| 摘要: | 活性污泥程序 (activated sludge process, ASP) 由於操作方便、成本低廉、技術成熟，現為最普遍之廢污水二級處理技術，但常遭遇污泥膨化 (bulking) 問題，導致放流水質惡化。傳統上以設置選種槽等方式改善上述問題，本研究則嘗試利用自製之小粒徑、低成本且不需回收之淘洗細砂 (elutriated microsand)，透過載體嵌合 (carrier docking) 以物理方式增加污泥比重，改善其沉降性。本研究自行研發連續式光柵沉降管柱 (continuous-light grid settling column, C-LGSC) (內徑長20 cm、有效深度143 cm)，評估載體嵌合技術，改善造紙廢水活性污泥沉降性之成效，並與本研究群前期研究，批次量筒 (內徑長6 cm、有效深度36 cm)、批次光柵沉降管柱 (B-LGSC) (內徑長12 cm、有效深度100 cm) 試驗結果評比。
本研究首先分析中部某造紙廢水處理場，自2000年11月至2002年10月，連續24個月之ASP操作數據。將放流水懸浮固體 (suspended solid, SS)SS與化學需氧量 (chemical oxygen demand, COD) 兩者月平均值進行線性迴歸，顯示放流水每單位SS貢獻2.6單位COD，且曝氣池生物分解的極限為52.1 mg/L COD。根據放流水質是否違反國家標準，並可將24個月的操作分為穩態與非穩態期；於穩態期間，SS違反放流水標準之風險為COD的3倍，且水質異常係導因於處理流量瞬間大幅變動 (小時尖峰係數達2.2)，因此增加生物膠羽的比重，改善終沉池污泥沉降性實為提升處理成效之關鍵。
測試自行開發之C-LGSC時，於批次沉降試驗完成後，在三個不同深度連續進流污泥，結果顯示，進流點深度不當設計將影響污泥沉降試驗，而良好之進流點約為液面下3/4有效水深的位置，對沉降之干擾最小，與實場終沉池之進流點類似。
接著利用C-LGSC進行批次沉降試驗，再進行固體通量分析 (solid flux analysis)，推算ASP系統理論設計與操作參數，結果終沉池表面積為1,800 m2，固體停留時間 (solid retention time, SRT) 為12 days，與前期1-L量筒及B-LGSC沉降試驗比較，顯示C-LGSC試驗顯著減少管壁效應。唯長期操作數據之分析結果，顯示該場之處理風險，可能導因於終沉池表面積過小及SRT值過短 (實場：900m2、6days)。
本研究最後以6種載體劑量進行三重複批次沉降試驗，若以未添加載體之污泥初始沉降速度 (initial velocity, V0) 為控制組，試驗組載體劑量為8 ~ 42 % (w/w)，結果顯示各組試驗之V0增加33 ~190 %，且V0增加比例隨載體劑量增加而遞增，上澄液之SS與COD亦呈改善趨勢。以固體通量法進一步分析載體嵌合成效，結果顯示終沉池表面積可縮減0.5 ~ 4.3倍，SRT可由12 days降至4 ~ 8 day，且載體劑量達16 % 時，即可有效改善實場終沉池表面積過小與SRT過短的缺點，但與前期研究結果交叉分析，顯示MLSS濃度、污泥沉降特性與載體粒徑，皆為影響載體嵌合技術成效之因素。
The activated sludge process (ASP) has been widely accepted as a secondary technology for wastewater treatment due to its operational convenience, low cost, and technical maturity. However, ASP often experiences bulking sludge problem, which deteriorates effluent quality. Conventionally the problem is approached by placing biological selectors preceding the ASP. This study instead proposes an alternative solution namely carrier docking to enhance sludge settleability by physically increasing sludge density with non-recovered elutriated microsand produced by using an elutriating method in our laboratory. We also developed a light grid settling column capable of continuous operation (C-LGSC) (20 cm ID × 143 cm EH) for evaluating sludge settleability. The settling data obtained were analyzed and compared with the data tested with 1-L graduate cylinders (6 cm ID × 36 cm EH) and the batch LGSC (B-LGSC) (12 cm ID × 100 cm EH) from our previous coworkers.
We first analyzed a set of 24-month data between November 2000 and October 2002. Linear correlation of monthly averages in effluent suggests, on the long-term basis, one unit of suspended solid (SS) contributing 2.6 unit of chemical oxygen demand (COD) in effluent and a biodegradation limit of 52.1 mg/L COD for the ASP treating pulp-making wastewater. The 24-month data were separated into 3 periods: stable, outbreak, and recovered period. During the stable period, the frequency of exceeding the national discharge standard in SS was three times of the one in COD. Hydraulic analysis showed dynamically wide fluctuation with a hourly peak factor (PF) of 2.2 being imposed on the 2nd settler. We concluded that higher density of biofloc structure is crucial to cope with the fluctuation for stable effluent quality.
The C-LGSC developed in this study was evaluated for continuous operation. Upon completion of batch settling for 30 minutes, sludge suspension was fed into the column continuously at three specific locations of different depths. In order to minimize hydraulic disturbance from the continuous feeding, it was clearly shown that sludge should be fed directly into sludge blanket at a depth about 3/4 of the effective height below the overflow weir. This situation is in agreement with the configuration of the full-scale final sedimentation tank.
We then conducted a series of batch C-LGSC tests and performed a solid flux analysis also developed in this study to estimate several key system parameters. The analysis resulted in a surface area of 1,800 m2 for the final settler and an SRT of 12 days for the ASP. The settling-controlled SRT should be compared with the SRT required for biological degradation and a longer one should be used for design and operation. Comparing with the test data obtained from our previous tests, it can be concluded that the wall effect adhered to C-LGSC was well eliminated. Along with the fact concluded from the 24-month operational data analysis, the solid flux analysis suggested that, for the full-scale units, surface area was undersized by 50% for the 2nd clarifier (900 m2) at a short SRT (6 days).
At last, we performed a series of batch settling tests using the C-LGSC at 6 different doses (8 ~ 42 % by weight) of microsand carrier each with triplicate runs. Using the test without carrier addition as the control, all the microsand-docked tests showed a significant increase of 33 ~ 190 % in initial settling velocities (Vo). Higher doses yielded higher Vo increases with a marginal trend at the higher ends of the doses. We also performed a solid flux analysis and concluded that carrier addition at a dose of 16 % may be used to compensate the inadequate design in surface area and SRT. However, comparative analysis with the previous tests indicated that MLSS concentration, settling property of the sludge, and carrier diameter all are important factors affecting the docking performance. |
