Ti(SO4)2混凝去除水中有機物及其污泥回收再利用之研究

Abstract

混凝膠凝污泥處理為現今污水處理程序中增加成本及造成環境污染的問題之一，故本實驗以硫酸鈦（Ti(SO4)2）取代傳統混凝劑，進行混凝膠凝實驗，探討Ti(SO4)2 去除水中有機物腐植酸（HA）之效果，並將混凝膠凝後之污泥回收再利用，經鍛燒後製備可再利用之二氧化鈦 HA-TiO2，藉由吸附及光催化實驗處理染料Acid Green 25（AG25），了解污泥回收再利用之可行性。混凝膠凝實驗中，探討不同混凝劑量（50、100、150、200、300、400 mg/L）及不同pH值（3、5、7、9、11、13），分析濁度、色度、TOC及UV254，獲得混凝最佳操作參數；經不同溫度鍛燒製備之HA-TiO2，以 FE-SEM、XRD 觀察觸媒表面結構、晶相結構、觸媒型態等特性；最後進行吸附及光催化實驗，透過控制不同鍛燒溫度（400、600、800℃）、HA-TiO2添加劑量（0.5、1.0、1.5 g/L）、pH值（3、5.5、9）及 AG25初始濃度（10、30、50 mg/L），藉由分析其色度及TOC去除率，探討吸附及光催化之最佳操作參數。 實驗結果顯示，添加150 mg/L Ti(SO4)2 去除100 ppm 之 HA 有良好的去除率，當混凝劑量添加不足時，硫酸鈦無法有效中和腐植酸電性，造成顆粒間無法凝聚；添加過量時，溶液中會發生電性逆轉的情形，產生再穩定現象，使溶液之濁度上升。同時當pH ≤ 11時，各項參數都有90%以上之去除率，當pH=13時，Ti(SO4)2 水解離子以負電荷為主，無法中和腐植酸電性，並發生溶液再穩定之現象，無法產生膠羽，無法透過混凝膠凝將 HA 去除。 觸媒特性分析結果顯示，600℃下鍛燒之HA-TiO2產生較為完整之顆粒，以圓形球狀為主，排列較為整齊緊密，晶相以銳鈦礦為主，經比對後與市售P25光觸媒具有最相似之晶型組成，當鍛燒溫度上升至800℃ 時，晶相組成將由銳鈦礦轉為金紅石，且不論以何種溫度進行鍛燒製備之觸媒，其表面元素組成以鈦及氧佔較大之百分比，而相較於市售P25，自製之HA-TiO2所包含之雜質較多。 吸附實驗中，於初始溶液pH=3，添加1 g/L 600℃下鍛燒之HA-TiO2，色度及TOC去除率分別為84%及80%，可得到最佳吸附效果，當鹼性條件下， HA-TiO2與AG25因靜電相斥而吸附效果下降，而添加過量之HA-TiO2並不影響吸附結果；光催化實驗方面，初始溶液pH=3並添加1 g/L 於600℃ 下鍛燒之HA-TiO2，為最佳光催化操作參數，色度及TOC去除率約為80%，經脫附後色度及TOC去除率分別為15%及10%，當添加過多之光觸媒時，光遮蔽效應發生，導致光催化效果下降。AG25隨著初始濃度上升而去除效果下降，染料脫附量同時隨著AG25初始濃度上升而增加。

Sludge disposal is one of the most costly and environmentally problematic challenges of wastewater treatment worldwide. In this study, titanium sulfate (Ti(SO4)2) was used as coagulant to remove humic acid (HA) which represent organic matters. The coagulation performance was evaluated by adjusting the coagulation dosage (50, 100, 150, 200, 300, 400 mg/L) and the different initial pH (3, 5, 7, 9, 11, 13) of solution. After coagulation and flocculation process, the sludge was dehydrated in an oven at 105℃ for 12 hours, and then calcined for 24 hours to produce titanium dioxide (HA-TiO2). These photocatalyst were characterized by FE-SEM, EDS and XRD. The adsorption and photodegradation of Acid Green 25 (AG25) were investigated. The optimal operating parameters were analyzed by controlling the calcination temperature (400, 600, 800℃), initial pH (3, 5.5, 9), the dose of HA-TiO2 (0.5, 1.0, 1.5 g/L) and initial concentration of AG25 (10, 30, 50 mg/L) in adsorption and photocatalytic experiments. When adding 150 mg/L coagulant into HA at pH≤11, the colority, UV254 and TOC removals were 99.5%, 96.0% and 92.0%, respectively. HA-TiO2 prepared from sludge, which calcinated at 600 ℃ showed regular round particles with a dimension of around 20-30 nm. The crystal structures of HA-TiO2 were Anatase and Rutile, which were similar to P25. The results show that AG25 can be removed from adsorption reaction with 1.0 g/L HA-TiO2, which calcinated at 600℃. When pH at 3, the discoloration and mineration rate were 84% and 80%, respectively. The degradation rate of AG25 was decreased when the initial concentration of dye increased. AG25 can be removed from photocatalytic reaction with HA-TiO2 and the degradation and mineralization rate were 15% and 10%, respectively.