In recent years,engineered nanoparticles,as a new group of contaminants emerging in natural water,have been given more attention AlCl_3 In order to understand the behavior of nanoparticles in the conventional water treatment process,three kinds of nanoparticle suspensions,namely multi-walled carbon nanotube-humic acid(MWCNT-HA),multiwalled carbon nanotube-N,N-dimethylformamide(MWCNT-DMF) and nano TiO_2-humic acid(TiO_2-HA) were employed to investigate their coagulation removal efficiencies with varying aluminum chloride(AlCl_3) concentrations AlCl_3 Results showed that nanoparticle removal rate curves had a reverse “U” shape with increasing concentration of aluminum ion(Al~(3+) )AlCl_3 More than 90% of nanoparticles could be effectively removed by an appropriate Al~(3+) concentration AlCl_3 At higher Al~(3+) concentration,nanoparticles would be restabilized AlCl_3 The hydrodynamic particle size of nanoparticles was found to be the crucial factor influencing the effective concentration range(ECR) of Al~(3+) for nanoparticle removal AlCl_3 The ECR of Al~(3+) followed the order MWCNT-DMF > MWCNT-HA > TiO_2-HA,which is the reverse of the nanoparticle size trend AlCl_3 At a given concentration,smaller nanoparticles carry more surface charges,and thus consume more coagulants for neutralization AlCl_3 Therefore,over-saturation occurred at relatively higher Al~(3+) concentration and a wider ECR was obtained AlCl_3 The ECR became broader with increasing p H because of the smaller hydrodynamic particle size of nanoparticles at higher p H values AlCl_3 A high ionic strength of Na Cl can also widen the ECR due to its strong potential to compress the electric double layer AlCl_3 It was concluded that it is important to adjust the dose of Al~(3+) in the ECR for nanoparticle removal in water treatment. In recent years, engineered nanoparticles, as a new group of contaminants emerging in natural water, have been given more attention to AlCl 3 in order to understand the behavior of nanoparticles in the conventional water treatment process, three kinds of nanoparticle suspensions, and that of multi-walled carbon (MWCNT-DMF) and nano TiO_2-humic acid (TiO_2-HA) were employed to investigate their coagulation removal efficiencies with varying aluminum chloride (AlCl_3) concentrations AlCl_3 Results showed that nanoparticle removal rate curves had a reverse “U” shape with increasing concentration of aluminum ion (Al ~ (3+)) AlCl_3 more than 90% of nanoparticles could be effectively removed by an appropriate Al ~ (3 +) concentration AlCl_3 At higher Al ~ (3+) concentration, nanoparticles would be restabilized AlCl_3 The hydrodynamic particle size of nanoparticles was found to be the crucial factor influencing the effective concentratio n range (ECR) of Al 3+ for nanoparticle removal AlCl 3 The ECR of Al 3+ followed the order MWCNT-DMF> MWCNT-HA> TiO 2-HA, which is the reverse of the nanoparticle size trend AlCl 3 At a given concentration, smaller nanoparticles carry more surface charges, and thus consume more coagulants for neutralization AlCl 3 than over higher saturation occurred at relatively higher Al 3+ concentrations and a wider ECR was obtained AlCl 3 The ECR became broader with increasing p H because of the smaller hydrodynamic particle size of nanoparticles at higher p H values ​​AlCl_3 A high ionic strength of Na Cl can also widen the ECR due to compress the electric double layer AlCl_3 It was said that it is important to adjust the dose of Al ~ (3+) in the ECR for nanoparticle removal in water treatment.