Study On Process And Performance Of Hydrolysis Of Municipal Organic Waste And Anaerobic Digestion Of Hydrolytic Liquid

There are several problems in the anaerobic digestion of municipal organic wastes, including homogeneous difficulty, hydrolysis slowness, and acid as well as ammonia restraints of high-solids content. To solve these problems, a combined batch hydrolysis- UASB process for the treatment of organic wastes was studied in this paper. Main researches were carried out on the hydrolysis of organic wastes, the treatment of the hydrolytic liquid by UASB, parameters and effects of the combined batch hydrolysis- UASB process for the organic waste treatment. Additionally, promotion effect of trace metal ions on the treatment of the hydrolytic liquid in UASB was also studied. Main research results were as follows.The hydrolytic effect of organic wastes was studied by the comparison among anaerobic leaching, anaerobic marination, anaerobic-anoxic marination, anaerobic-aerobic marination and effluent of UASB marination. The result shows the UASB effluent marination is the best way. The parameters of batch hydrolytic process include the hydrolytic time of 7⁸d, the dilution rate of 0.30⁰.70d-1, the solid-liquid ratio of 5⁸, the contact time of 6h on 1st day, and 24h after 1^st day.The hydrolytic rate is concerned with the surface area. The first-order hydrolysis model was modified by introducing the surface area to the traditional first-order model. The modified hydrolytic rate formula is . Where: n=1 (flat grain); n=2 (column grain); n=3 (global grain). The research on dynamics model shows that the hydrolytic rate constants of traditional first-order model, cylindrical model and spherical model are 0.2493, 0.5378 and 0.6741d-1, respectively. Compared with the traditional first-order model, the modified first-order hydrolytic model is a better way to forecast the concentration of organic substance in the reactor and effluent total COD.A novel quick start-up method of UASB was studied, that is, a high original quantity of inoculation sludge (50 % of the reactor volume), a relatively high hydraulic load, and the selection of sludge in the reactor. As sludge was adapted to water quality, the organic load gradually increased; the concentration of VFA was maintained at a high level, and dominant microbes in the anaerobic digestion sludge were selected. When the temperature ranged from 28℃to 35℃, the USAB reactor was successfully started up in 38d, the volume load arrived at 8.0kgCOD/(m3·d), and the removal rate was above 80%.When influent COD ranged from 8,113 to 12,971 mg/L in the UASB reactor, HRT was 21.5²8.5h; the upflow velocity was 10.6¹8.2m/d and the load was 9¹2 kgCOD/(m3·d), the removal rate of COD reached more than 90% and effluent VFA was 43⁷57mg/L. Compared with influent VFA, effluent VFA concentration decreased and phenomenon of VFA accumulation as well as acid restraint did not appear. Compared with influent ammonia nitrogen, effluent ammonia nitrogen increased from 176mg/L to about 1,900mg/L, but phenomena of ammonia nitrogen restraint also did not appear. The gas production was 2.03⁵.31L/(L·d), the gas production of unit COD was 0.21⁰.53L/gCOD and the content of CH4 was 58.9%⁸3.7%.The combined batch hydrolysis-UASB process can overcome disadvantages of VFA accumulation and ammonia restraint in the traditional anaerobic digestion of high-solids organic wastes. The volatile matter ranged from 65.18% to 77.60% in about 8 days; the removal rate of the volatile matter was 32.0%⁵6.9%; the dissolve-out of COD was 303.2⁴71.0gCOD/kgVS, and the gas production of organic waste was 91.0²35.5L/kgVS.Calculation model of effluent ammonia nitrogen in the combined batch hydrolysis- UASB process was established. Key parameter (return ratio) on control was considered as an analysis tool to prevent ammonia restraint efficiently. Moreover, a relationship between acid-alkali balance and pH was set up in the UASB reactor as a theoretical preference to avoid acid restraint.The optimum quantities of Fe, Co, Ni combination were 5.0 mg/L, 1.0 mg/L, and 1.0 mg/L, respectively. The experiment shows that the addition of trace metal ions will enhance the treatment effect and stability of UASB reactor; the average gas production per unit and gas conversion per unit COD increased by 21.5% and 11.4%, respectively.The addition of metal ions did not lead to changes of microbial community structure and dominant microbial categories. It, to some extent, made the proportion of dominant microbes ascend in the reactor. Possible mechanisms of the addition to promote the treatment of hydrolytic liquid include the improvement of the synthesis of dominant microbial cells and enzymes, as well as the activation of the enzyme catalysis in the biological reaction.