Wpływ sposobu prowadzenia fermentacji osadów ściekowych na produkcję biogazu

The aim of this study was to determine the influence of different processes of biochemical stabilization of sewage sludge on the following: biogas production, decomposition of organic matter, transfer of heavy metal ions to the liquid phase of sludge. The stabilization processes of interest in this work were: methane thermophilic digestion (55°C), mesophilic digestion (37°C), mesophilic digestion of thermophilically hydrolyzed sludge. To characterize biogas production in bioreactors, modified Gompertz equation was used. Higher biogas yields were obtained during thermophilic digestion, compared to the yields obtained under mesophilic conditions – 1.01 and 0.91 dm-3 from 1 g of the removed dry organic matter of sludge, respectively. Mesophilic digestion of thermophilically hydrolyzed sludge provided the highest biogas production, approximately 1.15 dm-3 from 1 g of the removed dried organic matter of sludge. A comparable degree of organic matter degradation was observed for all digestion processes, 35–41%. CH4 content in biogas during sludge mesophilic digestion, excluding 1st day, amounted to 59–64%, while during thermophilic digestion – 57–62%. Higher value of biogas production velocity coefficient while intensive growth phase of mixed microbes population (1.11 dm-3/d), during preliminary hydrolyzed sludge stabilization, in comparison to non-hydrolyzed sludge (0.87 dm-3/d), indicates the possibility of obtaining higher biogas production. Therefore it would be more beneficial to conduct mesophilic digestion of sludge which was preliminarily hydrolyzed at temperature of 55°C. The application of thermophilic digestion did not significantly influence the release of heavy metal ions to the stabilized sludge liquid. The concentration of zinc in the liquid was below 0.8 mg/ dm-3 during digestion. The concentration of the other metals was below 0.2 mg/ dm-3 for all digestion processes.