DETERMINATION OF IRON COLLOID SIZE DISTRIBUTION IN THE PRESENCE OF SUSPENDED CELLS - APPLICATION TO IRON DEPOSITION ONTO A BIOFILM SURFACE

Transport and deposition of colloidal Fe, Mn and Al oxides play key ro les in the cycling of toxic transition metals in aquatic environments because these colloids strongly bind transition metals. Further, attac hment of biological cells and biofilm growth on surfaces can indirectl y affect toxic metal distribution by influencing the deposition of col loidal oxides to surfaces. To elucidate the mechanisms governing these processes, deposition of colloidal oxides onto surfaces must be evalu ated in the presence of suspended and adherent bacterial cells. Both p article size and concentration are expected to influence deposition. A n experimental protocol was developed to determine the size distributi on of iron colloids in mixtures with suspended cells. A Ti(III) reagen t was used to reduce and dissolve colloidal Fe(III) from mixtures cont aining both suspended cells and Fe colloids. The size distribution of Fe(III) colloids in the original solution was then determined from the difference between size distributions before and after dissolution of Fe with Ti(III). The Ti(III) reagent dissolved over 95% of the Fe col loids without altering the size distribution of suspended bacterial ce lls, and the method accurately determined the size distribution of Fe colloids added to cell suspensions. The applicability of this protocol was tested by applying it to a study of the deposition of Fe(III) oxi de particles onto glass surfaces with and without biofilms of the bact erium Burkholdaria cepacia 17616. Experimental results using a laborat ory biofilm reactor indicated that the deposition rate of Fe(III) coll oids was not significantly affected by the presence of B. cepacia biof ilms or by the presence of previously deposited Fe. However, depositio n of Fe to reactor surfaces other than the glass surfaces may have int erfered with the analyses, and atomic absorption measurements showed a slight increase in Fe deposition onto glass surfaces with biofilms pr esent. Fe deposition to the composite of all reactor surfaces increase d with increasing colloidal particle size, indicating a dominance of i nterception and/or sedimentation in controlling Fe deposition on surfa ces in the biofilm reactor. Copyright (C) 1996 Elsevier Science Ltd