Technology
To understand AquaFinesse Industry products you must be prepared to change the way you think about water care and the cleaning of surfaces where biofilm is formed.
AquaFinesse was developed with the knowledge that biofilm is held together and protected by a matrix of excreted polymeric compounds called xPS. The extra cellular matrix protects the cells within it and facilitates communication among them.
Small water channels inside the biofilm provide nutrients and other properties needed for the survival and growth of living species like bacteria, archaea, protozoa and algae.
AquaFinesse patented products exist of efficient working environmentally friendly ingredients to mitigate the polymeric compounds - by opening and breaking down the biofilm, there where the problem starts. AquaFinesse has found the solution. AquaFinesse gives biocides the power they need to destroy bacteria in substratum surfaces in marine or freshwater environments which has been impossible until now.
KEMA institute in the Netherlands tested the effectiveness of the product AquaFinesse™ AF07 CoolPuck® for application in industrial cooling water systems and HVAC-utilities by stimulating bio film formation in a small scale cooling water system equipped with heat exchanger and cooling tower, using River Rhine (Dutch river) surface water. For accurate mitigation determination a bio film activity monitoring system called BioGeorge and a deposit fouling monitor called DATS were applied, extended with a metabolic enzymatic method based on Adenosine-5'-triphosphate (ATP). The effectiveness of the AF07 CoolPuck® product was tested with and without Na-hypo chlorite addition.
Surface water used for cooling industrial processes contains a wide scale of organic and in-organic substances as well as microbes. Surfaces exposed to surface water will directly be conditioned by adsorption of organic and an organic compounds followed by settlement of bacteria. Planktonic waterborne bacteria migrate to surfaces and attach improving their biotope by excretion of exopolymeric substances (xPS), forming gel like matrices in which the bacteria are enclosed. Eventually, areas of these matrices will join and form a contiguous bio film. Microbial multiplication in the bio film, incorporation of organic material and microbes from the water phase lead to an increase in the size and stability of the bio film (see schematic development figure 1).
Figure 1 Overview of bio film formation
Bio films provide shelter and protection for microbes against varying physical environmental circumstances and biocides (Carpentier & Cerf, 1993). The bio film xPS entraps nutrition and forms a diffuse on barrier, by which an oxygen gradient is developed. The oxygen is used in the surface layer of the bio film, leading to an aerobic outer side an anaerobic environment on the substrate underneath. As these various micro environments become established, there is an increased development of specific microbes that initiate and promote corrosion of metallic surfaces. Flemming (1994) showed that rather 'clean' cooling water utilities contain bio films in which microbes concentrations are 5 till 6 times larger compared to microbes present in the planktonic water phase.
The following operational problems in cooling water utilities occur due to increased bio film development:
Decreased efficiency of heat transfer
Deposition of bio films on the walls of a heat exchanger impairs the heat transfer and stimulates the deposition of calcium salts. The thermal conductivity of a bio film (0.6 W m-1 K-1) is comparable with that of water (Flemming, 1994), thereby leading to a much higher heat transfer resistance.
Increase of cooling water pumping costs
Bio films reduces the tube inside diameter and, hence, the effective cross-sectional area for flow. To achieve the same flow, the tube-side velocity must increase. This results in a pressure drop increase (Costerton et al., 1987), requiring greater pumping power to over-come the additional system head.
Increased risk of macro-fouling
Bio films stimulate the settlement of macro-organisms like mussels, oysters and barnacles (Flemming & Schaule, 1994). The settlement of these macro-organisms leads to a substantial decrease in diameter of cooling water piping, thereby leading to even higher pumping costs and eventually leading to a forced outage for removal of macro-fouling debris.
Increased corrosion
Deposition of microbes on metallic surfaces can lead to an increase in the speed of corrosion of these metals. This type of corrosion is called microbial influenced corrosion (MIC). Through-wall penetration of piping and heat exchanger tubing as localised corrosion, at rates 10 to 1000 times more rapid than those normally encounters, can result. Accelerated corrosion may occur as the result of corrosive metabolic products such as sulphides, ammonia, organic acids, or mineral acids. Application of noble materials (such as Monel) and biotoxic materials (such as copper) in practice does not give any guarantee of MIC resistance, with the exception of titanium.
Increase of health risks
Bio films can also serve as hosts for pathogenic microbes. Mainly in open recirculation utilities with cooling tower, the activity and growth (increase in numbers) of microbes (by an increased water temperature and sufficient oxygen and nutritional supply) can increase to such an extent that it can cause increased health risks for employees and complex buildings. The threat is particularly acute as bio films can suddenly slough off the substrate and be released in massive amounts into an area such as a cooling tower, where the pathogens can become airborne through aerosols and come in contact with people. Human pathogens often connected with cooling towers are Neagleria spp., Acanthamoebe spp., and Legionella pneumophila (Tyndall, 1993). Numerous outbreaks of Legionnaires' disease have been tied to outbreaks from cooling towers and HVAC (air conditioning) units.
Although initially thought to be more or less uniform, recent imaging with confocal microscopy has shown that a bio film is full of channels and voids where water, ions, suspended solids, and metabolites can accumulate. The xPS acts as a trap for nutrients dissolved in the water. The net effect is that conditions inside the bio film can be significantly different than in the bulk water.
By buffering their bacterial occupants from the bulk water, bio films provide shelter and protection for micro-organisms against varying physical environmental circumstances and biocides. Chlorine and peroxides are less active in removing bio films as always assumed. The full-grown bio film can also act as a diffusive barrier, by which an oxygen gradient is developed. The oxygen is used on the surface of the bio film, leading to an anaerobic environment on the conditioned surface (Figure 1). As these various areas (better: micro-environments or micro climatic areas) become established, there is an increased development of specific micro-organisms that cause and promote corrosion of the metallic surfaces.
Mitigation of bio film by AquaFinesse™ AF 07
Extensive tests have shown that the AquaFinesse products, although human and environmentally friendly work effective in different applications destroying the 'structure' and 'viability' of the bio film. This because the microbial growth and microbiological growth and processes, which are responsible for causing Microbial Influenced Corrosion (MIC) stagnate. Therefore the product is a valuable additive to biocides like Na-hypo chlorite for industrial and other applications. Adressing the bio film problem has a significant effect on the cleanliness of the environment, thus reducing risk to humans. Also importantly all oxidisers have an increased effect when used in combination with the AquaFinesse™ AF 07 Cool Puck the bio film is dislodged, and can no longer act to protect its inhabitants. This is why the AquaFinesse™ products are recommended as an essential part of maintenance in cooperation with a biocide. The solution to complex and and difficult to manage problems in cooling water processes can be found in the effective mitigation of the bio film with AquaFinesse™ AF 07, Cool Puck.