Mesophilic Anaerobic Co-Digestion of Vegetable Wastes and Swine Manure
Date Issued
2016
Date
2016
Author(s)
Lin, Yu-Shan
Abstract
In this study, the experiment of mesophilic (37±1℃) anaerobic co-digestion of swine manure (SM) and vegetable wastes (VW) was conducted to investigate the optimal operational condition and mixing ratio. The whole study includes two experiments. The first experiment was the co-digestion of digestate (the effluent of the primary digestion of swine manure) and vegetable wastes. This experiment was to evaluate if the gas production of digestate in the secondary digestion could be improved effectively after the supplement of proper carbon source under different hydraulic retention times (HRT) of 8, 10 and 12 days. The influent of the primary digestion was 5% TS swine manure, while the vegetable wastes used in the secondary digestion was controlled at 4% TS. Also, the carbon to nitrogen ratio (C/N) of feed mixture of co-digestion was prepared and controlled at around 30:1. The second experiment was the co-digestion of swine manure and vegetable wastes. This experiment was to evaluate the gas production and the limit of adding vegetable wastes at different mixing ratios of 1:0, 4:1, 3:1, 2:1 and 1:1 (SM:VW) under a relative high organic loading rate of 5-day HRT. The influent substrates including both swine manure and vegetable wastes were prepared at around 5% TS before mixing and feeding. The results of the first experiment showed that in test of adding 30% of vegetable wastes to the primary digestate as feeding mixture (12-day HRT) could improve the COD, TS and VS removal efficiencies of 5.5%, 7.81% and 15.77%, respectively, and also improve the gas production rate (GPR) and methane production rate (MPR) of 0.26 L/L/day and 0.12 L CH4/L/day, respectively. The results of the second experiment showed, at 5-day HRT, the test of using 100% swine manure (SM:VW is 1:0) had the best gas production performance with GPR, MPR and methane content of 1.70 L/L/day, 1.06 L CH4/L/day and 61.90%, respectively, and the COD, TS and VS removal efficiencies of 16.27%, 14.40% and 12.14%, respectively. In respect of adding vegetable wastes for co-digestion, the test of 4:1 (SM:VW) mixing ratio had the best gas production performance with GPR, MPR and methane content of 1.49 L/L/day, 0.77 L CH4/L/day and 51.33%, respectively, and the COD, TS and VS removal efficiencies of 16.95%, 13.27% and 11.73%, respectively. The results also showed to maintain the system working, the highest proportion of the vegetable wastes could be added was 33%, i.e. SM:VW of 2:1. The MPR of 0.54 L CH4/L/day and TS removal efficiency of 10.87% was observed during this testing period. Beyond this adding ratio of vegetable waste, imbalance of reactor would be occurred due to inhibition. To suppress the inhibition effect, addition of alkali (Sodium bicarbonate) to adjust the pH value of influent and reactor, the proportion of vegetable wastes could then lift up to 50%. In conclusion, the anaerobic co-digestion of swine manure and vegetable wastes with high solids concentration influent and organic loading rate was successfully proved, and a high gas production could be achieved in this study.
Subjects
anaerobic co-digestion
swine manure
vegetable wastes
methane
wastewater treatment
Type
thesis
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