Stevo Lavrnić

This study evaluated the performance of three full-scale treatment wetlands (TWs) operating under temperate rainy conditions in southern Chile, treating domestic wastewater (one vertical flow, VF) and graywater (one VF and one horizontal flow, HF). Water quality parameters – temperature, pH, oxidation–reduction potential, electrical conductivity, chemical oxygen demand (COD), total suspended solids (TSS), nitrogen species (NH4+-N, NO3--N, TN), phosphorus species (PO43--P, TP), and Escherichia coli – were monitored in influents and effluents over one year, with data analyzed across cold and warm periods. Effluent quality was further assessed against irrigation reuse standards. Results showed effluent temperatures consistently below 15 °C, along with different pH behavior in each TW. VF TWs exhibited more oxidative conditions than the HF TW, a pattern consistent across wastewater types and periods. All TWs removed TSS, COD, NH4+-N, NO3--N, PO43--P, and TP, achieving removal efficiencies between 20 and 95%, sustaining stable performance year-round, and VF effluents more closely meeting irrigation reuse standards. However, TN and pathogen removal remained limited, highlighting the need for further improvement and research. Overall, these TWs demonstrated a strong potential to produce effluents suitable for agricultural reuse, underscoring their applicability in Chile and other places with similar climatic conditions.

Agricultural water reuse involving the blending of treated wastewater (TWW) with conventional irrigation water in open irrigation networks is not explicitly regulated under Regulation (EU) 2020/741, which may present exposure pathways comparable to unblended direct reuse. This study assessed water quality dynamics along a fully operational irrigation canal network in Northern Italy, under real-scale hydraulic and agronomic conditions characteristic of reuse systems involving blending, in which TWW discharged from a wastewater treatment plant (WWTP) accounted for 68% to 86% of total canal flow. Over two irrigation seasons (2023–2024), 11 physical, chemical, and microbiological parameters were monitored at five points: one at the WWTP outlet, one upstream representing the conventional irrigation source, and three downstream of the confluence across 30 campaign days. Data were analyzed using generalized linear mixed models with sampling point as a fixed effect and sampling date as a block-level random intercept. The contribution of TWW to conventional irrigation water was primarily reflected in nutrient enrichment, with concentrations downstream of the confluence exceeding those of the conventional source by 48% to 59% for total nitrogen and 139% to 195% for total phosphorus, confirming the WWTP as the main nutrient source. In contrast, the effluent introduced no additional load for the parameters directly regulated under Regulation (EU) 2020/741 ( E. coli , biochemical oxygen demand (BOD₅), and total suspended solids (TSS)). TSS were significantly lower in TWW than in conventional irrigation water, leading to a 29% to 43% reduction in TSS after mixing, BOD₅ at the WWTP outlet did not differ significantly from that in conventional irrigation water, and for E. coli no significant effects were detected. However, BOD₅ increased significantly at one point after the confluence relative to the conventional source, from an input that could not be attributed to the effluent. Overall, these results demonstrate that although TWW accounted for the majority of canal flow in volumetric terms, it did not lead to generalized deterioration of irrigation water quality. Instead, it provided nutrient inputs that may be harnessed for agricultural reuse. This work presents one of the first systematic, real-scale assessments of TWW reuse through blending in a fully operational European irrigation district, illustrating the regulatory gap in Regulation (EU) 2020/741 and informing risk-based monitoring frameworks for reuse systems where blending occurs.

In Mediterranean regions, irrigation demand is rising while conventional water resources are becoming less reliable due to recurrent droughts, competing uses, and environmental constraints. Treated urban wastewater (TWW) is therefore gaining increasing attention as an unconventional resource capable of supplementing conventional irrigation supplies and supporting climate-change adaptation strategies. However, moving from isolated pilot schemes to implementation across large irrigation basins is complex. Reuse at this scale isn't a single pipeline linking one wastewater treatment plant (WWTP) to one field. Instead, it's part of a large, distributed, dynamic irrigation system serving many agricultural fields with varied crops and methods. Numerous, dispersed WWTPs produce TWW of varying quality, and the irrigation network conveys and mixes flows under different conditions.The key planning challenge is therefore to integrate TWW with conventional sources within a single allocation and operations framework that considers both water quantity and quality. Quantitatively, planners must synchronise TWW and conventional supplies by matching seasonal availability to spatially variable irrigation demand across multiple districts, often under pronounced temporal mismatches that make storage and operational regulation essential. Qualitatively, TWW may contain pathogens and chemical contaminants, requiring preventive risk management throughout conveyance, distribution, and on-farm application. In the European Union, Regulation (EU) 2020/741 formalises these requirements by mandating a site-specific Risk Management Plan (RMP) and defining four reclaimed-water quality classes (A–D) linked to minimum quality standards and intended agricultural uses. Basin-scale planning must integrate volumetric allocation, infrastructure, and compliance considerations across diverse crop–irrigation setups with varying quality-class requirements. Current assessments often treat TWW as isolated; a unified framework combining these aspects is missing.This study presents a novel, EU-aligned comprehensive methodology to assess and optimise the potential for agricultural reuse of treated wastewater in large, multi-district irrigation basins. The approach is designed to be generally applicable and adaptable to specific case studies, using routinely available stakeholder datasets integrated within a GIS-enabled framework. The methodology comprises six interconnected phases: (i) identification and spatial characterisation of areas suitable for reuse; (ii) area-specific resource–demand water balances (available resources versus irrigation requirements); (iii) assessment of current WWTP effluent quality according to Regulation (EU) 2020/741; (iv) determination of the reclaimed-water quality class required by currently irrigated surfaces based on crop type, irrigation method, and consumption mode; (v) definition of intervention scenarios to maximise reuse potential considering territorial and infrastructural constraints and irrigation needs; and (vi) identification of structural and operational measures prioritised over time to achieve sustainable, efficient, and EU-compliant outcomes.The methodology was applied in Northern Italy within the Consorzio della Bonifica Renana (CBR) multi-district irrigation system, in collaboration with the local water utility (HERA). The application demonstrates how the framework transforms accessible information into decision-ready priorities, identifying candidate districts, WWTP clusters, and phased intervention portfolios and clarifies key barriers (infrastructure, storage, management, monitoring capacity, and quality-class constraints) while outlining actionable pathways to enable safe, Regulation (EU) 2020/741 compliant reuse at basin scale.

Inspired by nature‐based solutions, constructed wetlands are increasingly acknowledged as effective wastewater treatment tools, with diverse structural designs suited to various contexts. In the present work, two typologies of these systems, a full‐scale farm wetland and three pilot scale systems, were tested in terms of nitrogen and phosphorus removal from agricultural runoff, as well as their potential to maintain treatment performance under intensified conditions and reduced space requirements. The farm wetland, a full‐scale surface flow wetland operating for more than 20 years on an agricultural farm in Italy, was monitored for different years. It showed high water retention rates (> 60% in most monitored years and up to 100% in some years) and high nutrient retention efficiencies, with TN retention generally exceeding 65% and TP retention exceeding 46%. However, the size of this system might be an obstacle to its wider application. With that goal, three pilot systems were tested, namely surface flow (SFCW) and horizontal sub‐surface flow (HFCW) constructed wetlands. The HFCWs were incorporated with two distinct compositions: one packed with gravel (HFCW‐G) and another containing 10% v/v biochar in addition to gravel (HFCW‐B). All CWs were monitored for 1 year, during which applied flow and nutrients concentration were studied as variables influencing their performance. The results showed that, overall, the SFCW performed the best, granting average TN reduction up to 78%, significantly higher in comparison to HFCW‐B and HFCW‐G (33% and 34%, respectively). In terms of TP removal, on average, the HFCW systems presented similarly high performances (43%) compared to SFCW system (33%). Seasonal fluctuations in nitrogen removal reflected a temperature and seasonal influence on the performance of the systems, particularly in the system containing biochar (HFCW‐B). This study therefore confirms that comparable or higher areal nutrient removal rates can be achieved under intensified operating conditions (e.g., increased hydraulic and nutrient loading rates), suggesting that farm wetland design might consider reduced footprint while maintaining treatment efficiency.

The treatment of sludge digestion liquid is a big challenge in wastewater treatment. If treated as normal wastewater, large amounts of nitrogen and phosphorus present in the sludge digestion liquid might be wasted when they could be reused in agricultural irrigation and reduce the consumption of artificial fertilizers. Thus, it is of utmost importance to deliver a simple and feasible strategy to treat sludge digestion liquid for agricultural reuse. In this study, a novel type of anaerobic fluidized bed membrane bioreactor system (US-AnFMBR) was developed by combining an ultrasonic processing unit and biochar in AnFMBR. The improvement of sludge properties, removal of pollutants performance and membrane fouling mitigation were achieved in this novel system. The optimal dose of BC (biochar) was 2.5 g·L⁻¹, and the optimal ultrasonic treatment conditions were 30 min at 26 W. The main contribution of ultrasound was to improve the activity of sludge microorganisms to adsorb and degrade more organic matter present in sewage. The system achieved the removal efficiencies of COD, NH₄⁺-N and PO₄³⁻-P up to 89.41%, 49.29% and 54.83%, respectively, and had a better mitigation effect in terms of membrane fouling. On the one hand, the biochar addition for COD removal performance was mainly manifested in membrane rejection performance. On the other hand, the combination of low-cost biochar and AnFMBR can also provide new ideas for the recycling of agricultural waste for biochar production. However, regarding the removal efficiency of NH₄⁺-N and PO₄³⁻-P, the US-AnFMBR system promoted the activity of starved sludge to preferentially absorb NH₄⁺-N compared with PO₄³⁻-P by statistical analysis. The US-AnFMBR can reduce the viscosity of sludge and release more small molecular substances, thus better mitigating membrane fouling. Long-term operation performance also revealed the excellent stability of the sludge digestion liquid treatment. The US-AnFMBR system achieves the recovery of nitrogen and phosphorus resources for subsequent agricultural recycling, and avoids the eutrophication of water ecosystems. Reclaimed water meets the nutrient requirements of typical crops during the growing season. To a certain extent, carbon emission reductions in agriculture can be achieved.

Agriculture is the major water user worldwide and it is expected to be negatively affected by climate change and water scarcity. The use of non-conventional water resources could be the solution to overcome this issue. In fact, treated wastewater has a constant availability during the year and it contains nutrients needed for crop growth. The aim of this research was a GIS-based assessment of the potential for treated wastewater agricultural reuse in the Forlì-Cesena province within the Emilia-Romagna region (Italy). The results showed that, for the selected study area, treated wastewater could satisfy up to 316% of yearly and 210% of irrigation season crop water needs at the actually irrigated areas. Furthermore, the availability of this alternative water resource could lead to an increase in irrigated areas. For the proposed scenario, which considered both the actually irrigated areas as well as the irrigable areas, crop water needs could be satisfied by up to 107% on the yearly level and 71% in the case of the irrigation season. Treated wastewater reuse feasibility was also investigated considering the minimum water quality requirements that were recently provided by the new Regulation (EU) 2020/741.

Free water surface (FWS) wetlands can be used to treat agricultural runoff, thereby reducing diffuse pollution. However, as these are highly dynamic systems, their design is still challenging. Complex models tend to require detailed information for calibration, which can only be obtained when the wetland is constructed. Hence simplified models are widely used for FWS wetlands design. The limitations of these models in full-scale FWS wetlands is that these systems often cope with stochastic events with different input concentrations. In our study, we compared different simple transport and degradation models for total nitrogen under steady- and unsteady-state conditions using information collected from a tracer experiment and data from two precipitation events from a full-scale FWS wetland. The tanks-in-series model proved to be robust for simulating solute transport, and the first-order degradation model with non-zero background concentration performed best for total nitrogen concentrations. However, the optimal background concentration changed from event to event. Thus, to use the model as a design tool, it is advisable to include an upper and lower background concentration to determine a range of wetland performance under different events. Models under steady- and unsteady-state conditions with simulated data showed good performance, demonstrating their potential for wetland design.

A non-waterproofed surface flow constructed wetland (SFCW), treating agricultural drainage water in Northern Italy, was investigated to gain information on the potential ability for effective pesticide abatement. A mixture of insecticide imidacloprid, fungicide dimethomorph, and herbicide glyphosate was applied, by simulating a single rain event, into 470-m-long water course of the SFCW meanders. The pesticides were monitored in the wetland water and soil for about 2 months after treatment. Even though the distribution of pesticides in the wetland was not uniform, for each of them, a mean dissipation of 50% of the applied amount was already observed at ≤7 days. The dissipation trend in the water phase of the wetland fitted (r² ≥ 0.8166) the first-order model with calculated DT₅₀ of 20.6, 12.0, 5.8, and 36.7 days for imidacloprid, dimethomorph, glyphosate, and the glyphosate metabolite AMPA, respectively. The pesticide behavior was interpreted based on the chemical and physical characteristics of both the substances and the water-soil system. Despite the fast abatement of glyphosate, traces were detected in the water until the end of the trial. The formation of soluble 1:1 complex between glyphosate and calcium, the most representative cation in the wetland water, was highlighted by infrared analyses. Such a soluble complex was supposed to keep traces of the herbicide in solution.