Carbon Dioxide Research Articles

Spectroscopic Investigation of the Role of Water in Copper Zeolite Methane Oxidation.

Methane is one of the most potent greenhouse gases; developing technology for its abatement is essential for combating climate change. Copper zeolites can activate methane at low temperatures and pressures, demonstrating promise for this technology. However, a barrier to industrial implementation is the inability to recycle the Cu(II) active site. Anaerobic active site regeneration has been reported for copper-loaded mordenite, where it is proposed that water oxidizes Cu(I) formed from the methane reaction, producing H2 gas as a byproduct. However, this result has been met with skepticism given the overall reaction is thermodynamically unfavorable. In this study, we use X-ray absorption and electron paramagnetic resonance spectroscopies to study the role of water in copper zeolite methane oxidation. We find that water does not oxidize Cu(I) to Cu(II) in CH4-reacted Cu-MOR. Further, using isotope label mass spectrometry, we detail an alternate source of the hydrogen byproduct. We uncover that, although water does not oxidize Cu(I), it has the potential to facilitate low temperature methane abatement through promotion of product decomposition to carbon dioxide and H2.

CO2 Laser Crystallization in Ambient for Highly Efficient FAPbI3 Perovskite Solar Cells.

Metal halide perovskite solar cells have achieved tremendous progress and have attracted enormous research and development efforts since the first report of demonstration in 2009. Due to fabrication versatility, many heat treatment methods can be utilized to achieve perovskite film crystallization. Herein, 10.6µm carbon dioxide laser process is successfully developed for the first time for perovskite film crystallization. In addition, this is the first time formamidinium lead triiodide solar cells by laser annealing under ambient are demonstrated. The champion cell produces a power conversion efficiency of 21.8%, the highest for laser-annealed perovskite cells. And this is achieved without any additive, passivation, or post-treatment.

EXAMINING EFFECTS OF AIR POLLUTION ON PHOTOVOLTAIC SYSTEMS VIA INTERPRETABLE RANDOM FOREST MODEL

Renewable energy plays a vital role in power generation and solar photovoltaic systems due to resource availability throughout the year. This work aims to investigate the impact of air pollutants and meteorological parameters on the performance of the photovoltaic systems locally, taking into consideration the advantages of the photovoltaic power potential of the SW part of Romania, where Craiova is located (average solar radiation intensity > 1350 kWh/m2/year). This study is based on a one-year dataset provided by a sensor that monitors particulate matter concentrations, volatile organic compounds, dioxide of carbon, ozone, noise, formaldehyde and three climate parameters (temperature, pressure, and relative humidity). The research methodology applies an innovative interpretable random forest model emphasising the implications of air pollution for photovoltaic systems. The proposed machine learning model was trained to predict the particulate matter level in air based on the basic environmental variable measurements. The study presents six random forest models of varying complexity, which reach the accuracy of classification for the selected problem up to 99%, and applies the Shapley Additive Explanations technique to interpret the decision-making model. The observation regarding the highest concentration of particulate matter occurring during cold months, which typically do not align with peak solar irradiance, underscores the importance of considering various environmental factors in solar energy planning. With its practical implications, this insight offers decision-makers valuable information about the feasibility of optimising solar energy generation despite seasonal variations in air pollution levels, directly addressing their needs and concerns.

Guyparkeria halophila: Novel cell platform for the efficient valorization of carbon dioxide and thiosulfate into ectoine

Utilizing carbon dioxide (CO2) for valuable chemical production is key to a circular economy. Current processes are costly due to limited microorganism use, low-value products, and the need for affordable energy. This study addresses these challenges by using industrial contaminants like thiosulfate (S2O32−) for CO2 conversion into ectoines. Ectoines, are important ingredients as pharmaceuticals and cosmetics. Here, six microbial genomes were identified as potential candidates to valorize CO2 and S2O32− into ectoine. After laboratory validation at 3 % NaCl, the fastest-growing strain, Guyparkeria halophila, was optimized at 6 %, 9 %, and 15 % NaCl, showing the highest specific ectoine contents (mgEct gbiomass−1) at 15 %. Batch bioreactors, combining optimal conditions, achieved maximum specific ectoine contents of 47 %. These results not only constitute the highest ectoine content so far reported by autotrophs and most of heterotrophs, but also the first proof of a novel valorization platform for CO2 and S2O32−, focused on pharmaceuticals production.

Benchmarking building energy consumption for space heating using an empirical Bayesian approach with urban-scale energy model

Calibration of an urban-scale building energy model is crucial for advancing building energy efficiency codes and policies to reduce carbon dioxide emissions whereas the accuracy of the model is challenged by performance gaps resulting from sparse data and uncertainties in modeling. An empirical Bayesian (EB) approach, incorporated a probability-based mixed-effects energy model and Monte Carlo Markov chain simulation, was developed to predict and benchmark building energy use intensity (EUI) for space heating, using the metering data of 2020 stochastically sampled district heating substations from a municipal utility database. The limitations, implementations and performances of different modeling strategy, including EB as well as Maximum Likelihood Estimation (MLE), Maximum A Posteriori (MAP) and Fully Bayes (FB) were compared. The results show that EB strategy achieved superior prediction performance than other strategies on the novel test dataset. The preparation, calibration, and validation efforts for implementing the EB approach were demonstrated. The proposed methodology is recommended as a robust approach for benchmarking urban-scale building EUI, distinguished from other machine learning approaches by requiring fewer training samples, better interpreting uncertainties in the data used, and exhibiting superior generalization capabilities. The proposed methodology was successfully demonstrated through the urban-scale benchmarking of space heating EUI in Beijing.

Integrative analysis of transcriptome and phytohormones reveals new genes network involved in shoot apical meristem development in maize under blue and red light

Blue and red light play a significant role in regulating transcriptional expression, phytohormone levels, and gene signal network reconstruction in the shoot apical meristem. To further elucidate the effects of red and blue light on transcriptional characteristics and phytohormone expression, and to explore signaling pathways and novel genes, we conducted comparative experiments under different light quality treatments. The results are as follows: a total of 22,327 genes were found to be effectively expressed, with a considerable number of alternative splicing events occurring concurrently. Furthermore, 1063 differentially expressed genes were identified, primarily associated with transcriptional variations resulting from the transition from blue light to red light. These differentially expressed genes are predominantly involved in KEGG annotations related to photosynthesis, DNA replication and carbon metabolism. The findings from targeted metabolism analysis reveal significant variations in 45 phytohormones, including ABA, auxin, CK, ETH, GA, JA, and SA. Correlation analysis between transcription and metabolism further indicates that IAA.Glc, IAA.Glu, TRP, mT9G, and GA53 show the strongest correlation with differentially expressed genes, with genes ssu1, ssu2, pep1, me3, and hsp90 displaying a significant relationship. Additionally, in the protein–protein interaction network, three novel genes (LOC100286132, LOC100510780, and LOC103653934) were identified as significant responding to the regulation of blue and red light. Following protein function analysis, the proteins were provisionally identified as ubiquitin conjugating enzyme-like, OXIDATIVE STRESS 3LIKE 2-like, and Ribosomal L 18p/L5e, respectively. Conclusively, it is depicted that the most significant impact of transitions between red light, blue light, and two light qualities lies in the transcriptional process of shot apical meristem of the C4 plant maize. This process is intricately linked to nitrogen availability, carbon dioxide assimilation capacity, and the stimulatory effects of auxin, cytokinin, and gibberellin. The expression of the putative L 18/L5e in blue and BTR light conditions may enhance transcript and synthesis capabilities of ribosome.

Sheep rotational grazing strategy to improve soil organic carbon and reduce carbon dioxide emission from spring wheat in an arid region

Sheep rotational grazing strategy to improve soil organic carbon and reduce carbon dioxide emission from spring wheat in an arid region

Carbon dioxide capture by aqueous glucosamine solutions: Pilot plant measurements and a theoretical study

Carbon dioxide capture by aqueous glucosamine solutions: Pilot plant measurements and a theoretical study

Cu-PORPHYRIN-BASED POLYMERS IN ELECTROREDUCTION REACTIONS OF GASES

In this work, the electrochemical properties of Cu-complexes of di- and tri-amino-substituted tetraphenylporphyrins in dichloromethane were investigated by the cyclic voltammetry method. Electrooxidation of porphyrins in a dichloromethane solution produced polyporphyrin films on the electrode. The formation of polymers occurs through the amino groups of phenyl substituents with the generation of phenazine and dihydrophenazine fragments. The surface morphology and thickness of polyporphyrin films were studied using a scanning electron microscope. The surface of the poly-Cu5,15-di(4′-aminophenyl)-10,20-diphenylporphyrin film is a network of fibers of about 5 µm long and 0.2-0.3 µm thick. The film thickness is 14 µm. The surface of poly-Cu5,10,15-tri(4′-aminophenyl)-20-phenylporphyrin has large branched agglomerates of indefinite shape; the film thickness is 22 µm. The catalytic activity of the obtained polyporphyrin films in oxygen and carbon dioxide electroreduction reactions were evaluated. Poly-Cu5,10,15-tri(4′-aminophenyl)-20-phenylporphyrin was found to be more catalytically active in both reactions, which is evidently associated with a more developed surface of the polymer.

Electrostatically driven kinetic Inverse CO2/C2H2 separation in LTA-type zeolites

The identical molecular size and similar physical properties of carbon dioxide (CO2) and acetylene (C2H2) make their adsorptive separation extremely challenging to achieve with most adsorbents. Reports on the separation of CO2 and C2H2 mixtures by zeolites are even rarer with the mechanism of adsorptive separation requiring further exploration. In this paper, we report that ion modulation of zeolite 5A promotes the difference in kinetic diffusion of CO2 and C2H2, realizing the inverse separation of zeolite from selective adsorption of C2H2 to selective adsorption of CO2. Creating a compact pore space restricting the orientation of gas molecules enables charge recognition. The positive electrostatic potential at the pore openings was utilized to hinder the diffusion of C2H2 between the cages while ensuring the transfer of CO2, increasing their diffusion differences in the pore channels and leading to the CO2/C2H2 kinetic selectivity of 31.97. Grand canonical Monte Carlo (GCMC) simulation demonstrates that the CO2 distribution in K-5A-β is significantly higher than that of C2H2. Dynamic breakthrough experiments verified the excellent performance of the material in practical CO2/C2H2 separation, for CO2/C2H2 (50/50 and 1/99, v/v) mixtures can be separated in one step thus directly generating high purity C2H2 (>99.95%), which provides a promising thought for the zeolite-based separation of CO2 and C2H2.

Local differences in robustness to ocean acidification.

Ocean acidification (OA) caused by increased atmospheric carbon dioxide is affecting marine systems a globally and is more extreme in coastal waters. A wealth of research to determine how species will be affected by OA, now and in the future, is emerging. Most studies are discrete and generally do not include the full life cycle of animals. Studies that include the potential for adaptation responses of animals from areas with different environmental conditions and the most vulnerable life stages are needed. Therefore, we conducted experiments with the widely-distributed blue mussel, Mytilus edulis, from populations regularly exposed to different OA conditions. Mussels experienced experimental conditions prior to spawning, through embryonic and larval development, a highly vulnerable stage. Survivorship to metamorphosis of larvae from all populations was negatively affected by extreme OA conditions (pH 7.3, Ωar, 0.39, pCO2 2479.74), but, surprisingly, responses to Mid OA (pH 7.6, Ωar 0.77, pCO21167.13) and Low OA (pH 7.9, Ωar 1.53, pCO2 514.50) varied among populations. Two populations were robust and showed no effect of OA on survivorship in this range. One population displayed the expected negative effect on survivorship with increased OA. Unexpectedly survivorship in the fourth population was highest under Mid OA conditions. There were also significant differences in development time among populations that were unaffected by OA. These results suggest that adaptation to OA may already be present in some populations and emphasizes the importance of testing animals from different populations to see the potential for adaptation to OA.

Contemporary roof pattern for energy efficient buildings: Air conditioning cost alleviation, CO2 emission mitigation potential and acceptable payback period

Buildings account for a significant portion of global energy use and consumption. Buildings have substantial energy consumption due to the use of heating, ventilation, and cooling systems. It is evident that the use of insulation materials and phase change materials (PCMs) in the design of buildings can effectively reduce the cost of air conditioning by reducing external heat gains and losses. Additionally, the use of environmentally friendly, cost-effective, and natural materials can be beneficial from an environmental standpoint. This paper aims to evaluate the potential for cost savings in the air conditioning of various PCMs and insulation-stuffed building roof configurations. In that respect, four types of phase change materials (HS29, HS36, FS42, and FS30) and four insulation materials (Therma cork, sawdust, aerogel, and sheep wool) were selected. The thermophysical properties of PCMs (solid and liquid state), insulation materials, and building elements were determined experimentally as per ASTM D 5334 standards. Ten various building roof models (contemporary roof pattern) are studied with four various PCMs and four various insulations. In addition, novel building roof design integrated with PCM/insulation were analysed numerically, related to environmental conditions that refer to two different scenarios in India (hot dry and composite climates). It further analyses the reduction in greenhouse gas emissions associated with different roof configurations. The aforementioned PCM/insulation materials were stuffed in the void spaces of the contemporary roof pattern. Thermo-economic analysis of novel roof design with PCM/insulation materials on air-conditioning costs, carbon dioxide emissions and payback time are compared with conventional roofs (CR) and contemporary roof patterns (CRP). The thermo-economic analysis was carried out based on the number of degree-hours of heating and cooling to determine the building's annual energy usage. HS29 PCM stuffed roof pattern (HS29RP) saved the highest total energy cost savings of 11.89/14.71 $/m2/year when compared with conventional roof and 11.35/13.89 $/m2/year compared with contemporary roof pattern for Jabalpur/Kota climatic conditions. HS29 PCM stuffed roof pattern (HS29RP) exhibits the maximum carbon emission mitigation of 215.32/275.37 kg/kWh when compared with conventional roof and 204.95/259.57 kg/kWh for climatic conditions of Jabalpur/Kota. While considering shortest payback span, sawdust stuffed roof pattern shows the minimum payback period of 0.69 and 2.15 years when compared with conventional roof and contemporary roof pattern. The findings of this research offer significant contributions to the development of energy-efficient building envelopes applicable to a wider range of buildings, including those with and without air conditioning systems.

Revisiting the Mechanism of Rapid Gas Decompression Failure in Silica-Reinforced NBR Composites: Effect of Interfacial Phenomena

Sudden pressure drop in elastomers saturated with high temperature-high pressure gas produces a type of failure known as Rapid Gas Decompression (RGD). Understanding the relationship between the RGD and the material behavior paves the way for better control of the RGD. It is the aim of the present work to study the effect of rubber-silica interfacial phenomena on the RGD resistance of nitrile butadiene rubber (NBR) composites. By grafting various degrees of a long-chain monofunctional silane onto the silica surface, composites having distinct levels of filler-induced mobility restrictions, and also controlled levels of interface strength were prepared. Also, to find the underlying mechanism responsible for controlling the RGD failure, an analysis of silica morphology, the cavitation strength, and the tear strength was performed for the composites. The RGD resistance was assessed under mild (70 MPa) and severe (cyclic test, 150 MPa) testing conditions using carbon dioxide gas. The obtained trend of the RGD damage was roughly correlated to the cavitation test, showing a higher resistance for the silica system having high filler-polymer interaction and bound rubber. It was suggested that the trend of RGD is more complicated to fully capture by a single physico-mechancial mechanism. Alternatively, inspired by the theory of fracture mechanics, it was suggested that the RGD can be better realized if the factors governing the driving force of RGD damage and the factors responsible for the resistance against the RGD are separated.

Synthesis of Propiolic and Butynedioic Acids via Carboxylation of CaC2 by CO2 under Mild Conditions

Carbon dioxide (CO2) is a greenhouse gas, and its resource use is vital for carbon reduction and neutrality. Herein, the nucleophilic addition reaction of calcium carbide (CaC2) to CO2 was studied for the first time to synthesize propiolic and butynedioic acids by using CuI or AgNO3 as catalyst, Na2CO3 as additive, and triphenylphosphine as ligand in the presence/absence of a hydrogen donor. The effects of the experimental conditions and intensification approach on the reaction were investigated. The reactivity of CaC2 is closely associated with its synergistic activation by the catalysts, solvent, and external intensification, such as the ultrasound and mechanical force. Ultrasound helps to promote the reaction by enhancing the interfacial mass transfer of CaC2 particulates. Mechanochemistry can effectively promote the reaction, yielding 29.8% of butynedioic acid and 74.8% of propiolic acid after 2 h ball milling at 150 rpm, arising from the effective micronization and interfacial renewal of calcium carbide. The present study sheds a light on the high-value uses of CO2 and CaC2 and is of reference significance for the nucleophilic reaction of CaC2 with other carbonyl compounds.

Insect tracheal systems as inspiration for carbon dioxide capture systems.

Membrane technology advancements within the past twenty years have provided a new perspective on environmentalism as engineers design membranes to separate greenhouse gasses from the environment. Several scientific journals have published articles of experimental evidence quantifying carbon dioxide (CO2), a common greenhouse gas, separation using membrane technology and ranking them against one another. On the other hand, natural systems such as the respiratory system of mammals also accomplish transmembrane transport of CO2. However, to our knowledge, a comparison of these natural organic systems with engineered membranes has not yet been accomplished. The tracheal respiratory systems of insects transport CO2 at the highest rates in the animal kingdom. Therefore, this work compares engineered membranes to the tracheal systems of insects by quantitatively comparing greenhouse gas conductance rates. We demonstrate that on a per unit volume basis, locusts can transport CO2 approximately ⁓100 times more effectively than the best current engineered systems. Given the same temperature conditions, insect tracheal systems transport CO2 three orders of magnitude faster on average. Miniaturization of CO2 capture systems based on insect tracheal system design has great potential for reducing cost and improving the capacities of industrial CO2 capture.

Real‐Time Product Detection during CO2 Electroreduction on SCILL‐Modified Cu Catalysts

AbstractModifying the chemical environment of active surfaces with ionic liquids (IL) is an emerging strategy for tailoring novel electrocatalytic systems, including carbon dioxide reduction (CO2RR). Although copper (Cu) catalysts have recently gained more attention in this field, their modification with ILs is yet to be investigated. This work tested a range of common hydrophobic ILs impregnated into carbon‐supported Cu catalysts, following the “solid catalyst with ionic liquid layer” (SCILL) approach. The latter was used to showcase the applicability of real‐time product detection for CO2RR employing electrochemical mass spectrometry. The observed patterns of C1 to C3 product selectivity offered valuable insights into the intricate reaction mechanism. In addition, increasing the size of the IL cation showed an opposite and significant effect on the reaction selectivity. The obtained qualitative results were partially compared with conventional long‐term experiments.

A Study on an Energy-Regenerative Braking Model Using Supercapacitors and DC Motors

This study presents an energy regeneration model and some theory required to construct a regeneration braking system. Due to the effects of carbon dioxide (CO2) emissions, there is increasing interest in the use of electric vehicles (EVs), electric bikes, electric bicycles, electric buses and electric aircraft globally. In order to promote the use of electric transportation systems, there is a need to underscore the impact of net zero emissions. The development of EVs requires regenerating braking system. This study presents the advantages of regenerative braking. This system is globally seen in applications such as electric cars, trams, and trains. In this study, the design specification, design methodology, testing configurations, Simulink model, and recommendations will be outlined. A unique element of this work is the practical experiment that was carried out using 1.5 Amps with no load and 2.15 Amps with a load. The discharge voltage was purely from the 22 W bulb load connected to the capacitor bank as we limited this study to the use of 1.5 Amps and it took 15 min for a full discharge cycle, after which no charge was left in the capacitor bank. The results showed that the discharge rate and charging rate for the regenerative braking system were effective but could be improved. The objective of this paper is to investigate how a supercapacitor works alongside a battery in regenerative braking applications. This study demonstrates that the superconductor used can deliver maximum power when required. Also, it can also withstand elevated peaks in charging or discharging current via the supercapacitor. Combining a battery with a supercapacitor reduces the abrupt load on the battery by shifting it to the capacitor. When these two combinations are used in tandem, the battery pack’s endurance and lifespan are both boosted.

Revolutionizing Rice: The Synthesis of Nature's Evolution and Biotechnology in C4 Rice

Agriculture plays a fundamental role in meeting the essential needs of humanity, yet numerous factors continuously influence agricultural production and productivity. Over time, evolving agricultural practices have significantly increased yields of staple food crops, thereby enhancing global food security. However, as the world's population continues to grow, there is a pressing need to further augment crop yields. Historically, increases in yield were achieved by expanding cultivated land, but rapid industrialization and urbanization have diminished available agricultural land and depleted natural resources essential for farming. In response to these challenges, enhancing crop photosynthetic efficiency has emerged as a pivotal strategy. Photosynthesis, the process by which plants convert sunlight into energy, has been optimized in various crops through evolutionary and biotechnological approaches. One such innovation is the adaptation of the C4 photosynthetic pathway into C3 rice, a staple food for billions worldwide. The C4 pathway, found in several efficient crops like maize and sugarcane, enhances carbon dioxide uptake and reduces photorespiration, leading to improved water and nitrogen use efficiency. This review explores the integration of nature’s evolutionary principles with cutting-edge biotechnological advancements in the development of C4 rice. By introducing the C4 pathway into rice—a traditionally C3 plant—scientists aim to dramatically increase its productivity and resilience to environmental stressors. This transformative approach not only holds promise for meeting future food demands sustainably but also addresses the challenges posed by climate change and resource scarcity. Moreover, the review examines the scientific basis, technological innovations, and potential agricultural implications of implementing C4 rice. It highlights the collaborative efforts of researchers, agronomists, and biotechnologists worldwide in reimagining rice cultivation to secure global food supplies while minimizing environmental impact. Ultimately, the integration of C4 photosynthesis into rice represents a significant step forward in agricultural innovation, poised to redefine food production capabilities and enhance global food security in the face of escalating population growth and environmental change.

Robust Nitrogen-Doped Microporous Carbon via Crown Ether-Functionalized Benzoxazine-Linked Porous Organic Polymers for Enhanced CO2 Adsorption and Supercapacitor Applications.

Nitrogen-doped carbon materials, characterized by abundant microporous and nitrogen functionalities, exhibit significant potential for carbon dioxide capture and supercapacitors. In this study, a class of porous organic polymer (POP) were successfully synthesized by linking Cr-TPA-4BZ-Br4 and tetraethynylpyrene (Py-T). The model benzoxazine monomers of Cr-TPA-4BZ and Cr-TPA-4BZ-Br4 were synthesized using the traditional three-step method [involving CH═N formation, reduction by NaBH4, and Mannich condensation]. Subsequently, the Sonogashira coupling reaction connected the Cr-TPA-4BZ-Br4 and Py-T monomers, forming Cr-TPA-4BZ-Py-POP. The successful synthesis of Cr-TPA-4BZ-Br4 and Cr-TPA-4BZ-Py-POP was confirmed through various analytical techniques. After verifying the successful synthesis of Cr-TPA-4BZ-Py-POP, carbonization and KOH activation procedures were conducted. These crucial steps led to the formation of poly(Cr-TPA-4BZ-Py-POP)-800, a carbon material with a structure akin to graphite. In practical applications, poly(Cr-TPA-4BZ-Py-POP)-800 exhibited a noteworthy CO2 adsorption capacity of 4.4 mmol/g, along with specific capacitance values of 397.2 and 159.2 F g-1 at 0.5 A g-1 (measured in a three-electrode cell) and 1 A g-1 (measured in a symmetric coin cell), respectively. These exceptional dual capabilities stem from the optimal ratio of heteroatom doping. The outstanding performance of poly(Cr-TPA-4BZ-Py-POP)-800 microporous carbon holds significant promise for addressing contemporary energy and environmental challenges, making substantial contributions to both sectors.

Comparison of Scenedesmus obliquus in CO2 Capture, Biolipid Production and Nutrient Removal

The cultivation of microalgae from municipal wastewater, while simultaneously removing nutrients from the water column, has the potential to aid biodiesel production and carbon dioxide fixation, thereby alleviating the pressure of energy shortages. In this research, different ratios of sodium bicarbonate and glucose were used to prepare simulated municipal wastewater. The results demonstrated that microalgae were most effectively treated under one-stage direct treatment conditions. During direct culture, the most effective treatment was observed for IAA-3, which exhibited a dry weight of 1.4363 g/L and a lipid content of 25.05% after stimulation with 0.0005 M NaHCO3. In contrast, NaHCO3-2 demonstrated optimal performance during the secondary culture, with a dry weight of 1.6844 g/L and a lipid content of 18.05%. Finally, the economic, social and environmental benefits of direct treatment (IAA-3) and secondary treatment NaHCO3-2 were analyzed. The benefits of direct treatment were found to be USD 0.50989/L, while those of secondary treatment were USD 0.43172/L. For each tonne of municipal wastewater treated, the carbon sequestration benefits of IAA-3 during direct treatment and NaHCO3-2 during secondary treatment were USD 0.45645 and USD 0.85725, respectively.