with high energy efficiency, productivity, and low global warming potential (GWP). In this experiment, an inclusive system analysis was accomplished for 3 years (2016–2019) of five mono-cropping production (MCP) systems namely rice (R), finger millet (FM), black gram (BG), horse gram (HG), pigeon pea (PP), and four intercropped systems viz. R+BG, R+HG, FM+ BG, and FM + HG. The key objective was to evaluate the flow of energy, carbon balance, and GWP of these varied production systems. Puddled rice was recorded as an energy-exhaustive crop (27,803 MJ ha−1), while horse gram was noted to have the lowest energy use (26,537 MJ ha−1). The total energy output from pigeon pea (130,312 MJ ha−1) and diversified intercropped systems (142,135 MJ ha−1) was 65.3% and 80.3% higher than mono-cultured systems, respectively. Rice and rice-based intercropping production systems showed higher carbon footprints (1,264–1,392 kg CO2 eq. ha−1). Results showed that R+BG and R+HG were the most energy-efficient production systems, having higher energy ratio (5.8 and 6.0), higher carbon efficiency (7.41 and 8.24), and carbon sustainability index (6.41 and 7.24) as against 3.30, 3.61, and 2.61 observed under sole cropping production systems. On average, rice and rice-based production systems had 7.4 times higher GWP than other production systems. In productivity terms, pigeon pea and FM+HG had higher rice equivalent yields of 8.81 and 5.79 t ha−1 and benefit-cost ratios of 2.29 and 1.87, respectively. Thus, the present study suggests that pigeon pea and finger millet-based intercropping systems were the most appropriate crop diversification options for the rainfed upland agro-ecosystem of the eastern region of India.

Environmental impact of Holstein Friesian and 3-breed crossbred dairy cows using a life cycle assessment approach applied to individual animals

This study aimed to set up a Life Cycle Assessment (LCA) approach at level of individual animals to assess the effects of a 3-breed crossbreeding program on the environmental impact of cows. It involved 564 cows, 279 purebred Holstein (HO) and 285 crossbreds (CR), originated from a 3-breed crossbreeding program based on the rotational use of Viking Red, Montebèliarde and HO sires and kept in 2 dairy herds of northern Italy (224 and 340 cows/herd, respectively). The reference unit of the LCA model was the lifetime of cows, from the birth to culling or death. Data were collected at different levels: individual animal-based data referred to the whole life (birth, calving, dry, cull or death dates, and milk production); individual test-date collection of body measures and BCS, used to predict body weight and to estimate energy requirements; common farm-based data concerning herd management (diets composition, and materials used). Data were used to compute: dry matter intake, milk and milk components production, gross income (GI) and income over feed costs (IOFC) pertaining to the lifespan of cows. An individual LCA-derived approach was set up to compute global warming potential (GWP), acidification and eutrophication potential (AP and EP, respectively), and land occupation (LO), which have been associated with different functional units (cow in her whole life or per d of life; kg of milk fat plus protein, and € of GI and of IOFC produced in the herd life). Data were analyzed using a generalized linear model including the fixed effects of genetic group (CR vs HO), farm and their interaction (genetic group x farm). Compared with HO, CR cows completed more lactations (+12%), had earlier first calving (-2 weeks), yielded more fat plus protein in milk both in the lifespan (+8%) and per d of life (+4%). Concerning the environmental impact, when compared with HO herd mates, CR cows had nominal greater emissions per cow in the whole life, similar emissions per d of life and nearly 3% lower GWP, AP and EP per kg of fat plus protein yielded in lifespan. Income over feed costs per unit of emission tended to be nearly 4% greater in CR compared with HO cows. Also the use of land tended to be lower in CR compared with HO in most indicators considered. In conclusion, LCA could be adapted to represent individual animals. Moreover, managing dairy cows according to a 3-breed rotational crossbreeding scheme may be regarded as a strategy that can contribute to mitigate the emissions and to improve the environmental impact of dairy operations.

Flow boiling heat transfer characteristics and correlation development of R290/R600a mixtures in an internally threaded tube

Excessive hydrofluorocarbons (HFCs) usage significantly contributes to the global warming. Therefore, there is a widespread shift toward natural refrigerants with low global warming potential (GWP). Among these alternative refrigerants, R290, R600a, and their mixtures have gained considerable attention. However, their flammability limits the charge. To decrease the equipment volume and reduce the refrigerant charge, internally threaded tubes have been introduced to enhance the heat transfer. Therefore, in this study, flow boiling experiments were conducted on R290, R600a, and mixtures inside an internally threaded tube, obtaining heat transfer data under a pressure of 0.216–0.416 MPa, heat flux of 10.5–73.0 kW m−2, mass flux of 70–190 kg m−2 s−1. To quantitatively discern the dominant heat transfer mechanism, a dimensionless number Nz was introduced. In the nucleate boiling dominant region, an increase in the heat flux markedly enhances the heat transfer, with pressure and mass flux playing minor roles. Furthermore, the heat transfer deterioration trend of the mixtures aligns with the variation trends of concentration slip and boiling range. In the convective heat transfer dominant region, a rise in the mass flux significantly increases the heat transfer coefficient, while the pressure and heat flux have minor effects. Additionally, at high R290 mole fraction and vapor quality, high surface tension maintains a continuous liquid film, enhancing the heat transfer. Furthermore, new heat transfer correlations for flow boiling inside the internally threaded tubes were established, which exhibit a mean relative deviation of −2.30 % and 8.80 % for the obtained experimental results and collected data, respectively.

Turbulence models performance to predict fluid mechanics and heat transfer characteristics of fluids flow in micro-scale channels

The predictability of the mathematical models on the details and the phenomenology for microscale flow conditions is an open topic in the literature. In this sense, this work evaluates the capacity of the following turbulence models: standard k − ε , RNG k − ε , k − ω standard, k − ω SST , Realizable k − ε , and Low-Re k − ε to predict the fluid mechanics and heat transfer characteristics of low Global Warming Potential (GWP) fluid flow in a 1.1 mm ID microchannel. These turbulence models are evaluated for Reynolds Numbers up to 104. The numerical results for velocity profile, friction factors, and Nusselt Numbers are validated with analytical and experimental data published in previous works for R134a, R1234yf, R1234ze(E), and R600a. Parametric behaviors of pressure drop and heat transfer coefficient are presented and analyzed. The results indicate that each of the models describes the qualitative behavior of flow and heat transfer processes. On the other hand, the quantitative results indicate that the Low-Re k − ε , k − ω , and k − ω SST models demonstrate an acceptable prediction of some variable’s behavior. Numerically, the Low-Re k − ε model presents an accurate prediction with the lowest mean absolute.

Performance of Heat Pump Air Conditioning with R1234ze (HFO) as a Refrigerant

The study shows that refrigerants R1234ze (E) and R1234ze (Z), known for their low global warming potential, are likely to become primary choices in heat pump air conditioning for residential and commercial use. The research evaluates the thermodynamic properties of R1234ze (Z) using experimental, thermodynamic, and numerical analyses. It addresses F-gas regulation requirements and aligns with the Paris Agreement goals by exploring various refrigerants, including R227ea, R114, R236fa, R134a, R1234ze (Z), and R245fa, as potential candidates for evolving industry needs. The analysis indicates that R1234ze (Z) outperforms other working fluids in heat pump applications, with an optimized theoretical coefficient of performance (COP) at a condensation temperature 22 K lower than critical temperatures. However, actual COP deviates due to a significant pressure drop, especially with inadequate volumetric capacity. A key finding is that a substantial portion of the pressure reduction is attributed to mitigating irreversible losses, estimated at a condensation temperature of 70–75°C, emphasizing the complex relationship between pressure and performance. The study suggests that R1234ze (Z) is more suitable for high-temperature applications than traditional air conditioning systems. In a parallel assessment, the initial calculation of the coefficient of performance for R245fa evaluates the reliability of a new refrigeration industry arrangement. Test results for heat pump technology reveal that R1234ze (Z) achieves an impressive COP of up to 3.60 at a buildup temperature of 90°C with a temperature differential of 45 K. This positions R1234ze (Z) as a suitable choice for heat pump applications prioritizing simplicity in system design.

Comparative life cycle assessment of light frame timber and reinforced concrete masonry structural systems for single-family houses in Luxembourg

The building sector's significant greenhouse gas emissions and energy consumption present added challenges to meeting European climate commitments amidst rapid population growth. In Luxembourg, single-family houses dominate the residential buildings, noticeably contributing to construction waste and CO2 emissions. This study compares the environmental impacts of a three-story reinforced concrete masonry single-family house and an identical timber building in Luxembourg, emphasizing greenhouse gas emissions and embodied energy. A cradle-to-grave life cycle assessment was conducted using Building Information Modelling (BIM) models to analyze the global warming potential and primary energy requirements. Environmental product declarations from the producers and the ÖKOBAUDAT German database were used to determine the environmental impacts of the materials. The results show that the timber building outperforms the concrete building with a 43.5% lower global warming potential, while the concrete building demonstrates a 15.6% reduction in primary energy demand. This aligns with the average outcomes of seven similar studies discussed in this paper, at 33.2% and 4.7%, respectively. Moreover, the timber building is 78.6% lighter than the concrete one. When evaluating benefits and loads beyond the system boundary, the timber building provides 3.6 and 4 times greater advantages in terms of global warming potential and primary energy, respectively, compared to the reinforced concrete masonry building. Additionally, the study explores the impact of reusing the floors in the timber building. The cradle-to-grave LCA reveals that reusing the timber slabs improves the building's global warming potential and primary energy by 2.4% and 1.2%, respectively. However, when considering the benefits and loads beyond the system boundary, floor system reuse exhibits a 38.9% surge in global warming advantages while reducing primary energy benefits by 28.1%. The findings advocate for a policy promoting timber construction and reuse in Luxembourg, aiming to achieve the net-zero emission target by 2050.

Comparative assessment of pyrolysis and Gasification-Fischer Tropsch for sustainable aviation fuel production from waste tires

The aviation industry is a major source of greenhouse gas emissions, making it critical to transition from traditional fossil jet fuels to eco-friendly sustainable aviation fuels (SAF). This change is essential to achieve the goal of net-zero emissions by 2030. Moreover, Waste tires presents a significant environmental challenge due to their durability and difficulty of disposal. Their toxic and flammable nature complicates storage and processing. To address these challenges, waste tires can be processed to SAF using thermochemical processes such as pyrolysis to bio-oil and hydroprocessing, or gasification to syngas and Fischer-Tropsch synthesis (GFT). While waste tires appear to be a viable feedstock,there have not been studies to date that thoroughly compared the most efficient thermochemical process of converting waste tires to SAF. This study compares the economic and environmental impacts of two waste tire based SAF production methods (Pyrolysis/hydroprocessing and GFT). Economically, both methods are more favorable compared to other SAF pathways such as alcohol to jet (ATJ) or hydroprocessing of esters and fatty acids (HEFA). Pyrolysis SAF costs more (0.78 USD/l) than GFT SAF (0.66 USD/l). Pyrolysis is sensitive to hydrogen costs, with a 30% price fluctuation significantly impacting its minimum fuel selling price (MFSP). In contrast, the GFT method is more influenced by catalyst costs. Environmentally, pyrolysis emits less CO2 (34.3 kg CO2 eq/kg SAF) compared to GFT (58.6 kg CO2 eq/kg SAF) but has a higher potential environmental impact in several categories, except for terrestrial ecotoxicity, where both methods are similar. Although pyrolysis has a lower global warming potential (GWP), it presents higher risks in toxicity and photochemical pollution.

Biochar from agricultural wastes: Environmental sustainability, economic viability and the potential as a negative emissions technology in Malaysia

Biochar used for soil amendment is considered a viable negative emissions technology as it can be produced easily from a wide range of biomass feedstocks, while offering numerous potential agricultural benefits. This research is the first to present a comprehensive sustainability assessment of large-scale biochar production and application in Malaysia. The five feedstocks considered comprise the country's most abundant agricultural wastes from palm oil (empty fruit bunches, fibres, palm fronds and shells) and rice (straw) plantations. Combined with process simulation, life cycle assessment and life cycle costing are used to assess the sustainability of biochar production via slow pyrolysis at different temperatures (300–600 °C), considering two functional units: i) production and application of 1 t of biochar; and ii) removal of 1 t of CO2from the atmosphere. The cradle-to-grave system boundary comprises all life cycle stages from biomass acquisition to biochar use for soil amendment. The positive impacts of the latter, such as carbon sequestration, fertiliser avoidance and reduction in soil N2O emissions, are also included. The global warming potential (GWP) is net-negative in all scenarios, ranging from −436 to −2,085 kg CO2 eq./t biochar and −660 to −933 kg CO2 eq./t CO2 removed. Per t of biochar, the systems with shells have the lowest GWP and those with straw the highest, all showing better performance if produced at higher pyrolysis temperatures. However, the temperature trend is opposite for all other 17 impacts considered, with fibres being the best option and fronds the worst for most categories. Per t CO2 removed, fronds have the highest impact in eight categories, including GWP, and shells the lowest in most categories. All impacts are lower for biochar production at higher temperatures. The main hotspot is the pyrolysis process, influencing the majority of impact categories and contributing 66–75 % to the life cycle costs. The costs range from US$116–197/t biochar and US$60–204/t CO2 removed. The least expensive systems per t biochar are those with straws and per t CO2 removed those with shells, while fronds are the worst option economically for both functional units. Utilising all available feedstocks could remove 6–12.4 Mt of CO2 annually, reducing the national emissions from the agricultural sector by up to 54 % and saving US$36.05 M annually on fertilisers imports. These results will be of interest to policy makers in Malaysia and other regions with abundant agricultural wastes.

An innovative ocean thermal energy conversion system with zeotropic Rankine cycle and direct contact membrane distillation for enhanced efficiency and sustainability

This research introduces an integrated ocean thermal energy conversion water and power cogeneration system (OTEC-WPCS), combining a Zeotropic Rankine Cycle (ZRC) with Direct Contact Membrane Distillation (DCMD) for efficient power and water production. The hydrofluoroolefins (HFOs), chosen for their zero ozone depletion potential (ODP) and extremely low global warming potential (GWP), are used as working fluid components in the ZRC. Additionally, DCMD is implemented for freshwater generation. A mathematical model is established, incorporating both thermodynamic and CFD simulations. The goal is to identify optimal operating conditions that maximize the output of the system. By coupling DCMD and ZRC in series, the system's efficiency reaches 8.92 %, an improvement of 5.71 % compared to a standalone ZRC system. This configuration allows for more efficient use of surface seawater heat compared to an ammonia-based Organic Rankine Cycle (ORC)-DCMD system. The enhancements include an increase in power and water production per unit mass flow of surface seawater by 0.55 kW/(kg·s) and 30 %, respectively. Over 60 % of the system's exergy destruction occurs in the DCMD modules and evaporator, while nearly 80 % of the capital cost is associated with the evaporator, condenser, and DCMD heat exchanger. Enhancing the DCMD module structure and heat exchanger can improve both energy and exergy efficiency, and economic feasibility.

Novel material-oriented valorization of biogas can achieve more carbon reduction than traditional utilization by bioelectricity or biomethane

Two novel biogas upgrading strategies that recover high-value chemicals or CO2 liquid fertilizer from biogas besides biomethane were evaluated from the view of global warming potential (GWP) through life cycle assessment in comparison with conventional approaches. Results show that the scenarios producing biomethane with nano calcium carbonate or CO2 liquid fertilizer from biogas present significantly lower GWP (–3.4 kgCO2-eq/Nm3-biogas and –4.4 kgCO2-eq/Nm3-biogas, respectively), compared to combined heat and power scenario (–2.4 kgCO2-eq/Nm3-biogas) and biogas upgrading by high pressure water scrubbing scenario (–1.3 kgCO2-eq/Nm3-biogas). The carbon sequestration and utilization from CO2-rich water significantly enhanced carbon reduction in overall biogas management. Furthermore, considering cleaner electricity in the future, strategies focusing on managing biogas for materials will align more with climate change goals than energy-focused strategies. This study provides insight for decision-makers in developing roadmaps for carbon reduction pathways in biogas-relating sectors.

Proper C/N ratio enhances the effect of plant diversity on nitrogen removal and greenhouse effect mitigation in floating constructed wetlands.

Treating wastewater with low carbon-to-nitrogen (C/N) ratios by constructed wetlands (CWs) is still problematic. Adding chemicals is costly and may cause secondary pollution. Configuring plant diversity in substrate-based CWs has been found to be a better way to treat low-C/N wastewater, but wastewater treatment in floating CWs needs to be studied. In this study, wastewater with C/N ratios of 5 and 10 were set in simulated floating CWs, and 9 combinations with plant species richness (SR) of 1, 3, and 4 were configured. The results showed that (1) increasing SR improved the total N mass removal (NMR) by 29% at a C/N ratio of 5 but not 10; (2) the presence of Oenanthe javanica in the microcosms increased the NMR by 13% and 20% with C/N ratios of 5 and 10, respectively; (3) increasing SR mitigated the net global warming potential (GWP) by 120% at a C/N ratio of 5 but not 10; and (4) a Hemerocallis fulva × O. javanica × Echinodorus parviflours × Iris hybrids mixture resulted in a high NMR and low net GWP. In summary, assembling plant diversity in floating CWs is an efficient and clean measure during the treatment of wastewater with a C/N ratio of 5.