環保固化材料結合輕質性骨材應用於固定化生物程序去除廢水碳與氮

Abstract

微生物固定化技術為利用物理或化學方法將微生物固定於載體內部。與傳統活性污泥法比較，微生物固定化技術具有占地面積小、污泥產量低、污泥濃度高、污泥停留時間長及不需進行迴流等優點，且在適當的水力傳導特性下微生物固定化之載體其內外可以產生不同濃度之溶氧梯度，使載體表面可進行好氧反應如硝化作用，而內部則可進行厭氧之脫硝作用。 應用於微生物固定化之載體可分為天然及合成兩種，天然載體對生物毒性小但易受微生物分解且機械強度不高，而合成載體雖然機械強度高，但製作過程通常較為繁複且使用之化學藥劑可能對生物具有毒性。本研究使用一農業資源化材料所製成之固化粉末及經高溫燒結之輕質性骨材為微生物固定化之載體，其中固化粉為主要之載體材料，而輕質性骨材則為增加載體之水力傳導特性之用。 本研究先以水力傳導特性及抗壓強度實驗測試固定化微生物中各材料之最佳配比，經測試重量比1:2:2 (污泥：輕質性骨材：環保固化材料)之比例可得一水力傳導係數介於 0.01~0.001 cm/s 固定化微生物載體，該載體於水中養護7天後可達20 kg/cm2之抗壓強度。 溶出實驗第一天其化學需氧量(COD)溶出值大於100 mg/L，導電度大於2 mS/cm，pH值大於11.5，濁度則高於80 NTU，但除了pH在20天後溶出實驗之讀值仍高於10以外，其於各項參數之測值於5天後皆顯示溶出量已非常微小且趨於穩定。 操作參數實驗顯示水力停留時間(HRT)、水中溶氧量、碳氮比(C/N)、填充率及曝氣模式皆對去除效果有影響，其中HRT = 6 hr到HRT = 18 hr， COD去除率可提升6%，硝化效率可提升11%，總氮去除率可提升11%。溶氧由2~4 mg/L提升至飽和溶氧時，硝化效率可提升21%，總氮去除率可提升20 %。C/N 由4增加為 12時，硝化效率可提升12%，總氮去除率可提升11%。填充率由6.3%增加至22%時，硝化效率可提升40%，總氮去除率提升24%。而1:1之曝氣模式則比連續曝氣模式之總氮去除率提升4%。加入活性污泥可有效提升硝化效率及總氮去除率，在HRT = 6 hr時，添加活性污泥的穩定硝化效率可提升約16%，總氮去除率可提升超過30%。

Cell immobilization is a technique of fixing microorganisms or living cells in a suitable matrix through physical or chemical reaction. In wastewater treatment, the technology of immobilization microbial cell dominant over conventional activated sludge processes in several ways, such as lower requirement of land space, lower biomass production, higher sludge concentration, longer sludge retention time and no sludge recycle. Moreover, when an adequate hydraulic conductivity is achieved, immobilized microbial cell will be able to carry out both aerobic and anaerobic reactions at the same time by using the difference of dissolved oxygen concentration at the surface and inside the cell. The matrix of immobilized microbial cell can be categorized into two groups: natural and synthetic. Natural matrices posess the advantage of smaller biological toxicity but lacks mechanical strength and is easily decomposed by microorganism. Synthetic matrices possess a better performance in mechanical strength, but the process of production may be complex and the chemicals used during the production may not be environmental friendly. This study used agriculture waste coagulant and lightweight aggregates for the production of microbial cell. With agriculture waste coagulant as the main matrix, lightweight aggregates are added for improvement of hydraulic conductivity. In this study, compression tests and permeability tests are carried out to determine the best ratio between activated slude, lightweight aggregate and agriculture waste coagulant. Results showed that at a ratio of 1:2:2 (activated slude: lightweight aggregate: agriculture waste coagulant), we can obtain a cell with hydraulic conductivity between 0.01~0.001 cm/s, and the compressive strength of 20 kg/cm2 can be achieved after 7 days of curing. The dissolution test showed that the immobilized cells elute COD over 100 mg/L, conductivity over 2 mS/cm, turbidity over 80 NTU and pH over 11.5 after the first day. However, the elute concentration of COD, conductivity and turbidity are found to be stable after five days of test, pH remained over 10 after 20 days of elution. Acclimation of microbial cells is found to be better by placing them in activated sludge than in synthetic wastewater, with COD removal rate increased from 90% to 95%，nitrification rate rate increased from 43% to 62%，TN removal rate increased from 42% to 55%. Experiment of different operating parameters showed that HRT, dissolved oxygen, C/N ratio, packing ratio and aeration mode can affect the efficiency of nitrification and denitrification. Nitrification rate and TN removal rate were enhanced 11% and 11% respectively when HRT was adjusted from 6 hr to 18 hr. When dissolved oxygen increased from the range of 2~4 mg/L to saturation concentration, the nitrification rate was enhanced 21% and TN removal rate was enhanced 20%. When C/N ratio increased from 4 to 12, nitrification rate was enhanced 12% and TN removal rate was enhanced 11%. The increase of packing ratio from 6.3% to 22% yielded an increase in nitrification rate and TN removal rate, which were 40% and 24% higher, respectively. And the aeration mode of 1 hour on and 1 hour off resulted in a 4.4% increase in TN removal rate compared to continuous aeration. When combining with suspended acticated sludge, nitrification rate and TN removal rate were enhanced 16% and 30% respectively while HRT was set at 6 hr.