厭氧薄膜生物處理低濃度廢污水

Abstract

本研究架設一組5L連續攪拌式厭氧生物反應槽結合1.2L旁流式薄膜槽之厭氧薄膜系統，在無限長之污泥停留時間下採序列式進出流方式處理低濃度合成廢水，觀察水力停留時間分別為2、1、0.5天及不同有機負荷及進流濃度下之處理效能。在啟動階段，縮短水力停留時間或提高進流有機物濃度以增加有機負荷可使甲烷菌易形成優勢族群而生質能源產量增多。提高有機負荷或進流有機物濃度供給足夠有機物總量使得產氣中甲烷含量和整體甲烷產量升高，也因此致使槽體中微生物有較佳之甲烷轉換率。在有機負荷為0.8 kg COD/ m3•d且水力停留時間為12小時之下，此系統之COD去除率高達98%，而出流水中COD含量約為8 mg/L，其平均甲烷轉換率為0.21 L CH4/ g COD。薄膜處裡單元能完全攔截生物污泥且進一步去除厭氧生物反應槽出流水中之溶解性COD，使得出流水質佳。在系統操作溫度 30 ± 5℃ 之下，約有40% 之COD因產生氣體溶解於水中或無法處理隨出流水放流而無法回收，而甲烷回收率隨水力停留時間由1天降至12小時而由76% 減少至60 %，顯示反應之水力停留時間越短則甲烷回收率越低。當進流COD濃度為400 mg/L時有最佳每日甲烷產量1.04 L。因操作時間不夠久且厭氧生物反應槽之出流水污泥濃度低，使得此系統在操作期間無明顯積垢問題產生，通量在4 到 4.2 L/ m2•h下透膜壓力一直保持於2 Kpa以內。以序列式方式操作此系統需要最少2小時之反應時間以確保完全混合及消耗有機物。

A 5L continuous stirred anaerobic bioreactor couple with a 1.2L crossflow membrane bioreactor (AnMBR) with solids retention time (SRT) infinite days were setup for treating synthetic low-strength wastewater at hydraulic retention times (HRTs) of 2, 1 and 0.5 days using sequencing batch reactor (SBR) processing. At startup condition, shorter HRT or higher influent COD concentation increased biogas production due to higher organic loading rate (OLR) or enhanced dominance of methanogenics. Higher OLR or higher influent COD concentration offer enough organic matters that lead to greater methane content and methane production, therefore, it can also result better methane yield. The chemical oxygen demand (COD) removal averaged 98 ± 2% corresponding to an average permeate COD of 8 ± 6 mg/L was achieved at 0.8 kg COD/ m3•d OLR and 12 hours HRT and averaged methane yield was 0.21 L CH4/ g COD. MF flat sheet membrane completely retain biomass as well as further remove soluble COD present after biological treatment to produce a high quality effluent. At temperature 30 ± 5℃, approximately 40% of COD was not available for methane recovery as a result of the COD loss by dissolved methane and untreated COD. The fraction of methane recovered decreased from 76 to 60%, with the decrease of HRT from 1 day to 12 hours. Optimal methane production is 1.04 L per day at 400 mg/L influent COD concentration. No obvious fouling happened during the operation because of short duration time and clean effluent from the anaerobic bioreactor. Transmembrane pressure (TMP) was below 2 Kpa while flux was between 4 to 4.2 L/ m2•h (LMH). Each cycle of SBR operation needs at least 2 hours for completed mixing and reaction in this system.