Ref 001 Microalgae Growth-Promoting Bacteria As ‘‘Helpers’’

ARTICLE IN PRESS

Water Research 38 (2004) 466–474

Microalgae growth-promoting bacteria as ‘‘helpers’’ for microalgae: a novel approach for removing ammonium and phosphorus from municipal wastewater
Luz E. de-Bashan, Juan-Pablo Hernandez, Taylor Morey, Yoav Bashan*
The Environmental Microbiology Group, The Center for Biological Research of the Northwest (CIB), P.O. Box 128, La Paz, B.C.S.23000, Mexico Received 20 February 2003; received in revised form 27 August 2003; accepted 15 September 2003

Abstract A combination of microalgae (Chlorella vulgaris or C. sorokiniana) and a microalgae growth-promoting bacterium (MGPB, Azospirillum brasilense strain Cd), co-immobilized in small alginate beads, was developed to remove nutrients (P and N) from municipal wastewater. This paperdescribes the most recent technical details necessary for successful co-immobilization of the two microorganisms, and the usefulness of the approach in cleaning the municipal wastewater of the city of La Paz, Mexico. A. brasilense Cd significantly enhanced the growth of both Chlorella species when the co-immobilized microorganisms were grown in wastewater. A. brasilense is incapable of significantremoval of nutrients from the wastewater, whereas both microalgae can. Co-immobilization of the two microorganisms was superior to removal by the microalgae alone, reaching removal of up to 100% ammonium, 15% nitrate, and 36% phosphorus within 6 days (varied with the source of the wastewater), compared to 75% ammonium, 6% nitrate, and 19% phosphorus by the microalgae alone. This study shows thepotential of co-immobilization of microorganisms in small beads to serve as a treatment for wastewater in tropical areas. r 2003 Elsevier Ltd. All rights reserved.
Keywords: Microbial immobilization; Microalgae; Plant growth-promoting bacteria; Wastewater treatment; Nitrogen removal; Phosphorus removal

1. Introduction Plant growth-promoting bacteria (PGPB) used as inoculants in agriculturalexperiments are common place for control of phytopathogens and for plant growth promotion [1]. Bacteria of the genus Azospirillum are well-known as PGPB for numerous crop plants [2]. Recently, one common strain, the type strain A. brasilense Cd was found to be capable of promoting many growth parameters of the unicellular microalgae Chlorella vulgaris [3], and change the cytology, lipid, and pigmentproduction by the microalgae [4–6]. Therefore,
*Corresponding author. Tel.: +52-612-123-8484X3668; fax: +52-112-54710. E-mail address: bashan@cibnor.mx (Y. Bashan).

it may be considered as a microalgae growth-promoting bacterium (MGPB). C. vulgaris is commonly used for tertiary wastewater treatment [7–10], yet it had not been demonstrated that the observed growth promotion might also yield improvecapabilities of microalgae to remove nutrients from natural wastewater. The microbial carrier chosen in this study were alginate beads. Immobilization of microalgae in polysaccharide gels is an experimental way to use these microorganisms for wastewater treatment [11,12] because it ameliorates the major difficulty of collecting enormous populations of cells developed during the treatment, hamperingregular microalgae treatments [9]. This study describes laboratory methods used to coimmobilize the two microorganisms in small alginate beads and to show that this artificial biological

0043-1354/$ - see front matter r 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.watres.2003.09.022

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association,enforced by close proximities of the microorganisms inside small polymer beads, enhanced the population of microalgae in the wastewater and improved the capacity of the microalgae in its main practical task—removing nitrogen and phosphorus from municipal wastewater.

2. Materials and methods 2.1. Microorganisms Two species of unicellular microalgae, Chlorella vulgaris Beijerinck (UTEX 2714) and C....