Volumen 27 (2023): Heft 1 (January 2023)

District Heating and Cooling (DHC) technology is widely recognised as a promising solution for reducing primary energy consumption and emissions. The 5th Generation District Heating and Cooling (5GDHC) network is the latest DHC concept characterised by low-temperature supply, bi-directional heating network operation, decentralised energy flows, and surplus heat sharing. Unlike the 4th Generation District Heating (4GDH) technology, the 5GDHC technology switched to a consumer/prosumer-oriented perspective. The introduction of 5GDHC solutions requires high investments, an important barrier to further developing DHC systems. Therefore, a novel pricing and business model could include introducing co-owners or energy managers into the system. Three different local market business models for 5GDHC at the community level have been tested. The reverse technical and economic simulation has been used for a feasibility study to determine the resources, business models, and combinations closest to the break-even point with lower costs and higher gains for all involved stakeholders.

Discharge measurement is the base of proper water management. The effective design and operation of hydraulic structures under both normal and extreme flow conditions depend on the quality of hydrological data. Understanding the water system requires consistent and long-term measurement. Despite that, the gauging station network is sparse, and its numbers are declining worldwide. This article aims to draw attention to the possibility of accurate flow measurement using existing hydraulic structures. Flow over a hydraulic structure profile is a physically well-defined phenomenon as the construction shape is fixed and simple compared to river profiles. The discharge can be derived from rating curves, turbine characteristics, and several easily measured variables. That allows continuous discharge measurement. The accuracy is compared with the gauging station on the river. Suitable technical solutions for ensuring and monitoring ecological flow are discussed.

The world’s leading indoor air quality guidelines provide for the identification of certain parameters with a specific limit value based on the latest empirical measurements, however, most of them do not have legal coverage and are voluntary. This leads to unequal assessment of indoor air quality, because there is an identifiable difference between the limit values set out in the various guidelines. And these values would be related to the results obtained during the experimental activities of the application of the specific parameters and the interpretation of their effects on human health. The aim of this IAQ guideline and IAQ certification review was to develop IAQ label for Nordic countries and to find gaps the legislation established by the Latvian government. The development of indoor air quality labels provides an opportunity to maintain and promote the optimal functionality of human physiological processes and the sustainability of the building.

Transport consumes around one-third of Latvia’s final energy demand being the largest sector that produces greenhouse gas emissions. In Latvia, in the year 2019, the share of renewable energy sources in the transport sector was only 4.8 % of the total gross consumption with a target of 7 % of not food-based biofuels by 2030. To tackle climate change problems, one significant task is reducing pollution in the transport sector by substituting fossil with biomass-based fuels. The goal of this study is to develop a methodology for evaluating biofuel production in Latvia considering economic, social, environmental, and technological aspects. A total of 16 specific criteria were selected for biofuel comparison. The methodology is based on a combination of two quantitative approaches, namely Life Cycle Assessment and Multi-Criteria Analysis. The proposed method aims to identify the most sustainable biofuel in Latvia according to a set of specific indicators.

In this paper, bi-level optimization model is proposed for optimal energy trading between microgrids (MGs) and distribution companies (Discos) with consideration of the renewable energies. The first level modelling is maximizing MGs’ profit and the second level is related to maximization of the Discos profit. In proposed system, power trading between MGs and Discos is considered. As well, renewable energies and demand management strategy are modelled in system for optimal energy consumption. The optimization modelling is solved by Particle Swarm Optimization (PSO), and results of the two case studies show optimal solution of prosed strategy in energy optimization.

In this paper, optimal coordination of the demand side under uncertainty of the energy price in energy market is studied. The consumers by demand response programs (DRPs) have optimal role in minimization of the energy generation costs in multiple energy system. The consumers can participate via local generation strategy (LGS) and demand curtailment strategy (DCS). The optimal coordination is considered as two stage optimization, in which minimization of the consumers’ bills is done in first stage. In following, the minimization of the generation costs is performed in second stage optimization. The LGS is taken into accounted through optimal discharging of plug electric vehicles (PEVs). Finally, numerical simulation is implemented to show superiority of the proposed approach to minimization of the energy generation costs.

The operation of the electrical systems is a major problem for electrical companies’ subject to uncertainties threatening. In this study, the optimal management of the energy demand in the electrical distribution grid is done by interval optimization approach under electrical price uncertainty. The management of the energy demand is implemented via incentive-based modelling of the demand response programs (DRPs). The incentive-based modelling as reserve, and based on bid price for reduction of the electrical demand at peak hours is proposed. The interval optimization approach is used for the minimization of the electrical price uncertainty effects. The main objective in the proposed approach is minimizing operation cost; epsilon-constraint method is utilized to solve the problem. Finally, an electrical distribution grid has been used at various case studies to numerical simulation results and positive effects of the proposed modelling under uncertainties.

Biomethanation is a prospective biogas upgrading method to integrate renewable energy grid with existing biogas grid. Biomethane can directly substitute fossil natural gas and be used in all energy sectors. The selection of packing material for the ex-situ biomethanation in biotrickling filter reactors can be based on the physical and chemical characterization of the carrier material. The packing material selected for biotrickling filter reactors supports hydrogenotrophic methanogenic growth and thereby increases the area for H² mass transfer. Chemical components and melting temperature analysis of wood ash material are carried out to determine optimal parameters for producing wood ash filter material. Physical characteristics of new wood ash filter material such as volume-specific surface area (m² m⁻³), the external porosity (vol. %) and bulk density (kg m−3) are carried out to compare this material with other carrier materials that have been used in biotrickling filter reactors before.

South Africa is a carbon-intensive country, with coal dominating the indigenous energy resource base; however, targets have been set to reduce the national carbon emissions. The transition from coal to cleaner sources of energy generation can be encouraged by the administration of new technologies. Hence, the study aims to review research progress on the pyrolysis of water hyacinth as a tool for the smooth transition to low carbon and climate-resilient economy. Water hyacinth is suitable for energy recovery due to its high carbon content and heating value. The outcome shows that pyrolytic products such as liquid, char and non-condensable gas fractions are beneficial. This paper contributes to policy and research deliberations on promoting and adopting pyrolysis technology in addressing South Africa’s energy crisis and water hyacinth invasion.

Microalgae cultivation at biogas plants creates joint benefits for using liquid digestate and exhaust gas from the CHP unit as nutrient and carbon sources for microalgae growing. This circular approach increases biogas production’s sustainability towards a bioeconomy and zero-waste perspective. This study aims to evaluate the potential environmental impacts in connection to a novel microalgae growing technology named Stacked Modular Open Raceway Pond (SMORP) as a side-stream process coupled with centrate and exhaust gases from a biogas plant. A comparative LCA according to ISO 14044 is performed between the innovative SMORP concept at the pilot level and a hypothetical scaled-up system. Primary data for the inventory are directly gathered from the microalgae growing test performed at the biosystems laboratory of the Institute of Energy Systems and Environment of the Riga Technical University. Secondary data are collected from literature mostly in terms of mass and energy balances considering the SMORP pilot project design. The results of the LCA include the main findings both at mid and endpoint categories according to the IMPACT 2002+ method. In addition, a sensitivity analysis for several different parameters has been investigated. Results show the feasibility of the coupled system and the possibility of having benefits once the system is scaled up. Nevertheless, the results show a critical dependency of the environmental performance on the local conditions, potentially affecting too high cultivation costs.

As the volume of textile waste steadily increases, mechanical, chemical and biological technologies for textile waste recovery are evolving. Also, the legal framework of the European Union has stated the commitments for promoting the recycling of textile waste in the Member States. So far, however, no decision-making algorithms have been developed for the selection of products recovered from textile waste. Within the present study, a hybrid multi-criteria decision-making algorithm for evaluating textile waste recovered products has been developed applying seven circular economic criteria – ‘Circular economy approach of the technology’, ‘Added-value potential of final product’, ‘Share of textile waste in total waste feedstock’, ‘Diversity of textile mix suitable for specific technology’, ‘Pre-treatment of waste feedstock’, ‘Recovery potential’ and ‘Maturity of a recovery technology’. The weighting of the criteria was determined by eight waste management experts. The results of the expert-based criteria evaluation show that the most important criteria are ‘Added-value potential of final product’ and ‘Circular economy approach of the technology’. The developed decision-making methodology has been adapted to nine textile waste recovered products – compost, refuse-derived fuel, ethanol, glucose, building insulation material from cement and textile waste mix, building insulation material from denim textile waste, terephthalic acid, recovered cotton and recovered polyester. The multi-criteria, decision-making ranking of the products textile shows that the highest potential for products recovered from textile waste is for glucose and terephthalic acid, while the lowest – for ethanol, compost and refuse-derived fuel.

Epoxy resins are widely used polymers from which a variety of products are derived and applied in many industries. Most epoxy resins are still obtained from mainly fossil feedstocks, such as epichlorohydrin and bisphenol A, which are also highly toxic. Additionally, fossil derived epoxy resin products are forming non-biodegradable waste at their end of life. Recently the number of studies aiming to find solutions and other raw materials for the replacement of fossil derived epoxy resins has increased, showing that bio-based epoxy resins are a promising alternative. An interesting alternative raw material for bio-based epoxy resins is epoxides derived from microorganisms, such as epoxidized microbial oil. This review article explores and compares the latest solutions for the use of microbial oils in the production of bio-based epoxides, outlines the prospects for their future use and points out the shortcomings of these solutions.

Despite the fact that university students have significant potential to influence the future state of the environment, few academic researchers have focused on environmental behaviour among university students in less developed and developing countries. In the extant literature, there is a need to assess the significance of value behaviour norm theory in different ‘private-sphere’ or ‘daily life’ human behaviours. This paper aimed to assess a possible chain effect between individual values, environmental consciousness and personal norms to promote private sphere Pro-Environmental behaviour among university students. (N = 267). Multiple regression analysis results revealed that Altruistic Values (AV), Egoistic Values (EGV), New Ecological Paradigm (NEP), and Ascription of Responsibility (AR) significantly predicted Pro-Environmental Behaviour (PEB). However, Biospheric Values (BV), Awareness of Consequences (AC), and Personal Norm (PPN) do not significantly predict Pro-Environmental Behaviour (PEB). The Value Behaviour Norm Theory (VBN) model explained a significant amount of variance (65.6 %) in predicting Private Sphere Pro-Environmental Behaviour in University Students. Results indicate that University students may benefit from awareness programs on the VBN model which may improve their Pro-Environmental behaviour.

The European honey bee Apis mellifera is the main pollinator for most crops used for human consumption. However, a number of diseases, parasites, pesticides and other factors that generally result in the widely described colony collapse disorder weakens honey bee colonies. In order to maintain the existing honey bee germ lines and facilitate the creation of new disease-resistant lines, it is necessary to ensure consistent breeding work, which would also allow the long-term preservation of the unique germplasm lines. One of the most promising solutions for the preservation of honey bee germplasm is the storage of honey bee drone semen. In recent decades, there has been a renewed interest in the preservation of honey bee drone semen using both cryopreservation and above-freezing storage methods. This review summarizes the latest developments in novel sperm storage technologies and their assessment by sperm quality and queen fertility indicators. Additionally, this article analyses the advantages and disadvantages of the reviewed solutions and outlines directions in which additional research would be needed to develop effective, available and affordable drone semen storage solutions. To the best of the authors' knowledge this is the first review of cryopreservation and above-freezing storage solutions of European honey bee Apis mellifera drone semen in the scientific literature.

To achieve the climate targets set by 2030 and become climate neutral by 2050, each Member State must develop a National Energy and Climate Plan (hereinafter NECP) containing practical and effective measures to achieve the targets. The research sought a connection between the measures or action lines in the Latvian NECP related to agriculture and forestry, the European Green Deal goals and related strategies. The effectiveness of the agricultural and forestry measures defined in the Latvian NECP was evaluated by defining appropriate indicators, an expert survey and a composite sustainability index. The results show that the effectiveness of agricultural and forestry measures is most influenced by quality, financing, and specificity factors. The lowest-scoring measures were specific measures whose impacts cannot be measured and are not explicitly mentioned in the European Green Deal. Therefore, the description of the measures should be more detailed, with specific activities, indicators to be achieved, and amounts and funding sources planned for each activity.

The concept of the new water treatment system was developed. A primary area was defined in which such technology is intended to be used: water treatment in compact flue-gas condensation systems for a low-power wood-fuelled biomass boiler. A prototype operating based on invented technology was built. An experimental plan was developed, and an experimental stand was constructed to determine the prototype’s efficiency. Based on the study’s results, it was concluded that the prototype could operate effectively in the laboratory environment: achievable efficiency is equal on average between 57.84 % and 88.09 % depending on the operating mode. The result is assessed as positive. TRL 3 has been reached.