Advances in Green Energy, Environment and Carbon Neutralization

1. Introduction

Population growth and industrialization have led to a rapid increase in the consumption of fossil fuels and resources [1,2,3], which has brought problems such as energy shortages and environmental pollution [4,5,6]. Furthermore, the use of fossil fuels increases greenhouse gases in the environment [7,8]. Rising concentrations of greenhouse gases in the atmosphere threaten ecosystems and economic development, contributing to global warming, rising sea levels, and frequent extreme weather [9,10,11]. Moreover, climate change can exacerbate health threats by increasing diseases caused by high temperature, air pollution, and waterborne infections [12,13]. In order to achieve carbon neutrality, multiple solutions are being developed to reduce greenhouse gas emissions in different sectors, including energy use, transportation, industrial production, construction, and agriculture [14,15]. For example, the production of bioenergy from algae is attracting attention [16,17]. Algae grow quickly, have a high lipid content, and can use CO₂ or wastewater as raw materials for production [18,19,20]. This process can reduce environmental pollution and simultaneously generate renewable energy, which is beneficial for reducing greenhouse gas emissions, making it a promising solution [21,22]. In summary, it is necessary and urgent to research and develop new solutions to achieve green energy production and reduce environmental pollution.

This Special Issue offers a variety of solutions to solve energy, environmental problems, and the achievement of carbon neutrality, which could be useful for scholars, engineers, students working in related fields.

2. Review of New Advances

A large amount of external natural resources is used in the production of the industry, the most important of which are energy and water [23]. A variety of approaches have been adopted to reduce energy and water use in industry. Oliveira and Matos assessed two case studies on Water and Energy Integration Systems (WEISs) in the Portuguese process industry according to several sustainability and strategic-aim-related indicators [24]. The results showed that WEISs are effective in terms of circular economy, eco-efficiency, and strategic objective achievement potential. The aggregated eco-efficiency indicator and recirculated heat over total energy consumption were improved by 4.00–6.46% and 6.69–8.58%, respectively. This work is an extension of the environmental and economic studies related to such systems to reduce energy and water consumption and achieve sustainable development goals. Future research should be carried out using industrial case studies and social aspects of sustainability.

Diesel engines are adopted in many fields, including transportation, power generation, and agricultural production, but their use emits a variety of pollutants such as CO₂, hydrocarbons and particulate matter, contributing to the greenhouse effect and threatening the environment and human health [25]. Using a mixture of diesel and alcohol is a viable way to address these issues. This does not require changes to the engine’s fuel system and can improve the efficiency of fuel combustion. Jin et al. prepared methanol/diesel/n-butanol and ethanol/diesel/n-butanol microemulsions under different temperatures using four different preparation methods [25]. It was found that temperature affected the composition of microemulsions. High temperatures can decrease the amount of cosolvent in ultrasonic processes by up to 25% because of the high-energy mode of ultrasound. The best solubilization was obtained at 45 °C, and the stability of the microemulsion was improved when a large proportion of low-carbon alcohols were applied. This research can provide ideas and methods for the development of low-carbon alcohol fuels.

The environmental burden affects global development, a systematic analysis of which is critical for the implementation of sustainable development of economy [26]. Török investigated the impact of decreasing hazardous substance emissions by technological developments on the sustainability of the environment in European Union (EU) countries during 2012–2022 [26]. The study showed that between 2012 and 2022, the total environmental burden in the EU did not decrease significantly. Eleven member countries had high economic output and a declining total environmental burden. Sixteen member countries had an increase in the total environmental burden, but the economic output was low. It was indicated that gross domestic product growth was an important reason for keeping the total environmental burden at the same level. It was suggested that member countries could be encouraged to maintain the implementation of environmental protection legislation in order to limit the high environmental burden on the society and economy.

Microalgae are considered promising feedstocks for the sustainable production of biofuels, but their application is limited by culture substrates [27]. Pyo et al. proposed an effective method to utilize CO₂ in the atmosphere and maintain microalgae biomass and lipid accumulation [14]. Results have shown that microalgae can use CO₂ in the air to grow and accumulate lipids. Under laboratory-scale experiments, the group with the addition of 5 mM CaCO₃ stably maintained pH and improved biomass concentration and lipid content by 17.68-fold and 9.58-fold, respectively, compared to the control group. Under bench-scale tests, cultures supplemented with 5 mM CaCO₃ increased biomass and lipid concentrations by 9-fold and 7.15-fold, respectively, compared to the untreated group. The technology can promote the carbonic anhydrase enzyme activity in microalgae, and convert CO₂ into bicarbonate, allowing algal cells to maximize its utilization. This cultivation system could provide a practical and promising method for industrialization to produce valuable products and remove CO₂ from the air.

Some industrial plants, such as chemical plants and petroleum plants, can emit volatile organic compounds (VOCs) during production [28]. In order to reduce VOCs emissions, the researchers have proposed a method to improve fuel conversion efficiency by recovering heat in repeated cooling and steam condensation in combustion. Park et al. developed a regenerative thermal oxidizer (RTO) and improved the structural design to reduce the fatigue of RTO and achieve stable combustion in the combustion chamber [29]. After 177 h of experiments, the VOC removal rate, oxidation efficiency and waste heat recovery rate reached 95%, 97.87% and 95.78%, respectively. Moreover, the nitrogen oxide concentration and fuel consumption were 3.9 ppm and 21.95%, respectively. In the future, the stability and safety of the system can be enhanced through digital twin-based long-distance monitoring.

Cities, as centers of people’s lives and production, consume about 75% of global energy and contribute 80% of global greenhouse gas emissions [30]. The building sector contributes about 40% of global carbon emissions, so there is a need to reduce its carbon emissions. Du et al. investigated an annual carbon emission accounting framework using the whole life cycle, and used LEAP-SD modeling to analyze and simulate the carbon emissions of buildings with Shenzhen as a case study [30]. The carbon emissions of Shenzhen’s urban building sector showed an upward trend from 2000 to 2022. Population effect, energy intensity effect and floor area effect are the key factors affecting carbon emissions. A 10% reduction in building energy consumption is expected to lead to a carbon peak in the building sector around 2030, with a peak of 32.30 MtCO₂ around 2038. In order to reduce carbon emissions, the efforts of collaboration between cities and the advancement of technology are very important.

3. Conclusions

The papers in the Special Issue “Advances in Green Energy, Environment and Carbon Neutralization 2022–2024” include research fields such as water and energy integration systems, low-carbon alcohol blended fuels, the trend in environmental load, microalgae cultivation systems, regenerative thermal oxidation devices and dynamic simulations of carbon emission peaks. These efforts focus on energy conservation and emission reduction and use different methods to assess or reduce greenhouse gas emissions in industrial production and residential life. The content contained in these articles complements the reader’s information and knowledge on the environment, energy, and carbon neutrality, and helps to stimulate further scientific and technological developments.