Elephants are vital to their ecosystems, acting as keystone species and ecosystem engineers that help maintain biodiversity and ecological balance. Their presence and behavior significantly influence the structure of their ecosystems. They help maintain the balance of different plant and animal species, enriching biodiversity. In the present article, the importance of elephants for nature and humans in the areas they inhabit is reviewed. The main anatomical and behavioral features of elephants and the specific care for them in zoo breeding are presented. In this aspect, a survey of the conditions and care for elephants in the zoos in Sofia and Athens was carried out. The importance of climatic factors in the respective regions was also highlighted. It was established that the conditions of breeding and care for the animals are maximally tailored to their characteristics and requirements, which is why the health status of all elephants bred in both zoos is very good. The cooperation between the zoos in Sofia and Athens is fruitful for the bringing up these exotic animals.

The report presents a project to study the synergy between fertilization and irrigation of agricultural crops. The goal is to optimize agricultural production processes to achieve Sustainable Agriculture in climate change conditions. Multifactorial experiments with macronutrients nitrogen, phosphorus, potassium, silicon, and micronutrients zinc and boron are described. Crop rotation as the most important element of agricultural practice is explained and the stages and modules of Precision Agriculture are presented. Results from a simulation-modeled experiment are given.

This paper conducts a comprehensive analysis of the construction cost associated with long-distance, large-scale Compressed Air Energy transmission via pipelines compared to electricity as a main energy carrier. The study indicates notable disparities in terms of compressed air energy transmission costs versus electrical transmission. The lower cost emphasizes the cost-effectiveness of Compressed Air Energy as a promising and economical method for energy transmission over varying distances. Another advantage of transmitting energy through compressed air pipelines is that it provides an opportunity to integrate the intermittent renewable energy sources such as solar and wind power more effectively. It puts a spotlight on Compressed Air Energy pipelines as a key topic for discussion and further investigation.

Anaerobic digestion is a biotechnological method of biogas generation from organic wastes. Anaerobic co-digestion can be considered as the instantaneous anaerobic digestion of two or more substrate and co-substrate mixtures. Anaerobic co-digestion is a pragmatic method to resolve the difficulties related to substrate properties and system optimization in single-substrate anaerobic digestion. During the last two decades our multidisciplinary team performed a lot of experiments of anaerobic co-digestion of different organic wastes activated sludge, cattle manure, swine manure, milk whey, wasted fruits and vegetables etc. Different ratios of mixtures of these organic wastes, in binary and triple mixtures, have been investigated in view to maximize the obtained energy (methane) production. The time for reaching of the process steady state in laboratory anaerobic digesters have been determined to be ten days’ period. Results obtained have shown that some binary mixtures are more perspective in regards to biogas production optimization. It has been found that the addition of 3rd substrate to some binary mixtures could lead to decrease of bioprocess effectiveness.

A portable muon telescope for monitoring of cosmic rays has been developed, based on GM counters shielded with lead adsorbers. The triple coincidence mode of operation results in a relatively good spatial resolution allowing to measure the cosmic ray flux, its east-west anomaly and also to detect the consequences of the special theory of relativity. The apparatus is suitable for long term observations of the cosmic ray flux and due to its simple and robust construction can also be used also for educational purposes.

In our modern world, technological developments on the one hand, and global warming and its consequences, on the other hand, cause us to feel the necessity for reliable, cost-effective, and clean energy. Using renewable energy sources paired with compressed air energy storage can be a good option that meets these expected criteria. Although a compressed air energy storage system (CAES) is clean and relatively cost-effective with long service life, the currently operating plants are still struggling with their low round trip efficiencies. This paper illustrates an up-to-date review of compressed air energy storage systems containing changes in the conventional process to improve performance and increase efficiency. Three main categories of compressed air energy storage technology, diabatic, adiabatic, and isothermal, are analyzed theoretically. In addition, three components of a compressed air energy storage system including compression system, reservoirs, and expansion system are discussed here in detail. The advantages, disadvantages, and the technological readiness of different types of CAES are discussed.

Photovoltaic solar panels remain one of the most commonly available avenues for acquiring renewable energy for small-scale end users but despite their promising potential their implementation continues to remain outside the realm of possibility for most. The combination of high upfront costs, long payback periods, and complex installation requirements results in a disincentive to purchase the technology and relies on significant appeals to morality as a driving force as opposed to purely economic incentives. An alternative implementation of photovoltaic arrays for small scale use combined with grid power supplement is herein proposed that better matches energy consumption profiles in the household and seeks to reduce cost and complexity. The system comprises a hydronic thermal storage system acting as hot water supply, furnace, and air conditioning for power regulation and distribution in combination with electrical distribution to home appliances using minor modification to the power supply. Currently used batteries, charge controllers, and inverters are eliminated and replaced with a single specialized outdoor central air-conditioning condenser unit that distributes electrical and thermal energy but would not supply electricity onto the grid. Examination of minor electronic modifications on common switched mode power supply topologies has found that regulation of a wide range of variable voltage solar electricity input is currently possible and does not cause overheat or other harm to the power supply. The proposal provides a workable solution to alleviate financial and technical burden on the individual and promotes the vision of a 100% renewable energy society while working within economic constraints.

Nowadays, there are still many challenges to overcome in order to enable long-termed human space exploration beyond low Earth orbit (LEO) and metabolic resources management (reliable air, water and food supply for the crew) is of utmost importance. Currently, Environmental Control and Life Support Systems (ECLSS) aim to overcome the challenge of constant re-supply from Earth requirement by revitalization of air and water. Here, we provide an overview of the existing and operating ECLSS on-board the International Space Station (ISS) as well as identify potential areas of technology development for biological ECLSS for long-term human space missions focusing on the inclusion of waste treatment and food production.

In the past 20 years Microbial fuel cells (MFCs) have been extensively studied regarding the possibility of transforming organic waste directly into electricity. There are significant differences between MFCs and conventional low temperature Fuel Cells (FCs), which make MFCs attractive: biotic catalyst at the anode; the anodic fuel is complex organic waste; MFCs operate under mild reaction conditions (neutral pH, temperature and pressure), close to ambient levels as optimum. Like chemical fuel cells, MFCs are composed of anode and cathode. Oxygen is an ideal electron acceptor for MFCs because of its high redox potential, availability, and sustainability. However, the Oxygen Reduction Reaction (ORR) is kinetically sluggish, resulting in a large proportion of potential loss. Also, working conditions are quite different because of the type of complex media in which MFCs operate. In order to overcome these limitations, catalysts are often used to lower the overpotentials and accelerate the kinetics of the oxygen reduction reaction. One of the main challenges is the development of efficient and stable cathode catalysts for MFCs. By far, Pt and Pt-based catalysts (PGMs) have been extensively used, due to their catalytic efficiency in gas-diffusion electrodes. But the high cost and low durability have significantly lowered their utilization in MFCs. A variety of non-precious metal catalysts have been developed for MFC applications including carbon-based catalysts, carbon supported composite catalysts, Me-based catalysts and biocatalysts. It is supposed that the ORR catalyst used for wastewater treatment in MFCs is simple to synthesize, cost-effective, durable after long-term operation in wastewater, tolerant to poisoning and able to restore catalytic activity after cleaning. In this regard carbon-based catalyst may be the most promising candidate for practical applications. This study reviews different carbon-based ORR catalysts for MFC applications for wastewater treatment and energy recovery.