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Effect of sewage sludge biochar on tomato (Solanum lycopersicum L.) cultivated in metal-contaminated soil

Mourgela Rafaila-Nikola

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Summary

The objective of this study was to investigate the effect of biochar on contaminated soil. In particular, the effect of biochar on tomato cultivation (Solanum lycopersicum L.) and in soil without plant interventions was examined. The soil was contaminated with aqueous solutions of Pb (II), Ni (II) and Zn (II). Biochar was produced at 400°C through pyrolysis of sewage sludge and characterized for its physicochemical properties. A corresponding characterization in terms of physicochemical properties was performed for the soil.The installation of the experiment took place in the nethouse of the Park for the Preservation of Flora & Fauna, which is located in the area of Akrotiri, Chania. The tomato plants were cultivated in pots for approximately 2 months. By the same time, pots without plants were placed for the same duration. For the pilot testing, there were four treatments, namely pots with unpolluted soil (controls), pots with soil contaminated with metals, pots with unpolluted soil mixed with biochar and pots with contaminated soil mixed with biochar.The effect of biochar on tomato cultivation was studied for approximately 2 months through monitoring plant growth and analyzing aqueous samples derived from the pots. At the end of the cultivation period, chemical analyses were performed on the aboveground and underground plant tissues and also on soil samples from all pots of the experiment. In this way, we studied whether biochar inhibited the mobility of metals from the soil solution to the plant.Regarding the pots without plants, chemical analyses of aqueous samples were performed during the experiment. After 2 months, chemical analyses were also performed on soil samples from all pots of the experiment. Thus, we investigated whether the biochar prevented metal leaching from the soil.After the completion of the plant growth experiments, phytotoxicity testing was performed on soil samples obtained from pots without plants in order to study the degree of toxicity reduction of the soil sample due to biochar addition.Based on the physicochemical characterization of the materials and the results of all experiments and tests that have taken place, it appears that, in short term, biochar increases the availability of substances. On the other hand, in long term biochar does not allow the uncontrolled mobility of substances, especially of substances that are considered as pollutants. Therefore, the pyrolysis of the sewage sludge leads to a significant reduction of the mobility and bioavailability of metals, causing a smaller ecological risk than the deposition of the sewage sludge in the environment. Biochar application in soil improves soil properties and remediates soil from pollutants, due to its adsorption capacity, large specific surface area and surface stabilization mechanisms of inorganic pollutants.

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