Biodegradability of biofilm extracellular polymeric substances.pdf

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Biodegradability of biofilm extracellular polymeric substances.pdf

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Biodegradability of biofilm extracellular polymeric substances

Biodegradability of biofilm extracellular polymeric substances Xiaoqi Zhang a,*, Paul L. Bishop b a Department of Civil and Environmental Engineering, University of Massachusetts Lowell, One University Avenue, Lowell, MA 01854, USA b University of Cincinnati, Cincinnati, OH 45221-0018, USA Received 17 December 2001; received in revised form 11 June 2002; accepted 14 June 2002 Abstract This study discovered that biofilm extracellular polymeric substances (EPS) are biodegradable by their own pro- ducers and by other microorganisms when they are starved. The study was performed in a comparative fashion to examine the biodegradability of biofilm EPS by the microorganisms from the original biofilm (its own producers) and from activated sludge (other microorganisms). Four distinctive phases were observed during EPS biodegradation. In the first phase, instantaneous concentration increases of carbohydrate and protein in the test solutions were observed when EPS was added; in the second phase, easily biodegradable EPS from the added EPS was quickly utilized; in the third phase, microorganisms began to produce soluble EPS, using the minimally biodegradable EPS left from the previously added EPS; in the fourth phase, cells consumed the newly produced EPS and microbial activity gradually stopped. This study suggests that EPS can be used as a substrate, and that the EPS carbohydrate can be utilized faster than the EPS protein. The EPS utilization rates (including carbohydrate and protein) in the activated sludge suspension were greater than those in the biofilm suspension. It may take microorganisms longer to get acclimated to a new nutrient environment if they are in a starved state. 2002 Elsevier Science Ltd. All rights reserved. Keywords: Carbohydrate; Protein; Lipid phosphate; Oxygen uptake rate; Activated sludge 1. Introduction Extracellular polymeric substances (EPS) come from the natural secretions of bacteria, cell lysis and hydro- lysis products. The predominant compo