以中空纖維膜處理半導體廠化學機械研磨(CMP)廢水回收之研究-以模廠試驗為例

Abstract

本研究利用自行設計之中空纖維UF薄膜過濾程序模組，處理半導體廠之化學機械研磨(CMP)廢水並評估濾液品質做為水回收之用途，再將濃縮液收集後，以截流式壓濾過濾廢水濃縮液截留固體物。於試驗中了解各項操作變因對過濾效能之影響，並同時研究CMP廢水處理、回收濾液及研磨砥粒可行性之CMP廢水處理回收技術。 本實驗之Oxide-CMP廢水水質分析，含奈米粒徑之研磨砥粒，其表面帶高負電荷使其穩定懸浮於廢水中造成高濁度現象，具有高導電度、高溶解性矽酸等特點，其廢水中COD及DOC並不高。實驗結果顯示，以掃流式中空纖維UF薄膜操作在2 bar中等壓力，及短時間進水5分鐘反洗1.5分鐘，包含0.5分鐘逆洗和1分鐘沖洗程序，較能延緩通量衰減，提升產水通量，通量回復率佳，有利於長時間操作。UF薄膜過濾對於Oxide-CMP廢水中濁度去除率佳，可達99.7%以上，濾液濁度可降至1 NTU以下，但對於導電度、矽酸及溶解性有機物質去除率較差，其濾液品質已足夠做為次級回收水用途。以板框式壓濾機做為截流式過濾，其對於固體物攔截效果非常好，濁度及總固體物去除率可達99 %以上，濾液濁度也可降至1 NTU以下，也可以做為回收水之用。本實驗中無任何添加化學藥劑之前處理，以最後截流過濾所取得研磨砥粒濾餅，其成分為相當高純度之SiO2，具有回收再利用之效益，也可減少處理後污泥產生，以薄膜程序處理Oxide-CMP廢水同時回收濾液及研磨砥粒並且零排放是可行的。 最後，依據模廠實驗結果來估算每噸CMP廢水回收處理費用，與傳統化學混凝沈澱後直接排放做分析比較。以本實驗薄膜程序處理Oxide-CMP廢水處理成本為24.7元/m3，因處理水可用於水回收，可省去污水費6.8元/m3及自來水費12.7元/m3，其處理成本可降低為5.2元/m3，具有回收之經濟成本效益及潛力。CMP廢水經模廠試驗處理後之水質可達回收再利用之水質標準，可以此模廠操作條件做為實廠之設計基準。

This study used a pilot test of the UF systems with hollow fiber membrane module to continuously treat oxide-CMP wastewater in semiconductor fabrication. The wastewater was treated to divided into permeate and concentrate by UF membrane. Then concentrate was filtered by press filter to separate solids from wastewater. The filter water estimated to reuse water. The purposes of this study are to investigate the effect of the operational conditions on the filtration efficiency, and to investigate the possibility of recycling the filter water and abrasives of silica simultaneously. The characteristics of oxide-CMP wastewater have high conductivity, turbidity and dissolved silicon. This CMP wastewater contains nano-sized abrasives and the large amount suspended colloids of high negative charge, so the turbidity is very high in CMP wastewater. The results showed that the successful operation of cross-flow UF with hollow fiber membrane test, the ratio between filtration and backwash periods is 5:1.5 minutes at operation pressure of 2 bar. This backwash procedure combined with cross-flushing for 1minute followed by backwashing for 30 seconds. In this conditions, the frequency of backwash fits the long-term operation could reduce irreversible fouling, and the permeate flux decline. Also, the flux recovery increased, and the permeate water is more productive. The UF membrane filtration to the removal of turbidity reached about 99.7%, the turbidity could decrease to less than 1 NTU. But the removal of conductivity, dissolved silicon and DOC didn’t seem to be efficient. The permeate water could be recycled as reused water. The dead-end filtration by press filter that intercepted the solid matter is great effect. The removal of turbidity and total solid could reach over 99%, the turbidity is about under 1 NTU. The filter water can provide the purpose of reused water, too. This test was not added any chemicals, so the cake is high purified silica by dead-end filtration. It is probable that reclaimed permeate water and silica abrasive simultaneously, and zero-discharge in CMP wastewater treatment. Finally, the result of the pilot test that established the cost of treatment compared with the conventional chemical coagulation process. The treatment water costs NT$24.7 per cubic meter by membrane treatment process of the pilot test. Due to the treatment water used for reusing water, this process could save NT$6.8 per cubic meter for drainage costs and NT$12.7 per cubic meter for city water costs. The cost of treatment CMP wastewater will be NT$5.2 per cubic meter by membrane treatment process. It has benefit of CMP wastewater reuse that the treated water could reach the quality standard of reused water. This pilot test could be the basic design for scale-up.