Verified email at rtu.lv
Vice-Rector for Research
Riga Technical University
Basanti Ekka, Inese Mieriņa, Tālis Juhna, Kristīna Kokina, and Māris Turks
Materials Today Communications, eISSN: 23524928, Published: June 2022 Elsevier BV
Dita Gudra, Sandis Dejus, Vadims Bartkevics, Ance Roga, Ineta Kalnina, Martins Strods, Anton Rayan, Kristina Kokina, Anna Zajakina, Uga Dumpis, Laura Elina Ikkere, Irina Arhipova, Gundars Berzins, Aldis Erglis, Juris Binde, Evija Ansonska, Aivars Berzins, Talis Juhna, and Davids Fridmanis
Science of the Total Environment, ISSN: 00489697, eISSN: 18791026, Volume: 823, Published: 1 June 2022 Elsevier BV
Basanti Ekka, Inese Mieriņa, Tālis Juhna, Māris Turks, and Kristīna Kokina
Cleaner Engineering and Technology, eISSN: 26667908, Published: April 2022 Elsevier BV
V. Denisova, L. Mezule, and T. Juhna
Water Practice and Technology, ISSN: 1751231X, Pages: 537-543, Published: 1 February 2022 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, Wolfgang Augustin, Stephan Scholl, Ana Pereira, Ana C. Barros, Idalina Machado, and Luis F. Melo
Journal of Environmental Engineering (United States), ISSN: 07339372, eISSN: 19437870, Volume: 148, Published: 1 February 2022 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, Dzintars Začs, Grigory Vasiliev, Maris Turks, Inese Mierina, Peter C. Sherrell, and Andris Šutka
Advanced Sustainable Systems, eISSN: 23667486, Published: December 2021 Wiley
Basanti Ekka, Sandis Dejus, and Talis Juhna
Journal of Dairy Research, ISSN: 00220299, eISSN: 14697629, Pages: 425-428, Published: 10 November 2021 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
Environmental Advances, ISSN: 26667657, Published: October 2021 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
Microorganisms, eISSN: 20762607, Published: August 2021 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
Polymers, eISSN: 20734360, Published: 1 April 2021 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
Energies, eISSN: 19961073, Published: 1 March 2021 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
Vide. Tehnologija. Resursi - Environment, Technology, Resources, ISSN: 16915402, Pages: 218-222, Published: 2021 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.
Advanced Sciences and Technologies for Security Applications, ISSN: 16135113, eISSN: 23639466, Pages: v-vi, Published: 2021
Agronomy Research, ISSN: 1406894X, Issue: Special Issue 1, Pages: 834-846, Published: 2021
Aigars Lavrinovičs, Linda Mežule, and Tālis Juhna
Algal Research, ISSN: 22119264, Published: December 2020 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
Microbiological Research, ISSN: 09445013, Volume: 241, Published: December 2020 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
2020 IEEE 61st Annual International Scientific Conference on Power and Electrical Engineering of Riga Technical University, RTUCON 2020 - Proceedings, Published: 5 November 2020 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
Water (Switzerland), eISSN: 20734441, Published: 1 February 2020 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.
Brigita Dalecka, Talis Juhna, and Gunaratna Kuttuva Rajarao
Journal of Water Process Engineering, ISSN: 22147144, Published: February 2020 Elsevier BV
Abstract The removal efficiency of diclofenac and ketoprofen for five fungal strains was examined. The synergistic effect between selected fungal strains using synthetic wastewater media was studied using both individual and mixed strains. The mixed cultures had no additional effect in reducing diclofenac and ketoprofen. In contrary, fungi removed pharmaceutical substances faster when growing individually. The results showed that T. versicolor monoculture removed diclofenac completely (>99.9 %) in non-sterile municipal wastewater within three hours of incubation and continued to show complete reduction within 14 days using fungal biofilm carriers. The mechanism of removal was proposed based on the laccase enzyme production and biosorption study which revealed that T. versicolor could used in both processes. Additionally, this study demonstrated that T. versicolor could be stable in the biofilm carriers, and thus able to compete with other microorganisms in wastewater to be a promising candidate to remove diclofenac from municipal wastewater during the treatment process.
Kristine Vegere, Rita Kravcevica, Andrey E. Krauklis, and Talis Juhna
Materials Today: Proceedings, eISSN: 22147853, Pages: 1984-1987, Published: 2020 Elsevier BV
Abstract Four different methods for zeolite A (Linde Type A; LTA) synthesis were investigated and compared. The four investigated synthesis methods were the microspheres, the metakaolin-based, the NaOH-accelerated metakaolin-based and the aluminosilicate gel-based methods, respectively. The impact of the hydrothermal synthesis temperature was studied at 60, 80 and 100 °C was studied for each of the methods. The final product (zeolite A) was characterized and compared using XRD, SEM, EDS, FT-IR and BET. The most efficient synthesis route, resulting in the purest product, was determined to be an aluminosilicate gel-based method (fourth) followed by a microspheres method (first), both being most efficient at 80 °C.
Agronomy Research, ISSN: 1406894X, Issue: Special Issue 1, Pages: 1099-1106, Published: 2020
J. Neilands, L. Mežule, V. Deņisova, T. Juhna, Kamila Gruškeviča and K. Tihomirova
Agronomy Research, ISSN: 1406894X, Issue: Special Issue 1, Pages: 771-780, Published: 2020
The aim of this study was to evaluate the effectiveness application of sequencing batch reactors (SBRs) for phosphorus removal compared to the conventional activated sludge (CAS) treatment system. The results showed that the removal efficiency of phosphorus reached about 99% at wastewater treatment plant with CAS system. At the same time, the maximum phosphorus removal efficiency can be achieved to 88% if the SBRs system operating parameters are optimized. Finally, this study demonstrated that even if granules are not fully developed, the SBR system is working with a good efficiency.
Ksenija Golovko, Kristina Tihomirova, Romans Neilands, Jurijs Resetilovs, Linda Mezule, and Talis Juhna
Water Science and Technology, ISSN: 02731223, eISSN: 19969732, Pages: 2191-2199, Published: 1 December 2019 IWA Publishing
Abstract The activated sludge process suffers from rapid load changes of ammonium (NH4), which may result in process failure during wastewater treatment. In this study, the response of activated sludge properties in terms of microfauna composition and sludge volume index (SVI5 and SVI30) on short-term increase of NH4 concentration (from 55 mg/l to 105 mg/l) was evaluated in batch scale reactors over 72 h. The results show that the first-step nitrification (NH4 transformation to nitrite (NO2)) was inhibited after 24 h, whereas the second-step nitrification (NO2 transformation to nitrate (NO3)) was not significantly affected. Sludge volume indices (sedimentation ability characteristics) SVI5 and SVI30 in the reactor with NH4–N shock concentration increased, whereas microfauna diversity decreased (Shannon-Weaver index decreased from 2.12 at 48 h to 1.23 at 72 h) leading to dominance of stalked ciliate Epistylis sp. Notable changes in inorganic carbon concentration (IC) were observed, indicating that rapid decrease of IC concentration leads to nitrification inhibition and challenges the overall process recovery. To conclude, short-term exposure of about two times higher concentration of NH4 caused significant changes in activated sludge properties by inhibiting NH4-oxidizing bacteria, reducing sludge microfauna diversity and deteriorating sludge sedimentation ability.
H. Aguedal, A. Iddou, A. Aziz, A. Shishkin, J. Ločs, and T. Juhna
International Journal of Environmental Science and Technology, ISSN: 17351472, eISSN: 17352630, Pages: 113-124, Published: 29 January 2019 Springer Science and Business Media LLC
Reduction in adsorption capacities of adsorbents is limiting of its wider application for water treatment. In this study, we developed a new approach for recycling diatomite to be used adsorbent. The laser scattering particle size analyzer, X-ray diffraction, scanning electron microscopy/energy-dispersive X-ray and Brunauer–Emmett–Teller analysis were used to evaluate the structural characteristics of treated samples. The adsorption efficacy of raw and heated diatomite at 300, 600 and 900 °C for textile dyestuff removal from wastewater was investigated. The characterization results show insignificant changes except some deconstructions were occurred after treatment at 900 °C. The maximum adsorption capacities were obtained at pH 2 and adsorbent dosage of 4 g L−1. The required time to reach the equilibrium was 30 min, and diatomite treated at 600 °C is acted as an excellent adsorbent. The kinetic studies were better described by the pseudo-second-order kinetic model. The isotherms experimental data showed that the adsorption of dye onto raw diatomite, DH300 and DH600 follows the Brunauer–Emmett–Teller isotherm model, but its adsorption onto DH900 conforms well to Freundlich isotherm model. Recycling of diatomite using thermal treatment was useful. At 600 °C which is considered the best regeneration temperature, the adsorbed dye was completely despaired, and around 73% was restored after three regeneration cycles.
Karima Menad, Ahmed Feddag, and Tālis Juhna
Journal of Inorganic and Organometallic Polymers and Materials, ISSN: 15741443, eISSN: 15741451, Pages: 1-16, Published: 15 January 2019 Springer Science and Business Media LLC
There is a need to develop effective and inexpensive methods for removal of heavy metals from contaminated water in developing countries. In this study, a novel microporous, microcrystalline, zeolite-type X high silica (NaX-500) sorbent was synthesized using hydrothermal method followed by calcination at 500 °C. Its sorption capacity to remove Cu(II) was tested in reconstituted water with and without humic acid (HA). Fourier transform infrared spectroscopy, chemical elemental composition, scanning electron microscopy, N2 adsorption–desorption measurement and X-ray diffraction analyses confirmed that NaX-500 has a micro-crystalline structure with micrometer-sized pores and a specific area of about 336 m2/g. The results showed that sorption of Cu(II) below 20 mg/L was described by pseudo-first-order kinetic model and above 500 mg/L by the second order model, whereas Dubinin–Radushkevich model (for all cases R2 values > 0.810) described best the sorption of copper(II) on NaX-500. The presence of HA was found to influence the adsorption efficiency as copper formed a complex with zeolite–HA, thus improving the adsorption capacities. This study shows that, the newly developed material is rapid and effective for the removal of copper from contaminated water both at low and moderate concentrations including from water with moderate concentration of humic substances.