Measuring and testing – Liquid analysis or analysis of the suspension of solids in a... – Content or effect of a constituent of a liquid mixture
Patent
1994-06-02
1996-02-06
Williams, Hezron E.
Measuring and testing
Liquid analysis or analysis of the suspension of solids in a...
Content or effect of a constituent of a liquid mixture
73 6141, 738665, G01N 500, C12M 300, G01M 1700
Patent
active
054888565
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a monitor for surveying the formation of deposit and/or growth, being especially but not exclusively a biofilm monitor, comprising a deposit reactor as well as a method for the use of this deposit monitor.
When drinking water flows through a mains, a small layer of bacteriological material, also called biofilm, will be deposited on the inner surface of the mains. The formation of this biofilm in systems for the distribution of drinking-water and in drinking-water installations is undesirable for technical, aesthetic and hygienic reasons. Research has shown that due to the formation of biofilm on the mains surface, the hydraulic resistance thereof can increase noticeably. In addition the biofilm can form a breeding ground for animal organisms of which some can be seen with the naked eye, such as the water sow bug (Asellus). Perhaps the hygienic aspect is even more important. Some types of bacteria which grow in the biofilm have pathogenic properties such as the Legionella bacteria, the perpetrator of the so-called Legionnaire's disease and also representatives of the Aeromonas family, which can cause diarrhoea. Growth of bacteria of the coli (bacillus) type in the biofilm can result in the water not complying with the legal requirements (absence of bacteria of the coli type in 100 ml drinking-water).
The formation of a biofilm is dependant upon the nature and the concentration of degradable matter ("sources of energy") in drinking-water. These sources of energy include organic and also certain inorganic compounds. There are however more factors which presumably play a part. The following can be mentioned: the type of material from which the mains are made (the one material restrains the growth of bacteria to a larger extent than the other), also the age of the mains material, the water temperature, the flow velocity and the occurrence of physicochemical processes such as adsorption and sedimentation.
In order to study the effect of certain circumstances on the formation of biofilm and/or to study the effect of the formation of biofilm on the quality of the drinking-water, use is made of so-called biofilm reactors. An important example of such a biofilm reactor is the "Roto Torque (RT)" reactor, which consists mainly of a stationary and an uprightly positioned cylinder sleeve formed by a tube section of a mains and a massive rotatable cylindrical block positioned therein. The liquid sample is introduced in a continuous fashion, and is then thoroughly mixed with previously introduced liquid by virtue of continuous rotation of the rotor and drained continuously, the residence time of the liquid particles in the reactor amounting to approximately 10 minutes. The Roto Torque reactor can, because of its constant mixing, be classed under the so-called CFSTR's (Continuous Flow Stirred Tank Reactor). A torque meter is connected to the rotor of the Roto Torque, by which the torque required for maintaining a certain speed of revolution is determined. With the development of biofilm on the inner surface of the sleeve the shear stress along the surface increases, as a result of which a larger torque will be necessary. The increase of the required torque is thus a measure for the formation of biofilm, which in this way is monitored indirectly.
In order to come as close as possible to real cicumstances several Roto Torque's can be placed in series in a Roto Torque System (RTS). This way an attempt is made to determine the influence of concentration gradients.
The Roto Torque reactor and the Roto Torque System are not always suitable for studying biofilm formation. In the first place the construction forms a hindrance: because of the implementation of a rotor set up inside the test pipe the latter will have to have a considerable diameter, for example 15 cm. Consequently this reactor is indeed suitable for tests on mains pipes but not for tests with service pipes. Secondly, the results will not always be exact and reliable due to the aforementioned indirect method of measuring the formation of biof
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US, H, 831 (Salanitro) 2 Oct. 1990 Statuatory Invention Registration.
Kiwa N.V.
Wiggins J. David
Williams Hezron E.
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