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The biogas production technology has improved over the last years for the aim of reducing the costs of the process, increasing the biogas yields, and minimizing the greenhouse gas emissions. To obtain a stable and efficient biogas production, there are several design considerations and operational parameters to be taken into account. Besides, adapting the process to unanticipated conditions can be achieved by adequate monitoring of various operational parameters. This paper reviews the research that has been conducted over the last years. This review paper summarizes the developments in biogas design and operation, while highlighting the main factors that affect the efficiency of the anaerobic digestion process. The study’s outcomes revealed that the optimum operational values of the main parameters may vary from one biogas plant to another. Additionally, the negative conditions that should be avoided while operating a biogas plant were identified.

With the increasing needs of clean water supplies, the use of biomass wastes and residues for environmental remediation is essential for environmental sustainability. In this study, the residues from winery and citrus juice industries, namely grape skin and orange peel, respectively, were first converted to hydrochars by hydrothermal carbonization (HTC) and then a cationic dye (methylene blue) adsorption was studied on hydrochars. Hydrochars from both feedstocks were produced at three different temperatures (180, 220, and 250 °C) and a fixed residence time (1 h) to evaluate the hydrochar’s performance on the dye adsorption. The hydrochars were characterized in terms of their pH, pH at point of zero charge (pHPZC), surface functionalities, and surface area. A batch adsorption study of the dye was carried out with variable adsorbate concentration, pH, and temperature. Two adsorption isotherms namely Langmuir and Freundlich models were fitted at 4, 20, and 36 °C. The thermodynamic properties of adsorption (Gibbs free energy (ΔG), enthalpy (ΔH) and entropy (ΔS)) were evaluated from the isotherms fittings. Results showed that the dye adsorption on both hydrochars was significant and followed Langmuir isotherm. The maximum adsorption capacity on citrus waste hydrochar was higher than the winery waste hydrochar at any corresponding HTC temperature. Although hydrochars showed the lowest surface area (46.16 ± 0.11 and 34.08 ± 1.23 m2/g for citrus and winery wastes, respectively) at 180 °C, their adsorption was the highest, owing to their maximum density of total oxygen functional groups (23.24 ± 0.22 and 32.69 ± 1.39 µmol/m2 for citrus and winery wastes, respectively), which decreased with the increase in HTC temperature. This research shows a sustainable route for the production of highly effective adsorbent materials at lower HTC temperatures from citrus and winery wastes.

This study describes a 70-day investigation of three identical groundwater heat pumps (GWHP) for heating two pig houses located on the same farm in West Germany. Two of the three GWHPs were installed in a piglet-rearing barn, the third in a farrowing barn. All three heat pumps were fed from the same extraction well. The aim of this study was firstly the empirical performance measurement of the GWHP systems and secondly the energetic evaluation of the systems on barn level by calculating the coefficient of performance (COP). Three different assessment limits were considered in order to better identify factors influencing the COP. In total, the heat pumps supplied thermal energy of 47,160 kWh (piglet-rearing barn) and 36,500 kWh (farrowing barn). Depending on the assessment limit considered, the COP in piglet-rearing barn and farrowing barn ranged between 2.6–3.4 and 2.5–3.0, respectively. A significant factor influencing the COP is the amount of electrical current required to operate the groundwater feeding pump. The average groundwater flow rate was 168.4 m3 d−1 (piglet-rearing barn) and 99.1 m3 d−1 (farrowing barn). In conclusion, by using energy from groundwater, GWHPs have the potential to substitute fossil fuels, thus saving them and avoiding CO2 emissions.

For the agricultural sector to develop sustainably in the future, progress toward more environmentally friendly technologies and methods is crucial. It is necessary to increase output while reducing the demand for energy, agrochemicals, and water resources. Although greenhouses can be utilized successfully for this purpose, significant technical advancements are required, especially when it comes to heating, to lower the use of fossil fuels and boost energy efficiency. Microwaves can warm plants without heating the entire greenhouse volume, which takes a significant amount of energy to compensate for heat loss in the outdoor environment. In this paper, through a thorough examination of the state of the art, a general overview of novel greenhouse heating systems based on radiation is reported. First, the strengths and weaknesses of microwave heating are discussed, and finally, the use of microwaves for soil sterilization is examined. All outcomes suggest these irradiation-based technologies can contribute significantly to energetically sustainable agriculture; moreover, they can be used to increase plant comfort.

A new approach for biomass liquefaction was developed and evaluated in a joint research project. Focus of the project, called FEBio@H2O, lies on a two-step hydrothermal conversion. Within step 1, the input biomass is converted employing a hydrothermal degradation without added catalyst or by homogeneous catalysis. Within step 2, the hydrogen accepting products of step 1, e.g., levulinic acid (LA) are upgraded by a heterogeneously catalyzed hydrogenation with hydrogen donor substances, e.g., formic acid (FA). As a result, components with an even lower oxygen content in comparison to step 1 products are formed; as an example, γ-valerolactone (GVL) can be named. Therefore, the products are more stable and contained less oxygen as requested for a possible application as liquid fuel. As a hydrothermal process, FEBio@H2O is especially suitable for highly water-containing feedstock. The evaluation involves hydrothermal conversion tests with model substances, degradation of real biomasses, transfer hydrogenation or hydrogenation with hydrogen donor of model substances and real products of step 1, catalyst selection and further development, investigation of the influence of reactor design, the experimental test of the whole process chain, and process assessment.

Water, as one of the main media of human existence on earth, is the basis of the functioning of most societies. This article discusses various activities related to water resource management and analyzes the evaluation of selected quality parameters of tap water in Poland and Ukraine. The aim of the manuscript was to compare opinions on tap water quality and habits of its use in Poland and Ukraine, taking into account different seasons of the year as periods of use of supplied water. The hypothesis of the study was that tap water parameters are evaluated differently in Poland and Ukraine at different times of water supply. Due to the complexity of research aspects, a mixed-methods research procedure was used, in which a literature review was combined with a survey and statistical analysis. For the purpose of the survey, the authors’ questionnaire “Survey of customers’ opinions on selected parameters of tap water supplied in Poland and Ukraine” was created. The results of the research confirmed the hypothesis and allowed for the development a model for the evaluation of parameters of tap water supplied on the territory of Poland and Ukraine and to get to know the expectations of customers of these countries. The presented model provides practical indications that can be used to optimize water supply and meet customers’ expectations, including improvement of water quality parameters.

The perennial rhizomatous grass giant reed (Arundo donax L.) can be exploited to produce hydrogen by dark fermentation. This implies a high availability of simple sugars, like glucose and xylose, and, thus, a pre-treatment is necessary to remove lignin and expose the holocellulose to enzymatic attack. This study aimed at evaluating the hydrogen production from giant reed hydrolysates. Giant reed dry meal was pre-treated with diluted NaOH (1.2% weight/weight), then the solid fraction was separated from the alkaline black liquor by filtration, enzymatically hydrolyzed with a cellulase blend (Cellic CTec2), and fermented in mesophilic batch conditions with a microbial consortium derived from pig slurry. The impact on hydrogen yield of initial pH was evaluated by comparing the hydrogen production from hydrolysates with not adjusted (5.3) or adjusted initial pH (8.7) using NaOH or alkaline black liquor. The highest hydrogen yield, 2.0 mol/mol of hexoses, was obtained with alkaline initial pH 8.7, regardless of how the pH adjustment was managed. The yield was 39% higher than that obtained in reactors with initial pH 5.3. In conclusion, thermo-alkaline pre-treatment followed by enzymatic saccharification and initial pH adjustment at 8.7 with the black liquor remaining after pre-treatment is a promising strategy to produce hydrogen from giant reeds in dark fermentation.

Interfacial interactions and wettability alteration remain as the main recovery mechanism when modified water is applied seeking to obtain higher oil recoveries. Fluid-fluid interaction could lead to the development of the called viscoelastic layer at the interface in oil-brine systems. This interfacial layer stabilizes thanks to the slow chemical interaction between oil polar compounds and salts in the brine. This study investigates the role of sulfate presence in injection brine that could possible lead to develop the interfacial viscoelastic layer and hence to contribute to the higher oil recovery. Furthermore, polymer flooding is performed in tertiary mode after brine flood to investigate/unlock the synergies and potential benefits of the hybrid enhanced oil recovery. Brine optimization is performed using the composition of two formation brines and four injection brines. Moreover, interfacial tension measurements and oil drop snap-off volume measurements are performed in parallel with the core flooding experiments to define the role of interfacial viscoelasticity as the recovery mechanism other than wettability alteration. Synthetic seawater spiked with double amount of sulfate depicted potential results of interfacial viscoelastic layer development and hence to contribute the higher oil recovery. Total oil recovery after secondary-mode using sulfate-modified water and tertiary-mode polymer flood was higher than the combination of seawater brine in secondary-mode and polymer flood in tertiary-mode. Nevertheless, experiments helped us concluding that the amount of sulfate added is a critical factor to obtain maximum oil recovery and to avoid pore-plugging problems. We, therefore, demonstrate that executing a detailed fluid optimization leads to promising laboratory results, potentially linked with an improvement in the economics of the field applications.