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Anaerobic digestion of solid cotton ginning waste and biochar production

Theocharis Nikolaos

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Summary

Nowadays, that the environmental problems are large enough and especially in Mediterranean countries, like Greece, the production of solid waste mainly from agro-industrial activities has an important role to play, since agriculture and livestock farming have been the main primary production sectors for many decades in this country. Of course, the abovementioned environmental problem could be considered as a possible alternative source of energy, which have already received praising critics. Specifically, through this thesis, the efficiency of ultrasonic pretreatment for the production of methane through the anaerobic digestion process, is examined. Furthermore, its adsorption capacity to toxic pollutants, which can be detrimental to aquatic environments, are also being examined.During these experiments, cotton substrate was used as the substrate for the anaerobic digestion process. The fibrous fraction of these wastes has a lignocellulosic origin, as it also contains significant amounts of nitrogen, phosphorus and potassium. These material is therefore considered particularly resistant to biodegradation by microbes and enzymes. Based on that, prior to anaerobic digestion, cotton gin waste pretreatment was applied using ultrasound, in order to study its effect on methane production, as well as on metal removal from aqueous solutions. As far as the latter is concerned, the efficiency of cotton gin waste biochar was also evaluated. During the time period of pre-treatment the samples were exposed to ultrasound for four different time intervals (15, 30, 60 and 120 minutes). The evaluation of the pretreatment process was carried out through soluble chemical oxygen demand and total phenols analyses. Subsequently, Biochemical Methane Potential (BMP) assays were performed, in order to determine the final biodegradability of anaerobic methanogenic digestion of organic substrates and the final amount of methane that is produced. The substrates for these tests consisted of cotton gin waste, samples before and after ultrasound pretreatment. The inoculum that was used during the procedure of the anaerobic digestion was sludge derived from a mesophilic anaerobic digester of an urban wastewater treatment plant. The most suitable combination of substrate and inoculum is the one that provides a more efficient methane production performance. In regard to the study of the removal of toxic metals from aqueous solution, ultrasound pretreated samples and biochars of the original waste were used as adsorbents. Biochars were obtained after pyrolysis of the material at two different temperatures, while the results of the study showed satisfactory levels of elimination. The results of this study have shown that ultrasound pretreatment led to a slight increase of the solubilization of the organic matter and the total phenols contained in the cotton gin waste. In particular, BMP yields showed that the sample being exposed to ultrasound for one hour produced more methane in comparison with the unprocessed waste (CGW).During the adsorption experiment was observed that the biochar produced at 400 ° C (Bio400) has a high adsorption capacity for toxic pollutants, such as copper (Cu) and lead (Pb), in aqueous environments.

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