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J Appl Phycol (2009) 21:353–360 DOI 10.1007/s10811-008-9376-7

Growth and removal of nitrogen and phosphorus by free-living and chitosan-immobilized cells of the marine cyanobacterium Synechococcus elongatus
Bily Aguilar-May & María del Pilar Sánchez-Saavedra

Received: 13 June 2007 / Revised and accepted: 10 September 2008 /Published online: 4 October 2008 # Springer Science + BusinessMedia B.V. 2008

Abstract This study investigated the growth rate of chitosanimmobilized cells of the marine cyanobacterium Synechococcus elongatus and its potential application in the removal of nitrogen and phosphorus for wastewater treatment. Immobilized cell cultures had a lag phase of growth due to the immobilization method, and their growth rate was similar to that of free-living cellcultures. Ammonia removal was higher in free cells (54%) than in immobilized cells (29%), but nitrate removal was similar in immobilized (38%) and free cells (44%); phosphorus removal was more efficient in free cells (88%) than in immobilized cells (77%). Chlorophyll a and protein content were higher in immobilized cells. Our study demonstrates that S. elongatus immobilized into chitosan capsules canremove nutrients and is able to maintain a growth rate comparable to that of free cells in culture. Keywords Chitosan . Growth . Immobilization . Nutrient removal . Synechococcus elongatus

Introduction The use of different techniques to immobilize microalgae and cyanobacteria has received considerable attention in recent years (Chevalier and de la Noüe 1985; Mallick 2002; Saeed
B. Aguilar-May : M.del Pilar Sánchez-Saavedra Departamento de Acuicultura, Centro de Investigación Científica y de Educación Superior de Ensenada, Km 107 Carretera Tijuana a Ensenada, Apartado Postal 360, Ensenada, Baja California Código Postal 22860, Mexico M. del Pilar Sánchez-Saavedra (*) P.O. Box 434844, San Diego, CA 92143, USA e-mail:

and Iqbal 2006). The most widely used naturalpolymers for the immobilization of live cells are κ-carrageenan and alginate (Chen 2001; Cohen 2001). Carrageenan is rather expensive, and the temperatures required for immobilization, ranging from 30°C to 50°C, may be too high for microalgae survival (Vorlop and Klein 1987). Alginate is less expensive and is the most popular matrix for immobilizing microalgae for water or wastewater treatment purposes(Lau et al. 1998). This latter fact may be due to its suitability for immobilization of viable cells (Kierstan and Coughlan 1985; Yabur et al. 2007). Recently, it has been suggested that chitosan can be used as an immobilization matrix, and a method of immobilizing live cells with chitosan has been described by Aguilar-May et al. (2007). Chitosan is a polymer that can be obtained from crab andshrimp shells in waste products from food-processing industries (Mallick and Rai 1994; Yan-Tan and Lee 2002). Moreover, chitosan has potential for use as an adsorbent for environmental and purification purposes (Crini 2006) and can be produced commercially at low market prices of US $6.60 to $15.43 per kg (Mallick and Rai 1994; Mucott and Harfeman 1996; Babel and Kurniawan 2003). Chitosan is apermeable, deacetylated linear polysaccharide that forms gel networks at room temperature (Vorlop and Klein 1987). In addition, it is biodegradable, non-toxic, and biocompatible; has a high affinity for organic compounds with negative loads; and is soluble in acidic solutions but insoluble in neutral or alkaline solutions (Pastor de Abram 2004). Chitosan has immunostimulant activity and is also effectiveagainst the bacteriostatic activity of fungi, bacteria, and viruses (Kurita 2006). These attributes are desirable properties in a suitable matrix for immobilizing live microalgae and cyanobacteria. Synechococcus is a dominant component of picophytoplankton in oligotrophic as well as eutrophic waters, where


J Appl Phycol (2009) 21:353–360

Synechococcus contribute substantially to...