This study investigated the removal of selenium (Se) and strontium (Sr) from water using a three-stage electrochemical reactor with integrated pH control. A total of 102 experiments were performed following a Box–Behnken design that varied the electrode material, applied current, number of electrodes, operating time, and initial pH to evaluate their effects on the Se and Sr removal efficiencies. The complete removal of Se was achieved under multiple conditions, even without pH control, while effective Sr removal required a high current and initial pH adjustment. The top performance for both elements was achieved with a 25 A current, four Fe electrodes, 15 min of operational time per phase (cycle), and a middle range of pH values, which resulted in 97.92% and 99.96% removals of Sr and Se, respectively. This research highlighted the novel approach of using electrochemical pH control to achieve high removal efficiencies of Se and Sr from water in a short operating time, which surpassed the efficiencies reported in previous studies.

The purpose of this work was development of a new method for the neutralization/purification of printed circuit boards wastewater (PCBW) originating from Zagreb, Croatia, using two industrial by-products. PCBW was characterized with low pH value (2.11) and high concentration of TDS (50190 mg L⁻¹), copper (4190 mg L⁻¹) and iron (2660 mg L⁻¹). Waste base (WB), by-product of the alumina production, and waste sludge, by-product of the electrochemical treatment of groundwater, were employed as neutralization/adsorption agents. Due to its high neutralization capacity WB was used for pH adjustment to pH 8 and heavy metals removal from both effluents, yet the final removal of the contaminants down to the regulated values was assessed by adsorption/coagulation with the iron and aluminum rich waste sludge. Following the combined treatment the removal efficiency of iron and copper was higher than 99.99% with their final concentration in the treated water of 0.151 mg L⁻¹ and 0.129 mg L⁻¹, respectively. Following the ozone base oxidation the removal efficiency of the organic contaminants was more than 83%. The successful application of the industrial waste by-products for neutralization/purification of the PCBW with the removal efficiencies of the contaminants comparable or better than those obtained with conventional treatment represented the main advantage of our presented method.

In water supply systems, pressure management in most cases is proven to be the most cost-effective activity related to water loss control. As an advanced method of pressure control, it is possible to use variable frequency drives for centrifugal pump control. Pressure regulation can be performed with constant pressure or with proportional pressure control. The application of proportional pressure control is particularly applicable in water supply systems as the operating pump performance is constantly adapting the pressure to the actual demand. Along with lower leakage losses, it also results in lower energy consumption and the elimination of non-stationary phenomena, thereby extending the pump lifetime. Therefore, the paper presents a theoretical discussion of the proportional pressure control. Possible savings are shown on the numerical example of water supply system of the city of Velika Gorica.

Sulfate is a soluble and chemically stable anion that cannot be destroyed, only separated, concentrated or transformed, and its removal from mine water and industrial effluents is increasingly driven by site-specific discharge limits, commonly of 250–1000 mg L⁻¹. This systematic review critically evaluates chemical precipitation, membrane, sorptive, biological and electrochemical technologies in terms of removal mechanism, achievable residual sulfate and unit treatment cost. Web of Science Core Collection and Scopus were searched on 20 June 2026 (publications 1999 to May 2026) and supplemented by citation searching, publisher platforms and regulatory sources. Eligible sources reported sulfate as an explicit target species with a removal mechanism, performance, operating or cost figure, whereas sources in which sulfate was only a background electrolyte, or which studied sulfide or sulfite without a sulfate figure, were excluded. Evidence was appraised by scale, water matrix and cost basis, without a formal risk of bias tool, and synthesized narratively. Search reproducibility, identification routes, screening and a random 20% sample of the data extraction were cross-checked by a second reviewer. A broadened sensitivity search indicated that relevant studies on matrices other than mine water and wastewater were under-retrieved. Reported and stoichiometrically derived costs were normalized per cubic metre and per kilogram of sulfate removed. Ninety-three sources were included (59 from the database searches and 34 from other sources), mostly journal articles, with evidence ranging from laboratory to full scale. Under representative mine water conditions, gypsum solubility limits inexpensive lime and limestone treatment to residuals of approximately 1200–1800 mg L⁻¹. Unit costs span nearly three orders of magnitude, from about 0.02 USD m⁻³ for constructed wetlands to about 18 USD m⁻³ for single-pass barium chloride precipitation and the heterogeneous evidence indicates an apparent tradeoff between cost and achievable residual. No technology combines low cost with low residual. Crossing the gypsum ceiling raises cost roughly three- to tenfold for mainstream polishing routes. In four common reference scenarios, treating concentrated water to 250 mg L⁻¹ costs about two to five times as much as partial treatment to about 1500 mg L⁻¹ for mainstream treatment trains at the range midpoints, with widely overlapping ranges. The evidence is limited by heterogeneous matrices, scarce standardized cost reporting and, for several technologies, laboratory-scale data. Hybrid trains pairing low-cost bulk removal with selective polishing and resource recovery emerge as the most defensible strategy. This review was not registered. Funding: European Union—NextGenerationEU.