Chromium occurs in nature mainly in its trivalent or hexavalent form. Hexavalent chromium Cr(VI) is particularly toxic to humans, animals, and plants. The extensive pollution of groundwaters with Cr(VI) necessitates the complete understanding of natural chromium oxidation and reduction mechanisms, both for assessing the risk of hexavalent chromium formation and for the development of techniques for the reduction and removal of Cr(VI) from contaminated water bodies. In this work, the possibility of hexavalent chromium reduction by discarded or low-cost materials, which contain reducing compounds, is investigated regarding the creation of a compact, pump-and-treat filter for Cr(VI) removal from groundwater.

Cross border areas face common challenges on water management, such as monitoring water demands and quality, because they share a common water basin for covering their water needs. This paper presents the first results of a new, accurate, sensitive and functional tool for assessing water quality, taking under consideration legislation and expert’s opinion, created in frame of the SAVE-WATER, Interreg IPA II Cross-border Cooperation Programme Greece-Albania 2014-2020. The project addresses the open problems and challenges by promoting a transnational common strategy for drinking water management and a shared management policy among three Greek and two Albanian cross border regions.

One of the most challenging yet promising technologies combining waste management with waste utilization for the production of a renewable fuel (biogas) is anaerobic co-digestion. This study investigated the anaerobic co-digestion of three organic waste streams: cheese whey wastewater (CWWW), pig slurry (PS), and food waste leachate (FWL). FWL and CWWW were combined to form a base mixture of constant composition (BM), which was subsequently blended with diluted PS at three BM/PS mass ratios: 25/75, 50/50, and 75/25 (% v/v). The mixtures were evaluated under mesophilic conditions through laboratory-scale batch experiments to assess the influence of substrate composition on biomethane production and organic matter removal. Physicochemical characterization of the individual substrates and mixtures included pH, volatile fatty acids, alkalinity, chemical oxygen demand (COD), and volatile solids (VS). Biochemical methane potential (BMP) assays were conducted, with daily and cumulative methane production systematically monitored throughout the experimental period. Methane production kinetics were evaluated by fitting the modified Gompertz model to the experimental data, enabling estimation of maximum methane production potential, maximum production rate, and lag-phase duration. Experimental results demonstrated that the 75/25 BM/PS mixture achieved the highest specific biomethane yield (525.9 CH₄ Nml/g VS_added) and maximum production rate (μ_m = 36.3 CH₄ Nml/g VS_added/d), alongside the highest removal efficiencies for COD (83.0%), TOC (87.9%), and VS (63.7%), compared with the 50/50 (309.9 CH₄ Nml/g VS_added) and 25/75 (156.5 CH₄ Nml/g VS_added) mixtures. The integrated assessment of methane yield, kinetic parameters, and organic matter removal enables comparative evaluation of the three mixtures and identifies the 75/25 BM/PS formulation as the most favorable mixing ratio for efficient co-digestion of these waste streams.