Industrial Water Treatment can be split into three distinct categories:

• Cooling Water
• Boiler Water
• Wastewater

Water treatment chemistry is studied in order to optimize industrial process waters reducing running costs by preventing or minimising problematic areas including corrosion, biological fouling, scale and bacterial discharge

App-Chem have a number of test kits / products specially designed to contain the most common parameters for a given industrial application.

Legionella Compliance Kit (L8)

Industrial Legionella Test

Engineer's Test Kit

Boiler Water Kit

Cooling Water Kit

Chemical Oxygen Demand (COD)

Non-Oxidising Biocides

Dipslides

Incubators

Corrosion Coupons

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Click here to view Corrosion Coupons and Racks

Chemical Inhibitors of Corrosion:

• Anodic - Species which change the chemical or physical nature of the metal oxide produced at the anode to enable it to prevent cation release
• Cathodic - Ions which interact with the ions produced at the cathode to generate films capable of restricting access of reducible species to the cathode
• Filming - Polar organic molecules capable of forming tenacious films all over the metal surface which restrict access of reactants

Corrosion is the eating away and eventual destruction of metals and alloys by chemical attack or oxidation. The rusting of ordinary iron and steel is the common most form of corrosion.

In Water Treatment Corrosion can cause various problems including metal loss, fouling, reduction of efficiency, increase of system back pressures, and corrosion sites can harbour bacteria.

Some factors influencing corrosion include: Materials - Galvanic Effects, Design - Crevices, Stagnation, Temperature gradient, Construction - Crevices, Weld effects, Flux, Debris, Operation - Scale, Deposits, Biofouling, Erosion, Cavitation, pH depression, Oxidising Biocides.

Metal oxide + lots of energy ---> Metal (blast furnace or electrolysis)

Metal ---> Metal oxide + lots of energy (combustion or corrosion)

Anodic	Cathodic	General
Nitrite	Nickel
Chromate	Zinc	Mercapto-benzotriazole
Borate	Polyphosphate	Benzotriazole
Benzoate		Tannins
Orthophosphate		Tolyltriazole
Orthosilicate	Calcium Bicarbonate	Manganese
Molybdate
Phosphinocarboxylate	Phosphinocarboxylate

The Effects:

• Insulation of heat-exchange surfaces
• Reduction in flow rates
• Reduction in tower thermal efficiency
• Blockage of valves, filter traps, dead-legs, distribution channels etc
• Corrosion (under slime and sulphate-reducers)
• Fungal rot of wooden cooling towers
• Slimes prevent corrosion inhibitors from reaching metal surfaces
• Amplification of potential pathogens (Legionella)

Evaporative cooling systems provide near ideal habitat for a wide range of micro-organisms for a number of reasons including temperature range of the system, nutrient and essential element supply, surface area and easy inoculation

Different treatment programmes can be used dependent upon a number of factors:

• Non-oxidising biocides including quaternary amines, phenolic compounds, isothiazolones and dibromoproprionamide can be used. The disadvantages of this type of system are that the chemicals are expensive, bacteria build up resistance to specific products and many are toxic to aquatic life. The advantages of non oxidising biocides are that they are non-corrosive, relatively stable and have long effective life.
• Oxidising biocide programmes use either chlorine, bromine, peroxide, ozone or chlorine dioxide. Their disadvantages are that overdosing can cause corrosion, they can be stripped out by aeration and they have a relatively short effective life. Their advantages are that they are relatively inexpensive, bacteria cannot develop immunity and they are relatively harmless to the environment.

Click here to view ATP Meter

Control of microbiological contamination is one of the most important jobs in water treatment, as uncontrolled microbial growth can lead to rapid fouling of systems. The proper use of microbial testing can help maintain a suitable biocide regime to counter this problem.

Although dipslides are generally considered to be the industry standard they have a number of shortcomings; results take 48 hours, only a small percentage of microorganisms present in the water system will grow on the standard media and the dangerous bacteria associated with industrial water treatment are not detected (e.g. Legionella, SRB’s).

ATP has been widely accepted by the water treatment industry as the standard method of determining microbiological contamination for over 15 years, having several advantages over other methods. including total test in less than a minute and every cell in the system is detected.

The ATP system we supply gives a result for Total ATP; to obtain a result for Free ATP, the sample must be filtered first. The relationship between the two is detailed below.

• tATP = fATP + microbial ATP
• tATP – fATP = microbial ATP

	Open Recirculating	Closed Recirculating
Pass	<300 RLU	<200RLU
Caution	300-750 RLU	200-500 RLU
Fail	>750 RLU	>500 RLU

Total ATP (tATP) is a measure of both the ATP within living cells and the ATP floating free in the water system (fATP). tATP is gives an immediate indication of the microbial control within a water system. Results in the ‘pass’ zone are under good microbial control whereas those in the ‘caution’ or ‘fail’ zone are not acceptable. Results in this region should be re-tested to ensure against false positives.

If the fail result is confirmed the following steps should be taken:

1. Check the biocide tanks and pumps to ensure biocide is being added to the system.
2. Check the history of biocide addition – if biocide or bio-dispersant have recently been added, this could indicate the presence of significant bio-film within the system. A fATP test can be used to determine if there are high levels of living microbes in the system (low free results) or if the high tATP readings reflect dead cells from biocide treatment (f ATP ≥ tATP). See below (biocide efficacy) for additional information on this approach.
3. Check circulation within the water systems – stagnant systems do not distribute biocide throughout the entire system.

If the biocide is being added correctly and there remains a high level of microbial contamination, it may be necessary to increase the dose of biocide or possibly switch to another biocide. Biocide resistance is to be expected after continuous use of a single type of biocide for a long time.

In assessing the efficacy of biocides it is important to recognise that different biocide mechanisms will produce different ATP effects on the microbes treated.

Lysing biocides such as quats, gluteraldehyde and oxidising biocides (chlorine, bromine, ozone) typically produce a rapid increase in fATP and a gradual diminishing of tATP as the microbial ATP is released into the system. Once fATP and tATP equalise, we can infer that most microbes are dead. The efficacy of the biocide can determined be by the rate at which this equilibrium is reached. Failure to equalise after 24 hours indicates that a population of microbes that have not been killed through the addition of biocide.

In contrast to the lysing biocides, many non-oxidizing biocides act as metabolic inhibitors. These types of biocides cause a rapid decrease in the tATP with little initial impact on the fATP. The reason for the difference is that they act by poisoning the systems within the microbes that produce ATP without affecting the cellular structure of the bacteria.

The result is that fATP will typically not rise significantly while tATP will see a large drop within a few hours. Low tATP may not accurately reflect microbial death, as energy drained bacteria may be revived if the biocide is removed, however, the rapid drop in tATP is a good indication of the biocide efficacy and that cell death should follow rapidly. There have been some reports of tATP actually increasing in the first few hours after the addition of a metabolic inhibitor. While unexpected, this can occur due to cells rapidly generating ATP in an effort to restart the cellular processes inhibited by the biocide. Regardless of the initial effect, the tATP should decrease within the first 24 hours. With metabolic inhibitors, efficacy is indicated by a decrease in tATP to the ‘pass’ zone in 24 hours.

This result is also observed with lysing biocides and may be used in lieu of the convergence end point. There is typically a convergence of tATP and fATP with the metabolic inhibitors as well, though this may not occur for several hours after the addition.

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