Author: EDITA SODAITIENĖ
Dissertation title: Removal of anionic and cationic pollutants by groundwater water treatment waste
Fields of science: Chemistry (N003)
Scientific supervisor: dr. Audronė Gefenienė
Defence of the dissertation: September 23, 2021
SUMMARY: Groundwater and surface water are very important components of the environment, so the supervision and control of water resources are the responsibility of each state. The developed legislation helps regulate water management issues, protects these natural resources from pollution, and creates a system of restrictions, prohibitions, and legal liability . Industrial wastewater can be connected directly to natural water resources or discharged into urban sewers. Wastewater discharged in this way affects water bodies or the operation of sewerage and wastewater treatment plants . In Lithuania, wastewater discharge is regulated by the Wastewater Management Regulation (Order No. D1-236) which was signed in 2006 and specifies the requirements for the discharge of both domestic and industrial wastewater into the environment. Controlled substances include total chromium, with MPLs (maximum permissible limits) of 2 mg L-1 in the sewage system and 0.5 mg L-1 in the natural system . Anodizing is an important and widely used electrochemical process for the surface treatment of metal and electronic parts . The anodizing process consists of surface cleaning and preparation followed by coating and finishing . To give color to the anodized coatings, the surfaces are dyed. The process is constantly improved to enhance the penetration of the dye into the pores . The effluent streams generated during the whole process are mixed before treatment, resulting in colored effluents containing various metal ions . It is very important to treat such wastewater in order to meet strict environmental requirements. Azo dyes are the largest group of azo compounds and the most widely used dyes in the industry. They are suitable for fiber dyeing, photoelectronic, printing systems, food technology, and biological reactions . There is currently a fairly large selection of dyes that are used for anodized aluminum dyeing. The use of complex metal dyes is a major concern for their environmental impact, as heavy metals in dyes are considered to be nonbiodegradable pollutants. In order to reduce environmental pollution by colored wastewater, the search for cheap and efficient adsorbents is very important. The need for environmental sustainability supports the idea of using a material generated during the treatment of clean groundwater as an adsorbent for the treatment of contaminated water. The purpose and objective of the groundwater treatment are to ensure the quality of drinking water so that it tastes good and is safe to use. During the process, a natural nanomaterial 124 rich in iron(III) compounds (groundwater treatment (GWT) waste), as a byproduct is produced. The physicochemical properties of GWT waste are similar to those of specially synthesized Fe(III)-containing adsorbents and catalysts. This dissertation presents research on sustainable processes for the removal of anionic chromium complex dye (Green) from aqueous solutions and real anodized aluminum dyeing effluents using GWT waste as an adsorbent or catalyst. As the dye contains chromium, the effluent from the anodized aluminum dyeing must be treated to remove not only the color but also the heavy metal ions. For this reason, the dye removal efficiency was evaluated not only by the change in the solution color but also by the change of the chromium concentration in the solution to be cleaned. In addition, the chemical behavior of the entire adsorption system was observed during the dye removal: changes in solution pH, iron, calcium, and aluminum concentrations. The adsorption properties of groundwater treatment (GWT) waste were also investigated by treating water contaminated with cationic pollutants (Pb(II) and Cu(II) ions). The catalytic properties of GWT waste were investigated in the Fenton reaction of oxidative degradation of chromium complex dye (Green). The efficiency of the removal of cationic and anionic pollutants was evaluated by conducting kinetic, equilibrium, and thermodynamic studies.