Abstract
In a mesophilic anaerobic digestion process, decayed waste activated sludge biomass fed to a digester formed soluble COD substrates, which were eventually converted to methane by anaerobic microorganisms. To improve the decomposition of the soluble materials, performance of a high-rate anaerobic digester was experimentally evaluated. A lab-scale moving-bed biofilm digester having 83.33 m2-carrier surface/m3-reactor was operated for 200 days with decreasing HRT from 20 days to 1 day, while comparing its response to a conventional chemostat digester. Although both reactors gave a comparable methane production until a 15-day HRT, the soluble TOC in the chemostat digester elevated to 3,000 mg/L at 4-day HRT suggesting washout of the anaerobic microorganisms. On the other hand, the moving-bed biofilm digester kept a reasonable methane production rate without accumulation of the soluble materials until 3-day HRT. When the HRT was reduced to 2 days, the soluble fraction decreased due to limited production of the decayed materials. To simulate the responses, an extended IWA-Activated Sludge Model was applied and individual kinetics were estimated. The simulation demonstrated that the relevant active anaerobic biomass (acidogens and methanogens) accumulated in the moving-bed biofilm digester showing high TVS digestion efficiency (25%) at even very short HRT.
