## 3 Decentralized Treatment Systems
### Surface, Open Water Systems and Groundwater Treatment
Again, the removal of OMCs from natural water (lake water) has been attempted in a one-year pilot-scale study, alongside a full-scale treatment, by testing the effectiveness of a combination of two types of GAC filters, with or without O\({}_{3}\) treatment. Ozonation in the pilot experiment effectively removed 72% of detected OMCs to levels <30%. The GAC columns showed breakthrough of OMPs and dissolved organic carbons, but the OMP removal performance of the two GAC materials was not affected by high contents of dissolved organic carbon. The breakthrough of OMPs was delayed in ozonated columns, possibly because of lower adsorption competition with natural organic matter. The lowest levels of OMPs were observed in GAC effluents using ozonated feed water, demonstrating the efficacy of combining ozone with GAC for managing OMP removal. On the opposite side, only a few OMPs were consistently removed in the full-scale process [158]. Groundwater provides more than 50% of drinking water consumption around the world. Nevertheless, it often contains elevated concentrations of contaminants. The paper by [PERSON] and [PERSON] reviewed the performance of nanoscale zero-valent iron (nZVI) in groundwater remediation, obtained in on-field demonstrations. The reductive transformation of contaminants such as chlorinated hydrocarbons and hexavalent chromium (CrVI) can be an effective method for removing multiple pollutants. The efficacy of nZVI in diverse groundwater remediation processes varies significantly depending on the water properties, the pollutants, the hydrogeology, the injection technology and the evaluation methods specific to nZVI. The review comprehensively evaluates the effects of unmodified, Pd-modified, surfactant-modified and carbon-modified nZVI in field tests, with the objective to provide a theoretical basis for the preparation and application of nZV for groundwater remediation [159]. The review by [PERSON] et al is focused on the nanomaterials associated with membrane-based groundwater purification. The mechanisms leading to increased adsorption capacity, reduced fouling and improved selectivity of membrane treatments in the presence of nanomaterials are elucidated, and the environmental sustainability is discussed, highlighting the possibilities to reduce energy and chemical consumption. In the case of large-scale implementation of this technology, factors such as scalability, cost-effectiveness and regulatory compliance are considered [160]. The removal of compounds such as hexachlorocyclohexanes (HCHs) and chlorobenzenes (CBs), reaching groundwater from pesticide post-production landfills, has been studied at both lab- and field-scale, applying a zero-valent iron/peat permeable reactive barrier (PRB). The barrier constructed by the \"funnels and gates\" concept with replaceable active materials was located in the northern plume area, where the concentration of sum HCH was below 50 \(\mathrm{\SIUnitSymbolMicro g}\)/L. The pilot system consisted of various cartridges alternatively filled with zero-valent iron or peat and sand. The treatment train relies on subsequent reductive dehalogenation and adsorption. The pilot system showed significant reduction efficiency with respect to the bench experiments. HCH and CB removal values on the eighth day operation were lower than ca. 82% and 60%, respectively, and highly decreased after two months of operation due to the loss of sorption capacity of peat bed and the passivation of iron chips. Further research in this area is recommended, but these results could be useful for further designs of full-scale PRBs for groundwater contaminated by organ chlorine pesticides [161]  
The dangerous and highly persistent per- and polyfluoroalkyl substances (PFASs) have been detected in drinking water in several European countries and the USA because of their ubiquitous presence in the abiotic and biotic environment. Treatments like sand-filtration, coagulation, flocculation, sedimentation, oxidation and disinfection are ineffective for the removal of PFASs.