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Nanofiltration (NF) technology has been widely used in drinking water treatment process and advanced wastewater reclamation due to its capability in effectively removing contaminants down to multivalent ions, while operating at lower pressure compared to reverse osmosis (RO). One of the major challenges in membrane filtration is fouling, since fouling deteriorates the performance of nanofiltration over time. Although many types of foulant can cause fouling, natural organic matter (NOM) is considered as a major foulant due to its recalcitrant properties and the fact that it is commonly found in natural water. In addition to this, the presence of divalent cations such as calcium could add the severity of fouling, as it is capable of forming bonds between NOM and between NOM-membrane surface. In water treatment processes, NOM is commonly removed by coagulation/flocculation using coagulant such as alum. Coagulation is also used as pre-treatment prior to membrane filtration, or used in conjunction with membrane filtration. Hybrid coagulation-nanofiltration is a technology that combines coagulation and nanofiltration as a part of drinking water treatment or advanced wastewater reclamation. This technique is found to effectively remove NOM while producing high permeate quality and quantity. Although many studies have looked into the interaction between NOM and calcium or the performance of membrane filtration with coagulation pre-treatment, none have attempted to investigate the interaction between foulant-foulant and membrane-foulant when NOM, calcium and coagulant are co-occurring. In addition to this, there exists a discrepancy between the observed permeate flux decline during filtration of sodium alginate, which is commonly used to model high molecular weight NOM, in the presence of calcium; while some studies reported that calcium ions were responsible for severe permeate flux decline, others reported that the permeate flux was improved in the presence of calcium. This study systematically investigated the interaction between NOM and calcium in the presence of coagulant. Permeate flux trends, permeate quality, feed characteristics