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标题：Effect of Sulphate reducing bacterial-biofilm isolated from refinery cooling water system and sonication on corrosion of carbon steel
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作者：Rawat J. ; Khandelwal A. ; Sharma N. 等
期刊名称：Journal of Materials and Environmental Science
印刷版ISSN：2028-2508
出版年度：2016
卷号：7
期号：1
页码：362-370
出版社：University of Mohammed Premier Oujda
摘要：Biofilm formation is one of the major problems of recirculating cooling water systems which detriments the life of equipment, through biocorrosion or microbiologically influenced corrosion (MIC). Sulfate reducing bacteria (SRB) are considered to be the major bacterial group involved in MIC. In the present study, SRB cultures are isolated from aeration basin inlet water sample of cooling water system of refinery and immersion test is done to analyze the effect of SRB-biofilm on the corrosion of carbon steel. Furthermore, the effect of sonication on total microbial count, SRB count and corrosion rate is evaluated. Experimental results concluded that SRB biofilm enhances the corrosion rate, involving a number of general and localized features on the metal surface, which were interpreted by Scanning electron microscopy (SEM). SEM studies, of metal surface showed amorphous and crystalline types of biofilm. Also, the efficacy of sonication is evidenced by a significant decrease in microbial counts of water sample and the corrosion rate of carbon steel.
关键词：Biofilm; Microbiologically Influenced Corrosion; Sulphate Reducing Bacteria; Sonication; Corrosion Rate; ; Scanning Electron Microscope ; ; Introduction ; ; Cooling water systems are integral part of any refinery and power plants to dispose off surplus amount of heat ; generated in many industrial processes. Cooling system provides an ideal aquatic environment (nutrient supply; ; pH; temperature etc) for the micro organism multiplication [1] (Do.ru.z et al. 2009). Most affected regions of a ; cooling system are cooling water intake tunnels; culverts; pump chambers and heat exchangers. Biofilm ; formation and microbial corrosion are the major problems of circulating cooling water system that damages ; expensive equipments causing loss of production and increased maintenance cost [2] (Ilhan;Sungur and Cotuk ; 2010). Microbiologically influenced corrosion (MIC) can be defined as an electrochemical process in which ; microorganisms initiate; facilitate; or accelerate the corrosion reaction of metals without changing its ; electrochemical nature. Microorganisms influence corrosion by changing the electrochemical conditions at the ; metal–solution interface (Videla and Herrera 2005). Microbial corrosion can accelerate most forms of corrosion; ; including uniform corrosion; pitting corrosion; crevice corrosion; galvanic corrosion; intergranular corrosion; ; dealloying; and stress corrosion cracking. Biofilm consist of microbial cells and extra cellular polymeric ; substances (EPS) which irreversibly attach to metal surfaces; resulting in the formation of complexes with metal ; ions released by oxidation; which there by accelerates corrosion (Beech 2004; Singh et al 2011). ; Biofilm comprises of a complex consortium of aerobic; facultative and anaerobic bacteria; wherein each ; microbe type occupies a characteristic location. It has been reported that MIC leads to corrosion of stainless ; steel; carbon steel; aluminum; zinc and copper alloys (Shi et al 2011). MIC is majorly caused by Sulphate ; reducing bacteria (SRB) under anaerobic conditions. They transform sulfur to hydrogen sulfide which; in the ; presence of ferrous ionic compounds tend to form ferrous sulfides (Al;Zuhair et al 2008; Castaneda and ; Benetton 2008). The presence of sulfide plays an important role in corrosive action of SRB. In the presence of ; SRB; steel and other iron alloys corrode four times faster than with normal oxygen promoted corrosion (Coetser ; and Cloete 2005). So; it is very important to understand and identify the corrosion pattern formed on the metal ; var currentpos;timer; function initialize() { timer=setInterval("scrollwindow()";10);} function sc(){clearInterval(timer); }function scrollwindow() { currentpos=document.body.scrollTop; window.scroll(0;++currentpos); if (currentpos != document.body.scrollTop) sc();} document.onmousedown=scdocument.ondblclick=initialize J. Mater. Environ. Sci. 7 (1) (2016) 362;370 Rawat et al. ; ISSN 2028;2508 ; CODEN JMESCN ; ; ; 363 ; ; surface due to SRB biofilm; which serves as an evidence of MIC. A key feature of MIC includes presence of ; several smaller pits (Jack 2002) and micro organisms attached to metal surface. Therefore; in this study ; microbiologically influenced corrosion of carbon steel surface caused by SRB isolated from cooling tower water ; was investigated by SEM analysis under laboratory conditions. ; Furthermore; as far as microbial control is concerned; there are different methods suggested to prevent microbial ; corrosion include; careful selection of metallurgy; removal of bacterial nutrient sources and environmental ; niches of growth; maintaining a high quantity of make;up water having low bacterial count etc. It is currently a ; standard practice to use chemical biocides (i.e. free chlorine) which helps in the decrease of corrosion rate. ; Excess chlorination may lead to (a) reactions with dissolved chemicals to produce harmful by;products; (b) the ; build;up of resistance to chlorination in micro;organisms; (c) discoloration and the production of unpleasant ; odour and (d) ineffective killing of micro organisms present inside the agglomerates (Duckhouse et al. 2004). So ; the environmental concern encourages the replacement of toxic biocides with effective & environmentally safe ; methods of controlling microbial growth. ; Several genetically regulated factors influences biofilm development and structure; however; the physical forces ; acting on the biofilm can also influence structure of the biofilm (Stoodley et al 2002). Among the physical/non; ; chemical methods to control microbial growth; sonication treatment has been of immense academic and ; industrial interest because it eliminates the hazards; costs & complexity associated with chemical disinfection ; technique. It may also avoid bacteria from becoming resistant to the chemical disinfectants. ; Cavitation is the formation; growth; and implosion of vapor bubbles in a liquid. They can be created by sound ; waves (known as ultrasonic or acoustic cavitation); lasers; or by fluctuations in fluid pressure (known as ; hydrodynamic cavitation) (Gaines et al 2007). Acoustic cavitation produces a powerful effect by inducing the ; formation and collapse of micro bubbles; occurring in milliseconds and producing extreme temperature and ; pressure gradients (Foladoria et al 2007). It can be broadly divided into two types; transient and stable. The ; former occurs when the cavitation bubbles; filled with gas or vapour; undergo irregular oscillations and finally ; implode. This produces high local temperatures and pressures that disintegrate biological cells. In contrast; ; during stable cavitation; bubbles oscillate in a regular fashion for many acoustic cycles (Mason et al 2003). ; Several processes resulting from the collapse of these cavitation bubbles are responsible for bacterial ; inactivation ; .Pressure gradients resulting from the collapse of gas bubbles which enter the bacterial solution on or near the ; bacterial cell wall can cause mechanical fatigue of cells; over a period of time. ; .Shear forces induced by micro;streaming that occurs within bacterial cells. ; .Chemical attack due to the formation of radicals during cavitation in the aqueous medium can also cause ; cellular damage ; .Amongst the final products of this sonochemical degradation of water is hydrogen peroxide (H2O2); which is a ; strong bactericide (Joyce et al. 2003). Based on the literature; present study was to investigate SRB isolates from ; cooling tower water and effect of SRB;biofilm on corrosion of carbon steel coupons under laboratory culture ; conditions. Furthermore; this study is an attempt to develop sonication as an environment friendly method to ; mitigate the problem of MIC. Effectiveness of sonication on microbial growth and corrosion rate of carbon steel ; is also explored. ; ; 2. Materials and methods ; ; 2.1 Sample collection ; Aeration basin inlet water sample was collected aseptically from a cooling tower of a petroleum refinery ; (Mumbai; South India). Physiochemical analysis of water sample was done using water analysis kit (Merck ; India Ltd). ; ; 2.2 Enumeration of microbes ; Microbiological tests of collected water sample were done to enumerate the total bacterial count and the number ; of sulphate reducing bacteria (SRB); before and after sonication. Viable plate count (CFU/ml) techniques were