超音波對超濾薄膜積垢生成之影響

Abstract

超音波輔助薄膜過濾程序，可以用來有效清除超濾薄膜過濾溶解性有機物所造成之積垢。本研究應用低頻超音波(20 kHz)及高頻超音波(40 kHz)清洗超濾薄膜積垢，藉由超音波之氣穴現象將不可逆積垢清除，並配合NaOH浸泡，達到更佳之去除效果。藉由膠體層析法(GFC)觀察在不同超音波及不同震盪時間下，對腐植酸分子大小變化，震盪時間愈久，凝聚現象愈明顯，且在高頻超音波下降解能力較好，因為波長短、擠壓停留時間短、產生氣穴現象較多、OH基相對也較多，較能將腐植酸破壞降解。 用超音波輔助薄膜過程序，不同孔徑(10 kD和100 kD)下，以不外加超音波清洗、低頻超音波清洗、高頻超音波清洗下，其通量回復率為37%、90%、82%和23%、80%、68%，小孔徑較大孔徑效果好且低頻清洗較高頻佳，大孔徑薄膜由於孔徑內部積垢量較多，難深入清洗，通量回復率以小孔徑較大孔徑薄膜為佳；低頻波長長且擠壓停留時間長，所產生的氣穴現象較能將表面積垢物帶走，能將薄膜清洗比較乾淨，薄膜表面積垢受低頻氣泡崩壞現象較高頻效果佳。 結合NaOH浸泡輔助清洗，以低頻超音波清洗、高頻超音波清洗下，其通量回復率分別提升至99%、94%和98%、92%，藉由OH基氧化水解有機積垢物，並將表面膠體層或孔隙內積垢分解，且在超音波發射瞬間可以觀察到氣泡將具濁度物體從表面帶出，使得超音波氣穴現象將積垢物帶離薄膜表面，獲得較佳的清洗效果。

The ultrasound assisted membrane filtration process can effectively remove fouling of ultrafiltration membrane filtration caused by dissolved organic matters product. In this study, low frequency (20 kHz) and high frequency (40 kHz) was applied for removal of fouling substances, cavitation phenomenon of ultrasound to remove irreversible fouling with the combination of NaOH to achieve better removal efficiency. By observing the gel filtration chromatography (GFC) with different ultrasound frequency and time, and the molecular size of humic acid, the longer time of ultrasound, coagulation phenomenon is more domination. Therefore, the degradation rate if better under high frequency of ultrasound, the shorter of the wavelength, the compress detention time is shorter with more dominant of cavitation phenomenon, and more OH radical produced, the humic acid can completely degrade. The ultrasound assisted membrane filtration process with different pore diameter under absent of ultrasound cleaning、low frequency and high frequency of cleaning, with flux recovery of 37%、90%、82% and 23%、80%、68% respectively. Small pore has better result than large pore while low frequency of ultrasound has higher cleaning efficiency. This is because fouling more likely to happen in large pore and it is hard to clean the inner part. Low frequency will have longer wavelength and compress detention timer, this will removed fouling of membrane surface. The combination of NaOH to assisted cleaning at low and high frequency ultrasound of cleaning, the flux recovery can enhanced up to 99%、94% and 98%、92%. The additional NaOH can make OH radical oxidized and hydrolysis the organic fouling. The data results suggest that cavitation associated with NaOH may produce more bubbles collapse phenomena, which can easily ensues fragmentation or abrasion on surface fouling.