Experimental Study On The Rapid Start-up And Phase-separation Of Two-phase Anaerobic Treating Organic Wastewater

At the beginning of the 70th, Ghosh and Pohland firstly proposed the concept of two-phase anaerobic according to the anaerobic biological digestion mechanism and the microorganism group theory. Acid-formers and methane-formers were physically separated in two reactors, where optimum environmental conditions for each group of organisms would be provided to enhance the overall process stability and control. Two reactors in series were respectively acidogenic reactor (acidogenic phase) and methanogenic reactor (methanogenic phase).In this paper, the start-up and phase-separation of two-phase anaerobic reactor designed for experiment were investigated, so to seek the rapid start-up method and to study the effect of phase-separation. Glucose and starch were used as the organic-carbon source of the synthetic wastewater in this study. Two phases were both UASB reactors. Starting up at low organic loading, the influent COD was increased quickly and HRT was shortened, so that acidogenic phase could work in acidic condition as soon as quickly. Pulverous Ca(OH)2 was added intermittently into acidogenic phase to keep the effluent pH 7.0±0.3, so that methanogenic phase could work in optimal condition. After 36 days of operation, Respectively 69% and 64% of total bioparticles were more than 1.0mm in acidogenic reactor and methanogenic one. On the 36ed day, two-phase anaerobic system was achieved optimal COD removal efficiency (96.66%) at HRT of 17.03h and VLR of 8.46kgCOD/(m3·d) and hydraulic surface loading of 0.059(m3/m2·h), when HRT, VLR, hydraulic surface loading and COD removal efficiency were respectively 5.42h, 27.32kgCOD/(m3·d), 0.195m3/m2·h, 30.21% in acidogenic phase, and 11.61h, 8.90kgCOD/(m3·d), 0.091m3/m2·h, 95.21% in methanogenic phase. So two-phase anaerobic reactor achieved rapid start-up successfully.The microorganism in acidogenic UASB was mainly bacilli and a few cocci, which in methanogenic UASB was mainly Methanococcus and Methanosarcina. After the investigation of granular sludge and microorganism in reactors, it was believed that the granular sludge was shaped through irregular core, extrusion and bridging, division and growth, shear and accretion.Sodium molybdate was included in the feed as the inhibitor in the phase-separation experiment. The concentration of MoO42- was 2.0mmol/L.After the addition of MoO42-, the effluent COD in acidogenic reactor was increased. After MoO42- was omitted from the feed, the effluent COD of acidogenic phase was finally about 4500mg/L.The COD efficiency decreased from 26%～34% before to 23%～27%。Acidfication rate in acidogenic phase increased to 60% above by molybdate addition. The effluent of methanogenic phase was improved. For that the MoO42- was bacteriocidal to MPBs which did not recover, it could be used to kill the MPBs and achieved nearly complete phase separation in in acidogenic phase. During the phase-separation experiment period, the appearance of the granular sludge in acidogenic phase was hoar out and black in. As the granular was bigger, the shape was more irregular, the texture was more incompact. The granular sludge was ellipse and rough. The granular sludge above 3.0mm in diameter began to break.