結合鹼化與超音波法降解污泥中鄰苯二甲酸酯類(PAE)之研究

Abstract

鄰苯二甲酸酯類 (phthalate acid esters, PAEs) 被廣泛地運用於工業用途中，由於使用含PAEs產品可導致PAEs流至污水處理廠內，而實行污水處理過程中，高分子量PAEs如鄰苯二甲酸二正丁酯 (dibutyl phthalate, DBP)、鄰苯二甲酸二-(2-乙基己基) 酯 [di-(2-ethylhexyl) phthalate, DEHP] 與鄰苯二甲酸丁基苯甲酯 (butylbenzyl phthalate, BBP) 等容易附著於污泥顆粒表面上，隨之傳入污泥處理單元而不易處理，因此，利用污泥前處理程序去除污泥中所含之PAEs實有其必要性。本研究係結合鹼化與超音波程序做為前處理法降解污泥中之PAEs，期能有效減少污泥中PAEs之含量，以利後續生物處理之進行。 污泥中DBP、DEHP與BBP之初始濃度分別為718、215與8毫克/公斤-乾重，污泥前處理實驗係添加不同濃度之氫氧化鈉於污泥中，均勻攪拌24小時後進行超音波反應。超音波之頻率為20仟赫茲，超音波密度為1瓦特/毫升，強度為55瓦特/平方公分，污泥總固體濃度則為3%。中央合成設計 (central composite design, CCD) 設定鹼化與超音波前處理之變異參數分別為氫氧化鈉濃度 (0 - 8毫莫爾) 與超音波反應時間 (0 - 15分鐘)。 污泥經氫氧化鈉鹼化後，僅對DBP具明顯去除效果，DEHP與BBP則無顯著去除，同時，每加入1毫莫爾氫氧化鈉即可增加8.37毫克/公升之溶解性化學需氧量 (soluble chemical oxygen demand, SCOD)。結合鹼化與超音波前處理後，鹼化前處理對DBP去除之貢獻程度高於90%，且對SCOD上升之貢獻程度高於60%。由CCD與反應曲面法對SCOD上升之分析結果得知，最佳氫氧化鈉濃度與超音波反應時間分別為68毫莫爾與10分鐘。

Phthalate acid esters (PAEs) are widely used in various industries where the usage of PAEs containing products leads to the entrance of PAEs into wastewater treatment plant. During wastewater treatment processes, higher molecular weight PAEs including dibutyl phthalate (DBP), di-(2-ethylhexyl) phthalate (DEHP) and butylbenzyl phthalate (BBP) could be easily attached to the surfaces of sewage sludge and transferred to sludge treatment units. Therefore, sludge pretreatment to remove PAEs before sludge treatment and disposal is necessary. In this study, alkalization combined with ultrasound was adopted for removing the PAEs from sewage sludge. The initial DBP, DEHP and BBP concentrations in sewage sludge were 718, 215 and 8 mg/kg-dw, respectively. Pretreatments were carried out by adding sodium hydroxide (NaOH) individually for designed concentrations to sewage sludge and mixing gently for 24 hours followed by sonication. The frequency of ultrasound was 20 kHz with the ultrasound power density and power intensity of 1 W/mL and 55 W/cm2. The total solids (TS) concentration of the sewage sludge was 3%. The central composite design (CCD) was used in this study to find out the better operation condition which the designed parameters were NaOH concentration (0 - 80 mM) and sonication time (0 - 15 min). NaOH alkalization of sewage sludge led to DBP removal only; removals of DEHP and BBP were almost zero. Increase of the soluble chemical oxygen demand (SCOD) in pretreated sewage sludge was 8.37 mg/L per 1 mM NaOH addition. Alkalization was responsible for more than 90% of DBP removal and more than 60% in SCOD increase in the alkalization-sonication pretreatment. The optimal NaOH concentration and sonication time were estimated as 68 mM and 10 min based on the CCD and response surface plots, respectively.