Wastewater treatment plants (WWTPs) are evolving from pollution control facilities into resource recovery hubs, aligning with circular economy principles. However, assessing their transition requires robust methodologies that integrate environmental, economic, and circularity dimensions. This study aims to evaluate the sustainability and circularity performance of a WWTP in Cyprus upgraded with additional treatment stages to recover nutrient-rich sludge for fertilizer and treated water for irrigation. To achieve this, a combined methodological framework was applied, incorporating standardized Circularity Assessment (based on ISO 59,004), Life Cycle Assessment (LCA), and Life Cycle Costing (LCC). Circularity was assessed using a dual-indicator approach: "resource flow indicators" (covering material, energy, and economic flows) and "circular actions indicators" (capturing process optimization, repurposing, cascading, and regeneration). Environmental and economic impacts were quantified using LCA and LCC, respectively, while sensitivity analyses explored the effects of renewable energy integration and process simplification. Results show that while the upgraded WWTP enhances circularity through increased resource recovery and high-value product generation, it also incurs higher environmental impacts and operational costs due to energy-intensive technologies (distillation, reverse osmosis, and nanofiltration), increasing the impacts in values that can achieve +60 % in some impact categories. Sensitivity scenarios demonstrated that reducing energy demand and increasing renewable energy use can improve sustainability outcomes, with the higher average impact reduction achieving -20 %, though often at the expense of circularity performance. The study highlights the trade-offs between maximizing resource recovery and minimizing environmental and economic burdens, emphasizing the need for optimized process design and supportive policy frameworks to enable WWTPs to function as effective circular economy enablers. The findings show that advanced treatment technologies enhance circularity through increased resource recovery, but also entail elevated energy demands and limited economic viability. While frameworks like ISO 59,004 support multidimensional assessment, further methodological development is needed to guide sustainable decision-making.

The escalating water demand in Cyprus has necessitated the exploration of alternative water resources. The available water, which relies on rainfall and dam storage supplemented by methods such as desalination and aquifer enrichment, is inadequate to meet the current water demand. As a solution, Cyprus is utilizing reclaimed water for irrigation, in full compliance with both local and EU regulations. To address sustainable water management in Cyprus, a minimal liquid discharge (MLD) system is assessed for its environmental feasibility. A system incorporating reverse osmosis (RO), a multi-effect distillation (MED) evaporator, and a vacuum crystallizer (VC) is proposed for treating reclaimed water from the wastewater treatment plant (WWTP) in Larnaca. The proposed system aims to control the salinity (2500 mg/L) that limits the use of recovered water to the irrigation of non-sensitive types of crops, while recovering salt (sodium chloride). A life cycle assessment (LCA) was conducted, comparing the proposed MLD system with a reference system based on RO technology, where water is recovered, and brine is rejected back into the sea. The environmental feasibility was assessed via comparing 16 different environmental impact categories. Based on the analysis, the reference study provided a positive numeric value for most of the impact categories that were examined. Thus, it was concluded that the reference study has an overall negative impact on the environment, whereas the proposed MLD system demonstrated an overall positive impact, mainly due to low ecotoxicity.

With water availability being one of the world’s major challenges, this study aims to propose a Zero Liquid Discharge (ZLD) system for treating saline effluents from an urban wastewater treatment plant (UWWTP), thereby supplementing into the existing water cycle. The system, which employs membrane (nanofiltration and reverse osmosis) and thermal technologies (multi-effect distillation evaporator and vacuum crystallizer), has been installed and operated in Cyprus at Larnaca’s WWTP, for the desalination of the tertiary treated water, producing high-quality reclaimed water. The nanofiltration (NF) unit at the plant operated with an inflow concentration ranging from 2500 to 3000 ppm. The performance of the installed NF90-4040 membranes was evaluated based on permeability and flux. Among two NF operation series, the second—operating at 75–85% recovery and 2500 mg/L TDS—showed improved membrane performance, with stable permeability (7.32 × 10⁻¹⁰ to 7.77 × 10⁻¹⁰ m·s⁻¹·Pa⁻¹) and flux (6.34 × 10⁻⁴ to 6.67 × 10⁻⁴ m/s). The optimal NF operating rate was 75% recovery, which achieved high divalent ion rejection (more than 99.5%). The reverse osmosis (RO) unit operated in a two-pass configuration, achieving water recoveries of 90–94% in the first pass and 76–84% in the second. This setup resulted in high rejection rates of approximately 99.99% for all major ions (Cl⁻, Na⁺, Ca²⁺, and Mg²⁺), reducing the permeate total dissolved solids (TDS) to below 35 mg/L. The installed multi-effect distillation (MED) unit operated under vacuum and under various inflow and steady-state conditions, achieving over 60% water recovery and producing high-quality distillate water (TDS < 12 mg/L). The vacuum crystallizer (VC) further concentrated the MED concentrate stream (MEDC) and the NF concentrate stream (NFC) flows, resulting in distilled water and recovered salts. The MEDC process produced salts with a purity of up to 81% NaCl., while the NFC stream produced mixed salts containing approximately 46% calcium salts (mainly as sulfates and chlorides), 13% magnesium salts (mainly as sulfates and chlorides), and 38% sodium salts. Overall, the ZLD system consumed 12 kWh/m³, with thermal units accounting for around 86% of this usage. The RO unit proved to be the most energy-efficient component, contributing 71% of the total water recovery.

Potassium mining activities result in the discharge of highly saline wastewaters, creating severe environmental impacts in water and soil. This study evaluates the environmental performance of a novel pilot system developed in the framework of the LIFE Brine-Mining project. The system comprises membrane, precipitation and thermal technologies, recovering high-purity water and five valuable resources from it: magnesium hydroxide, calcium carbonate, calcium sulfate, sodium chloride, and potassium chloride. A cradle-to-grave Life Cycle Assessment (LCA) was performed following the standards ISO14040 and EN15804 and using 1 m³ of potassium wastewater as functional unit. The LCA results indicated that the novel system environmental impact is mainly affected by the use of chemicals (20.63 × 10⁰ kg/FU) during its operation and energy consumption (1.39 × 10¹ kWh/FU). The chemical use dominates areas like the Abiotic Depletion, and the Eutrophication Potential, and the Water Depletion Potential. The novel pilot system was compared with another novel configuration that treated a brine from coal mining activities and with a conventional method of potassium brine management, which is the disposal in underground old mines. The potassium brine treatment system exhibited lower environmental impact than the coal mine brine system, and outperformed compared to the conventional disposal method.

The environmental management of highly saline coal mine wastewater presents a critical challenge for European mining regions, particularly under the constraints of the EU Water Framework Directive. This study presents a cradle-to-grave life cycle assessment of a novel zero liquid discharge (ZLD) system developed under the EU-funded LIFE Brine-Mining project and deployed at the Ziemowit mine in Poland. The system was designed to treat coal mine brine (TDS ~80 g/L) and recover valuable resources, including high-purity water, sodium chloride, magnesium hydroxide, calcium carbonate, and calcium sulphate. The assessment was conducted in accordance with EN 15804 using the Environmental Footprint v3.1 methodology, ecoinvent v3.10, and a functional unit of 1 m³ of saline wastewater inflow, covering all life cycle stages from raw material extraction to end-of-life and resource recovery (Module D). The results indicate a fossil-based global warming potential of 73.86 kg CO₂ eq. per functional unit, with 66% attributed to operational electricity consumption (module B6, 44 kWh/m³) and 29% to auxiliary chemical consumption (module B1). Three key environmental hotspots were identified: module B1 dominates ozone depletion potential (67%), module B6 dominates acidification potential (66%), and raw material extraction (module A1) dominates abiotic depletion of minerals and metals (43%). Resource recovery credits (Module D) offset 11.80 kg CO₂ eq. of GWP-fossil, cause the ADP-minerals and metals indicator to become net negative, and reduce the water deprivation potential by approximately 50%. A sensitivity analysis confirmed that results are robust to ±10% variations in wastewater inflow, with GWP-total varying within a narrow −0.5% to +0.6% range once the volume-proportional nature of chemical and electricity consumption is correctly accounted for. These findings provide a quantitative sustainability baseline for the scale-up and replication of integrated ZLD technologies in the European mining sector, demonstrating that circular brine treatment can simultaneously address regulatory water quality targets, reduce primary resource consumption, and deliver measurable environmental credits aligned with EU circular economy and sustainable development objectives.

Water reclamation from municipal wastewater treatment plants is a critical strategy for addressing freshwater scarcity in water-stressed regions. This study presents a comparative cradle-to-grave Life Cycle Assessment of three treatment configurations applied to tertiary-treated effluent from a wastewater treatment plant (WWTP) in Cyprus. The three studied systems comprise a conventional single-pass reverse osmosis (RO) unit, serving as the baseline and resulting in salt disposal (Scenario I); an integrated Zero Liquid Discharge (ZLD) system, combining membrane (nanofiltration and reverse osmosis) and thermal (multi-effect distillation and vacuum crystallization) units, resulting in NaCl recovery (Scenario II); and a selective resource recovery configuration combining chemical precipitation (with the recovery of CaCO₃, Mg(OH)₂, and NaCl), RO, and a low-temperature crystallizer unit (Scenario III). The environmental impacts were assessed in SimaPro 10.3 using EF 3.1 across 16 midpoint categories with a defined functional unit of 1 m³ recovered water. Based on the SimaPro results and the conducted analysis, Scenario II performed worst in 13 of 16 impact categories, with increases up to +395% (human toxicity, non-cancer) relative to Scenario I, driven by its high thermal electricity demand (12.21 kWh/m³, over four times the baseline’s) under the fossil fuel-dominated Cypriot grid. Scenario III’s Module D credits (recovered NaCl, Mg(OH)₂, CaCO₃) reduced burden by up to 96% in individual categories but did not reverse any impact category to net-negative values. On the weighted single score, the baseline (280 µPt) outperformed both Scenario III (345 µPt) and Scenario II (1038 µPt), a nearly fourfold gap between the best and worst configurations. Sensitivity and Monte Carlo analysis confirmed this ranking as robust, while showing that a 20% increase in recovered-product credit is sufficient to reverse ionizing radiation to net-negative in Scenario III. Overall, selective resource recovery narrows, but does not reverse, the environmental burden of advanced brine treatment relative to conventional disposal.