Experiment Research And Simulation Study On Optimization Of Biogas Production Efficiency From Hydrilla Verticillata

Hydrilla verticillata?HV? shows good water quality restoration function in contaminated water, which has been widely used to solve water eutrophication and heavy metals pollution in rivers and lakes. However, HV grows fast and when HV enters the decaying stage, the pollutants absorbed by HV will return to the water, which will result in more serious pollution if no action is taken. Utilization of anaerobic digestion technology to treat HV will not only solve the environmental problems caused by the decaying HV, but also produce methane-rich biogas as clean energy. Therefore, this study carried out anaerobic digestion experiments on HV to investigate the biogas potential of HV. In order to improve biogas production performance of HV, NaOH pretreatment was adopted, and the effects of concentration of NaOH, pretreatment time and sludge inoculums on biogas production were also be analyzed. Based on the experiment research, model and simulation study on anaerobic digestion of HV was carried out, and anaerobic digestion model No. 1?ADM1? was used during the model study. A modified ADM1 model was developed for HV through sensitivity analysis and parameter estimation. The main conclusions of the research are as follows:?1? The preliminary experiment results showed that using HV?without pretreatment? as the substrate resulted in biogas yield of 219.56 L/Kg TS and methane yield of 81.74 L/Kg TS, indicating that anaerobic digestion technology is applicable to the resourceful treatment of HV.?2? The optimization experiments used HV?with pretreatment? as substrate proved that moderate NaOH concentration and pretreatment time could improve biogas production to some extent, but when NaOH concentration becomes higher, the digestion process would be inhibited due to the rise of osmotic pressure caused by Na+, which instead reduced biogas production. The optimization experiments were designed by Response Surface Methodology?RSM?, and experimental data were analyzed by Design-Expert software. The results showed that the best pretreatment conditions are: NaOH concentration of 0.19mol/L, pretreatment time of 9.95 h and sludge inoculums of 21.23%, and methane yield modeled by software under these conditions is 148.42 L/Kg TS, which is near to the experiment result 146.50 L/Kg TS. The methane yield under the best pretreatment conditions is 79.22% higher than that without pretreatment, showing that NaOH pretreatment could effectively improve biogas production performance of HV. Besides, the RSM used in this study has also been proved to be feasible and effective, which could help researchers to find the best pretreatment conditions more precisely than orthogonal experiments.?3? Based on ADM1, simulation study on anaerobic digestion of HV which used experimental data as data sources has been conducted. The simulation study showed that k_dis, k_hydpr, k_maa, k_mac, k_mh2, K_saa and K_sac are sensitive parameters that influenced simulation results. The sensitive parameters were then optimized by parameter estimation, and ADM1 with parameter estimation could well predict experimental results, and then the accuracy of the model has been verified with experimental data under the best pretreatment conditions. The verified model were then used to simulate the dynamic variation processes of fatty acids, biomass and inhibition effects, which preliminarily revealed the internal reaction mechanisms of anaerobic digestion of HV.