以臭氧處理煉焦廢水之效能評估

Abstract

摘 要 傳統煉焦廢水以生物處理為主，生物處理單元之處理功能有其極限，因此須考慮預處理技術及生物處理單元後之高級氧化處理技術。臭氧化處理由於不產生污泥及餘臭氧可快速自解不會造成二次污染，相對於其他高級氧化處理方法有其環境上之優勢。本研究藉由臭氧化改變廢水特性，進一步經由此特性對生物處理程序中，基質降解與菌相影響之深入瞭解，探討臭氧化之應用時機和方式。 臭氧化易受pH值影響反應機制，形成不同性質之反應產物，造成生物處理之複雜性，所以本研究臭氧化實驗採用氣泡管柱臭氧化反應器，在Semi-Batch操作下，以pH值及臭氧化時間之效應，進行不同臭氧程序反應動力及特性探討，並進一步以臭氧化結合生物處理程序操作。預臭氧化結合活性污泥(O3/ASP)之操作以BOD5�TOC、比攝氧率及比基質降解為操作指標，後臭氧化結合生物活性碳處理(O3/BAC)則以生物毒性、BOD5�TOC及基質降解為操作指標。同時藉由分子生物技術對生物處理適用菌相之瞭解與掌握，以助提昇臭氧化結合生物處理程序之操作效益。 實驗結果顯示預臭氧氧化初期以基質減少為生物降解主要影響因子，pH=4之臭氧氧化條件結合生物處理則有助於提高生物降解性。預臭氧化廢水馴養後(O3/ASP)之菌相增加分解PAH、苯甲醛、脫氨基水楊酸、poly(3-hydroxybutyrate-co-3-hydroxyvalerate)及脫硝之菌屬。比較不同pH臭氧操作條件結合生物處理，以pH=4之生物處理(O3/ASP)菌相較多樣化。顯見預臭氧化結合生物處理增加菌相之多樣性生態。 後臭氧化若以礦化為目的則以中性臭氧化條件之反應速率最快。由BOD5�TOC生物降解性指標看，臭氧化顯然提昇生物可分解性，以pH=9較佳；水蚤急毒性則在臭氧化條件為中性時，毒性減量最佳。總體而言後臭氧化操作以中性pH為最適化。由菌相分析瞭解後臭氧結合生物處理，以硝化、脫硝類菌屬、降解酚還原硝酸塩等菌屬為主要菌種族群。後臭氧結合BAC之處理效率約有10%提昇空間，若能加強硝化及馴化可分解環狀物質之菌屬，則仍有提昇生物降解效率之空間。

Abstract The activated sludge process is the traditional method to treat coke oven wastewater which may have some drawback and inadequate. In order to treat the high pollution strength wastewater, the pre and post -treatment techniques were considered, of which ozonation was focused. According to the highly oxidative nature, ozone can oxidize pollutants without generating hazardous end products, and the surplus ozone gas can self-decompose quickly. Ozonation has been applied in water treatment for decades and the results are demonstrated successfully. Ozone applied in wastewater treatment has shown the feasibility and treatability in recent years. This merging technology may expend from treating textile wastewater to hard-to-degrade wastewater, i.e. coke oven wastewater. The ozonation experiments are the main focus of this study, some controlling factors are discussed as well. The level of pH would affect the reaction modes of ozonation, direct or free radical reaction mechanism, the treated coke oven wastewater under various pH conditions entering into biological system would have impacts on the microbial system. Therefore, the characters of the ozonation substrate depletion, the relationship between microbial community structure and substrate depletion are investigated. This study also investigated the amount and timing of ozone dose applied into reaction system. The ozonation experiments were conducted in a semi-batch bubble column reactor. The treated wastewater was discharged into biological system to investigate the biodegradation. The biodegradable index of pre-ozonation combined activated sludge process (O3/ASP) is based on BOD5/TOC, specific oxygen uptake rates, and specific substrate depletion. The index of post-ozonation combined biological activated carbon is based on bioassay, BOD5/TOC and substrate depletion. Meanwhile, by using the molecular biotechnology to explore the microbial community would benefit to understand the process of combination of ozonation and biological treatment. On the early stage of pre-ozonation, experiments results reveal that the substrate reduction is the major effect factor to the biodegradation; at pH = 4, the combination of ozonations and biological treatment would enhance the biodegradation. An acclimated microbial community from post-ozonation wastewater (O3/ASP) increases degradation of PAH 、 benzaldehyde、aminosalicylate、poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and ammonia. Comparing the different pH operating condition of ozonation, under the conditions of ozonation combined with biological treatment and O3/ASP at pH = 4 could result in various microbial community. Thus, it could be concluded that the combination of pre-ozonation and biological treatments would increase the variety of microbial community. Taking BOD5/TOC as a biodegradation index, it could be observed from the results that ozonation could enhance biodegradation, and pH=9 is the optimum conditions. In the Daphnia Acute toxicity test, the toxicity reduction was significant under neutral condition. Using microbial community structure to reveal the process of the combination of post-ozonation and biological treatments is still based on the bacteria groups, such as nitrified bacteria and denitrifying bacteria. Although, there is not significant result comes from the combination of post-ozonation and BAC, the rate of biodegradation still can be improved if the nitrifications and amount of bacteria which comes from the acclimated aromatic compound have been enhanced or added in this experiment.