ABSTRACTUrban ponds are widely recognised as high-emission hotspots of greenhouse gases (GHGs), mainly in the form of methane. Whereas hyper-eutrophication also simultaneously presents an opportunity to harness algal biomass for substantial energy recovery. The present study addresses this dual challenge and opportunity by studying Hauz Khas Pond, a 15-acre hyper-eutrophic urban pond in South Delhi, India. This pond receives a continuous inflow of treated effluent to maintain water levels in the pond.Comprehensive long-term monitoring of nutrient dynamics, water quality, and biomass generation revealed persistent hyper-eutrophic conditions with TSI of 197.6 ± 10.7 with minor seasonal fluctuations. Continuous nutrient loading ((PO₄³⁻: 4–8 mg L⁻¹, NO₃-N: 1.9-3.13 mg/L),and shallow depth (1-2.5m), is causing high algal productivity and benthic methanogenesis leading to high methane emissions (~1.7 times freshwater systems). Although biomass assessment revealed average standing algal biomass in pond of approximately 183 tonnes and 43% of which is excess eutrophic biomass (approx. 80 tonnes) and can be harnessed for energy recovery without affecting ecological health of aquatic life in pond. The harvested algal biomass was characterized using biochemical methane potential assays, which demonstrated competitive methane yields under anaerobic digestion. This recoverable fraction alone holds methane generation potential of about 20000 m3 equivalent 0.37 m3m-2. This finding indicates the possibility of an in situ energy recovery system. Since India has sufficient solar energy availability Power-to-Gas technology is further being proposed to enhance the methane percentage upto 95%.This technology involves injecting renewable hydrogen into the anaerobic digestion process, which upgrades the biogas produced to pipeline- grade methane.By combining nutrient management, continuous harvesting, and integrating renewable energy, this nature-based algal harvesting approach can achieve controlled emissions while enhancing urban water quality. Our research redefines eutrophic urban lakes as multifunctional blue-green infrastructure that seamlessly integrate sustainable water management, climate mitigation, and circular bioenergy recovery in rapidly urbanizing regions.Keywords: Bioenergy recovery; Blue–green infrastructure; Circular bioeconomy; Nature-based solutions; Urban eutrophic lakes; Methane emissions; Algal biomass harvesting; Anaerobic digestion

Amidst the exponential global population growth, the integration of drones into precision crop production emerges as a pivotal strategy for optimizing agricultural processes. With projections indicating a required increase of over 60

In the past few decade’s urbanization, changing rainfall patterns, and inadequate precipitation are a few of the major reasons for dried urban lakes. Many such lakes are successfully revived using effluent from nearby sewage treatment plants. However, high nutrient loading and concentrated surface flow leads to problems like eutrophication followed by high greenhouse gas emissions (GHG). Majority of these lakes are shallow which has higher GHG emissions compared to the deeper lakes. India’s urban lakes are suffering from the similar fate. Study conducted in South Delhi, India reflects high phosphate and nitrate concentrations in the lake. Due to this, lakes are highly eutrophic and biomass concentration varies between 2 - 4.5 gL-1. Considering volume and biomass concentration, carbon dioxide sequestration comes out to be 1.2 Kg CO2/Kg of biomass. It was also seen that the average methane yield from microalgae is around 56%. It was found that total GHG potential was 5.856 Kg CO2-equivalent/ Kg of biomass which makes eutrophication a serious environmental issue. It is worth noting that microalgae in lakes decreases CO2, simultaneously increasing CH4 emissions which has 27-30 global warming potential (GWP) and relatively harmful for environment. In the past few decades studies reflected CH4 is responsible for 72 % of the climatic change (in CO2-equivalents) from lakes and inland waterbodies. The current study highlights the consequences of eutrophication in urban lakes with treated domestic discharge and suggests proper lake water quality management. Nevertheless, microalgae harvesting, and anaerobic digestion can be used to mitigate GHG and recover energy for a better and sustainable future.

The long-term health and ecological stability of urban water bodies are intrinsically linked to their water quality. This study assesses the current ecological state of the hyper-eutrophic, warm polymictic Hauz Khas Lake in Delhi, India, which has been rejuvenated with Sewage Treatment Plant (STP) effluent and suffered from eutrophication since then. The primary objective was to evaluate the lake's health by analyzing major physical, chemical, and biological parameters and to quantify changes over an eight-year period. Water quality was assessed using the Water Quality Index (WQI) and Trophic State Index (TSI), with further statistical analysis conducted via Principal Component Analysis (PCA). Our findings reveal that the lake is under significant stress from elevated nutrient inputs (NO₃-N: 1.9–3.13 mg/L, PO₄³⁻: 4–8 mg/L), resulting in a hyper-eutrophic state of 191.66 ± 10.68 (2022–23). The WQI ranged from 44.28 to 64.28, indicating medium to poor water quality with a slight degradation compared to 2015 data. PCA results show a significant intensification of interactions among water quality parameters over the last eight years, with the variance explained by the first two principal components increasing by 37.5 % and 28.57 %, respectively. This study concludes that while the STP-based rejuvenation strategy has maintained the lake's physical existence, it has led to severe hyper-eutrophication, highlighting the urgent need for advanced nutrient management strategies for urban lake conservation

The energy crisis has highlighted the need for a significant change in Kosovo’s lignite-based electrical energy system, particularly greater investments in renewable energy sources. These sources would provide greater price stability, centralized accessibility, and relatively affordable investment costs. This research tries to analyze the basic attitudes behind the behavior of the students from the agricultural faculty in Kosovo in order to acquire a better understanding of their preferences for renewable energy source purchases, using the Best–Worst Scaling (BWS) method and cluster analysis. Students’ perspectives on renewable energy show strong environmental and price conscientiousness in BWS methods (first and second rank), while the rate of eco-skeptic students reaches only 23% in the cluster analysis, which is a very promising sign of the younger generation’s growing dedication to sustainability. Students, as future decision-makers, can play a critical role in making the transition to a more sustainable and resilient agricultural system. Green transition in Kosovo can be reached by combining the importance of dissemination and marketing tools with the pressing demand for renewable energy solutions, which might be interesting not only for Kosovo, but (considering the expectable enlargement) also for the EU.

Agriculture accounts for a significant economic share in less-developed countries, especially Kosovo, where there is a lignite-dominated energy supply. Lignite’s partial replacement with locally produced renewable energy sources could play an essential role in reducing farmers’ costs and preparing the country for EU accession. Using a sample of 120 farmers, the Best–Worst Scaling (BWS) technique was used to assess farmers’ preferences for renewable energy applications and to measure the importance of seven key characteristics associated with the willingness to become energy self-sufficient. The results show a significant preference for “lower energy costs” and “environmental friendliness”. Using cluster analysis, it is shown in a statistically reliable way that while the decisions of smaller farms are influenced by economic factors and the role of energy self-sufficiency is negligible, a non-negligible share of larger farms already have already adopted self-sufficiency in energy production (solar panels, byproducts) and also consider the environment and convenience aspects necessary in their decisions. Farmers play an important role in local economic development. Therefore, regulatory schemes with differentiation by farm size may play an important role in promoting local energy management in Kosovo and similar less developed countries.

Agrivoltaic systems (AVS) allow the simultaneous use of land—as a limited resource—for crop production and electricity generation. This paper introduces the development prospects of AVS in Hungary with insights into international trends. The most important part is a complex economic analysis and a unit cost analysis of a 38 MWp capacity AVS, considering the most typical basic data in electricity and apple production. The applied risk analysis is based on a Monte Carlo simulation, the distribution function, and probabilities. To introduce the economic facet of the competitiveness of AVS, a comparative analysis was carried out between AVS, ground-mounted photovoltaic (GM-PV) systems, and conventional apple production systems (ConAPS). In the most probable scenario, the AVS was financially attractive (NPV = 70 million EUR under 30 years). Our correlation analysis shows that feed-in tariff (FIT) price and the role of financing are considered the dominant economic factors. A favorable FIT price enhances the profitability of AVS; however, it makes GM-PV systems more profitable compared to AVS, so it negatively affects the competitiveness of AVS systems. AVS operations result in a more balanced unit cost of apples and of electricity compared to the independent operation of GM-PV systems and of ConAPS; in addition, it allows for land saving and more intensive land use.

Energy stands as a vital stimulus for societal, economic, and technological progress globally. Energy self-sufficiency has emerged as a strategic goal for many nations, driven by concerns over energy security, sustainability, and economic resilience. Within this context, Kosovo relies heavily on fossil fuels and insufficient alternative energy sources, making it tough to achieve self-sufficiency in agriculture. The agricultural domain relies extensively on energy to power various of its operations, rendering energy self-sufficiency a compelling avenue for addressing associated challenges. By serving as a benchmark that evaluates the current status and charts a prospective roadmap for fostering the renewable energy sector in Kosovo, the SWOT analysis delineates internal strengths and weaknesses alongside external opportunities and threats. Emphatically, the study highlights the indispensability of public awareness campaigns, capacity-building initiatives, and streamlined access to financial resources. Additionally, the study emphasizes the pivotal role of project preparation, credit accessibility, financing costs, and equity financing facilitation in bolstering the nation's prospects for realizing its energy self-sufficiency objectives, otherwise Kosovo may struggle to meet its energy goals.

This study delves into the intricate landscape of biomass utilization within the food and energy markets. It entails a systematic review of the existing literature with the aim of unraveling the complexities of the food and energy discourse, especially in the context of significant market factors influencing biomass use for food and energy. We leveraged the Scopus database to examine 73 pertinent scientific articles carefully selected following the PRISMA framework. The articles were analyzed using the advanced qualitative data analytics tool NVivo 12 Plus. Furthermore, we employed the Biblioshiny R-package tool to extract valuable insights from the metadata, unveiling pivotal trends and providing descriptive statistical details. The findings offer comprehensive insights into the debate on biomass utilization from 2010 to 2023, tracing the influence of the COVID-19 pandemic. We identify regions that have made notable contributions and highlight those that require increased attention. The analysis underscores the collaborative nature of this field, with 281 authors contributing to 39 different sources. Surprisingly, the observed annual growth rate of −10.93% indicates a potential decline in research output in this field. Nevertheless, the sources identified in our research provide a valuable roadmap for further research exploration of the biomass–food–energy nexus.

This study introduces the most important energy trends and global food systems, as well as the relationship between the human development index (HDI) and energy supply and the relationship between energy prices and food prices. Based on seven important indicators as variables in 18 relevant countries worldwide, before and after the pandemic, with the help of cluster analysis and comparative analysis, five different primary energy clusters were created and analyzed. Our results prove the high volatility of the composition of these clusters within a short period. Another important finding is that renewable energy sources (RES) are probably not viable options for the largest (developed and developing) countries in the short term. The human development index and food production per capita are the lowest in the renewable energy cluster and the highest in countries dominated by nuclear energy and oil with typically the highest GDP, since they are able to finance the price hike in both food and energy markets. Generally, it can be stated that although there is a relationship between the measured indicators, it is not constant in all cases. Our results and methodology may be a good basis for further research to examine the relationship between the most important relevant indicators in different countries, as well as the effect of a global crisis on strengthening food and energy security.

The energy use of residues from agriculture, forestry, and solid waste can foster the transition towards a more renewable energy supply. This paper analyzes the energy potential of the above-mentioned sources for energy applications in Kosovo. The analysis is based on statistical data from different studies and reports, analyzing and calculating them to determine the theoretical and energy biomass potential. Kosovo can increase its self-sufficiency by taking advantage of its rich but under-utilized potential of biomass energy sources. This is a novelty study in this area, considering Kosovo lignite-dominated heat energy and electricity consumption and the available special literature. According to our estimates, the theoretical potential is 6.13 million tons/year, while the biomass energy potential should be around 4.57 million tons/year, including approximately 74.6% of biomass, which can be used for energy needs (heating and electricity). Based on the data and calculations, the available and usable potential shows biomass as an energy source with high potential in Kosovo; its share is very low, but it is reasonable to grow for both environmental and economic reasons.

Power-to-biomethane (bio-P2M) is a novel technology that combines the long-term storage of periodically available renewable energy sources (RES) and the upgrading of biogas. This article introduces a complex economic analysis of a 1 megawatt electric (MWel) capacity bio-P2M system based on economic characteristics considered to be typical in practice. The evaluation includes an investment analysis to present the basic scenario, a sensitivity analysis and a unit cost calculation to show the economic viability, the cost structure and the possible reserves of the synthetic natural gas (SNG) as a final output. The risk analysis is executed using Monte Carlo simulation, and the final results are the mean and standard deviation of the outputs, distribution functions and probabilities. Our results show that a significant state subsidy would be needed to boost competitiveness either in terms of investment costs (44% in our calculation) or in technology development to improve technological effectiveness. Another important competitiveness issue is the full utilization of the plant and the lowest possible price for the electricity used. If both cannot be optimized at the same time, then the first one is more important. Natural gas prices and the full utilization of waste heat might result in smaller changes.

Over the years, energy is becoming an essential factor with an impact on social, economic, and environmental aspects. More than 2.5 billion people are connected to agriculture worldwide, so the importance of agricultural energy production has become increasingly important. This study provides a comprehensive review of renewable energy, environment, and farm publication trends. Two hundred articles from 1988 to 2022 were analyzed, with special attention devoted to the last three extreme years, using the Scopus database and the Bibliometrix tool for analysis and visualization. Research on this topic experienced significant developments after 2008, with many fluctuations being revealed. Historically, China and the USA were the most productive countries in agricultural energy production advancements. However, in the last three years, the research center’s respective contributions have undergone major changes. China maintained its dominance, but the importance of the USA fell sharply, and new centers (India, Poland) appeared. Biogas is the most popular method which is used and searched in this area between 1988–2022 since it includes both sustainability and locality. However, between 2020–2022, the importance of the circular economy has been highlighted in the literature. Complex energy systems, dual use of land, and energy storage might be the most important challenges for future research.

The use of faecal sludge (FS) in anaerobic digestion (AD) requires a perfect knowledge of their composition. Considered as a very heterogeneous material, the high variability of FS can disturb biodigesters’ functionality and impact biogas production. Unique in West Africa, Kossodo’s biogas plant in Ouagadougou receives sludge from septic tanks and pit latrines. To evaluate the quality of sludge discharged in this treatment plant and its ability for AD, a characterization of 130 FS trucks from several onsite sanitation facilities was carried out. Physico-chemicals, including heavy metals and microbiological parameters, were analyzed using standard protocols. A biochemical methane potential test was employed to evaluate biogas yield. Results showed that raw sludge averaged 1.12% total solids (TS), 54.74% volatile solids (VS), 9253 mg/L chemical oxygen demand (COD), and 1645 mg/L biochemical oxygen demand (BOD). Settled faecal sludge exhibited higher levels of total coliforms, E. coli, helminth eggs, and heavy metals. Heavy metal levels met AD standards defined by VDI 4630, with decreasing toxicity order: Zn > Mn > Cu > Cr > Ni > Pb > As ≥ Hg. The carbon-to-nitrogen (C/N) ratio was 6.7 ± 4.3, indicating unsuitability for AD. Sludge settling increased C/N ratio by 46%, which was still below optimal AD conditions (20–30). Methane yield of raw and settled FS averaged 61 ± 0.2 and 156 ± 3.2 NL CH4/kg VS removed, respectively. Co-substrate addition could enhance the methanogenic yield of these sludges. This study provides a valuable database on the characteristics of FS, supporting sustainable recovery options.

Environmental and comfort value of renewable energy sources is a less studied area. The article introduce the economic value of these characteristics, related to social determinants. The data basis is representative of the Hungarian population above 18 years of age, by gender, age and level of education. Our model estimation was developed by hybrid choice context in latent class modelling. In addition to the usual WTP (willingness to pay) calculation, we also used WTI (willingness to invest) calculations. The results show that the value of environmentally-friendly nature in Hungary exceeds the convenience factor. The latter cannot be significantly detected for the majority of the Hungarian population. This statement is supported by results for both fuels and boilers. Our findings show the strong attachment of the Hungarian average person to the use of firewood and natural gas, which are very typical in Hungarian heat consumption. Regarding socially selected consumer groups, strong correlation can be observed between social capital supply, income level, access to information and environmental awareness in Hungary. Regarding policy implications, our results in development of clusters may be useful for the establishment of a selective support policy and two clearly identifiable groups should be highlighted in the energy policy.

Our results introduce the preferences and attitudes of farmers and the internet-orientated population regarding renewable energy sources (RES) in Kosovo. The research included 243 internet-orientated participants and 30 farmers. The data was gathered through questionnaires (in both groups) and deep interviews (just in farmers). The results showed that the awareness of RES was high for especially solar, wind and hydro energy, the relationship among them was very strong. It was justified that firewood was typically used by respondents with low income, but not considered as renewable energy source, similarly to Hungary and the USA. A special feature of Kosovo is that electricity has very high importance for the man in the street, even for heating. Better education, higher income and environmental-consciousness definitely support better knowledge of RES, similarly to international tendencies. Males and employed participants had more knowledge about RES than females, or unemployed ones. Moreover, the results showed that the participants prefer environment rather than convenience, which is also typical of less wealthy countries. Our results might be useful as a typical less developed country case study for international comparison and helps to eliminate the unknown willingness in RES for the development of future agricultural strategies in Kosovo.

Circular economy is a key pillar of the EU's strategy to achieve the objectives of the European Green Deal. The majority of cities already have development plans for different time horizons. Still, they now need to rethink their sustainability targets in a new framework, taking into account the principles of the circular economy model. There is also the challenge of what concrete steps a city needs to take to develop a circular economy, and how it can achieve its vision.Cities are growing year by year, not only in terms of population but also in their role in environmental protection and energy management. This trend is particularly true in Hungary, where the ratio of the urban population is much larger than the global average. From a legal point of view, local authorities currently have little responsibility in regulating sustainability and are mainly able to influence these processes only indirectly. The characteristics of the small and medium-sized cities analysed in this article differ from that of large cities in several aspects. Sustainability problems are typically smaller, but fewer financial resources are available to solve these problems and knowledge of circular management is generally more limited.In this study, we focus on the following areas: the areas of urbanization, the characteristics of small and medium-sized cities, the circular economy options that can be applied to them, briefly present some good practices and, based on our research, the types, levels, pillars, sequencing and basic elements of interventions needed to develop a circular economy locally. We believe that coherently applying them at the right level can make it possible to establish a local circular economy model, maintain the system, and finally get the support of the local inhabitants, businesses, and possibly external actors.In the framework of our related research work, a unified model, measurement and evaluation system focusing on small and medium-sized cities has been developed, including the main drivers of sustainability and the circular economy. Still, at the same time, they can be utilized in the context of municipal and urban planning and operation. In this paper, we present some partial results of this research. The results of our research work may draw attention to some elements of the logic of the circular economy, highlighting the interventions that are possible for small and medium-sized towns to reach their sustainability goals.

Eutrophication has a significant negative impact on the ecosystem since it depletes the planet's biological resources and is further responsible for climate change. It is caused by both endogenous and exogenous nutrient enrichment. This phenomenon degrades the water quality and simultaneously increases the greenhouse gases emission from waterbodies resulting in climate change Inland waterbodies contain enormous amounts of nutrients such as phosphorous, nitrogen, and carbon. Thus, it becomes essential to restore these nutrients using proper sustainable approaches. Algae-based technologies have received a lot of attention these days because of environmentally friendly and inexpensive treatment. About 70% of the nutrient load from wastewater can be removed using such technology. The recovered algal biomass after wastewater treatment contains various biomolecules which can be used for the producing of value-added products such as bioenergy in the form of biomethane and biodiesel, cosmetics and pharmaceuticals along with the synthesis of nanoparticles. Therefore, the primary goal of this review is to inform readers about the possibilities of a low-cost integrated biorefinery based on microalgae for resource recovery and to mitigate eutrophication and greenhouse gas emission from water bodies.

Flat plate collectors (FPCs) are the leading solar thermal technology for low-medium range temperature applications. However, their expansion in developing countries is still lacking because of their poor thermal performance. Improving the thermal performance of flat plate collectors (FPCs) is a crucial concern addressed in this review This study comprehensively discussed the performance improvement methods of FPCs, such as design modification, reflectors, working fluid, and energy storage materials, by covering current issues and future recommendations. Design factors such as coating and glass cover thickness, thickness of absorber plate and material, air gap between the glass cover and absorber plate, and riser spacing, along with insulation materials, are examined for their impact on FPC performance. Absorber design changes with selective coatings for improving the heat transmission rate between the working fluid and absorber are critical for enhancing collectors’ thermal output. The nanofluids utilization improved FPC’s thermal performance in terms of energetic and exergetic outcomes in the 20–30% range. Moreover, adding a heat storage unit extends the operating hours and thermal output fluctuations of FPCs. Research suggests that employing turbulators and nanofluids as heat transfer fluids are particularly effective for enhancing heat transfer in FPCs. This comprehensive review serves as a critical tool for evaluating and comparing various heat transfer augmentation techniques, aiding in the selection of the most suitable option.