|
|
|
|
Fouling, contamination and corrosion of cooling water systems
Micro- and macrofouling, fouling of membranes, Legionella, microbial corrosion
|
|
|
Mitigation of micro- and macrofouling
Both microfouling (biofilms) and macrofouling (mussels, hydroids, et cetera) have to be mitigated in order to ensure the continuous operation of the cooling system in production processes, including the production of energy. Too much fouling in the cooling system can impair its performance and lead to physical damage in the construction.
In general, mitigation of biofilms is performed in two ways - mechanically, by (abrasive) sponge rubber balls or by tube-cleaning rubber plugs, or by dosing with chemicals like chlorine, ozone and non-oxidative compounds which are toxic or only surface active.
For mitigation of macrofouling usually natrium hypochlorite is applied but other (non-)oxidative additives may be used. Over the last few decades, KEMA has been engaged in R&D for new mitigation methods and improvements of existing methods to reduce the use of biocides, in order to meet environmental legislation and to reduce costs, while still having maximum effect. The result is a new regime in chlorination called Pulse Chlorination®. This method is accepted as "Best Available Technique" (BAT) by the European legislative authorities. Another successfully implemented method is heat treatment, normally referred to as "thermoshock". Besides chlorine and heat treatment, a large number of both oxidative and non-oxidative methods and mechanical options such as self-cleaning mussel strainers are available to combat fouling.
|
|
|
Fouling of membranes
Our expertise and experience with biofouling in water systems also includes consultancy in the field of biofouling of membrane filtration installations. We have a unique combination of thorough biological knowledge and experience in membrane technology, which enables us to perform fundamental scientific research in this area as well as advise you on practical solutions for membrane biofouling.
|
|
|
Microbially influenced corrosion
Micro-organisms will directly effect surfaces exposed to surface water. These micro-organisms can cause a significant increase in the speed of corrosion of metallic surfaces. This form of corrosion is called ‘Microbially Induced Corrosion’ (MIC). Accelerated corrosion can occur as a result of corrosive metabolic products such as sulphides, ammonia, mineral and organic acids. Moreover, microbes can participate actively in the reactions that produce corrosion. Microbial activity can induce corrosion where it would not occur otherwise or influence the initiation or propagation of corrosion. Estimates show that 20% of all corrosion damage in heat exchangers are caused or influenced by micro-organisms.
Essentially, MIC has been observed in all raw waters including fresh waters, brackish waters, and seawater. Application of biotic materials (Copper) and noble materials in practise fails to give any guarantee for MIC resistance, with the exception of titanium.
KEMA is using the MIC-kit™ III for the detection of problem-causing bacteria involved in MIC supported by light microscopic techniques (DICOM), Scanning Electron Microscopy (SEM), and X-ray Micro Analysis (RMA) for detection of characteristic MIC structures.
|
|
|
Control of Legionella
KEMA possesses the expertise for execution, drawing up, and reviewing of risk assessments and control procedures (including procedures for prevention of contamination and infection) for Legionella pneumophila. Our expertise, which has been developed for and in co-operation with industry, concerns industrial ‘grey’ process water, recirculating cooling water systems and civil tap-water systems. Our strength is the combination of biological knowledge and technical expertise.
In this field KEMA works intensively with the engineering bureau Iv-Consult. Both companies together form the ideal combination of multidisciplinary engineering, knowledge of microbiology and water related installations, guaranteeing quality and a no-nonsense approach.
Our ‘Legionella-services’ include:
Control of Legionella in domestic water:- performance of risk analyses and, where necessary, ‘quick scans’ for priority ranking
- performance of technical surveys
- drawing up of the master advice plan (consisting of guidance procedures, the outlines of the log-book, including advice on installation adjustments and technical drawings)
- producing c.q. updating of technical drawings
- detailed explanation and implementation of technical improvements
- adjustment of the master advice plan in light of the investigations which have been made
- performing audits where risk analyses have been carried out.
Control of Legionella in ‘grey water’ and cooling water- cooling tower screening
- water and biofilm sampling
- advice on water treatment
- biofilm monitoring (BioGeorge™) optionally in combination with scaling monitoring (DATS™ III)
- research / R&D
- testing biocides.
The procedure and guidelines for management advice
The following procedure conforms to the ‘Tijdelijke regeling Legionella-preventie in leidingwater’ (The temporary mains water regulation for Legionella prevention), as published in the Dutch ‘Staatscourant nr. 199’ of October 13, 2000. Installations are tested according to the laws of the Building Services Research Institute ISSO (Institution for the study and promotion of research in the field of building services). The Legionella master advice is written according to the method of the model master plan as published by the Ministry of Housing, Spatial Planning and the Environment (VROM 13945/173). The adjustment of installations (and accompanying drawings) has to be executed according to NEN 1006 and the VEWIN work sheets.
Legionella standards for domestic water:- < 50 cfu/L: no reason for anxiety
- > 50 cfu/L: action necessary: shutdown of installation(s) & disinfection, informing personnel and intensifying control procedures.
Legionella standards for cooling water:- < 1000 cfu/L: no reason for anxiety
- >1000 - <10.000 cfu/L: reason for anxiety and action necessary
- >10.000 cfu/L: severe alarm, action necessary, disinfection of the cooling water system, informing personnel and intensifying control procedures.
For more information please contact us.
|
|
|
|
[download] Legionella in cooling water (.pdf 220 kb)
|
|
|
[download] Cooling water systems as potential source for Legionellosis (.pdf 217 kb)
|
|
|
|
|
|
|
|
|
|
