REPOSITORY > RESULTS

Abstract

The reuse of municipal wastewater for secondary purposes is a sustainable approach to managing water scarcity. For this reason, we examined the processes that occur simultaneously during the additional treatment of water from the outflow of a small biological wastewater treatment plant (SBWTP) using different zero-valent iron nanoparticles (nZVI) and complementary water remediation methods. We studied three different types of nZVI: those synthesized in the laboratory, Nanofer STAR, and Nanofer25 slurry. The laboratory-synthesized nanoparticles proved unsuitable for water purification due to the release of boron, while Nanofer STAR exhibited too low a reactivity. Nanofer25 slurry, which proved to be the most suitable, was used to optimize the amount of nZVI and the operating parameters (mixing and settling times) for removing selected pollutants from the water. To achieve the desired disinfection efficiency of more than 90%, an nZVI concentration of 0.25 g/L was required. When the mixing time exceeded 400 min, bacterial regrowth and element desorption occurred. At nZVI concentrations below 0.25 g/L, iron particles settled less effectively after nanoremediation due to their stabilization by organic matter. The optimized nanoremediation process removed most bacteria and organic pollutants from the water. The remaining bacteria were removed using sodium dichloroisocyanurate, while the remaining organic contaminants were eliminated by adsorption onto activated carbon. After nanoremediation, the ammonia content increased slightly; however, the ammonia was removed in the subsequent treatment step by ion exchange using zeolites. Thus, a multistep remediation procedure for the reuse of municipal wastewater was established.
Immobilization is one of the most effective methods for remediating contaminated soil. The soil is mixed with additives, leading to the formation of an inert composite. For this study, the most contaminated part of the soil from the site of the former Old Zinc Works in Celje was used. The soil was classified as hazardous waste because the limit concentration for water-soluble Zn was exceeded. We investigated the effectiveness of various industrial wastes—paper ash, coal fly ash, ladle slag from steelmaking, and red mud from bauxite processing—as additives for soil immobilization. Paper ash, coal fly ash, and ladle slag have the potential to form hydration products that chemically immobilize contaminants. Red mud was not hydraulically active and was partially neutralized. Experiments using small amounts of additives showed that the immobilization of potentially toxic elements (PTEs) was consistent with the known pH-dependent behavior of cationic metals (Cd, Pb, and Zn) and molybdenum (Mo), which occurs as an oxyanion. The increased immobilization efficiency of the composites over time was associated with the formation of new minerals through hydration and pozzolanic reactions. Adsorption of pollutants was the main immobilization mechanism when red mud was used. Composites containing paper ash, coal fly ash, and red mud met the applicable inertness limit values and were therefore environmentally acceptable, whereas composites containing ladle slag exceeded the limit for Mo in the aqueous eluate. Combining paper ash with other additives, compared with binary systems, increased immobilization efficiency and improved the geotechnical properties of the composites. All composites except those containing ladle slag have potential applications as building materials for the remediation of contaminated sites, particularly in geotechnical embankments or fills.