Removal Of Trace Arsenic From Water By Chitosan Flocculation-ultrafiltration

Arsenic pollution of water is a critical problem in the world. It aggravates the shortage of water resources. Thus, it is meaningful to develop a green, economical and effective technology to remove trace arsenic from drinking water. In this work, the chitosan flocculation-ultrafiltration integrated process to remove trace arsenic in water was studied.The methods of arsenic determination were explored. As the atomic adsorption spectroscopy determination had more merits than kinetic-spectrophotometric determination and voltammetric determination, it was chosen to determine the trace arsenic in this work.Main factors affecting the arsenic removal were investigated systemically. The results indicate that pH value 4.6, chitosan concentration 0.36 g/L, stirring power 8.11×10^-2 W and settling time 40 min were the optimal conditions. Both of the concentration of As(Ⅴ) and As(Ⅲ) in the arsenic-containing simulated water were about 0.1 mg/L, and after the flocculation-ultrafiltration process, the concentration of As(Ⅴ) reduced within 0.01 mg/L, and that of As(Ⅲ) reduced to about 0.02mg/L. The As(Ⅴ) removal reached more than 93% and the As(Ⅲ) removal reached 80%. When the feed pH value was 9.2, the As(Ⅴ) removal was about 60%, and As(Ⅲ) removal was about 55%. The arsenic removal was not obviously affected by the operation pressure and crossflow velocity of ultrafiltration process. With increasing temperature and molecule weight cut off (MWCO) of the membrane, the arsenic removal had a descent trend. And with increasing transmembrane pressure, crossflow velocity, MWCO and temperature, the flux had an ascent trend.Under the condition of feed pH value 4.6, transmembrane pressure 0.1 MPa, crossflow velocity 5.653 cm/s, temperature 30℃and PAN30,000 membrane, chitosan flocculation-ultrafilitration process was used to remove the arsenic in tap water. The result indicates that the arsenic removal reached 89.9%, and the total arsenic content decreased from 0.067 mg/L to 0.0068 mg/L. It reached the international standard restricting the arsenic content of drinking water below 0.01 mg/L.Moreover, the fouling of the ultrafiltration was investigated, and the methods of cleaning ultrafiltration membrane were explored. The results indicate that the chitosan flocculant was the main pollutant causing membrane fouling. The flux recovery was about 58% after hydraulic cleaning, and that was only 2.7% after cleaning with NaOH (pH=12). The fouled ultrafiltration membrane can be better cleaned with hydrochloric acid (pH=2), and the flux recovery can reach above 72%.