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.

Highlights

  • Microalgae are widely used in aquaculture as live feeds for several aquaculture species such as molluscs, fish, penaeid prawn larvae and rotifers (Brown, 2002)

  • 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

  • Comparable flocculation efficiency was obtained in flocculation with Magnafloc® (LT 25 and LT 27) to those obtained in flocculation using chitosan

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Summary

Introduction

Microalgae are widely used in aquaculture as live feeds for several aquaculture species such as molluscs, fish, penaeid prawn larvae and rotifers (Brown, 2002). Intensive cultivation for production of large quantities of microalgae biomass requires a proper harvesting technique. Different production systems require a proper selection and optimization of the harvesting method and these must accommodate to the requirement of the final form of the algal cells and the subsequent processing steps of the harvesting and formulation methods. Flocculation or sedimentation occurs when particles in liquid settle to the bottom of the tank due to gravitational force and fluid drag force. This method of solid-liquid separation is preferred for harvesting large cells like

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