Centre for Water in Urban Areas

The present study investigates major organic foulants in ultrafiltration (UF) of treated domestic wastewater and their removal in slow sand filtration. Identification and quantification of major foulants was conducted in lab-scale experiments. Quantified results suggest that biopolymers (large molecular protein-like and polysaccharide-like materials) are major organic foulants in UF. This conclusion was verified to be reproducible in pilot-scale UF tests. The removal of biopolymers in slow sand filtration was carried out using pilot-scale sand filters. Longer than one year investigation demonstrates that the elimination of biopolymers takes place in the active upper sand layer mainly due to biological degradation. Filtration rate, temperature and biopolymer concentration in feed water affect the performance of slow sand filtration. Though slow sand filtration removes biopolymers and slow down fouling development in downstream membrane filtration, operational conditions of UF (filtration flux and duration) exhibit a significant influence on trans-membrane pressure (TMP) development. Based on pilot-scale tests, sustainable operational conditions are suggested in the present work for UF of slow sand filtrate