Treatment Of Livestock Biogas Slurry By Waterfall-Floating Bed System

Biogas project can achieve the goal to make livestock waste harmless, minimization and recycling. At the same time, biogas can play an important role in easing the contradiction between supply and demand of rural energy and protecting the rural environment and the development of rural economy. But the subsequent processing problems of biogas slurry cannot ignore. The biogas slurry is the residual liquid from livestock manure through anaerobic fermentation, belongs to high concentration organic wastewater. It will cause eutrophication of water, agricultural pollution, deterioration of soil quality and other environmental issues if not properly handled with biogas slurry.As an in-suit water remediation technology, Ecological Floating Bed System (EFBS) possessed many advantages, such as low operating cost and convenient maintenance management. Waterfall reoxygenation can use sewage gravitational potential energy effectively, especially in Chongqing. The technology can reduce the construction cost. In view of this, the paper intends to use these two technologies into the backend process of biogas slurry treatment. Through waterfall reoxygenation, biogas slurry goes into EFBS for purification. Firstly, this paper studies the factors and parameter optimization in waterfall reoxygenation process. And then, EFBS is designed and constructed to evaluate its decontamination efficiency. At last the paper studies the optimum operation parameters of Waterfall-Floating bed system in order to provide the scientific basis for backend processing of biogas slurry from livestock and poultry farms.Waterfall reoxygenation experiment indicates that biogas slurry can obtain good oxygen filling effect in the condition of H=70cm, B=25cm, h=20cm. Reoxygenation rate first increases then decreases in a certain height range. Reoxygenation rate reaches a maximum at height of70cm. The drop shape of biogas slurry is water column when B=10cm. Meanwhile the drop shape of biogas slurry is water curtain when B is between15and30cm. Reoxygenation rate increases with the increase of the width in water curtain form, but the growth trend become slowly. Reoxygenation rate decreases with the increase of the depth.In static floating bed experiment, Canna indica and Eichhornia crassipes can growth normally in3kinds of biogas slurry concentration, especially in medium concentration. The removal rate of COD in EFBS with C. indica in high, medium and low concentration is63.78%,71.43%and73.50%, respectively. The removal rate of TN in EFBS with C. indica in high, medium and low concentration of biogas slurry is75.39%,80.11%and90.11%. The removal rate of NH4+-N in EFBS with C. indica in high, medium and low concentration of biogas slurry is82.56%,90.41%and92.36%. The removal rate of TP in EFBS with C. indica in high, medium and low concentration of biogas slurry is79.13%,88.14%and94.63%. Meanwhile the removal rate of COD in EFBS with E. crassipes in high, medium and low concentration of biogas slurry is75.51%,81.69%and77.32%. The removal rate of TN in EFBS with E. crassipes in high, medium and low concentration of biogas slurry is83.87%,87.75%and91.03%. The removal rate of NH4+-N in EFBS with E. crassipes in high, medium and low concentration of biogas slurry is87.99%,86.16%and89.02%. The removal rate of TP in EFBS with E. crassipes in high, medium and low concentration of biogas slurry is84.17%,81.53%and93.66%, respectively. As a whole, EFBS with C. indica and E. crassipes have higher decontamination efficiency in medium and low concentration of biogas slurry than that in high concentration. E. crassipes has a stronger adaptation to high concentration of biogas slurry than C. indica. The EFBS with E. crassipes has higher decontamination efficiency than EFBS with C. indica. There are differences between two EFBSs in the ability of removing pollutants. For NH4+-N、TP, EFBS with C. indica is better than EFBS with E. crassipes, but for COD and TN is the opposite.The experiment in compound ecological floating bed system (CEFBS) shows that the treatment effect for each pollutant is better in CEFBS than that in EFBS. The CEFBS shows high decontamination efficiency compared with EFBS (p<0.05). That indicates that packing can help pollutants removal, especially combination packing.Dynamic experiment is operated under a condition of continuous water input. The result indicates that extending the hydraulic retention time (HRT) is advantageous to the pollutant removal. When HRT=ld,3d,5d and7d, the average removal rate of COD is9.07%,21.40%,32.46%and39.16%. The average removal rate of TN is11.56%,27.07%,39.50%and50.49%. The average removal rate of NH4+-N is6.52%,16.54%,23.90%and28.54%. The average removal rate of TP is7.46%,16.95%,26.89%and35.03%. The growth of removal rate gets slowly with the extension of HRT.The accumulative total removal rate of COD, TN, NH4+-N and TP is87.87%,83.37%,87.75%and79.35%in waterfall-floating bed system, respectively. Effluent concentration of COD and TP is under urban sewage discharge standards level1 standard B. Effluent concentration of TN and NH4+-N is under urban sewage discharge standards level1standard A.