• Energy Research

Effective management of recyclable plastic waste is critical for environmental sustainability and economic viability. Blockchain technology has transformative potential in addressing the challenges of plastic waste management. Currently, the inefficiency of plastic recycling systems results in low recycling rates and significant environmental impacts due to poor sorting, contamination, and limited technology application. However, innovations such as chemical recycling, solvent-based techniques, and biotechnology offer promising advances in the management of plastic waste. Blockchain technology provides a transparent, decentralized ledger that enhances traceability and incentives through smart contracts, decentralized applications (DApps), and digital watermarks. These blockchain solutions can improve waste tracking, automate payments, and reward participants who recycle responsibly. Although significant investment in technology and education is required, integrating blockchain with the Internet of Things (IoT) and artificial intelligence (AI)-driven analytics could revolutionize plastic waste management by creating transparent, efficient, and collaborative recycling ecosystems. Blockchain technology has immense potential to redefine the management of plastic waste and promote a sustainable, circular economy.

Bacterial metabolism determines the effectiveness of biological treatment of wastewater. Therefore, it is important to define the relations between the species structure and the performance of full-scale installations. Although there is much laboratory data on microbial consortia, our understanding of dependencies between the microbial structure and operational parameters of full-scale wastewater treatment plants (WWTP) is limited. This mini-review presents the types of microbial consortia in WWTP. Information is given on extracellular polymeric substances production as factor that is key for formation of spatial structures of microorganisms. Additionally, we discuss data on microbial groups including nitrifiers, denitrifiers, Anammox bacteria, and phosphate- and glycogen-accumulating bacteria in full-scale aerobic systems that was obtained with the use of molecular techniques, including high-throughput sequencing, to shed light on dependencies between the microbial ecology of biomass and the overall efficiency and functional stability of wastewater treatment systems. Sludge bulking in WWTPs is addressed, as well as the microbial composition of consortia involved in antibiotic and micropollutant removal.

Anaerobic membrane bioreactor (AnMBR) technology is emerging as an alternative to conventional anaerobic treatment due to its complete biomass retention, short start-up time, high effluent quality, and small footprint. This paper provides a general overview of the application of AnMBRs for industrial and municipal wastewater treatment. The potential benefits of AnMBRs are discussed, such as the degradation of organic matter for energy production, the concentration of nutrients for subsequent reclamation, or the effective removal of organic contaminants for water reuse. To explore the technology for energy-neutral wastewater treatment, the recovery of methane, hydrogen, and ethanol is summarized, highlighting the problems of dissolution of methane in permeate and competition between sulfate-reducing bacteria and methanogens for organic matter. Recovery of water and nutrients for reuse, e.g., for algae production, is reported. Since membrane fouling remains a challenge in membrane operation and leads to increased operation and maintenance costs, methods to reduce fouling are highlighted. Future research prospects related to the application of AnMBR in resource recovery plants and fouling management are emphasized.

Polyphenols that are abundant in various organic wastes can inhibit anaerobic degradation of these wastes. This study investigated the effect of the concentration of individual phenolic acids (p-OH benzoic, vanillic, ferulic, sinapic, syringic, and p-coumaric acids) and their mixture on the methane potential of distillery stillage. An increase in phenolic acid concentration adversely affected biogas production and composition, as well as the methane-production rate. The inhibition constants for methane production were 0.5–1.0 g/L of individual phenolic acids and 1.5 g/L of the mixture of these acids. At lower concentrations, the phenolic acids were utilized as a carbon source, but the process was impeded when their concentrations exceeded the threshold value, due to their negative effect on microbial growth. When distillery stillage was spiked with vanillic acid, two-phase methane production was observed. Spiking distillery stillage with vanillic, p-coumaric, syringic, or ferulic acids affected anaerobic digestion the most; 2 g/L of these acids completely inhibited methane production. With 4.0 g/L of all individual phenolic acids, no methane production was observed. As the concentration of these phenolic acids increased from 0.5 to 4.0 g/L, the abundance of methanogenic Archaea, in which acetoclastic methanogens predominated, decreased by about 30 times.

The effective management of waste-activated sludge (WAS) presents a significant challenge for wastewater treatment plants (WWTPs), primarily due to the sludge’s high content of organic matter, pathogens, and hazardous substances such as heavy metals. As urban populations and industrial activities expand, the increasing volume of WAS has intensified the need for sustainable treatment solutions. Conventional approaches, such as landfilling and anaerobic digestion, are frequently ineffective and resource-intensive, particularly when dealing with the protective extracellular polymeric substances (EPS) that render WAS resistant to biodegradation. Thermal pretreatment methods have gained attention due to their ability to enhance the biodegradability of sludge, improve dewaterability, and facilitate resource recovery. These processes function by breaking down complex organic structures within the sludge, thereby increasing its accessibility for subsequent treatments such as anaerobic digestion. The integration of thermal treatment with chemical methods can further optimize the management process, resulting in higher biogas yields, reduced pathogen content, and lower environmental risks. While thermal disintegration is energy-intensive, advancements in energy recovery and process optimization have made it a more viable and environmentally friendly option. This approach offers a pathway to more sustainable and efficient sludge management practices, which align with the goals of reducing waste and complying with stricter environmental regulations.

Anaerobic digestion (AD) is an effective technology for the sustainable management of organic agricultural waste, producing both biogas and nutrient-rich digestate. This study aims to review and evaluate different methods for obtaining valuable products from digestate, with a focus on innovative and sustainable approaches. The main objectives are to identify effective technologies for the recovery of nutrients and organic matter, assess their environmental and economic impact and outline the challenges and prospects in this area. The review covers established techniques (with a technology readiness level (TRL) of six to nine, indicating their maturity from pilot to full scale) such as struvite precipitation and ammonia stripping, which are very effective in recovering nitrogen and phosphorus from digestate and converting it into valuable biofertilizers. Struvite, for example, offers an option for slow-release fertilizers that reduces dependence on synthetic fertilizers. A comparative analysis shows that ammonia stripping can efficiently capture nitrogen and produce fertilizer without harming the environment. New methods, such as microalgae cultivation, use digestate as a nutrient source for the production of biofuels and bioplastics, contributing to renewable energy and sustainable material production. The study also examines composting and vermicomposting, where digestate is converted into nutrient-rich soil conditioners that significantly improve soil health and fertility. The production of biochar through pyrolysis is highlighted for its benefits in improving soil properties and sequestering carbon, providing a dual benefit for waste management and climate change mitigation. Membrane technologies, including ultrafiltration (UF) and reverse osmosis (RO), are being investigated for their effectiveness in nutrient recovery, despite challenges such as membrane fouling and high operating costs. The study highlights the potential of these valorization processes to improve the sustainability and economic viability of AD systems and to align with circular economy principles. The results suggest that the continuous optimization of these technologies and the integration of recycling processes are crucial to overcome existing challenges and realize their full potential.

Aerobic granule characteristic in sequencing batch reactors treating high-nitrogen digester supernatant was investigated at cycle lengths (t) of 6, 8 and 12 h with the COD/N ratios in the influent of 4.5 and 2.3. The biomass production (Y obs) correlated with the extracellular polymeric substances (EPS) in grams per COD removed. Denitrification efficiency significantly decreased as the amount of EPS in biomass increased, suggesting that organic assimilation in EPS hampers nitrogen removal. Granule hydrophobicity was highest at t of 8 h; the t has to be long enough to remove pollutants, but not so long that excessive biomass starvation causes extracellular protein consumption that decreases hydrophobicity. At a given t, reducing the COD/N ratio improved hydrophobicity that stimulates cell aggregation. At t of 6 h and the COD/N ratio of 2.3, the dominance of 0.5-1.0 mm granules favored simultaneous nitrification and denitrification and resulted in the highest nitrogen removal.

The anaerobic digestion (AD) of livestock blood represents a sustainable solution for the management of waste generated by the meat processing industry while simultaneously generating renewable energy. The improper treatment of livestock blood, which is rich in organic matter and nutrients, can result in environmental risks such as water pollution, soil degradation, and greenhouse gas emissions. This review examines a range of AD strategies, with a particular focus on technological advances in reactor design, pretreatment, and co-digestion, with the aim of optimizing process efficiency. While the high protein content of blood has the potential to enhance biogas production, challenges such as ammonia inhibition and process instability must be addressed. Innovations such as bio-carriers, thermal pretreatment, and co-digestion with carbon-rich substrates have demonstrated efficacy in addressing these challenges, resulting in stable operation and enhanced methane yields. The advancement of AD technologies is intended to mitigate the environmental impact of livestock blood waste and facilitate the development of a circular bioeconomy. Furthermore, the possibility of utilizing slaughterhouse blood for the recovery of valuable products, including proteins, heme iron, and bioactive peptides, was evaluated with a view to their potential applications in the pharmaceutical and food industries. Furthermore, the potential of utilizing protein-rich blood as a substrate for mixed culture fermentation in volatile fatty acid (VFA) biorefineries was explored, illustrating its viability in biotechnological applications.