Chitosan enhanced coagulation of algal turbid waters – Comparison between rapid mix and ultrasound coagulation methods

• Ultrasound enhanced coagulation/flocculation of low algal turbid waters was studied.
• Simultaneous effect of chitosan and ultrasound on turbidity removal was studied.
• A comparison with conventional rapid mixing/flocculation process was conducted.
• Ultrasound mixing may be performed in lieu of rapid mixing for coagulation process.
• Ultrasound power density, flocculation time, pH-chemical-dosage effects were studied.

Presence of algae is considered as an undesirable water pollutant in drinking water sources such as reservoirs and at water and wastewater treatment plants causing odor, taste and other severe health issues. In this study, ultrasound-chitosan enhanced coagulation/flocculation process for treating algal turbid water was developed. The possibility of performing ultrasound mixing in lieu of conventional rapid mixing was evaluated. The effects of several process parameters such as chemical dosages, pH, ultrasound exposure time, concentration factors and flocculation and sedimentation times were studied. Two comparative studies, i.e., a comparison between ultrasound-alum and ultrasound-chitosan flocculation of algal turbid waters as well as a comparison with conventional rapid mix and direct flocculation were conducted. The results from this study reveal that ultrasound enhanced method can produce clear supernatant water with greater than 98% turbidity reduction. A power density of 0.1–0.25 W/mL was sufficient to provide adequate mixing for chemical distribution and pin-floc formation. The concentration factor for ultrasound-enhanced coagulation/flocculation was determined to be 30 with an optimum ultrasound exposure of 1 min followed by a 20 min flocculation process. This study confirms that ultrasound-chitosan enhanced flocculation process may provide additional benefits for algal cell harvesting compared to the conventional rapid mix method.

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