Chlorinated pesticides are a group of synthetised chemicals, that have a cyclic structure, a certain number of chlorine atoms and are being used for insect termination. They belong to a group of persistent organic pollutants with low volatility and good solubility in lipids, which are toxic to humans and animals. Due to the widespread use of chlorinated pesticides in the last century, they are still present in the air, water and sediments, despite the ban on their production and use in Europe and the USA.
Adsorption is one of the methods for water and soil purification. Various polymer resins, mineral oxides and activated carbon are used as adsorption agents. However, biochar presents a cheaper and more sustainable alternative. Biochar is a product produced during the pyrolysis of biomass at hypoxic conditions. Because of its characteristics, such as high porosity, large active surface and the presence of functional groups, biochar makes a good adsorption agent. The properties of biochar are greatly influenced by pyrolysis conditions and the type of starting raw material, i.e., biomass. Adsorption of pollutants onto biochar depends on several factors, including the amount of adsorbent (biochar), adsorption time, amount of pollutant, presence of other substances and temperature.
In my master's thesis, I determined the adsorption capacities of four types of biochar, which differed in biomass (oak, spruce, beech, wheat bran) and the proportion of chlorinated pesticides adsorbed on them (lindane, heptachlor, dieldrin). I also checked whether there was an effect of pollutant concentration on adsorption. In all cases, I shook the biochar with a pesticide solution of a certain concentration on a rotary shaker, and then determined the concentration of unadsorbed ions in the solution by gas chromatography (GC-ECD). From this, I calculated the adsorption capacity and the percentage of adsorption, and after comparing the results, I chose beech biochar as the most suitable adsorption agent, as it had the highest adsorption capacity. Heptachlor turned out to be the pesticide that binds to all types of analysed biochar to the greatest extent, therefore its removal with adsorption is the easiest. I also noticed a correlation between the concentration of the pollutant and the adsorption capacity of the adsorbent, namely the correlation is approximately linear in most cases. Adsorption is affected by many other factors, which were constant in my experimental work and were not the subject of research.
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