Study of Salt Effect on Semi-Continuous Anaerobic Digestion of Food Waste with Modified First-Order Model

Abstract

Abstract In semi-continuous anaerobic digestion, organic material feed sometimes may not be consumed completely in one day and it may considerably help to increase biogas production of next day. Such occurrence is called ’biogas accumulation phenomenon’, which cannot reflect the real biogas production from next day’s feed. In this test, first-order model was modified to solve this problem. Compared with first-order model, k values of modified first-order model had smaller relative standard deviation for each week with better fitting degree. Modified first-order model was then verified using food waste with different theoretical biogas production. Therefore, it can be concluded that the modified model can remove biogas accumulation phenomenon effectively. However, this model didn’t perform well in methane production fitting. The modified first-order model was utilized to study the variation trend of biogas production from anaerobic digestion of food waste with increasing salt concentration in the reactor. Results showed that when salt concentration in reactor increased from 0.69 to 2.12 g.-L−1, biogas production experienced increasing first and then deceasing. 0.98 to 1.27g-L.−1salt concentration was more appropriate for biogas production (653-718L.-kg−1 VS) and when salt concentration increased to 1.36-1.61 g.-L−1, inhibition phenomenon began. Biogas production (363-420L.-kg−1 VS) was further suppressed with 1.68-2.12 g.-L−1salt concentration. At this time, the ratio of volatile organic acids to the total inorganic carbon (VOA/TIC) increased to 0.24-0.58, showing anaerobic digestion process was unstable.