Full Length Research Paper

Effect of different flocculants on the flocculation performance of microalgae, Chaetoceros calcitrans, cells

Zuharlida Tuan Harith¹, Fatimah Mohd Yusoff¹, Mohd Shamzi Mohamed², Mohamed Shariff Mohamed Din³ and Arbakariya B. Ariff^1,2*

¹Laboratory of Industrial Biotechnology, Institute of Bioscience, University Putra Malaysia, 43400 Serdang, Selangor, Malaysia.

²Department of Bioprocess Technology, Faculty of Biotechnology and Biomolecular Sciences, University Putra Malaysia, 43400 Serdang, Selangor, Malaysia.

³Faculty of Veterinary Medicine, University Putra Malaysia, 43400 Serdang, Selangor, Malaysia

*Corresponding author. E-mail: arbarif@biotech.upm.edu.my. Tel.:  603 8946 7591. Fax: 603 89467510.

Accepted 19 June, 2009

   Abstract

The possibility of using flocculation technique for the separation of microalgae, Chaetoceros calcitrans, biomass from the culture broth was investigated. The flocculation experiments were conducted in 500 mL beaker using culture broth obtained from 10 L photobioreactor. The harvesting efficiency of 90 and 60% was obtained in flocculation without flocculants conducted for 10 days at 27ºC (in light and dark) and 4ºC (dark), respectively. Harvesting efficiency higher than 90% with short settling time was achieved by adjusting the culture pH to 10.2 using either sodium hydroxide (NaOH) or potassium hydroxide (KOH). Improved cell viability (> 80%) and settling time with a slight improvement of flocculation efficiency was achieved by the addition of polyelectrolytes flocculant (Magnafloc^® LT 27 and LT 25). However, the flocculants were only functioned when the pH of the microalgae culture was pre-adjusted to a certain value that promotes cells entrapment and surface charge neutralization prior to flocculation process. The flocculation efficiency and cell viability obtained in flocculation with Magnafloc^® (LT 25 and LT 27) was comparable to that obtained in flocculation with chitosan. When chitosan and Magnafloc^® (LT 25 and LT 27) were used as flocculants, the highest flocculation efficiency of C. calcitrans cells was observed at pH 8 and 10.2, respectively. Substantial increased in sedimentation rate was observed with increasing flocculants dosage though the flocculation efficiency and cell viability were not significantly varied.

Key words: Flocculation, microalgae, Chaetoceros calcitrans, polyelectrolyte, chitosan.