Khan Mohiuddin, Danielsen Steffen, Johansen Katja, Lorenz Lindsey, Nelson Sara, Camper Anne
a Department of Chemical Engineering and Bioengineering , Washington State University , Pullman , WA , USA.
Biofouling. 2014 Feb;30(2):153-67. doi: 10.1080/08927014.2013.852540. Epub 2013 Dec 11.
Application of environmentally friendly enzymes to remove thin-film composite (TFC) reverse osmosis (RO) membrane biofoulants without changing the physico-chemical properties of the RO surface is a challenging and new concept. Eight enzymes from Novozyme A/S were tested using a commercially available biofouling-resistant TFC polyamide RO membrane (BW30, FilmTech Corporation, Dow Chemical Co.) without filtration in a rotating disk reactor system operated for 58 days. At the end of the operation, the accumulated biofoulants on the TFC RO surfaces were treated with the three best enzymes, Subtilisin protease and lipase; dextranase; and polygalacturonase (PG) based enzymes, at neutral pH (~7) and doses of 50, 100, and 150 ppm. Contact times were 18 and 36 h. Live/dead staining, epifluorescence microscopy measurements, and 5 μm thick cryo-sections of enzyme and physically treated biofouled membranes revealed that Subtilisin protease- and lipase-based enzymes at 100 ppm and 18 h contact time were optimal for removing most of the cells and proteins from the RO surface. Culturable cells inside the biofilm declined by more than five logs even at the lower dose (50 ppm) and shorter incubation period (18 h). Subtilisin protease- and lipase-based enzyme cleaning at 100 ppm and for 18 h contact time restored the hydrophobicity of the TFC RO surface to its virgin condition while physical cleaning alone resulted in a 50° increase in hydrophobicity. Moreover, at this optimum working condition, the Subtilisin protease- and lipase-based enzyme treatment of biofouled RO surface also restored the surface roughness measured with atomic force microscopy and the mass percentage of the chemical compositions on the TFC surface estimated with X-ray photoelectron spectroscopy to its virgin condition. This novel study will encourage the further development and application of enzymes to remove biofoulants on the RO surface without changing its surface properties.
应用环保型酶去除薄膜复合（TFC）反渗透（RO）膜生物污垢，同时不改变RO膜表面的物理化学性质，是一个具有挑战性的新概念。在一个运行58天的旋转盘式反应器系统中，使用市售的抗生物污垢TFC聚酰胺RO膜（BW30，FilmTech公司，陶氏化学公司），在未进行过滤的情况下，对诺维信公司的8种酶进行了测试。运行结束时，用三种最佳酶——枯草杆菌蛋白酶和脂肪酶、葡聚糖酶以及基于聚半乳糖醛酸酶（PG）的酶，在中性pH值（约7）和50、100、150 ppm的剂量下，对TFC RO膜表面积累的生物污垢进行处理。接触时间为18小时和36小时。活/死染色、落射荧光显微镜测量以及对酶处理和物理处理的生物污染膜的5μm厚冷冻切片显示，100 ppm的基于枯草杆菌蛋白酶和脂肪酶的酶以及18小时的接触时间最适合从RO膜表面去除大部分细胞和蛋白质。即使在较低剂量（50 ppm）和较短孵育期（18小时）下，生物膜内可培养细胞数量也下降了超过5个对数。100 ppm和18小时接触时间的基于枯草杆菌蛋白酶和脂肪酶的酶清洗可将TFC RO膜表面的疏水性恢复到初始状态，而仅进行物理清洗会使疏水性增加50°。此外，在这种最佳工作条件下，对生物污染的RO膜表面进行基于枯草杆菌蛋白酶和脂肪酶的酶处理，还能将原子力显微镜测量的表面粗糙度以及X射线光电子能谱估计的TFC膜表面化学成分的质量百分比恢复到初始状态。这项新研究将推动酶在去除RO膜表面生物污垢同时不改变其表面性质方面的进一步发展和应用。
