STUDY ON A NOVEL PILOT SCALE VODF PROCESS OF BIOLOGICAL POLLUTANTS REMOVAL FOR DOMESTIC SEWAGE

Studying an efficient oxidation ditch (OD) process is still a popular topic in wastewater treatment plants (WWTPs). The study evaluated a pilot-scale novel saving energy and variable-velocity oxidation ditch with fine bubble (VODF) constructed in Xi'an 4th WWTP, which is used to enhance nutrient (nitrogen and phosphorus) removal. The pilot operated steadily at a treatment scale of about 50 m(3)/d for about 130 days. Activated sludge (AS) hydraulic performance by horizontal velocity (HV), structure character and dominant filamentous bacteria caused bulking and performing of nutrients removal were analysed. The results indicated that the novel OD can meet the requirement of saving energy under stable running state. Also the string effluent nutrient arrives at the first class in discharge standard of pollutants for municipal wastewater treatment plant (GB18918-2002). By changing ditch widths, different HVs in anoxic and aerobic zones of mixing activated sludge can be obtained. At the same time, the influence of the sludge structure on HV was studied in order to plan future ditch design and operation of aeration and compeller. According to our study, Microthrix parvicella was dominated filamentous bacteria causing limited bulking of AS. However, the polyporous structure captured the particle pollutants and improved effluent quality. Therefore, the concentrations of total chemical oxygen demand (TCOD), NH4+-N, total nitrogen (TN), total phosphorus (TP) and suspended solid (SS) of effluent were less than 50, 5, 15, 1 and 20 mg/1, respectively under the stable operations when SRT, HRT, DO concentrations at aeration bottom section, SS and water temperature were about 12-15 days, 11-15 h, 0.6-1.2 mg/l, 3000-5500 mg/l and 15-26 degrees C. The proposed VODF system was demonstrated to be an attractive enhanced biological nutrient removal process for WWTPs due to relatively high nutrient removal, robust sludge sediment and energy savings.