Effects of Carbon Source, Carbon Concentration, and Chlorination on Growth Related Parameters of Heterotrophic Biofilm Bacteria |
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Authors: | BD Ellis P Butterfield WL Jones GA McFeters AK Camper |
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Institution: | (1) Technology Planning and Management Corporation, Scituate, MA 02050, USA, US;(2) Montana State University, Bozeman, Bozeman, MT 59717, USA, US |
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Abstract: | Abstract
To investigate growth of heterotrophic biofilm bacteria, a model biofilm reactor was developed to simulate a drinking water
distribution system. Controlled addition of three different carbon sources (amino acids, carbohydrates, and humics) at three
different concentrations (500, 1,000, and 2,000 ppb carbon) in the presence and absence of chlorine were used in separate
experiments. An additional experiment was run with a 1:1:2 mixture of the above carbon sources. Biofilm and effluent total
and culturable cells in addition to total and dissolved organic carbon were measured in order to estimate specific growth
rates (SGRs), observed yields, population densities, and bacterial carbon production rates. Bacterial carbon production rates
(μg C/L day) were extremely high in the control biofilm communities (range = 295–1,738). Both growth rate and yield decreased
with increasing carbon concentrations. Therefore, biofilm growth rates were zero-order with respect to the carbon concentrations
used in these experiments. There was no correlation between growth rate and carbon concentration, but there was a significant
negative correlation between growth rate and biofilm cell density (r=−0.637, p= 0.001 control and r=−0.57, p= 0.021 chlorinated biofilms). Growth efficiency was highest at the lowest carbon concentration (range = 12–4.5%, amino acids
and humics respectively). Doubling times ranged from 2.3–15.4 days in the control biofilms and 1–12.3 days in the chlorinated
biofilms. Growth rates were significantly higher in the presence of chlorine for the carbohydrates, humics, and mixed carbon
sources (p= 0.004, < 0.0005, 0.013, respectively). The concept of r/K selection theory was used to explain the results with respect to specific growth rates and yields. Humic removal by the biofilm
bacteria (78% and 56% for the control and chlorinated biofilms, respectively) was higher than previously reported literature
values for planktonic bacteria. A number of control experiments indicated that filtration of drinking water was as effective
as chlorination in controlling bacterial biofilm growth.
Received: 26 March 1999; Accepted: 3 August 1999; Online Publication: 15 February 2000 |
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