Simultaneous Removal Of Carbonaceous Materials And Nitrogen With Two Stage Upflow Anaerobic Sludge Bed-aerobic Biofilter (UASB/BF) Combined Bioreactor

With the batch experiment inoculated with the anaerobic granular sludge, the possibility of simultaneous denitrification and menthanogenesis was investigated by the profile of the substrate degradation after adding nitrate to the strict anaerobic system. In the anaerobic granular sludge system containg nitrate denitrification was dominate and methanogenesis didn't start until the denitrification was accomplished. Nitrite appeared to accumulate during the denitrification. After inoculating little amount of aerobic active sludge to the anaerobic system, the rate of denitrification increased and the strength of nitrate accumulation decreased.To achieve a biological treatment process of low cost and high efficiency, a new combined wastewater treatment process combined the characteristic of the upflow anaerobic sludge bed and the aerobic biofilter (UASB/BF), was designed. The result indicated that the excellent effluent and effective nitrification guaranteed from the aerobic post-treatment which ran always in a low organic load followed by the UASB stage which played a great role of removing most of the organic pollutants, the two stages behave with each other harmoniously and stably. During the whole experiment the following hydraulic detention time were tested: 12 h, 10 h, 8 h, 5 h, corresponding to the organic loading of 1.0, 1.2. 1.5, 2.0 g COD L-1 d-1 and the total nitrogen loading of 62.5,75.3, 82.8, 159.3 mg N L-1d-1. When the hydraulic detention time was above 8 h, the COD removal remained stable with 19.57 mg · L-1 of the average effluent COD and 96.06% of the COD removal efficiency, and when the hydraulic detention time decreased to 5 h, the effluent COD increased only to 33.53 mg · L-1 with 92.14% of removal efficiency. With the different hydraulic detention time mentioned above, the corresponding TN effluent average is 5.38 mg · L-1, 6.30 mg · L-1, 6.56 mg · L-1, 11.25 mg · L-1 and the TN removal efficiency is 82.79%, 19.91%, 76.25% , 67.83 %, respectively. The overall SS in the final effluent which kept clear were kept below 13 mg/l. At least 85% of the incoming carbonaceous material was removed in the UASB stage, the total sludge production of thesystem varies between 0.14~0.17 kg TS/ kg CODremoval.The compactness and settleability of the granules growing under microaerobic condition observed was lower than that of the anaerobic granules and the distribution of the granules increased. The ratio of volatile suspended solid to total suspended solid was in the range of 77.5-83%. Even under microaerobic condition for at least 14 months, The granular sludge also remained a relatively high methanogenic activity.