The Study On The Two-Phase Anaerobic Digestion Of Municipal Sludge

With the economical development, the work of strengthening the municipal drainage and constructing the waste water buildings had been making in all places, and more wastewater treatment plant would produce a great deal of sludge with high water containing rate. Casually disposing these untreated sludge will cause the new pollution, and this charge is almost same as that of sewage disposal. So it becomes a more attention-getting discussion in the world's environmental circles that how to make the volume-vast and composition-complicated sludge inoffensive and energy-producing by scientific process.According to the characteristics of the sludge of Xi'an city's wastewater treatment plants, the paper adopted two-phase anaerobic digestion to treat sludge, and compared its results with the signal-phase anaerobic digestion data, then made a theoretical analysis.Some conclusions were inferred from the tests include: Volatile solids (VS) reductions of 38.87%, and chemical oxygen demand (COD) reductions of 43.45%, and pH is about 7.5 , and gas yield and gas production rate of 3.00 L/gVS·d and 6.33 volume per culture volume per day, respectively, at an high hydraulic retention time 12.35 days (acid-phase:1.25d, methane-phase: 11. 1d) and a low loading rate of 2.65kg VS/m~3·d.Overall, a two-phase WAS digestion process could be operated at one-half the HRT and double the loading rate of a conventional high-rate digester (the conventional high-rate digest's HRT wasl5.07~25d, and the loading rate was 0.6～1.5 kgVS/m~3·d). At the same HRT, the two-phase system's performance was considerably a little better ,the organic substances reductions were higher, and the volatile fatty acids (VFA) concentration fewer, so the process ran more stably, Especially when loading shock happened, it could resisted strongly. And the two-phase system had a high-gas yield, the gas-production rate of the methane-phase of the two-phase system can be 1.17 times that of signal-phase ones, and methane content was high to 72.18%.After making the heat energy analysis, We found while in common days but the extremely coldest winter days, the two-phase system could produced enough methane totransform into heat that completely satisfied all the reactor's heat cost, even there was some heat remained. We also educed the kinetics model for two-phase anaerobic digestion of sludge on the basis of conclusion of tests. Acid-phase:K2=0.0178g"1?d"1, Sn=22.2022 g/L, Y=4.6425gVSS/gCOD, Kd=0.902d1; Methane-phase: K2=0.0058g"1?d1, Sn=17.5345g/L> Y=4.0096 gVSS/gCOD, K<,=0.2181 d1.