| In China, the production of FW attained 10 million tons/year and occpied 50% of municipal solid waste, almost 60% of FW has not reached necessary stabilization.Most of the FW is landfilled or untreated and can cause many environmental problems in the transportation and storage such as contamination of soil and groundwater, generating greenhouse gases and odor due to volatile organic compounds of FW rapid decomposition. Anaerobic digestion (AD) of FW has been proven to be an efficient and green technology for solids reduction and biogas production in recent years. However, anaerobic digestion was found unstable when FW was used as mono-substrate due to high moisture, organic contents and biodegradability, which may encounter various potential inhibitors, including fast VFAs production from starch and free ammonia from protein. Biogas production from AD of FW was investigated in this present paper. The AD were carried out based on anaerobic co-digestion of FW and cattle manure(CM); anaerobic co-digestion of FW and rice straw (RS); biogas production from FW with different anaerobic digestion technologies;trace elements on anaerobic co-digestion of FW and CW; optimization of VFAs production in anaerobic co-digestion of FW and CM on trace elements influence to overcome the inhibition from higher concentration of salts and lipids.The main contents are as follows:1, In order to improve the efficiency of the anaerobic digestion of FW, anaerobic digestion of FW in batch test (BT), semi-continuous anaerobic digestion test (SCT), solid-liquid two-phase anaerobic digestion test (SLT) were investigated in this present paper. The results indicated that a highest biogas yield and methane levels could be obtained in the SLT system. The maximum daily biogas yield of FW in SLT, SCT and BT was 430mL·gVS-1d-1,270mL·gVS-1d-1 and150mL·gVS-1d-1, respectively. The maximum methane levels of FW in SLT, SCT and BT was 68%,57% and 50%, respectively.The volatile fatty acids (VFA) production and utilization efficiency in SLT were both improved significantly, organic loading rate (OLR) could achieves 9gVS·L-1d-1,which increased by 50% compared with SCT. Consequently, the anaerobic digestion of FW in SLT to afford high organic loading rate showing superior performance on SCT and BT stabilization.2, Effects of pH on anaerobic digestion of food wastes(FW) were investigated. Anaerobic digestions of FW were carried out at pH of 5,6,7,8 at 35℃. Experimental results showed that pH value could affect daily biogas yield and CH4 content significantly. The suitable pH values were more favorable to anaerobic digestion of FW. Total biogas yield (3692mL) and CH4 content (55%) increased to maximum and the more activity of methanogenic bacteria at pH value of 7(T3). Proper pH value could improve the stability of digestion system and activity of methanogenus. VFAs contained more than 60% of acetic acid. The content of acetic acid and butyrate attained maximium of 77%when initial pH was 7. And no inhibition of ammonia nitrogen was found in modified anaerobic digestion systems.3, The anaerobic digestion efficiency of mixture of FW and CM were investigated in this experiment. Anaerobic batch co-digestions of FW and CM were carried out in anaerobic bottles of 5L at initial total solid (TS) concentration of 6.7% at 35℃.The effects of FW and CM TS ratio (0:1、1:1、2:1、3:1、4:1、1:0) on anaerobic digestion were investigated. The experimental results showed that, anaerobic digestion of mixture of FW and CM, daily biogas yields based on VS and CH4 content were significantly improved. The total biogas yields(574.15ml·gvs-1) and CH4 content(69.78%) increased to maximum at FM to CM ratio of 2 (T3). There were no inhibition of VFAs of T1-T5 for all digestions with pH of 6.0-8.0, while when the concentration of FW is higher, the concentration of VFAs is increased markedly, when mono-digestion of FW, excessive amount of VFAs was accumulated, which is increased to 35600mg·L-1 on the 7th day. The methanogenic activity by using acetic acid or butyric acid all was higher than that by using propionic acid. There were no inhibition of ammonia nitrogen of T1-T5 for all digestions. The concentration of ammonia nitrogen increased sharply first and then decreased slowly, finally rised slowly. For engineering application at 35℃, at initial TS concentration of 6.7%, the FW and CM TS ration of 2:1.4, Anaerobic co-digestion of food waste (FW) and rice straw (RS) in continuously stirred tank reactor (CSTR) at high organic loading rate (OLR) was investigated. Co-digestion studies of FW and RS with six different mixing ratios were conducted at an initial volatile solid (VS) concentration of more than 3gVS/L.The biogas production, methane contents, degradation efficiency of VS, chemical oxygen demand (COD) and volatile fatty acid (VFAs) were determined to evaluate the stability and performance of the system. Results showed that the co-digestion process had higher system stability and higher volumetric biogas production than mono digestions. Increase in the FW content in the feedstock could increase the methane yield and shorten retention time. The efficiency of co-digestion systems mainly relyed on the mixing ratios of FW and RS to some extent. The highest methane yield was 60.55 mL·gVS-1d-1 at a mass ratio (FW/RS) of 3:1, which was 178% and 70% higher than that of mono digestions of FW and RS.respectively. Consequently, the anaerobic co-digestion of FW and RS could have superior stability and better performance than mono digestions in higher organic loading system.5, In order to improve the efficiency of anaerobic co-digestion of FW and CM, in this experiment the effect of trace elements (Fe, Co,Ni) on anaerobic co-digestion performance of FW and CM were investigated in batch mode.The results showed that the addition of Fe, Co,Ni not only improved system stability but also greatly enhanced volumetric biogas production.The biogas yield, the content of methane of T1-T5 were above 4000mL and 60%,respectively, and compared with control, which increased by 55%and 20%,respectively.The changing trend of VFAs and ammonia nitrogen were smooth,there was no acidification occurred and ammonia inhibition, but the result of CK was the opposite. When added trace elements the absorbency value of coenzyme F420 begun to rise slowly, after the 15th day it steady at between 0.55 and 0.65,but the absorbency value of coenzyme F420 of CK was opposite. So supplement of trace elements is an important approach for enhancement of anaerobic co-digestion performance of FW and CM.6, In order to find out the impact of trace elements on the anaerobic co-digestion of FW and CM,getting the optimal concentrations combination of iron, cobalt and nickel on the VFAs production. On the basis of single factor experiments,a central composite design of three factors and three levels and response surface methodology was adopted. The quadratic regression mathematics model was established, and regarding VFAs production as response composed the response surface and contour. The effects of concentration of trace elements and their interaction on VFAs production with mixed food waste and cow manure were investigated.The result showed that, optimal concentrations of three elements was iron:1.05 mg·mL-1, cobalt:0.02 mg·mL-1 and nickel 0.53 mg·mL-1. Under these conditions, the predicted VFAs production was 3670ppm, while the experimental value was 3668ppm,which was corresponded to the predicted value. |
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