Talis Juhna
@rtu.lv
Vice-Rector for Research
Riga Technical University
RESEARCH INTERESTS
Water research
Scopus Publications
Scopus Publications
Brigita Dejus, Pāvels Cacivkins, Dita Gudra, Sandis Dejus, Maija Ustinova, Ance Roga, Martins Strods, Juris Kibilds, Guntis Boikmanis, Karina Ortlova,et al.
Elsevier BV
Marta Zemīte, Daina Pūle, Olga Kiriļina-Gūtmane, Laima Ķimse, Mārtiņš Strods, Jurǵis Zemītis, Linda Mežule, Olga Valciņa, and Tālis Juhna
Royal Society of Chemistry (RSC)
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.
Aigars Lavrinovičs, Linda Mežule, Pāvels Cacivkins, and Tālis Juhna
Elsevier BV
Mairis Iesalnieks, Raivis Eglītis, Tālis Juhna, Krišjānis Šmits, and Andris Šutka
MDPI AG
Titanium dioxide (TiO2) coatings have a wide range of applications. Anatase exhibits hydrophilic, antimicrobial, and photocatalytic properties for the degradation of organic pollutants or water splitting. The main challenge is to obtain durable anatase nanoparticle coatings on plastic substrates by using straightforward approaches. In the present study, we revealed the preparation of a transparent TiO2 coating on polymethylmethacrylate (PMMA), widely used for organic optical fibres as well as other polymer substrates such as polypropylene (PP), polystyrene (PS), and polycarbonate (PC). The films were spin-coated at room temperature without annealing; therefore, our approach can be used for thermo-sensitive substrates. The deposition was successful due to the use of stripped ultra-small (<4 nm) TiO2 particles. Coatings were studied for the photocatalytic degradation of organic pollutants such as MB, methyl orange (MO), and rhodamine B (RB) under UV light. The TiO2 coating on PMMA degraded over 80% of RB in 300 min under a 365 nm, 100 W mercury lamp, showing a degradation rate constant of 6 × 10−3 min−1. The coatings were stable and showed no significant decrease in degradation activity even after five cycles.
Atis Skudra, Gita Revalde, Anna Zajakina, Linda Mezule, Karina Spunde, Talis Juhna, and Kristiana Rancane
Elsevier BV
Kristina Kokina, Linda Mezule, Kamila Gruskevica, Romans Neilands, Ksenija Golovko, and Talis Juhna
MDPI AG
The inhibition effect of rapid variations of pH in wastewater on activated sludge was investigated in laboratory-scale sequencing batch reactors (SBR). The toxic influence of pH 6.5 and 8.5 was examined. The experiment with pH 8.5 was preferable to formation of high FA concentration and showed a low risk of inhibition of second step nitrification (conversion of nitrites to nitrates). However, the reactor at pH 6.5 showed inhibition of first-step nitrification (conversion of ammonia to nitrites) caused by FNA formation. High ammonia levels caused a decrease in the overall microfauna population, whereas low–enhanced gymnamoebae, Zoogloea, and Chilodonella sp. population increased after 72 h of inhibition. Destructive acidic pH influence caused sludge washout from the reactor and, therefore, higher organic load on ASP and intensive sludge foam due to Zoogloea higher population.
Basanti Ekka, Inese Mieriņa, Tālis Juhna, Kristīna Kokina, and Māris Turks
Elsevier BV
Dita Gudra, Sandis Dejus, Vadims Bartkevics, Ance Roga, Ineta Kalnina, Martins Strods, Anton Rayan, Kristina Kokina, Anna Zajakina, Uga Dumpis,et al.
Elsevier BV
Basanti Ekka, Inese Mieriņa, Tālis Juhna, Māris Turks, and Kristīna Kokina
Elsevier BV
V. Denisova, L. Mezule, and T. Juhna
IWA Publishing
Abstract Drinking water disinfection or inactivation of pathogenic microorganisms is an essential step to minimize infection risks and decrease the incidence of waterborne diseases. Recently, chitosan nanoparticles (CNs) have been highlighted as an antimicrobial agent for a wide range of applications due to their natural antimicrobial properties, and low or no toxicity risk for human health. In this study, we generated CNs from three different molecular weight (MW) chitosan (low, medium, high) at various concentrations (0.25, 0.5 and 2% (w/v)). After the CNs preparation and quality assessment, the antimicrobial activity was evaluated by measuring the log reduction of Gram-negative bacteria E. coli as a model microorganism for faecal pollution. The results demonstrated that 0.25% of medium MW CNs are optimal for more than 99.99% reduction of cultivable E. coli and 97% inactivation of metabolically active E. coli. These results indicated that CNs were able to inhibit the growth of cultivable and metabolically active E. coli in tap water and demonstrated the potential use of CNs as an alternative antimicrobial agent in drinking water disinfection.
Marta Zemite, Linda Mezule, Kamila Gruskevica, Kristina Kokina, Janis Rubulis, Talis Juhna, Nathalie Gottschalk, Franca Dömer, René Jagau, Katharina Röwe,et al.
American Society of Civil Engineers (ASCE)
Mārtiņš Vanags, Linda Mežule, Arnita Spule, Juris Kostjukovs, Krišjānis Šmits, Aile Tamm, Talis Juhna, Svetlana Vihodceva, Tanel Käämbre, Larisa Baumane,et al.
Wiley
Basanti Ekka, Sandis Dejus, and Talis Juhna
Cambridge University Press (CUP)
Abstract The objective of the research presented in this Research Communication was to access the environmental impact of the Latvian dairy industries. Site visits and interviews at Latvian dairy processing companies were done in order to collect site-specific data. This includes the turnover of the dairy industries, production, quality of water in various industrial processes, the flow and capacity of the sewage including their characteristic, existing practices and measures for wastewater management. The results showed that dairy industries in Latvia generated in total approximately 2263 × 103 m3 wastewater in the year 2019. The Latvian dairy effluents were characterized with high chemical oxygen demand (COD), biological oxygen demand (BOD) and total solids (TS). Few dairy plants had pre-treatment facilities for removal of contaminants, and many lacked onsite treatment technologies. Most facilities discharged dairy wastewater to municipal wastewater treatment plants. The current study gives insight into the Latvian dairy industries, their effluent management and pollution at Gulf of Riga due to wastewater discharge.
Brigita Dalecka, Martins Strods, Pavels Cacivkins, Elina Ziverte, Gunaratna Kuttuva Rajarao, and Talis Juhna
Elsevier BV
Abstract Fungi have been shown to be good candidates to remove pharmaceuticals. However, the pilot-scale application mainly deals with the strict growth conditions and competition between microbial communities from wastewater. Thus, the bioaugmentation for removing the pharmaceuticals in municipal wastewater by Trametes versicolor and Aspergillus luchuensis using fluidized bed pelleted bioreactor was studied. To find the optimal performance of bioaugmentation by both fungi periodical biomass volume, 10 and 50 g per 1.25 L bioreactor, were tested. The removal of nutrients, pharmaceutical substances, and changes in the pH value, laccase activity, and total cell number of microorganisms were analyzed. The results showed that bioaugmentation has an effect in removing NH4-N and lower accumulation of NO3-N, whereas PO4−3-P and TOC did not show a significant effect on the reduction of nutrient load compared to the control without fungal addition. The results of removal efficiency for diclofenac, carbamazepine, and sulfamethoxazole showed that there was no significant effect on the removal while the highest removal efficiency (> 90 %) for ibuprofen, ketoprofen, and metoprolol was achieved by both fungi with periodical addition with 50 g of biomass after an incubation time of 3 hours. Finally, the data analysis with AI-based experimental design indicated that A. luchuensis can be a useful fungus for pharmaceutical removal and implies a perspective approach for optimization of fluidized bed pelleted bioreactor. Overall, the obtained results and the use of an AI-based platform is a promising approach for the optimization and operation of fluidized bed pelleted bioreactors.
Aigars Lavrinovičs, Fredrika Murby, Elīna Zīverte, Linda Mežule, and Tālis Juhna
MDPI AG
Four microalgal species, Chlorella vulgaris, Botryococcus braunii, Ankistrodesmus falcatus, and Tetradesmus obliquus were studied for enhanced phosphorus removal from municipal wastewater after their exposure to phosphorus starvation. Microalgae were exposed to phosphorus starvation conditions for three and five days and then used in a batch experiment to purify an effluent from a small WWTP. After 3-day P-starvation, C. vulgaris biomass growth rate increased by 50% and its PO4 removal rate reached > 99% within 7 days. B. braunii maintained good biomass growth rate and nutrient removal regardless of the P-starvation. All species showed 2–5 times higher alkaline phosphatase activity increase for P-starved biomass than at the reference conditions, responding to the decline of PO4 concentration in wastewater and biomass poly-P content. The overall efficiency of biomass P-starvation on enhanced phosphorus uptake was found to be dependent on the species, N/P molar ratio in the wastewater, as well as the biomass P content.
Ilze Irbe, Inese Filipova, Marite Skute, Anna Zajakina, Karina Spunde, and Talis Juhna
MDPI AG
In this study unique blended biopolymer mycocel from naturally derived biomass was developed. Softwood Kraft (KF) or hemp (HF) cellulose fibers were mixed with fungal fibers (FF) in different ratios and the obtained materials were characterized regarding microstructure, air permeability, mechanical properties, and virus filtration efficiency. The fibers from screened Basidiomycota fungi Ganoderma applanatum (Ga), Fomes fomentarius (Ff), Agaricus bisporus (Ab), and Trametes versicolor (Tv) were applicable for blending with cellulose fibers. Fungi with trimitic hyphal system (Ga, Ff) in combinations with KF formed a microporous membrane with increased air permeability (>8820 mL/min) and limited mechanical strength (tensile index 9–14 Nm/g). HF combination with trimitic fungal hyphae formed a dense fibrillary net with low air permeability (77–115 mL/min) and higher strength 31–36 Nm/g. The hyphal bundles of monomitic fibers of Tv mycelium and Ab stipes made a tight structure with KF with increased strength (26–43 Nm/g) and limited air permeability (14–1630 mL/min). The blends KF FF (Ga) and KF FF (Tv) revealed relatively high virus filtration capacity: the log10 virus titer reduction values (LRV) corresponded to 4.54 LRV and 2.12 LRV, respectively. Mycocel biopolymers are biodegradable and have potential to be used in water microfiltration, food packaging, and virus filtration membranes.
Linda Mezule, Baiba Strazdina, Brigita Dalecka, Eriks Skripsts, and Talis Juhna
MDPI AG
Semi-natural grassland habitats are most often limited to animal grazing and low intensity farming. Their potential in bioenergy production is complicated due to the heterogeneity, variation, accessibility, and need for complex pre-treatment/hydrolysis techniques to convert into valuable products. In this research, fermentable sugar production efficiency from various habitats at various vegetation periods was evaluated. The highest fermentable sugar yields (above 0.2 g/g volatile solids) over a period of 3 years were observed from habitats “xeric and calcareous grasslands” (Natura 2000 code: 6120) and “semi-natural dry grasslands and scrubland facies on calcareous substrates” (Natura 2000 code: 6210). Both had a higher proportion of dicotyledonous plants. At the same time, the highest productivity (above 0.7 t sugar/ha) was observed from lowland hay meadows in the initial stage of the vegetation. Thus, despite variable yield-affecting factors, grasslands can be a potential resource for energy production.
Atis Skudra, Linda Mezule, Karina Spunde, Gita Revalde, Anna Zajakina, Madara Ziņģe, and Tālis Juhna
Rezekne Academy of Technologies
Mercury UV-C light sources are long known to be efficient for microbial inactivation and have been widely used. At the same time, the radiation, if used in inappropriate doses and spectral regimes, can also cause harmful effects to human tissue. The aim of the study was to evaluate the applicability of the novel UV light sources from thallium – antimony at different UV-C. For the research specially made light sources were produced. The influence of UV-C radiation in the range of 200 - 280 nm was tested on Gramnegative bacterium Escherichia coli, both with mercury and thallium. More than 99.99 % inactivation of E. coli cells was obtained after 10 min contact time for thallium – antimony UV-C light source, demonstrating the potential of the produced lamps.
Aigars Lavrinovičs, Linda Mežule, and Tālis Juhna
Elsevier BV
Abstract Three microalgal species, Desmodesmus communis, Tetradesmus obliquus and Chlorella protothecoides were studied for enhanced phosphorus removal from municipal wastewater. Microalgae were first exposed to phosphorus deficit conditions for 7 and 14 days and then inoculated in filtered primary or secondary wastewater from a small municipal wastewater treatment plant at ambient temperature and CO2 concentration. D. communis and T. obliquus strains showed higher biomass growth rates in secondary wastewater after 7-day starvation period, while C. protothecoides grew better in the same effluent without starvation. All strains were able to achieve nearly complete (>99.9%) removal of dissolved inorganic phosphorus (DIP). Moreover, D. communis and T. obliquus showed ~89% DIP reduction within 24 h after 7-day phosphorus starvation. Dissolved inorganic nitrogen removal for all algal strains did not exceed 50% for any of the treatments. All three strains were able to store excess phosphorus within their cells as polyphosphate and the highest Poly-P content was observed in cultures grown in primary wastewater. Poly-P concentration in C. protothecoides reached 250 μg mg−1. At the same time no correlation between Poly-P and P removal was observed. The efficiency of nutrient (P) removal from municipal wastewater to ultra-low levels (
Brigita Dalecka, Martins Strods, Talis Juhna, and Gunaratna Kuttuva Rajarao
Elsevier BV
Discharge of organic load from treated wastewater may cause environmental eutrophication. Recently, fungi have gained much attention due to their removal of pharmaceutical substances by enzymatic degradation and adsorption. However, the fungal effect in removing nutrients is less investigated. Therefore, two fungal species, the white-rot fungus T. versicolor as a laboratory strain and the mold A. luchuensis as an environmental isolate from the municipal wastewater treatment plant, were studied to determine the fungal potential for phosphorus, nitrogen, and the total organic carbon removal from municipal wastewater, carrying out a batch scale experiment to a fluidized bed pelleted bioreactor. During the batch scale experiment, the total removal (99.9 %) of phosphorus by T. versicolor was attained after a 6 h-long incubation period while the maximal removal efficiency (99.9 %) for phosphorus from A. luchuensis was gained after an incubation period of 24 h. Furthermore, both fungi showed that the pH adjustment to 5.5 kept the concentration of nitrogen constant and stabilized the total organic carbon reduction process for the entire incubation period. The results from the fluidized bed bioreactor demonstrated opposite tendencies on a nutrient removal comparing to a batch experiment where no significant effect on phosphorus, nitrogen, and total organics carbon reduction was observed. The obtained results from this study of batch and fluidized bed bioreactor experiments are a promising starting point for a successful fungal treatment optimization and application to wastewater treatment.
N. Assimakis, A. Ktena, C. Manasis, E. Mele, N. Kunicina, A. Zabasta, and T. Juhna
IEEE
In this work we study applicability of Kalman filters as decision support for early warning and emergency response system for infectious diseases as CoVID-19. Here we use only the actual observations of new cases/deaths from epidemiological survey. We investigated the behavior of various time varying measurement driven models. We implement time varying Kalman filters. Preliminary results from Greece and Latvia showed that Kalman Filters can be used for short term forecasting of Co Vid-19cases. The mean percent absolute error may vary by model; some models give satisfactory results where the mean percent absolute error in new cases is of the order of 2%-5%. The mean absolute error in new deaths is of the order of 1–2 deaths. We propose the use of Kalman Filters for short term forecasting, i.e. next day, which can be a useful tool for improved crisis management at the points of entry to a country or hospitals.
Brigita Dalecka, Caroline Oskarsson, Talis Juhna, and Gunaratna Kuttava Rajarao
MDPI AG
Fungi have been shown to be promising candidates to be used in removal of pharmaceutical compounds during wastewater treatment processes. However, fungal growth, including removal efficiency, can be affected by several factors, such as temperature and the pH. The ability of fungal isolates to grow in the presence of carbamazepine, diclofenac, ibuprofen, and sulfamethoxazole was tested. Removal efficiency results indicated that a fungal isolate of Aspergillus luchuensis can completely (>99.9%) remove diclofenac from a synthetic wastewater media without a pH correction within 10 days of incubation. Furthermore, the results of the biosorption test for A. luchuensis indicate that this isolate uses the biosorption mechanism as a strategy to remove diclofenac. Finally, the results demonstrate that A. luchuensis can remove >98% of diclofenac in non-sterile wastewater without a pH correction immediately after biomass inoculation on biofilm carriers while Trametes versicolor requires an incubation period of at least 24 h to completely remove diclofenac. Therefore, this isolate is a promising candidate for use in removal of pharmaceutical compounds from wastewater with typical pH 7.8, minimizing a requirement of the pH correction.