Biofouling and microbial corrosion problem in the thermo-fluid heat exchanger and cooling water system of a nuclear test reactor

Abstract

This article discusses aspects of biofouling and corrosion in the thermo-fluid heat exchanger (TFHX) and in the cooling water system of a nuclear test reactor. During inspection, it was observed that >90% of the TFHX tube bundle was clogged with thick fouling deposits. Both X-ray diffraction and Mossbauer analyses of the fouling deposit demonstrated iron corrosion products. The exterior of the tubercle showed the presence of a calcium and magnesium carbonate mixture along with iron oxides. Raman spectroscopy analysis confirmed the presence of calcium carbonate scale in the calcite phase. The interior of the tubercle contained significant iron sulphide, magnetite and iron-oxy-hydroxide. A microbiological assay showed a considerable population of iron oxidizing bacteria and sulphate reducing bacteria (10(5) to 10(6) cfu g(-1) of deposit). As the temperature of the TFHX is in the range of 45-50 degrees C, the microbiota isolated/assayed from the fouling deposit are designated as thermo-tolerant bacteria. The mean corrosion rate of the CS coupons exposed online was approximately 2.0 mpy and the microbial counts of various corrosion causing bacteria were in the range 10(3) to 10(5) cfu ml(-1) in the cooling water and 10(6) to 10(8) cfu ml(-1) in the biofilm.

The CQ ratio of surface energy components influences adhesion and removal of fouling bacteria

“…Biofouling on the surfaces of heat exchangers, ships' hulls, pipelines, and other structures causes serious problems (Kerr et al 2003;Eguı´a et al 2008;Rao et al 2009;Andrewartha et al 2010). A thin layer of bacterial biofilm on the surfaces of heat exchangers significantly reduces heat transfer performance (Little and Lavoie 1979;Rao et al 2009).…”

Microbial Fouling in a Water Treatment Plant and Its Control Using Biocides

“…Water used for industrial purposes, contains dissolved ions, gases, organic matter, micronutrients, microorganisms and macroorganisms Venkateswarlu, 1990 . Thus, a thorough monitoring of all the above parameters is required for effective utilization of the water for industrial purposes Flemming, 2002;Rao et al, 2009 . The data thus obtained, can be used as baseline information, which is to be rigorously adhered to, during the operation of the plant.…”

“…In addition to the general composition of the feed water, the fouling trend is also dependent upon the chemical constituents, as they can potentially influence the progression of the fouling phenomena. Furthermore, the presence and diversity of microorganisms in the feed water might also play a role in the microbial fouling profile and biofilm formation of in a unit Rao et al, 2009 . Generally, microorganisms exist predominantly as multicellular communities called biofilms attached to surfaces Allison and Gilbert, 1992;Costerton et al, 1995 . In the initial phase of biofilm development, ambient water quality and nutrient chemistry at the solid/liquid interface influence the settlement of primary colonizers. The exopolymeric matrix of the biofilm provides structural stability, and anionic constituents such as nitrate, phosphate, silicate from bulk water make the biofilm milieu a nutrient niche Rao et al, 1997;Rao, 2003 .…”

“…The exopolymeric matrix of the biofilm provides structural stability, and anionic constituents such as nitrate, phosphate, silicate from bulk water make the biofilm milieu a nutrient niche Rao et al, 1997;Rao, 2003 . Biofilm formation in industrial cooling circuits poses serious problems, wherein they reduce heat transfer efficiency resulting in a significant pressure drop in the condensers as well as impairing the performance of ancillary systems Bott, 1995;Rao et al, 2009 . Heavy water D 2 O production plants need good quality water with very low dissolved oxygen concentration for heavy water production. The Heavy Water Plant, Kota, India, is an indigenous production unit, using the bi-thermal H 2 O-H 2 S exchange process.…”

“…Pseudomonas bacteria counts were made using King s B medium Bergan, 1981 . Sulphate reducing bacteria were counted using Postgate medium Rao et al, 2009 . The bacterial counts were represented as colony forming units per milliliter cfu mL -1 when plated on agar medium.…”