Abstract
Biofilm is defined as a complex multi-species microbial community highly and specifically organized attached to the surface through an hydrated polymeric matrix known as EPS (extracellular polymeric substances), which represents the primary constituent of the biofilm. The industrial problems associated with the biofilm growth are the subject of many studies concerning the water system and the cooling tower. Cooling towers are very important part of many industrial systems, like refinery and gas extraction plant. The driving force for heat transfer is the temperature difference between the two components in direct contact or separated by surfaces, which are at different temperatures, and the decrease of this parameter can negatively affect the entire process. The biofilm formation on heat exchanger surfaces of the cooling towers, known as biofouling, strongly reduces the heat transfer efficiency. The monitoring of the benthonic communities growth within a cooling tower is not an easy task due to logistical issues mainly related to sampling difficulties. This study aims to realize a biofouling control strategy that allows a more efficient biomonitoring of the biofilm growing in a cooling tower. The developed monitoring system was tested using samples of make-up water taken from a cooling tower at a full scale Refinery located in Northern Italy. This experimental apparatus (Model System) allowed the monitoring of biofilms growth that develops from make-up water entering cooling tower and to test the effectiveness of several additives that are usually used in real systems, in order to control the development of biofouling. The refinery make-up water was characterised in order to describe the composition and the structure of the microbial communities by applying in situ hybridization techniques (Fluorescence in Situ Hybridization, FISH). The refinery make-up water fed a continuous recirculating system [maximum volumetric flow rate=2 mL/min] that exploits a “Coupon evaluation Flow Cell (BST FC 71©Biosurface Technologies Corporation)” made in black anodized aluminium, with a single flow channel, that uses standards microscope coverslips as a viewing window. Through this window, it is possible to monitor over time the growth of the biofilm on the coverslips surface placed inside the flow chamber by a simple phase contract microscopy analysis (1000X). The biofilm formation rate was estimated during the early phase of biofilm formation (rbf (5 days growth) =1.4*104 cells/mm2*d) and after a prolonged period (rbf (20 days growth) =2.4*104 cells/mm2*d).The effectiveness of additives provided by Chimec S.p.A. was also tested in order to evaluate the impact on biofilm formation.
