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Isolation and determination of the energy content of grease and oil in wastewater treatment plants on the island of Crete

Tatas Nikolaos-Rafail

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Summary

Fats and oils are the main organic components of urban wastewater, and their removal is considered necessary as they hamper the operation of Wastewater Treatment Plants (WWTPs) and have negative impacts on the environment.The aim of the present thesis is to isolate fats and oils from the overlying layer of degreasers from WWTPs in Crete and to evaluate their energy content. Within the framework of the thesis, sampling was carried out from the WWTPs of Chania, Rethymnon and Heraklion, in three different time periods (09/2021, 11/2021, 01/2022). The samples were then subjected to the extraction procedure in order to determine their concentration of fats and oils, and their Higher Heating Value (HHV) was measured.Due to the high heterogeneity of the samples between the WWTPs, the separation of the results was based on the form of the samples (liquid or solid). For the liquid samples, the highest average concentration of fats and oils was found in the Heraklion WWTP (23.1 ± 8.4 g/L). Samples from the Rethymno and Chania WWTPs were found to have concentrations of 19.4 g/L and 7.9 ± 3.4 g/L, respectively, while the average concentration for all the WWTPs together was 19.1 ± 9.7 g/L. Regarding solid samples, the average concentration of fats and oils in the Chania WWTP was found to be higher (490.6 ± 246.4 mg/g) compared to the Rethymnon WWTP (122.2 ± 7.7 mg/g), while the average concentration for all WWTPs together was 367.8 ± 265.8 mg/g. No solid sample was collected from the Heraklion WWTP.Regarding the energy content of the isolated fats and oils, samples from the Heraklion WWTP showed the highest average HHV (43,6 ± 0,7 MJ/kg), compared to Chania (42,0 ± 1,8 MJ/kg) and Rethymno (40,2 ± 3,3 MJ/kg), while the average of all WWTPs was found to be (41,9 ± 1,0 MJ/kg).In conclusion, despite the great heterogeneity of the original samples, the values of the calorific value and therefore the energy content are similar. Furthermore, the high energy content of the isolated fats and oils makes them an ideal raw material for the production of alternative fuels, such as biodiesel, which can be used to meet the energy needs of WWTPs.

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