###### Abstract  
A novel polyacrylonitrile (PAN)-based ultrafiltration (UF) hollow-fiber membrane was newly synthesized for nanofiltration (NF) applications. This semi-fully NF hollow-fiber membrane was characterized using a variety of analysis techniques. The membrane exhibited higher negative charge and hydrophilicity and lower surface roughness compared to the pristine UF hollow-fiber membrane. Experiments to study the performance and fouling were simulated under laboratory conditions in a cross-flow system and in-out mode using organic compounds, namely, humic acid and sodium alginate. The removal efficiencies of humic acid and sodium alginate were 65% and 73%, respectively, in the pristine hollow-fiber membrane and 93% and 95%, respectively, in the proposed membrane. The flux decline by natural organic matter was less in the case of the proposed membrane compared to that in the pristine membrane. To mitigate organic fouling on the proposed membrane, sodium hypochlorite (NaCIO) was used as a chemical enhanced backwashing agent. At a NaClO concentration of 1 mg/L with a backwashing time of 30 s, an optimal flux recovery of 92.1% of the initial permeability of the PAN-NF hollow-fiber membrane was achieved with less membrane degradation. The results of this study will provide practical insight and act as a technical guide for NF-based plant engineers/operators. n +
Footnote †: journal: Applied  
1  
e +
Footnote †: journal: Applied  
1  
e +
Footnote †: journal: Applied  
1 State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210023, China; [EMAIL_ADDRESS]  
while spiral wound membranes offer packing densities up to 1000 m\({}^{2}\)/m\({}^{3}\)[9]. In recent years, hollow-fiber (HF) membranes with various benefits over both spiral wounds and tubular modules have been reported; compared to the previous two modules, HF membranes have higher fouling resistance [10], higher packing density [9], lower requirements of pretreatment and maintenance, and higher volumes of permeate [11], which allow for the direct treatment of drinking water resources. However, the development of an HF NF membrane with high separation selectivity is crucial for drinking water treatment. Many researchers have found that physical backwashing can enhance membrane performance as it results in a higher cleaning efficiency with respect to particulate matter and colloids [12; 13; 14]. However, organic fouling can be hardly controlled during physical backwashing in HF membranes [15; 16]. Some of the main chemical cleaning methods used for mitigating membrane organic fouling are cleaning in place (CIP) and chemical enhanced backwashing (CEB) [17]. CIP is a more efficient fouling control method than CEB due to its higher cleaning agent concentrations and soak temperatures, high treatment costs, and low operation efficiency [18]. In recent applications of drinking water treatment systems involving chemical cleaning, sodium hypochlorite (NaOCI) was found to be the most common oxidant for organic-fouling control during membrane cleaning because it effectively restores membrane permeability and is relatively less environmentally hazardous compared to other chlorine-based chemicals [18; 19]. Intensive CEB, in terms of both frequency and concentration of the chemical reagent, may enable long-term operation of membrane processes for water and wastewater treatment [20]. During long-term operation using a membrane separation system, the optimization of chemical cleaning is essential to reduce the operating cost [21]. Some important factors to be considered when applying NaCIO-assisted CEB technology in pressure-driven membrane cleaning are flushing time, backwashing time, backwashing repeating frequency, chemical dosage, chemical cleaning times, and chemical cleaning repeating frequency. [PERSON] et al.