Chlorella vulgaris is of great importance in numerous exploratory or industrial applications (e.g., medicals, food, and feed additives). Rapid quantification of algal biomass is crucial in photobioreactors for the optimization of nutrient management and the estimation of production. The main goal of this study is to provide a simple, rapid, and not-resource-intensive estimation method for determining the algal density of C. vulgaris according to the measured parameters using UV–Vis spectrophotometry. Comparative assessment measurements were conducted with seven different methods (e.g., filtration, evaporation, chlorophyll a extraction, and detection of optical density and fluorescence) to determine algal biomass. By analyzing the entire spectra of diluted algae samples, optimal wavelengths were determined through a stepwise series of linear regression analyses by a novel correlation scanning method, facilitating accurate parameter estimation. Nonlinear formulas for spectrometry-based estimation processes were derived for each parameter. As a result, a general formula for biomass concentration estimation was developed, with recommendations for suitable measuring devices based on algae concentration levels. New values for magnesium content and the average single-cell weight of C. vulgaris were established, in addition to the development of a rapid, semiautomated cell counting method, improving efficiency and accuracy in algae quantification for cultivation and biotechnology applications.

In recent years, the environmental impacts of plastic production and consumption have become increasingly significant, particularly due to their petroleum-based origins and the substantial waste management challenges they pose. Currently, global plastic waste production has reached 413.8 million metric tons across 192 countries, contributing notably to greenhouse gas emissions. Bioplastics have emerged as eco-friendly alternatives, with bioplastic carrier bags composed of 20% starch, 10% additives, and 70% polybutylene adipate terephthalate (PBAT) being the focus of this research. This study aimed to evaluate the biodegradation of these bioplastic bags under industrial composting conditions, addressing the gap in the existing literature that often lacks real-world applicability. A large-scale composting experiment was conducted using 37.5 tons of manure/wood and 50 tons of biopolymer bags over 12 weeks. Results showed that compost temperatures peaked at 70 °C and remained above 50 °C, pH levels stabilized at 8.16, and electrical conductivity was recorded at 1251 μs cm⁻¹. Significant changes were observed in key metrics, such as the carbon-to-nitrogen ratio and organic matter content. Disintegration tests revealed that 95% of the bags disintegrated by the 12th week, though ecotoxicity tests indicated varying germination inhibition rates. Advanced analytical methods (Fourier transform infrared spectroscopy, gas chromatography coupled with mass spectrometry) highlighted morphological and chemical transformations in the bags. This research enhances understanding of bioplastic degradation in real-world composting environments and suggests potential improvements to existing standards, promoting sustainable waste management solutions.

Bioplastics have emerged as a promising alternative to conventional plastics, marketed as environmentally friendly and sustainable materials. They provide a variety of methods for efficient waste management contributing to the goals of the circular economy. At their end-of-life stage, bioplastics can generate added value through aerobic and anaerobic biological treatments (composting or anaerobic digestion). In this study, biomethane potential (BMP) tests were carried out under mesophilic conditions on eight different catering biodegradable plastics available in the market and certified as being biodegradable under industrial composting conditions. Chemical analysis of the biodegradable plastics included elemental analysis, Fourier-transform infrared spectroscopy, and inductively coupled plasma–optical emission spectrometry. Key differences were observed in total solids (TS) and volatile solids (VS) contents between the studied biopolymer products. TS values ranged between 85.00 ± 0.26% (Product 8) and 99.16 ± 0.23% (Product 4), whereas VS content ranged between 64.57 ± 0.25 %wm (Product 6) and 99.14 ± 0.17 %wm (Product 4). Elemental analysis (elements C, H, N, S, and O) was used to estimate the theoretical methane production (ThBMP) of each product. The highest ThBMP (538.6 ± 8.7 NmL/gVS) was observed in Product 4 correlated with the highest C and H contents, while the lowest ThBMP (431.8 ± 6.1 NmL/gVS) was observed in Product 2. Significant differences were recorded between BMP values according to the chemical composition of the polymers. The average of BMP values ranged between 50.4 ± 2.1 NmL/gVS and 437.5 ± 1.0 NmL/gVS. Despite being characterized by the same composition (cellulose/cellulose derivatives and calcium carbonate), Products 2, 3, and 6 revealed significant differences in terms of TS, VS, ThBMP, and BMP. Furthermore, a significant statistical relationship (p < 0.001) was found between time (days) and BMP values of the eight products (R² = 0.899–0.964) during the initial phase. The study confirmed that cellulose-based materials can convert efficiently under mesophilic conditions into methane, at a relatively short retention time; hence, they can be regarded as a promising material for co-digestion with feedstock in industrial anaerobic biogas plants. In contrast, biodegradation of polylactic acids (PLA) does not occur under mesophilic conditions, and hence, pre-treatment of the polymers is recommended. Moreover, PLA-containing products are highly affected by the presence of other components (e.g., polybutylene adipate terephthalate and cellulose/cellulose derivatives).

The current energy crisis and waste management problems have compelled people to find alternatives to conventional non-renewable fuels and utilize waste to recover energy. Pyrolysis of plastics, which make up a considerable portion of municipal and industrial waste, has emerged as a feasible resolution to both satisfy our energy needs and mitigate the issue of plastic waste. This study was therefore conducted to find a solution for plastic waste management problems, as well as to find an alternative to mitigate the current energy crisis. Pyrolysis of five of the most commonly used plastics, polyethylene terephthalate (PET), high- and low-density polyethylene (HDPE, LDPE), polypropylene (PP), and polystyrene (PS), was executed in a pyrolytic reactor designed utilizing a cylindrical shaped stainless steel container with pressure and temperature gauges and a condenser to cool down the hydrocarbons produced. The liquid products collected were highly flammable and their chemical properties revealed them as fuel alternatives. Among them, the highest yield of fuel conversion (82%) was observed for HDPE followed by PP, PS, LDPE, PS, and PET (61.8%, 58.0%, 50.0%, and 11.0%, respectively). The calorific values of the products, 46.2, 46.2, 45.9, 42.8 and 42.4 MJ/kg for LPDE, PP, HPDE, PS, and PET, respectively, were comparable to those of diesel and gasoline. Spectroscopic and chromatographic analysis proved the presence of alkanes and alkenes with carbon number ranges of C₉–C₁₅, C₉–C₂₄, C₁₀–C₂₁, C₁₀–C₂₈, and C₉–C₁₇ for PP, PET, HDPE, LDPE, and PS, respectively. If implemented, the study will prove to be beneficial and contribute to mitigating the major energy and environmental issues of developing countries, as well as enhance entrepreneurship opportunities by replicating the process at small-scale and industrial levels.

Biochars as soil amendments have been reported to improve soil properties and may have an important role in the mitigation of the consequences of climate change. As a novel approach, this study examines whether biochar and digestate co-application can be utilized as cost-effective, renewable plant nutrients. The effects of two types of biochar—wood chip biochar (WBC) and animal bone biochar (ABC), applied alone or in combination with an anaerobic digestate—on soil physicochemical properties, on the levels of selected elements, and on growth yields of ryegrass were studied in laboratory experiments. Most parameters were significantly affected by the treatments, and the investigated factors (biochar type, application rate, and the presence of digestate), as well as their interactions, were found to have significant effects on the characteristics investigated. The easily soluble phosphorus content (AL-P₂O₅) of the soil increased in all WBC and ABC biochar treatments, and the presence of digestate caused a further increase in AL-P₂O₅ in the case of anaerobic digestate-supplemented ABC treatment (ABCxAD). The pH increased in both ABC and WBC treatments, and also in the case of ABCxAD treatments. Similar increases in the salt content were detected in ABC-treated samples and in ABCxAD treatments at higher application rates. WBC increased the water holding capacity and carbon content of the soil. Phytotoxic effects of biochars were not detected, although higher doses resulted in slower germination. Combined biochar–digestate applications resulted in increased plant yields compared to sole biochar treatments. Thus, biochar–digestate combinations appear to be applicable as organo-mineral fertilizers.

Algae communities as primary producers are essential elements of aquatic ecosystems and contribute significantly to oxygen production, carbon dioxide fixation, and nutrient transport processes in water bodies. The use of algae-based carbon capture and storage technologies does not produce harmful by-products that require disposal, and the resulting algal biomass can be valuable across various industrial sectors. In this study, model experiments were conducted to develop sequential absorption–microalgae hybrid CO₂-capture methods. To facilitate CO₂ capture from flue gases, wood biomass ash (WBA), an agricultural by-product, was utilized for its alkaline properties, while the flue gas scrubbing medium was regenerated by algae that restored alkalinity during their growth. In our experiments, one of our goals was to determine the optimal conditions for achieving maximum algal biomass growth in the shortest possible time. The suitability of WBA for flue gas cleaning was tested via simulation of CO₂ introduction. Moreover, a method was developed to determine the dissolved inorganic carbon content with the use of an OxiTop device monitoring the changes in pressure. The applied device was a closed, static, and pressure-based respirometer originally designed to determine the biological activity of microorganisms in both solid and liquid samples. In addition, the effects of CO₂-enriched WBA extract on algae cultivation were also analyzed, confirming that it imposed no growth inhibition and identifying the concentration (10% WBA) that optimally promoted algal growth. The optimal initial algal concentration and nutrient conditions for maximum growth were also determined.