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Potential for energy production of biosolids in Crete

Loizos Spyridon

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Summary

Nowadays, the rapid population growth and the global industrial development have led to a huge increase in the daily produced biosolids. The needs that have arisen due to ever-increasing trend of waste production, cannot be met by the methods used in the past. The energy utilization of biosolids is the best solution for their management, as it is an environmentally friendly method, which utilizes the huge quantities of the produced biosolids, by exploiting them as a fuel for energy production.The purpose of the present diploma thesis is to assess the potential for energy utilization of biosolids in Crete. Initially, samples of biosolids were collected from 7 Wastewater Treatment Plants (WWTPs), in the 4 Prefectures of Crete. From the Prefecture of Chania, samples from the WWTPs of Chania and Platanias were collected, from the Prefecture of Rethymnon from the WWTP of Rethymnon, from the Prefecture of Heraklion from the WWTPs of Heraklion and Malia and from the Prefecture of Lasithi from the WWTPs of Elounda and Ierapetra. These samples, were collected from the secondary treatment, while in the WWTPs where the primary treatment and the digestion process takes place, samples of primary, mixed and digested sludge were collected too. Then, the samples were placed in an oxygen bomb calorimeter, in order to measure their calorific value. The measurements were repeated 3 times, to minimize the possibility of error and find a reliable average value. Also, the percentages of Total Solids (ΤS) and Volatile Solids (VS) were measured.According to the results of the measurements, the calorific value (Higher Heating Value, HHV) of the biosolids of Crete ranges from 15.090 MJ/kg to 24,834 MJ/kg, with the highest calorific values to be found on the biosolids that were collected from the primary treatment, in WWTPs of Chania (24,834 MJ/kg) and Heraklion (23,649 MJ/kg). Based on these values, it is concluded that those biosolids can be a stand-alone fuel for energy production, worthily replacing widely used fuels such as lignite, synthetic carbon gas, palette, wood, paper, plastic, rubbish and carbon. Furthermore, it is observed that in the WWTPs where the digestion process takes place, the calorific value of the biosolids that were collected from the secondary treatment, is bigger than that of the biosolids collected from the digestion process. The calorific value of the digested biosolids ranges from 15.090 MJ/kg to 16.982 MJ/kg.At the same time, the solar drying method was selected in a closed installation for partial sludge drying and the gasification method for its energy utilization. According to the measurements, the energy content of the biosolids collected, was capable of covering the energy needs of the system and to achieve autonomous combustion of biosolids for energy production.

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