配合混凝前處理之截流式微過濾薄膜回收處理淨水場砂濾反沖洗水之研究：實驗室評估

Abstract

為解決台灣地區淨水場砂濾反沖洗水回流至淨水處理單元造成加藥量控制不易和產生原蟲及化學物質長期累積，以及颱風暴雨期間，砂濾反沖洗水回流造成淨水場處理單元負荷過大的問題，本研究將以截流式(Dead-end)微過濾薄膜去除砂濾反沖洗水中之懸浮物質及微生物等污染物質，以利過濾水經消毒後可直接作為公共給水；同時微過濾薄膜將配合不同前處理方法，期望能增加薄膜之產水率。本研究主要使用新竹第一淨水場反沖洗水與東興淨水場反沖洗水，分別利用0.5 □m及1.0 □m之微過濾薄膜，以固定壓力(0.65 kgf/m2)抽真空方式，將此兩股砂濾反沖洗水通過薄膜處理後供水。而在前處理方法方面，分別採用沈澱前處理與混凝/膠凝前處理。 結果顯示，當反沖洗水中之次微米級(sub-micron scale)顆粒粒徑與薄膜孔徑大小相近時，將會使薄膜產生嚴重之孔洞阻塞(pore blocking)，且無法藉由薄膜反沖洗來回覆既有之通量。而兩淨水場反沖洗水經截流式微過濾薄膜直接處理後之水質在濁度、大腸桿菌數及總菌落數方面可符合我飲用水水質標準，但溶解性有機物去除效率不佳。在前處理方法對薄膜通量之影響方面，先行將反沖洗水沈澱後再經薄膜過濾，於短期操作下雖可使薄膜之通量提高，但隨著操作時間之增加卻會產生極嚴重之孔洞阻塞，並不利於薄膜長期操作。另外，新竹第一淨水場反沖洗水經混凝/膠凝後直接薄膜過濾將能有效提升通量，且當混凝劑加藥量與瓶杯試驗最佳加藥量相同時，薄膜通量將有最佳提升效果；而東興淨水場之反沖洗水經混凝/膠凝後，不論加藥量為何，薄膜通量均無法有效提升，造成上述兩淨水場反沖洗水實驗結果差異之原因在於影響薄膜混凝/膠凝通量之因素相當複雜，其結果是許多影響因子之交互作用而成，如顆粒大小、混凝/膠凝機制、膠羽結構皆會造成薄膜通量之影響。

Recycling of the spent filter backwash water (SFBW) has been a burden for water treatment plants due the difficulty in chemical dosing especially during the typhoon and heavy storms and the accumulation of protozoa. The objective of this investigation is to use membrane technology, a dead-end MF, to remove the suspended solids and the microorganism particularly Cryptosporidium and Giardia from the SFBW. The goal is to use the membrane permeate as drinking water after disinfection. Different pretreatment methods were performed to SFBW before the membrane filtration to enhance the membrane flux. In this investigation, the SFBW were collected from Hsinchu First Water Treatment Plant and Tonghsing Water Treatment Plant. The SFBW was filtered through a polyterafluoroethylene (PTFE) membrane of pore size 0.5 □m and 1.0 □m at low vacuum pressure (0.65 kgf/cm2). Sedimentation and coagulation/flocculation were used as pretreatments. The result indicates that the flux declined seriously when the size of the sub-micron particles in the SFBW is close to the pore size of the membrane due to pore blocking. The quality of membrane permeates of SFBW from both water treatment plants, namely, turbidity, total coliform and total bacteria counts, complies with the current Drinking Water Quality Standard of Taiwan EPA. The DOC was reduced slightly after membrane filtration. Sedimentation pretreatment improved the membrane permeate flux in the beginning, but it caused serious pore blocking in the long run. On the other hand, pretreatment by coagulation/flocculation improved the membrane permeate flux of the SFBW from Hsinchu First Water Treatment Plant. However, it did not improve the membrane flux of the SFBW collected from Tonghsing Water Treatment Plant due to the complex factors such as particle size, coagulation condition, and fractal dimension of floc.