Experimental test materials and methods Experimental properties of cow dung and kitchen waste Fresh cow dung is taken from a dairy farm with a total solids content (TS) of 160 gL-1, diluted with a ratio of 13 g of cow dung water, and fully stirred. The 20-mesh sieve was used to filter out the cellulose, and the obtained cow dung liquid was placed in a refrigerator-20 for use. Food waste is taken from discarded food in a canteen, including vegetables, fruits, bread, cheese, and meat.
After mixing, use a chopper to about 510mm. One reclaim is sufficient for the entire test. For the characteristics of experimental cow dung and kitchen waste. The VS, COD, protein and fat content in the kitchen waste was 16 times, 14.6 times, 241% and 4 times higher than the cow dung respectively. The ammonia nitrogen of kitchen waste and cow dung accounted for 25.1% and 8.2% of Kjeldahl nitrogen, respectively, indicating that some of the ammonia nitrogen was present in the cow dung before digestion, while the nitrogen in the kitchen waste was mainly in the form of protein during the digestion process. Degrade and release.
The test unit reactor was placed in a greenhouse at 352. The acidification reactor is a continuous stirred reactor with a total volume of 1L, the rotation speed is 110rmin-1. The methane phase reactor is CSTR, the effective volume is 2L, and the stirring speed is 30rmin-1. Each group includes an acidification reactor and a methane phase reaction. The water is fed in and out once a day, and the effluent of the acidified phase acts as the influent of the methane phase.
Test protocol and operation inoculation: the cow dung digestive juice of a long-running medium-temperature anaerobic digester was used as the inoculum in the methane phase reactor, and the inoculation volume was 30%. The total proportion of the kitchen waste and cow dung was set to 4 Test combination. The first group of materials was all cow dung, and the ratio of VS to cow dung and kitchen waste in groups 2, 3 and 4 was 11, 13 and 16, which is 5.6%, 15% by weight of kitchen waste. 257%.
The cow dung was thawed at room temperature one day in advance, and the kitchen waste and cow dung were put into proportion according to the proportion. The residence time of the acidification reactor was controlled at 3 days, and the retention period of the methane phase reactor was 10 days. Continuous sampling was started after the gas production was stabilized (the gas production fluctuation was less than 5% per day), and the average value was determined and calculated.
Test Results and Discussion pH and VFA concentrations are pH and VFA concentration data in acidified and methane phase reactors. Compared with the first group, the concentration of VFA in the acidification phase reactors of the second, third and fourth groups added to the kitchen waste was greatly improved, especially the amount of kitchen waste added was 15% by weight and 25.7% by weight. In group 3 and 4, the total concentration of VFA was 9.93gL-1 and 8.95gL-1, respectively. It is particularly noteworthy that the concentration of propionic acid in the acidification phase of Groups 3 and 4 was very high, being 4.83 and 3.93gL-1, respectively. To the total concentration of VFA is 48% and 44%. The pH values ​​of the acidification phase reactors of Groups 2, 3, and 4 are lower than the pH of 6.45 for cow dung digestion, respectively 537, 500 and 493. More interesting is Although the amount of kitchen waste added to the Group 4 reactor was higher than that of Group 3, the total amount of VFA produced was not higher than that of Group 3. This may be the result of interaction between pH and hydrolysis of organic matter to form VFA: the production of VFA results in a decrease in pH, while the decrease in pH will inhibit further production of VFA. In the fourth group, the proportion of kitchen waste is high, the initial rate of hydrolysis is fast, and the pH value is also decreased. Therefore, the inhibition occurs earlier, and the result is that the concentration of VFA produced by the third group is not high.
Unlike the acid phase reactor, the pH in the methane phase reactor is between 7.27.4, which is relatively stable. The total concentration of residual VFA in the 3rd and 4th methane phase reactors exceeded 2gL-1, indicating that a considerable part of the VFA was not converted and utilized by methanogens. Among the three organic acids, propionic acid accounted for the highest proportion, accounting for 62%, 95% and 68% of the total VFA in the 2nd, 3rd, and 4th reactors, respectively, while the first group of reactors accounted for only 16%. %. It can be inferred that the addition of kitchen waste will increase the possibility of propionic acid inhibition, and the high concentration of propionic acid in the acidified phase will continue to the methane phase reactor, resulting in certain propionic acid inhibition.
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