Macroalgae can be a viable alternative to replace fossil fuels that have a negative impact on the environment. By mixing macroalgae with other substrates, higher quality biogas can be obtained. Such biogas is considered one of the most promising solutions for reducing climate change. In the work, new studies were conducted, during which biogas yield was investigated in a three-stage bioreactor (TSB) during the anaerobic digestion of Cladophora glomerata macroalgae with inoculants from cattle manure and sewage sludge at different organic loading rates (OLR). By choosing the optimal OLR in this way, the goal was to increase the energy potential of biomass. The research was performed at OLRs of 2.87, 4.06, and 8.13 Kg VS/m³ d. After conducting research, the highest biogas yield was determined when OLR was 2.87 Kg VS/m³ d. With this OLR, the average biogas yield was 439.0 ± 4.0 L/Kg VS_added, and the methane yield was 306.5 ± 9.2 L CH₄/Kg VS_added. After increasing the OLR to 4.06 and 8.13 Kg VS/m³ d, the yield of biogas and methane decreased by 1.55 times. The higher yield was due to better decomposition of elements C, N, H, and S during the fermentation process when OLR was 2.87 Kg VS/m³ d. At different OLRs, the methane concentration remained high and varied from 68% to 80%. The highest biomass energy potential with a value of 3.05 kWh/Kg VS_added was determined when the OLR was 2.87 Kg VS/m³ d. This biomass energy potential was determined by the high yield of biogas and methane in TSB.

Sewage sludge was treated with nanoscale zero-valent iron (nZVI) to enhance biogas and methane (CH₄) production, and the influence of key parameters on the material’s anaerobic digestion (AD) efficiency was analyzed using sigmoidal mathematical models. In this study, three dosages of nZVI (0.5%, 1.5% and 3%) were added to the anaerobic sludge digestion system to enhance and accelerate the sludge decomposition process. The results showed that cumulative biogas yield after 41 days of digestion increased by 23.9% in the reactor with a nZVI dosage of 1.5%. Correspondingly, the highest CH₄ production enhancement by 21.5% was achieved with a nZVI dosage of 1.5% compared to the control. The results indicated that this nZVI dosage was optimal for the AD system, as it governed the highest biogas and CH₄ yields and maximum removal of total and volatile solids. Additionally, to predict biogas and CH₄ yields and evaluate kinetic parameters, eight kinetic models were applied. According to the results of the modified Gompertz, Richards and logistic models, the nZVI dosage of 1.5% shortened the biogas lag phase from 11 to 5 days compared to the control. The Schnute model provided the best fit to the experimental biogas and CH₄ data due to highest coefficients of determination (R²: 0.9997–0.9999 at 1.5% and 3% nZVI dosages), as well as the lowest Akaike’s Information Criterion values and errors. This demonstrated its superior performance compared to other models.

In this study, the effects of graphene-based nanomaterials—specifically graphene nanoplatelets (GNPs) and graphene oxide (GO) nanosheets—on methane (CH₄) production during anaerobic digestion (AD) of thermally hydrolyzed sewage sludge were investigated. Anaerobic digestion was carried out over a 40-day period under mesophilic conditions in batch digesters with a volume of 2.65 L. The influence of various dosages of GNPs and GO nanosheets on methane yields was assessed, including a comparison between GNPs with different specific surface areas (320 m²/g and 530 m²/g). The highest CH₄ yield (194 mL/g-VS_added) was observed with a GNP dosage of 5 mg/g-TS and a surface area of 530 m²/g, showing an increase of 3.08% compared to the control. This treatment group had the greatest positive effect also on the degradation of organic matter, with total solids (TS) and volatile solids (VS) removal reaching 34.35% and 44.18%, respectively. However, the GO dosages that significantly decreased cumulative CH₄ production were determined to be 10–15 mg/g-TS. Graphene oxide at dosages of 10 and 15 mg/g-TS reduced specific cumulative CH₄ yields by 4.03% and 5.85%, respectively, compared to the control, indicating CH₄ yield inhibition. This lab-scale study highlights the potential for integrating GNPs into full-scale, continuously operated wastewater treatment anaerobic digesters for long-term use in future applications.

The use of microalgae as a raw material for biogas production is promising. Macroalgae were mixed with cattle manure, wheat straw, and an inoculant from sewage sludge. Mixing macroalgae with co-substrates increased biogas and methane yield. The research was carried out using a three-stage bioreactor. During biogas production, the dynamics of the composition of the microbiota in the anaerobic chamber of the bioreactor was evaluated. The microbiota composition at different organic load rates (OLRs) of the bioreactor was evaluated. This study also demonstrated that in a three-stage bioreactor, a higher yield of methane in biogas was obtained compared to a single-stage bioreactor. It was found that the most active functional pathway of methane biosynthesis is PWY-6969, which proceeds via the TCA cycle V (2-oxoglutarate synthase). Microbiota composition and methane yield depended on added volatile solids (VS_added). During the research, it was found that after reducing the ORL from 2.44 to 1.09 kg VS/d, the methane yield increased from 175.2 L CH₄/kg VS_added to 323.5 L CH₄/kg VS_added.

Noise pollution has become an increasingly discussed environmental problem in recent years. Developing a traffic infrastructure and recent sustainability goals require new solutions to mitigate noise pollution. This paper investigates the efficiency of the noise barrier made entirely of recycled materials. This solution would help achieve the United Nations sustainable development goals (SDGs). The proposed barrier target SDGs are: Good Health and Well-being (SDG 3); Industry, Innovation, and Infrastructure (SDG 9); Sustainable Cities and Communities (SDG 11); Climate Action (SDG 13). The changed barrier parameters were the parameters of the perforated panel and the air gap behind the porous material. To solve the optimisation problem, the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) method was used. The results showed that the proposed barrier configuration was the following: perforation shape—round, perforation diameter—5 mm, increment angle perforation—30°, thickness of the perforated panel—10 mm, porous absorbing material (composite rubber granule and hemp shive panel (RGHS))—50 mm thick, 20% of hemp shive content, air gap between absorbing material and the rigid backing—100 mm. The total thickness of the noise barrier was 180 mm. The acoustic parameters of the noise barrier structure were: α_avg. = 0.24, peaking at 0.51 (1250 Hz) and R_W = 39.7 ± 1.0 dB. These results indicate that the proposed barrier made of recycled materials could be a sustainable alternative for noise pollution mitigation and improving people’s quality of life.

Plastic and waste production has increased significantly in recent years. According to the various predictions the plastic production is not slowing down in the near future. Since 1960, plastic production has risen to 322 million tonnes in 2015 and expected to double in the next 20 years (Lusher et al., 2017). According to the 2020 statistical data, the leading sectors in plastic demand are packaging, building and construction, with 40.5% and 20.4% respectively. In 2019, an estimated 41% of plastic packaging waste was recycled in the EU. Despite the advantages of plastic recycling technologies, there are also a number of problems. Mechanical recycling refers to the processing of plastics waste into secondary raw material or products without significantly changing the material’s chemical structure. In this paper, we focused at the problem of plastic micro fibre (PMF) waste, which generated during mechanical recycling. The possibilities of using PMF for sound absorption applications are tested. For primary acoustic characterisation PMF was not treated thermally or bound using other materials. The controlled parameter of the material is density. The density of material changed from 100 to 300 kg/m3. The PMF sound absorption characterisation was performed using standard transfer function method (ISO 10534-2). The acoustic performance of materials predicted with acoustic porous materials Delany-Bazley-Miki model. The aim of this paper is to gain the essential knowledge about the plastic micro fibre sound absorption performance to find the possible recycling application for sound absorption.