The management of activated sludge remains a major challenge for wastewater treatment plants due to its limited dewaterability and downstream disposal concerns. Conventional sludge conditioning often relies on chemicals that pose long-term environmental hazards. In response, this study investigated the potential application of filamentous fungi Trichoderma atrobrunneum and Trichoderma reesei for sludge conditioning after biological wastewater treatment. Fungal-assisted treatment significantly improved sludge settleability and dewaterability, reducing sludge volume index (SVI) from poor settling values (>180 mL/g) to 75–95 mL/g, and increasing sludge dewaterability by 65–75%. The process involved hydrolytic enzyme production by metabolically active fungi and the formation of dense fungal-sludge aggregates through hyphal bridging, reducing the need for external enzyme addition or chemical conditioners. Notably, T. atrobrunneum showed particularly high laccase productivity (up to 46.92 ± 4.25 U/mL). Fungal conditioning also significantly decreased sludge phytotoxicity from moderately high to low within 72 h of treatment. Moreover, due to the biocontrol properties of Trichoderma, fungal-conditioned sludge exhibited high antagonistic activity against Fusarium spp. in dual-culture assays, inhibiting plant pathogen growth by up to 95% and suggesting on added value for treated sludge intended for agricultural applications. Therefore, the study demonstrates filamentous fungi, particularly T. atrobrunneum, as promising conditioning agents for waste sludge treatment. By combining sludge aggregation, in situ enzyme production, improved dewaterability, and enhanced reuse potential within a single process, fungal conditioning offers an environmentally friendly alternative to conventional approaches, while providing additional benefits for downstream sludge management.

ABSTRACT Spent coffee grounds (SCG) are extensively generated as a byproduct of coffee production and consumption. Improper disposal of SCG contributes to greenhouse gas emissions, environmental pollution, and the loss of valuable resources when landfilled or discharged into sewage systems. In response, this study investigates the biodegradation potential of SCG using selected wood‐decay fungi known for their ability to secrete a wide spectrum of lignocellulose‐degrading enzymes and degrade complex organic compounds. White rot fungi, such as Irpex lacteus, Pleurotus dryinus, and Trametes versicolor, were cultivated in SCG‐containing media to evaluate the degradation efficiency, fermentable sugar dynamics, and fungal enzyme secretion patterns. All tested fungi were able to metabolize SCG and exhibited active enzyme secretion during cultivation. P. dryinus and T. versicolor efficiently secreted both cellulases and laccases, with T. versicolor demonstrating laccase activity of 721.193 ± 41.72 U/L, indicating high oxidative potential. Fungal cultivation and enzyme production resulted in a significant carbohydrate degradation in SCG. The most significant decrease was observed in P. dryinus, which achieved a 43.32% reduction in SCG carbohydrates, while T. versicolor and I. lacteus ensured reductions of 39.07% and 35.55%, respectively. The findings demonstrate that SCG can serve as a low‐cost substrate for fungal enzyme production, particularly for laccase generation by T. versicolor, while simultaneously enabling SCG biomass degradation. Together, the study shows the potential of white rot fungi for the biological treatment of SCG, contributing to the development of more sustainable strategies for coffee waste valorization as an alternative to environmentally harmful disposal routes.

Microbial contamination in mechanical ventilation systems remains a challenge for maintaining healthy indoor environments, particularly in educational buildings with high occupant density. Although modern HVAC systems aim to ensure good indoor air quality, unfavorable conditions can create niches for microbial growth, contributing to sick building syndrome and respiratory risks. This study examined bacterial and fungal contamination in the ventilation systems and auditoriums of a university building fully renovated in 2022, equipped with contemporary AHUs operating on 100% outdoor air with no recirculation, F7/M5 filters, and continuous schedules. Sampling was performed during two contrasting periods: summer (unoccupied) and autumn (occupied), to explore how occupancy and environmental conditions (temperature and relative humidity) influence contamination patterns. Air samples were collected using a microbial air sampler, and duct surfaces were swabbed; temperature and relative humidity were recorded at each sampling point. Additional samples were taken near an air handling unit. Bacterial counts ranged from 65 to 265 CFU/m & sup3; in room air and reached up to 12 100 CFU/m(2) near AHUs, with increases during the occupied autumn period. Fungal contamination was generally lower (0-70 CFU/m & sup3;) but intensified in summer under high humidity conditions (>80% RH). These findings suggest that renovation and modern ventilation systems alone do not eliminate microbial risks and that operational factors such as humidity control and maintenance remain critical. The study fills an important gap by providing evidence of contamination dynamics in a modern system and underscores the need for preventive strategies to safeguard indoor air quality in educational facilities.

The study investigates the application of white rot fungi for reactor–scale microalgae harvesting and explores the mechanisms underlying the algal–fungal interactions and their impact on biomass composition. Enzymatic analysis and microscopy revealed that the formation of algal-fungal complexes and successful harvesting are coupled with fungal cellulose-degrading enzyme production and hydrolytic processes of microalgae cells. Fluorescence intensity decreased by over 80% in cells stained with Calcofluor-white after interaction with white rot fungi, indicating the reduction in cellulose content in microalgal cells caused by fungal enzymatic activity. These enzymes also caused significant cell damage and more than 50% decrease in microalgae cell size. The presence of cellulolytic enzymes broadens the potential application of the resulting biomass in various biotechnological applications. Moreover, reactor-scale bioflocculation resulted in over 95% T. obliquus and almost 85% C. vulgaris harvesting efficiency from secondary wastewater within less than 24 hours, demonstrating the method's scalability and industrial applicability.

Membrane filtration is a safe and sustainable water treatment method; however, membrane fouling remains a major challenge that limits its broader application. Modified membranes for fouling mitigation have been extensively studied, including photocatalyst incorporation for organic matter degradation and biofouling control. However, no commercially available photocatalytic membranes exist to date, possibly owing to the lack of understanding of their properties. Furthermore, conventional microbiological test methods commonly used in membrane research are insufficient for accurately assessing membrane antibiofouling properties. Mixed-matrix dual-layer membranes with varying concentrations of zinc oxide nanoparticles were prepared and characterized using multiple testing approaches. Despite achieving >99.999% reduction in cultivable Escherichia coli, viability assays revealed that only half of the cells were dead, with the rest entering a viable but nonculturable (VBNC) state and forming microcolonies, resulting in misleading CFU-based results. Additionally, Pseudomonas aeruginosa biofilm formation was evaluated using fluorescence staining to assess extracellular polymeric substance (EPS) production. While P. aeruginosa survived and multiplied on the photocatalytic membranes, biofilm maturation was inhibited, with EPS protein production reduced by up to 84% compared with the unmodified reference.

Wastewater treatment plants (WWTPs), particularly activated sludge systems, generate significant amounts of various types of waste, including screenings, primary sludge, and secondary sludge. While substantial research has been conducted on the recovery and valorization of sewage sludge, the treatment and utilization of screenings remain underexplored. In response, this study investigates the potential of white rot fungi to degrade cellulose-containing waste screened during the preliminary treatment and examines the production patterns of lignocellulolytic enzymes in the presence of this waste. The studied fungi exhibited variable enzymatic responses depending on the type of substrate, however, their adaptability highlighted the potential in fungal-mediated bioconversion processes. P. dryinus and T. versicolor were identified as strong and adaptive candidates for oxidative enzyme production, with P. dryinus showing laccase activity up to 1691.75 ± 12.22 U/mg and degrading 44.46% of carbohydrates in tested screenings. I. lacteus and B. adusta were predominantly observed in cellulolytic enzyme production, with B. adusta ensuring a 43.49% reduction in carbohydrate content of screenings. As a result of fungal cultivation in WWTP waste, the production potential of 34 to 46 kg of sugars per ton of screenings was determined. Therefore, the study presents a promising approach for the sustainable treatment of screenings and the development of waste management and resource recovery strategies for WWTP-derived waste.

Municipal sewage sludge, a by-product of wastewater treatment plants, presents environmental challenges due to its complex composition. Particular concern is the lipophilic and aliphatic compounds that pose risks to the environment and human health. This study focuses on the efficient removal of those compounds from sewage sludge using several organic solvents (hexane, toluene, chloroform, dichloromethane, acetone, hexane-methanol mixture, ethanol, and methanol) and ionic liquids (ILs) like tetrakis(hydroxymethyl)phosphonium chloride and 1-ethyl-3-methylimidazolium acetate by solvent extraction techniques. To determine optimal conditions, various factors such as solvent types, contact time, and temperature were examined. The results reveal that solvent polarity significantly impacts extract composition, with non-polar solvents like hexane and toluene yielding profiles characteristic of lipid-type compounds. An in-depth analysis of contaminants present in the sewage sludge was studied by Fourier-transform infrared spectroscopy (FTIR). Additionally, nuclear magnetic resonance (NMR) was used to identify the extracted compounds, including triglycerides, aliphatic esters, aliphatic alcohols, and free carboxylic acids. NMR provides data on the composition of the sewage sludge and indicates that among all the solvents used, tetrakis(hydroxymethyl) phosphonium chloride was the most suitable solvent for removing lipophilic and aliphatic compounds. Regeneration potential and reusability of the IL were conducted and verified by NMR. The results showed that tetrakis(hydroxymethyl) phosphonium chloride ionic liquid could be used for several extraction cycles. Identifying these compounds in the extracted mixture demonstrates that it adds value and potential for various applications. Towards environmental sustainability and circular economy, this effort develops strategies for the safe management, disposal, and recyclability of sewage sludge and, the reduction in environmental and health hazards associated with organic compounds.

The current research is devoted to the development and characterization of green antimicrobial polymer biocomposites for food packaging applications. The biocomposites were developed by melt compounding on the basis of two different succinate polymer matrices with varying chain stiffness—polybutylene succinate (PBS) or its copolymer with 20 mol.% of polybutylene adipate (PBSA). Fungi chitosan oligosaccharide (C98) and crustacean chitosan (C95) were used as antimicrobial additives. The rheological properties of the developed biocomposites were determined to clear out the most suitable temperature for melt processing. In addition, mechanical, thermal, barrier and antimicrobial properties of the developed biocomposites were determined. The results of the investigation revealed that PBSA composites with 7 wt% and 10 wt% of the C98 additive were more suitable for the development of green packaging films because of their higher ultimate elongation values, better damping properties as well as their superior anti-microbial behavior. However, due to the lower thermal stability of the C98 additive as well as PBSA, the melt processing temperatures of the composites desirably should not exceed 120 °C. Additionally, by considering decreased moisture vapor barrier properties, it is recommended to perform further modifications of the PBSA-C98 composites through an addition of a nanoclay additive due to its excellent barrier properties and thermal stability.

BackgroundAchieving climate neutrality is a goal that calls for action in all sectors. The requirements for improving waste management and reducing carbon emissions from the energy sector present an opportunity for wastewater treatment plants (WWTPs) to introduce sustainable waste treatment practices. A common biotechnological approach for waste valorization is the production of sugars from lignocellulosic waste biomass via biological hydrolysis. WWTPs produce waste streams such as sewage sludge and screenings which have not yet been fully explored as feedstocks for sugar production yet are promising because of their carbohydrate content and the lack of lignin structures. This study aims to explore the enzymatic hydrolysis of various waste streams originating from WWTPs by using a laboratory-made and a commercial cellulolytic enzyme cocktail for the production of sugars. Additionally, the impact of lipid and protein recovery from sewage sludge prior to the hydrolysis was assessed.ResultsTreatment with a laboratory-made enzyme cocktail produced by Irpex lacteus (IL) produced 31.2 mg sugar per g dry wastewater screenings. A commercial enzyme formulation released 101 mg sugar per g dry screenings, corresponding to 90% degree of saccharification. There was an increase in sugar levels for all sewage substrates during the hydrolysis with IL enzyme. Lipid and protein recovery from primary and secondary sludge prior to the hydrolysis with IL enzyme was not advantageous in terms of sugar production.ConclusionsThe laboratory-made fungal IL enzyme showed its versatility and possible application beyond the typical lignocellulosic biomass. Wastewater screenings are well suited for valorization through sugar production by enzymatic hydrolysis. Saccharification of screenings represents a viable strategy to divert this waste stream from landfill and achieve the waste treatment and renewable energy targets set by the European Union. The investigation of lipid and protein recovery from sewage sludge showed the challenges of integrating resource recovery and saccharification processes.

The growing demand for novel enzyme producers to meet industrial and environmental needs has driven interest in lignocellulose-degrading fungi. In this study, lignocellulolytic enzyme production capabilities of environmental fungal isolates collected from boreal coniferous and nemoral summer green deciduous forests were investigated, using Congo Red, ABTS, and Azure B as indicators of cellulolytic and ligninolytic enzyme productions. Through qualitative and quantitative assays, the study aimed to identify promising species for lignocellulose-degrading enzyme secretion and assess their potential for biotechnological applications. Primary screening tests showed intensive enzyme secretion by certain isolates, particularly white rot fungi identified as Trametes pubescens and Cerrena unicolor. These fungi exhibited high efficiency in degrading Congo Red and Azure B. The isolates achieved up to a 93.30% decrease in Congo Red induced color intensity and over 78% decolorization of Azure B within 168 hours. Within 336 hours, these fungi reached nearly 99% removal of Congo Red and up to 99.79% decolorization of Azure B. Enzyme activity analysis confirmed the lignin-degrading capabilities of T. pubescens, which exhibited laccase activity exceeding 208 U/mL. Furthermore, Fomitopsis pinicola showed the highest cellulose-degrading potential among the studied fungi, achieving cellulase activity over 107 U/L during Congo Red decolorization. Previously undescribed enzyme-producing species, such as Peniophora cinerea, Phacidium subcorticalis, and Cladosporium pseudocladosporioides, also demonstrated promising lignocellulolytic enzyme production potential, achieving up to 98.65% and 99.80% decolorization of Congo Red and Azure B, respectively. The study demonstrates novel candidates for efficient lignocellulolytic enzyme production with broad biotechnological applications such as biomass conversion, wastewater treatment, textile dye and other complex chemical removal, and environmental remediation.

Global water scarcity is a threat that can be alleviated through membrane filtration technologies. However, the widespread adoption of membranes faces significant challenges, primarily due to membrane biofouling. This is the reason why membrane modifications have been under increasing investigation to address the fouling issues. Antibacterial membranes, designed to combat biofouling by eliminating microorganisms, offer a promising solution. Within this study, flat sheet ultrafiltration (UF) membranes with integrated photocatalytic zinc oxide (ZnO) nanoparticles were developed, characterized, and assessed through filtration and fouling tests. The antibacterial properties of the membranes were conducted in static tests using Gram-negative bacteria—Escherichia coli—and natural tap water biofilm. The results demonstrated a notable enhancement in membrane surface wettability and fouling resistance. Furthermore, the incorporation of ZnO resulted in substantial photocatalytic antibacterial activity, inactivating over 99.9% of cultivable E. coli. The antibacterial activity persisted even in the absence of light. At the same time, the persistence of natural tap water organisms in biofilms of modified membranes necessitates further in-depth research on complex biofilm interactions with such membranes.

The perception of sewage sludge has been shifting from waste to resource, leading to various technological proposals for its management and resource recovery. This study explores a two-step sewage sludge treatment using different pathways—physical-alkali followed by physical-acid, and physical-acid followed by physical-alkali hydrolysis—to understand the efficiency of organic matter (OM) and Kjeldahl nitrogen extraction, and protein solubilization. Hydrolysis of the sewage sludge was performed with 3 M H2SO4 and 2.8 M NaOH and combined with physical treatment—thermal, ultrasonication, microwave irradiation, and cavitation. The results showed that cavitation chemical hydrolysis in an alkaline environment (CCH-alkali) extracted the highest amount of OM—up to 79.0%. When further cavitation chemical hydrolysis in an acid environment (CCH alkali–acid) was performed, OM extraction reached 90.2%. Physical-alkali treatment showed better performance in resource recovery from secondary sludge (SS) in both treatment steps. The highest protein extraction rate of 23,046 mg/L in the supernatant was obtained using SS treatment with microwave chemical hydrolysis in an alkaline environment (MCH-alkali). Although physical-acid treatment resulted in reduced protein solubilization and OM extraction, it provides a higher protein hydrolysis rate. Organic nitrogen compounds were better extracted with thermal-alkali treatment, reaching 95.3% removal. The study showed that different physical treatment methods demonstrate selective resource recovery or extraction performance.

Sewage sludge is a type of waste that has high health and environmental risks associated with its reuse. Moreover, sludge has been neglected in global circular economy targets because it is generated in considerably lower quantities than municipal solid waste. At the same time, European Union's transition towards circular economy has set the need to reduce the amount of waste and to promote the production of secondary raw materials. Many countries have developed national strategies for sludge management to reach their sustainability goals. In Latvia, the current sludge management approaches include land application, composting and anaerobic digestion which all utilize sludge as an organic fertilizer. As an alternative to current management practices, resource recovery is put forward as a solution that is in agreement with EU policy. Carbohydrates (including cellulose), proteins and lipids were selected as candidates for energy and materials recovery from sludge. For the first time, this study demonstrates a comprehensive assessment of Latvian municipal sewage sludge composition and offers the theoretical yields of secondary resources on a yearly basis. Primary, secondary, and anaerobically digested sludge from 13 wastewater treatment plants (WWTPs) in Latvia was characterized in this study. The most abundant sludge type - secondary sludge - contained 18.5% proteins, 9.8% lipids and 2.6% cellulose per TS. On a yearly basis, secondary sludge from all Latvian WWTPs could provide 2530 t proteins, corresponding to 750 t protein-based fertilizer. Primary sludge contained 23.9% proteins, 9.1% lipids and 7.1% cellulose per TS. Primary sludge could provide 763 t/a carbohydrates, including 545 t/a cellulose. The currently available secondary and digested sludge would yield 727 t bioethanol, corresponding to 4.0% of the national biofuel consumption. This work applies the concept of resource recovery to the Latvian wastewater sector and shows the potential of simultaneously addressing waste and wastewater management issues.

Lignocellulosic biomass is a significant source of sustainable fuel and high-value chemical production. However, due to the complex cross-linked three-dimensional network structure, lignin is highly rigid to degradation. In natural environments, the degradation is performed by wood-rotting fungi. The process is slow, and thus, the use of lignin degradation by fungi has not been regarded as a feasible technology in the industrial lignocellulose treatment. Fungi produce a wide variety of ligninolytic enzymes that can be directly introduced in industrial processing of lignocellulose. Within this study, screening of ligninolytic enzyme production using decolorization of ABTS and Azure B dyes was performed for 10 fungal strains with potentially high enzyme production abilities. In addition to standard screening methods, media containing lignin and hay biomass as carbon sources were used to determine the change in enzyme production depending on the substrate. All selected fungi demonstrated the ability to adapt to a carbon source limitation; however, four strains indicated the ability to secrete ligninolytic enzymes in all experimental conditions-Irpex lacteus, Pleurotus dryinus, Bjerkandera adusta, and Trametes versicolor-respectively displayed a 100%, 82.7%, 82.7%, and 55% oxidation of ABTS on lignin-containing media and 100%, 87.9%, 78%, and 70% oxidation of ABTS on hay-containing media after 168 h of incubation. As a result, the most potent strains of fungi were selected to produce lignocellulose-degrading enzymes and to demonstrate their potential application in biological lignocellulose pretreatment.

L. pneumophila counts increased by more than ten-fold in the P-reduced domestic hot water system once the heat exchanger setpoint was periodically lowered.

Tertiary wastewater treatment with microalgae incorporates environmental sustainability with future technologies and high exploitation costs. Despite the apparent ecological benefits of microalgae-assisted wastewater treatment/biomass-based resource production, technological improvements are still essential to compete with other technologies. Bio-flocculation instead of mechanical harvesting has been demonstrated as an alternative cost-effective approach. So far, mostly filamentous fungi of genus Aspergillus have been used for this purpose. Within this study, we demonstrate a novel approach of using white-rot fungi, with especially high potential of algae—Irpex lacteus complex that demonstrates efficiency with various microalgae species at a broad range of temperatures (5–20 °C) and various pH levels. Harvesting of microalgae from primary and secondary wastewater resulted in 73–93% removal efficiencies within the first 24 h and up to 95% after 48 h. The apparent reuse potential of the algae—I. lacteus pellets further complements the reduced operating costs and environmental sustainability of bio-flocculation technology.

Business-as-usual municipal sewage sludge (MSS) management practices could impact significantly on public health and the environment. Administrative costs for municipal wastewater treatment plants account for more than 50 %. To reduce administrative costs, the EU has called for the reuse of waste to make it part of the circular economy. One of the options for MSS is reuse to recover bioresources. Because of toilet paper, the main component of the total solids in MSS is cellulose, which could be recovered by chemical or biological processes. Crystalline cellulose is of great use in various fields such as biomedical, pharmaceutical, mechanical and others. There are various solvents to dissolve cellulose present in renewable sources to recover. However, these solvents are not widely used at MSS. This review focuses on solvent options for MSS. It also develops an environmentally friendly protocol for the recovery of nanocellulose from primary MSS using alkali-based solvent systems.

Incorporation of various alternative resources as co-digestion substrates aids to reduce the consumption of agricultural crops for biogas production. However, the efficiency and limitations of these co-substrates is still not fully understood. Use of biomass waste remaining after enzymatic hydrolysis for high value chemical fermentation, meat processing and dairy wastewater primary sludge as co-substrates in an agricultural resource anaerobic digestion plant is tackled within this study. The results showed that anionic surfactants (<200 ppm) can be used to improve fat, oil and grease (FOG) solubility in water and, at the same time, enhance the biomethane potential of FOG-containing sludge by increasing it from 1374.5 to 1765 mLCH4/gVS for meat processing wastewater primary sludge, and from 534 to 740 mLCH4/gVS for dairy wastewater primary sludge, when agricultural digestate is used as a substrate and sludge loading is not more than 10% from the volatile solids loaded. At the same time, only 549.7 mLCH4/gVS was produced as 30-day BMP when 5% biomass hydrolysis waste was used. Biomass hydrolysis waste co-digestion with primary sludge from dairy and meat processing wastewaters has an antigenic effect, and separate substrate anaerobic digestion gave a better results, thus, showing that excessive combination of various waste resources can be inhibitory for biogas production and the appropriate substrate selection and combination is a technical challenge for the biogas industry.

The aim of this paper is to show the way – how to develop LED UV-C prototype of disinfection devices with safety solution to user, using UV-C light emitting diode for different small surfaces disinfection in public transport system. In order to achieve the aim of the paper, the prototype for disinfecting small surfaces in public transport using UV-C spectrum irradiation have been developed. The designs of prototype cases or parts thereof are created in Autodesk Fusion 360, while the designs of the printed electronic plates have been developed in the program Autodesk Eagle. The ranges of irradiation sources used in the prototypes were tested on a spectrometer at Laboratory of High-Resolution Spectroscopy and Light Source Technology, Institute of Atomic Physics and Spectroscopy, University of Latvia, while the efficiency of disinfection was determined in the Water Research and Environmental Biotechnology Laboratory, Riga Technical University. Two different bacterial cultures were used for microbiology tests: E.coli and S.aureus. In order for UV irradiation not to affect passengers of public transport, the prototypes were equipped with safety systems that prevent exposure of humans to UV-C irradiation. In order to determine the energy efficiency of equipment, only power measurements have been made before the supply and control elements of prototypes over a single cycle and power measurements on irradiation sources over a single cycle. UV-C irradiation is effective disinfection method and we should continue to search for ways to implement it even more, meanwhile looking for ways to protect living things from unwanted harm via irradiation.

Flexible antibacterial materials have gained utmost importance in protection from the distribution of bacteria and viruses due to the exceptional variety of applications. Herein, we demonstrate a readily scalable and rapid single-step approach for producing durable ZnO nanoparticle antibacterial coating on flexible polymer substrates at room temperature. Substrates used are polystyrene, poly(ethylene-co-vinyl acetate) copolymer, poly(methyl methacrylate), polypropylene, high density polyethylene and a commercial acrylate type adhesive tape. The deposition was achieved by a spin-coating process using a slurry of ZnO nanoparticles in toluene. A stable modification layer was obtained when toluene was a solvent for the polymer substrates, namely polystyrene and poly(ethylene-co-vinyl acetate). These coatings show high antibacterial efficiency causing >5 log decrease in the viable counts of Gram-negative bacteria Escherichia. coli and Gram-positive bacteria Staphylococcus aureus in 120 min. Even after tapping these coated surfaces 500 times, the antibacterial properties remained unchanged, showing that the coating obtained by the presented method is very robust. In contrast to the above findings, the coatings are unstable when toluene is not a solvent for the substrate.