Energy recovery technology from municipal solid wastes(MSW) has been increasingly established in many countries. Conversion of the organic fraction of MSW to methane through anaerobic digestion can be a viable approach for both energy recovery and safe disposal of MSW. In this connection, possibility of anaerobic digestion of food waste was investigated by using batch assay and continuous experiment.
The biochemical methane potential(BMP) of several food waste components was determined in order to compare the extents and the rates of their conversion to methane. As the high concentration of sodium ion present in food waste of our country can cause inhibition problem during anaerobic digestion, anaerobic toxicity assay(ATA) was carried out in order to quantify the toxic effect of sodium. Also, comparison of single-phase with two-phase process was made by evaluating operation results from continuous experiment.
Results obtained from this study were as follows ;
1. Ultimate methane yields and conversion rates of food waste components: The methane conversion rate of food waste was first order reaction, and the ultimate methane yield is 0.51, 0.38, 0.35, 0.28, and 0.27 L $CH_4$/g VS for meat, fish, grain, raw vegetable, and heat treated vegetable, respectively.
2. Methane yields and conversion rates of food waste according to sources : The values of ultimate methane yields varied according to the sites, and those for restaurant, KAIST, rural area, and APT was 0.36, 0.33, 0.32, and 0.32 L $CH_4$/gVS, respectively.
3. Sodium ion inhibition to methane conversion : The ultimate methane yield was little affected by sodium ion concentration up to 2g $Na^+$/1. However, as increasing sodium ion concentration to 4, 6, 8, and 10 g/1, the ultimate methane yield was decreased to 5.5, 17, 20, and 33 %, respectively.
4. Performance of single-phase upflow reactor : As the organic loading rate was increased to 2, 4, and 6 g VS/L.d, the specific methane yield gradually increased to 0.75, 1.3, and 1.7 L $CH_4$/L.d, respectively, however the reduction efficiency of organic matter decreased 74, 64, and 56 %, repectively.
5. continuous operation of two-phase process : The rate of hydrolysis of food waste in acidogenic reactor is about 73% at dilution rate of 0.6 $d^{-1}$. However, as increasing the dilution rate with effluent from methanogenic reactor up tp 0.93 $d^{-1}$, the rate of hydrolysis was increased to 90 % at a volumetric loading rate of 12 g VS/L.d. In methanogenic UASB reactor, COD removal efficiency was maintained about 85 % up to loading rate of 10 g COD/L.d. At this loading rate, specific methane yield was about 3.3 L $CH_4$/L.d.