Nitrogen (N-2) is a key nutrient for ecosystem functioning and one of the main limiting factors for its productivity. However, its excessive input, particularly due to anthropogenic activities, can cause adverse consequences, such as soil acidification, eutrophication and reduced biodiversity. High nitrogen concentrations in surface waters are often associated with agricultural and urban sources of pollution. In this study, surface water samples from the Varazdin and Krapina-Zagorje Counties in the period from November 2022 to April 2023 were analysed. The results showed that total nitrogen values were in accordance with regulations at 14 locations, with concentrations in excess of 2.40 mg/L N at the remaining locations, which indicates a possible anthropogenic impact.
The Krapina River, located in the Hrvatsko Zagorje region, is exposed to anthropogenic pollution due to discharges of untreated urban and hospital wastewater. The aim of this research was to determine the bacteriological quality of water and surface sediments by analysing the presence of indicators of faecal pollution. Sampling was carried out from the river source and the sources of two tributaries, as well as downstream after the confluence of the Krapinica River. Intestinal enterococci and faecal coliforms were already recorded at the sources of the river and its tributaries, with their concentrations significantly increasing downstream due to the inflows of urban and hospital wastewater. The concentrations of indicator bacteria in the sediment were higher than in the corresponding free water. Based on the concentration of bacteria indicating faecal pollution, the Krapina River does not meet the criteria for bathing and recreation. Wastewater treatment prior to its discharges into the river is crucial for reducing anthropogenic impact on the ecosystem, while systematic water and sediment quality monitoring can contribute to the adoption of effective river protection measures.
This research studies the reuse of 50 % concentrate from reverse osmosis (RO), obtained from textile wastewater (TWW) as an alternative source in the irrigation of basil (Ocimum basilicum). In order to maximally reuse water and retain nutrients, a hybrid ultrafiltration system and RO were used.The basil irrigated with a RO concentrate had the largest share of dry matter (14.96 %) and nutrient intake, particularly of P2O5 (1.37 %), K2O (4.39 %) and Cu (8.58 mg/kg). Although the TWW contained more Mn, Ca and Mg, it resulted in a lower biomass, probably due to ionic imbalance or stress caused by microelements.The water used from the water supply system lead to the lowest growth and nutrient intake. These results indicate that the 50 % RO concentrate, which is often considered waste, can be safely reused for irrigation in agriculture, thus supporting the objectives of circular economy by reducing the consumption of drinking water.
Like many other cities in the world, the City of Zagreb faces increasingly destructive urban flash floods. The aim of this paper is a more accurate determination of their characteristics to enable more effective protection measures against them. Zo this end, a detailed analysis of two flash floods that occurred on 3/4 July 1989 and 24/25 July 2020 was used. The formation of flash floods in Zagreb is specific, since they are partly a result of torrential flooding by mountain streams flowing down from Mt. Medvednica into the urban area. Based on a small number of available data, an attempt was made to define the effectiveness of the retention storage built on the & Ccaron;rnomerec watercourse in mitigating floods downstream of the dam. It was determined that flash floods in Zagreb mostly occur in the warm period of the year, from June to August, during the night, from 9 pm to 1 am.
Karst aquifers, vulnerable to salinization and overexploitation, experience unfavorable trends due to climate change, with significant socio-economic and environmental consequences. A thorough understanding of the structure of a karst aquifer and its functioning is crucial for its effective protection. The most effective strategy to reduce the unpredictability associated with this hydrological 'black box'is to conduct research and measurements directly in the system and notjust at its inputs and outputs. This study presents the results of hydrological monitoring of a cave stream in the U & ccaron;ka Cave System, which has been a reliable source of water for over 40 years. In addition, speleological explorations have mapped the underground hydrological network and also revealed a significant extension of the cave, providing opportunities for improved management of existing and potential discovery of new water resources.
The derived pyrolysis or gasification biochar products are porous, inexpensive and have a potential to be used as an adsorbent for wastewater treatment. This study examines the effectiveness of removing heavy metals (cadmium (Cd) and lead (Pb)) and nutrients in the form of ammonium (NH4+) and phosphate (PO43-) from synthetic wastewater using biochar obtained by a special process of gasification of sewage sludge in a pilot plant. Batch adsorption experiments were carried out to determine the adsorption capacity of biochar for selected pollutants. The results of PO43-and NH4+ removal at the pH of the initial solutions, show a reduction of PO43-concentration by over 20% and NH4+ concentration by 8% within 24 hours, which, expressed in absolute quantities of the removed pollutant, was 215 mg/L for PO43-, and 115 mg/L for NH4+. When analyzing the removal of Cd2+ and Pb2+, experiments were performed at the initial pH (3.1-3.2), and then with an adjusted value of pH=7, which resulted in significantly better results for the removal of these cations within 24 h: over 20% of Cd2+ and almost 50% of Pb2+.
Agricultural activities are widespread in the Kara & scaron;ca-Vu & ccaron;ica catchment area, the northern part of the Mura-Drava-Danube Biosphere Transboundary Reserve (TBR MDD). A nitrate transport model was developed to estimate nitrate concentrations in groundwater within this area. Despite the high input values, the results showed low nitrate concentrations (<50 mg/L). The northern part of the catchment area bordering the TBR MDD showed the lowest nitrate levels. Considering the biodiversity and natural landscapes of the TBR MDD, special attention should be paid to potential contaminations, especially nitrates, due to their harmful effects. Given that the results represent an optimistic perspective, ongoing research, and monitoring are key to preserving the integrity of this ecologically significant area.
Water pollution is a serious and increasing threat to environment and human health. EU water politics is directed towards reaching good quality status of all environmental waters. Final effluents from wastewater treatment plants are considered significant contributors to surface water quality deterioration. This study reports physicochemical characteristics of two streams in Me & dstrok;imurje (Croatia) that receive final effluents from municipal wastewater treatment plants:Trnava and Bistrec-Rakovnica. 16 physicochemical parameters were analysed during four years of research: temperature, pH, conductivity, dissolved oxygen, saturation, suspended solids, alkalinity, hardness, BOD, COD and nutrients including ammonium, nitrate, nitrite, total nitrogen, orthophosphate and total phosphorus. From the measurement results, the ecological quality of streams was assessed according to Croatian regulation on water quality. Water quality of both streams is degraded by nutrient content, with nitrates and total nitrogen being the major contributors to nutrient pollution in every year of monitoring. Besides discharge from wastewater treatment plants, both streams are exposed to other pressures that affect physicochemical characteristics and surface water quality, such as agriculture and untreated sewage. More effective and concrete protective and restorative measures need to be considered promptly to achieve a mandatory quality status of these watercourses.
Surface water quality monitoring is one of the most important management tools for the river basin water quality management. Existing surface water quality monitoring systems were established decades ago with different goals, and therefore today are not fully harmonized to the requirements of the WFD EU.The obtained data and information used follow the difficulties of connecting the quantity and quality of surface waters due to the inconsistency of hydrological monitoring and surface water quality monitoring. This results in lack of quality data, lack of use of mathematical models, and lack of appropriate in, formation for making reliable decisions for water quality management.The analysis of the existing water quality monitoring based on the collected available data, as well as the need for its improvement, is presented in the case study of the transboundary rural Sutla River Basin.The proposed methodology, based on the shortcomings, proposes necessary steps for the improvement of existing monitoring as the purpose of the "tailor-made" surface water quality monitoring.
Faecal pollution indicators, Escherichia coli and intestinal enterococci, are routinely tested during monitoring of seawater quality for bathing, in accordance with the Regulation on seawater quality for bathing (OG 73/08). These tests can be extended to include additional microbiological indicators, such as P. aeruginosa, a bacterium that causes skin, eye and ear infections in cases of exposure to contaminated water. The purpose of this research has been a testing for Pseudomonas aeruginosa presence in bathing seawaters of urban beaches in the western part of the City of Rijeka under different environmental conditions. Data from a research conducted from 2012 to 2014 and in 2023 have been processed, and the HRN EN ISO 16266:2008 method used for testing P. aeruginosa in seawater samples. According to research results, the seawater quality for bathing in the City of Rijeka area is slightly to moderately loaded with P. aeruginosa, whose occurrences are significantly affected by precipitation and freshwater inflows. Monitoring of routine indicators does not fully exclude a possibility of contact and infection of bathers with P. aeruginosa bacteria.
The Krka River estuary is a unique, internationally recognized natural phenomenon in the karst of northern Dalmatia (Croatia). Nutrient-poor water from the small Krka River enters the sea under narrow tidal range conditions and creates a highly stratified system with a sharp halocline separating brackish and marine layers. Highly stratified estuaries are rare and are found along small Mediterranean rivers. Freshwater phytoplankton entering the estuary from Lake Visovac, a widening of the river, dies in the salinity gradient of the halocline. Suspended particles accumulating in the halocline significantly heat up the halocline in summer. Microbial decomposition of organic matter releases nutrients into the marine layer of the upper estuary, causing a development of marine phytoplankton subsurface blooms. In the lower estuary, phytoplankton blooms are superficial because growth at greater depths is limited by light. The mixing of fresh water and the sea, especially in the halocline (freshwater/ seawater interface), dramatically changes the balance of chemical reactions. The halocline is a microlayer in which toxic substances accumulate as well. The cycling of elements is present in the estuary.
Fish processing industry plays an important role in global economy. Due to a growing scope of production and the resulting generation of increasingly larger quantities of waste (fish heads, fins, entrails, skin, bones, meat unfit for consumption and the process effluent), the treatment and recycling of waste is a global trend in line with global tendencies of environmental protection, conservation of water resources and converting of waste into useful products. This waste is partially used for producing less valuable products, such as fishmeal, oil, fertilizer and silage. However, in order to achieve the full potential of the waste and to produce high-value bioactive compounds, such as proteins, amino acids, peptides, enzymes, collagen, gelatin, polyunsaturated fatty acids (PUFA), vitamins, minerals and other high-value compounds, various chemical, biological and innovative extraction methods are applied, some of which still at scientific research stages. By evaluating waste based on the creation of new products, it is possible to achieve a more environmentally friendly use of marine resources and a greater economic benefit for the fish processing sector. Therefore, the main goal of this work is to point out the value of solid and liquid waste generated in fish processing, provide an overview of the composition and properties of bioactive compounds isolated from waste, present procedures and research related to their isolation, as well as their application in different industries.
The paper analyses all the available series of minimum and maximum annual flows calculated at 13 hydrological stations along the course of the Sava River in Croatia. Only official data of Croatian Meteorological and Hydrological Service (DHMZ) from Zagreb have been used. The lengths of the series are different, and observation breaks within certain series have been noticed. The last year included in the analysis is 2022. A decreasing trend of minimum annual flows has been observed at all hydrological stations. The values of linear regression coefficients indicate that the decline process behaves differently at each of the stations. It ranges from an average of 2.2 m3/10 years at the Rugvica station to an average of 7.4 m3/10 years at the Davor station. Analyses of the differences in the series of minimum annual flows between neighbouring hydrological stations show certain irregularities that indicate probable errors in the determination of minimum annual flows at some stations. These can be most probably explained by instability (erosion or backfilling) of the riverbed bottom and the insufficient number of measurements at low water levels, which causes constant changes in the lower parts of the flow curves. Regarding the series of maximum annual flows, an increasing trend has been observed at most stations, with some not indicating any trend. The highest increasing trend of 61 m3/10 years on average has been observed at the Podsused station. The decreasing trend of 14 m3/10 years on average has been measured only at the Zupanja station. The series of differences in maximum annual flows between the neighbouring stations greatly differ, which indicates insufficiently accurate measurements (determination) of maximum flows. This is probably consequential to insufficient number of flow measurements at high water levels and thus insufficient reliability of the determined flow curves in flooding areas.
The paper analyses the series of water levels (1920-2021) and discharges (1926-2021) observed at the Zagreb hydrological station on the Sava River. Significant variations between the series of minimum and average annual levels were determined. In the 1920-1974 sub-period, no trends were observed. In the 1975-1993 sub-period, a more significant downward trend (about 2 m) was observed. Minimal annual water levels are an indicator of the lowering (erosion) of the riverbed bottom. In 1983, a submerged weir, named Te-To sill, was constructed. It is located about 6400 m downstream of the Zagreb hydrological station. The lowering of the Sava riverbed bottom on the Zagreb profile stopped in 1994. In the 1994-2021 period, the minimum and average annual water levels rose by about 70 cm. A series of maximum annual water levels in the 1920-2021 period showed a statistically insignificant increase. At the Sava Podsused hydrological station, about 11 km away, the process of varying minimum and average annual water levels occurs similarly, but with a slight time shift, as it does at the Sava Zagreb hydrological station.The minimum and average water levels there began to decline simultaneously, while the increase began seven years later (in 2001). At the Sava Catez hydrological station, which is located in Slovenia, the minimum annual water levels decreased in 1967, eight years earlier than at the Sava Zagreb location. For the series of minimum annual flows of the Sava near Zagreb, a statistically significant drop in average annual flows was observed in the 1979-2021 sub-period (Q=71.4 m3/s) compared to the previous 1926-1978 sub-period (Q=88.3 m3/s). A statistically significant drop in average annual flows was observed in the 1981-2021 sub-period (Q=287 m3/s) for a series of average annual flows of the Sava near Zagreb compared to the previous 1926-1980subperiod (Q=326 m3/s). Fora series of maximum flows in the recent 2004-2021 sub-period (Q=2033 m3/s), a statistically significant increase was observed compared to the previous 1926-2003 sub-period (Q=1772 m3/s). For a series of average annual flows in the 1926-2021 period, the value of the Hurst exponent was 0.691. A series of average daily flows of the Sava near Zagreb was analysed using the day-to-day flow variability (DTDQ) method.
The idea of this paper is to present the main results of a comprehensive analysis of the Sava and Drina low water discharges in the area of the Drina river mouth. The paper presents the quantitative characteristics of low discharges that are generally used as a basis for designs of the majority of water management and hydrotechnical facilities. The particular focus is a detailed analysis of the length of low discharge periods below the initial discharges, which were determined for selected durations from the curves of average daily discharge durations. A new approach was applied which, in addition to the classic probabilistic analysis of minimum annual and minimum average monthly discharges, also includes the analysis of the length of continuous low discharge periods with discharges lower than the discharges of characteristic durations, their intra-annual distribution and representation. The basic data used for the calculation of low discharges are the official data of the Croatian Meteorological and Hydrological Service from Zagreb (DHMZ) and the Republic Hydrometeorological Institute of Serbia from Belgrade (RHMZ) at the hydrological stations (HS) & Zcaron;upanja and Sremska Mitrovica on the Sava River and Radalj on the Drina River.
Water losses in water supply systems is measured by the difference between the volume of water abstracted at the source/water intake and the volume of water delivered to consumers at the same time. Rational management of water resources imposes the obligation to reduce water losses (leakage). Moreover, in the last two decades the topic of water loss reduction in water supply systems has been considered in the context of climate change adaptation measures. The EU Framework Water Directive prescribes the implementation of the principle of cost recovery from water services, i.e. the realization of profits by public water services providers based on abstracted (not on delivered) water quantities. Since more than 50% of water abstracted for public water supply in the Republic of Croatia is lost, the application of the mentioned principle requires an urgent reduction of water losses in water supply systems. The paper provides a systematic review and calculation patterns of direct and iterative methods for localising water losses based on the comparison of working pressures measured in a water supply system and those predicted by the design solution for the same water supply system. Namely, this method of localizing water leaks in water supply systems can be very attractive for reducing water losses because it is selective, thus avoiding the costs of complete rehabilitation of all suspect pressure sections. In this context, the application of the mentioned methods is shown on the example of a hypothetical symmetrical water supply network, where the calculation forms are implemented in the computer code created in the Python programming language. In conclusion, the paper provides a critical discussion and guidelines for future research.
The impact of the spatial arrangement of electrodes and their electric potential was analysed, as well as the position and intensity of the sink/source in a recirculating electrochemical (EC) device (reactor) for purifying water with increased strontium concentration.The used method was numerical modelling, with a calibration of the parameters of the numerical model based on the measurements on a laboratory device with the same geometric characteristics and boundary conditions. In the implementation of numerical simulations, two layouts using a total of 8 aluminium electrodes were analysed. 4 cathodes (C) and 4 anodes (A) were arranged in two blocks (C-AA-C and A-C-C-A; C-A-C-A and C-A-C-A), two sink positions, and intensities of sink/source ranging from 0.05 l/s to 0.5 l/s. The presence of strontium ions in water (Sr2+) was interpreted as particles with a charge of 3.2 center dot 10-19 C and diameter of 1.2 center dot 10-8 m, which, through the coupling of the hydrodynamic and electrostatic 3D model, are transported through the model domain and/or retained on the electrode plates. The quantification of the effect of a particular tested configuration variant is expressed as the ratio of the number of model strontium particles that are permanently retained on the electrodes and that are summarily introduced into the device during the simulation period. The results of the research conducted on the recirculating EC device show that the efficiency of purification primarily depends on the source/sink intensity, and the arrangement of the electrodes and the position of the sink secondarily. According to the results of the numerical model, the electrode configurations C-A-A-C and A-C-C-A are 7% more efficient than C-A-C-A and C-A-C-A. At the lowest measured source and sink flow rate (Q = 0.05 l/s), the effect of strontium retention on the electrodes is 2.5 times higher than in the case of the highest source and sink flow rate (Q = 0.5 l/s).The position of the sink located right next to the edge of the dividing wall results in 8% less accumulation of strontium on the electrodes than in the case when the sink is placed at a greater distance from the dividing wall. Applying a different voltage to individual pairs of electrodes results in a lower consumption of electricity (33%) and a more uniform distribution of strontium accumulation on the electrodes; however, the removal effect is reduced by 31%.
