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Anaerobic co-digestion of animal-derived residues for methane production and investigation of digestate uses

Tsokanis Konstantinos

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Summary

The subject of this dissertation thesis is the anaerobic co-digestion of animal-derived residues for methane production and the investigation of digestate uses. For reaching this goal, which was the most efficient biogas production and a quality product capable of being used as soil improvers were studied three different types of livestock manure: cow, sheep, chicken manure and slaughterhouse waste (sample of bladders and intestines with their content after having been processed out properly). Sample sludge was also taken from the mesophilic anaerobic digesters of the Municipal Wastewater Treatment Plant of Chania in order to be used as a process inoculum with a concentration of volatiles in reactors equal to 15 g VS/L and a constant mixing ratio, taking the volatile solids into account, Substrate / Inoculum (SIR) equal to 0,5. The tests for the estimation of the biochemical methane potential were performed for 55 days under mesophilic conditions in batch reactors with a nominal volume of 250 mL and a working volume of 100 mL, which were placed in a conditioned incubator at a constant temperature of 35 °C. According to the results of these tests, the substrate that led to the production of a larger amount of methane was the slaughterhouse sample mixture (SH) with 420 mLCH4STP / gVSadded. Following the substrates of chicken (PM), cows (CM) and sheep (SM) manure with 194, 191 and 170 mLCH4STP / gVSadded, respectively. After that, it was verified that manure mixing (MIX: from cows, sheeps and chickens) demonstrated lower methane production potential than that of the initially substrates (168 mLCH4STP / gVSadded). After the completion of the experimental procedure, a series of analytical methods were used to determine total and volatile solids, total alkalinity and volatile acids, soluble chemically required oxygen (sCOD), total phenols, ammoniacal nitrogen, phosphorus and metals. Finally, from the determination of metals it was concluded that because of their acceptable concentrations based on the national legislation, the digested sludge from the various substrates could be used in the agricultural sector without causing negative-adverse consequences on both the environment and public health.

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