模型廠薄膜生物反應系統處理低碳氮比廢水之研究

Abstract

薄膜生物反應系統 (Membrane bioreactor, MBR) 為結合傳統活性污泥法與薄膜分離技術處理廢污水之新技術。MBR相較於傳統生物處理方式具有佔地面積小及污泥產量少等優點，且其高品質的出流水質可以符合未來更嚴格之放流水標準且達到水回收之目標。然而MBR目前最大的缺點即薄膜積垢現象，薄膜積垢會造成滲透液量下降，因此必須更頻繁清洗且替換薄膜因而增加操作成本。薄膜積垢乃由多種因素造成，其中又以操作條件及污泥特性最為重要。因此， MBR操作成功與否，薄膜通量與其廢水特性之影響為一重要關鍵。本研究即針對MBR應用於低碳氮比廢水進行模型廠試驗，並探討薄膜通量對於模型廠MBR處理低碳氮比廢水之影響。 由實驗室試驗結果顯示低碳氮比廢水具氨氮降解性，且污泥停留時間控制為8天時，其仍可行硝化作用，將氨氮完全硝化。MBR模型廠試驗於水力停留時間為1.92小時下控制薄膜通量為5.95、7.14及8.93 L/m2-h (LMH)，污泥停留時間為12天及10天。平均進流水質TSS、COD、BOD5及NH3-N為60、75、46及40 mg/L，經MBR處理後其處理效率分別為89、82、90及95%，且薄膜通量對其處理效率影響不明顯。透膜壓力隨著薄膜通量的增加而上升。在污泥停留時間控制為10天且薄膜通量為7.14 LMH時有最小之薄膜積垢速率5.33x1011m-1d-1且每單位薄膜面積有最大滲透液量12.86 m3/m2，故為本模型廠研究之最佳操作條件。

The membrane bioreactor (MBR) is a new technology for wastewater treatment, in which membrane filtration is combined with the conventional activated sludge process. The advantages of MBR over conventional treatment include small footprint and less sludge production. Moreover, MBR produces superior effluent quality, capable of meeting more stringent future discharge limits and wastewater reclamation goals. One of the major disadvantages of MBR is membrane fouling, which is related to the critical flux. Membrane fouling leads to the permeate flux decline, making more frequent membrane cleaning and replacement necessary which increases operating costs. Several factors can contribute to membrane fouling, out of which operation parameters and sludge characteristics are reported as the foremost. Therefore, for a successful MBR operation it is essential to quantify the effect of membrane-flux and the wastewater characteristics on the performance of MBR. In the present study is to confer the effects of membrane flux on the performance of a pilot-scale membrane bioreactor treating industrial low C/N wastewater. From the result of bench study, the low C/N wastewater can be degraded NH3-N even when SRT was operated under 8 days. The conditions of MBR pilot were under HRT at 1.92 hrs, membrane flux at 5.95, 7.14 and 8.93 L/m2-h (LMH), SRT at 12 and 10 days. The average TSS, COD, BOD5 and NH3-N concentrations in the influent of MBR pilot were 60, 75, 46 and 40 mg/L, respectively. As a result of MBR operation, TSS, COD, BOD5 and NH3-N were removed maximally of 89, 82, 90 and 95%, respectively. It was found that the effect of pretreatment using coagulation and flocculation on MBR performance was insignificant. The trans-membrane pressure (TMP) is found to increase with increase in membrane-flux. The lowest fouling rate of 5.33x1011m-1d-1 associated with a highest permeate/membrane-area ratio of 12.86 m3/m2 was obtained under SRT of 10 days and flux of 7.14 LMH. Based on the experimental results, a SRT of 10 days with a flux of 7.14 LMH is selected for the pilot-scale MBR operation.