Long-term direct ultrafiltration without chemical cleaning for purification of micro-polluted water in rural regions: Feasibility and application prospects

Water treatment technologies that feature a simple operation, affordable cost, and low chemical addition are necessary to achieve the goal of supplying clean water to rural regions. In this study, an automated-control direct ultrafiltration (UF) process without chemical cleaning was operated and investigated using the micro-polluted surface water at a mountain village in China as feed. During the approximately 2.5-year operation, the UF process operated steady without pretreatment and chemical cleaning, and clean drinking water that met the Chinese drinking water standard (GB 5749-2006) was continuously available. Despite occasional shock loading (84.7 NTU), the turbidity (the major contaminant of feed water) was low (0.3 +/- 0.1 NTU) in the effluent, and the filtration resistance remained at (14.7 +/- 0.7) x 1012 m(-1) except for the initial increase. Compared with organic substances, inorganic substances were dominant constituents of cake layer. Alumina or silica particles were easily removed by frequent backwashing and were distributed on the outer surface (newly formed) of cake layer. In contrast, the bulk cake layer was predominantly composed of CaCO(3 )scales, indicating its major role in membrane fouling. Regarding organic fouling, low-molecular-weight hydrophilic carbohydrate-like compounds, which were related to bacterial activities, were dominant compositions (91.5%). Proteobacteria made a major contribution to bacterial communities (52.2%). Because of the simple process (almost unattended) and no chemical cleaning, the operation and maintenance cost was only 5.3 cents.m(-3) during the entire operation. These findings demonstrate that direct UF without chemical cleaning has significant application potential in rural regions with micro-polluted water.