Anaerobic Immobilization Biotechnology for Treating Low Strength Synthetic Wastewater: Effect of HRT and COD Concentration on Treatment Performance

厭氧生物處理程序能產生甲烷作為生質氣體，且相較於好氧生物處理，其耗能與廢棄污泥產量皆較低，故應用於處理都市污水具有發展潛勢，然而，厭氧微生物生長緩慢，使得處理低強度都市污水需較長的水力停留時間，且生物固體易流失，因此研究將生物固定化技術(Entrapped mixed microbial cell, EMMC)應用於厭氧處理程序，利用生物固定化技術大幅提高微生物濃度與污泥停留時間，縮短水力停留時間，克服厭氧生物處理程序應用於低強度都市污水處理上的限制。 研究建置一實驗室規模的24 L單槽連續式反應槽之厭氧固定生物系統，在35℃下處理低強度脫脂奶粉(Non-fat dry milk, NFDM)合成污水，操作參數包含有機負荷OLR (0.6、1.2 kg/m3/d)、水力停留時間HRT (4、8、16、32小時)、以及進流COD濃度(200、400、800、1600 mg/L)，探討各項操作參數對於厭氧固定生物系統除碳及產氣效能的影響。 厭氧固定生物系統連續操作381天以上，整體效能達到80%以上之COD去除率以及44.7%以上之甲烷回收率。當HRT在16小時以上，COD去除率能穩定維持在90%以上，當HRT小於8小時，COD去除率明顯降低；系統產氣受到進流COD濃度影響，在固定HRT下甲烷含量與氣相甲烷產量隨進流COD濃度降低而減少，但在進流COD濃度200 mg/L下仍能維持59%以上的甲烷含量，使甲烷回收率在HRT 4小時仍能維持44.7%以上；而OLR的提升有助於提高系統的除碳產氣效率，對於VRE與甲烷產率有正相關的效果。 整體而言，厭氧固定生物系統優於典型厭氧處理系統，較高的SRT為系統提高優勢，其處理成效顯示出厭氧固定生物系統在不同的操作條件下均能達到較高的COD去除率、甲烷含量與甲烷回收率，因此，結合生物固定化技術與厭氧處理程序，在適當的操作條件下，具有處理低濃度都市污水的發展潛力。Anaerobic biological treatment processes (ABTPs) can produce methane as biogas during wastewater treatment, and consume less energy and waste less sludge compared with aerobic biological processes. As a result, ABTPs show promise in treating domestic wastewater. However, the slow growth rate of microorganism, the requirement of longer hydraulic retention time, and the easily washed-out biosolids have been found while ABTPs treat low-strength domestic wastewater. Therefore, this study employed an immobilization biotechnology of entrapped mixed microbial cell (EMMC) to ABTPs. The immobilization biotechnology was used to enhance biomass concentration, highly increase sludge retention time, and shorten hydraulic retention time which overcome the restraints of ABTPs when treating low-strength domestic wastewater. A laboratory-scale anaerobic immobilization bioreactor system (AIBS) which contained single continuous stirred-tank with 24 L volume was constructed and used to treat low-strength synthetic wastewater of non-fat dry milk (NFDM) at 35℃.The operation parameters including organic loading rate (0.6, 1.2 kg/m3/d), hydraulic retention time (4, 8, 16, 32 h), and influent COD concentration (200, 400, 800, 1600 mg/L) were used to evaluate the effect of each parameter on carbon removal and methane production of AIBS. After continuous operation of more than 381 day, total COD removal rate and methane recovery efficiency were higher than 80% and 44.7%, respectively, over the range of values tested HRT and COD. When HRT operated above 16 h, the COD removal rates were stably higher than 90%. When HRT operated below 8 h, the COD removal rates significantly decrease. Methane production during the AIBS operation was affected by influent COD concentration. At a constant of HRT, methane content and methane production rate decreased with decreasing of influent COD concentration. However, the methane content was stably higher than 59% when influent COD concentration of 200 mg/L. Hence, the methane recovery efficiency was higher than 44.7% when HRT operated below 4 h. An increase in OLR improved the efficiency of carbon removal and methane production, and OLR has a positive correlation with both VRE and methane production rate. In conclusion, the performance of anaerobic immobilization bioreactor system is better than typical anaerobic treatment process. The advantage of higher SRT improves AIBS. From experimental results, AIBS performs higher COD removal rate, methane content, and methane recovery under different operating conditions. Therefore, the combination of immobilization biotechnology and anaerobic biological treatment process could be potentially used for treatment of low-strength domestic wastewater under appropriate operating conditions