Myacide AS/S1/S15 and S30 are highly active bactericides, which can be used as key components in water treatment formulations. The following examples demonstrate the efficacy of Myacide AS (2-Bromo-2-nitropropane-1,3-diol or Bronopol) in typical treatment conditions in both laboratory studies and field trials.

LABORATORY TRIALS
Laboratory Simulated Cooling Tower

The efficacy of Myacide AS at 75ppm and another commercially available biocide, 5% Methylene bisthiocyanate (MBT) at 200ppm was studied using a model recirculating water system. The systems were treated with biocide on a once weekly basis and, as the results in Figure 1 show, Myacide AS was superior in reducing bacterial numbers to very low levels. This would also indicate that a lower dose would have been sufficient to achieve control.

Figure 1 – Comparative Biocide Activity in a Laboratory Model Cooling Tower

Laboratory Testing for Efficacy of Microbicides used in Cooling Systems to US ASTM E645-91

Myacide S1 (20% solution of Myacide AS) and other water treatment biocides, Isothiazolones (CIT/MIT), a quaternary ammonium compound (Quat), 2,2-Dibromo-3-nitrilopropionamide (DBNPA), 2-(Thiocyanomethylthio) benzothiazole/ Methylenebisthiocyanate (TCMTB/MBT) and Dichlorophen, were tested according to ASTM guideline E645-91.

Water taken from a cooling tower, which had not been dosed with biocide for one week, was inoculated with a mixed bacterial inoculum containing aerobic waterborne bacteria including L. pneumophila. The biocides were added to the inoculated water and the bacterial count measured over 72 hours. The results are shown in Figure 2. An effective level of biocide is that which produces a 99% (2-log) or greater reduction in sample counts after the selected exposure time. Myacide S1 at 50ppm active was shown to be effective after 24 hours.

Figure 2 - Comparative Biocide Activity in Cooling Tower Water inoculated with a Mixed Bacterial Culture

This test was modified to challenge Myacide S1 and CIT/MIT at similar concentrations at pH8 against a single inoculum of P. aeruginosa. These results are shown in Figure 3. Myacide S1 at 25ppm (active ingredient) was effective after 24 hours and retained control over the full 72 hours.

Figure 3 - Comparative Biocide Activity in Cooling Tower Water at pH8 Inoculated with a Single Pseudomonas species

Legionella Kill Tests

In a suspension test, sterilised cooling tower water seeded with L. pneumophila serotype 1 (NCTC 11192) was treated with selected biocides and stored at 20°C for 0.5 to 24 hours. Myacide AS at 50 and 100ppm required 4 to 6 hours to reduce the number of organisms from an initial count of 105 c.f.u./ml to an undetectable level. This was comparable to DBNPA at 20ppm, CIT/MIT at 28ppm and Chlorinated phenolic thioether at 20 and 40ppm (all concentrations expressed as active ingredient).

Laboratory Simulated Cooling Tower

In a model cooling tower experiment, sterile cooling tower water (500ml) seeded with Legionella pneumophila serotype 5 (NCTC 11405), was treated with selected biocides and recirculated at 800ml/hour. In the control and in the system treated with Peracetic acid at 10.5ppm the number of viable bacteria declined slowly from 106 to 105 c.f.u./ml over 48 hours. No viable bacteria were recovered following the treatment with Bronopol at 50ppm for 24 hours. CIT/MIT at 14ppm required 48 hours for the same effect.

FIELD TRIALS
Cooling Tower at a Pharmaceutical Manufacturing Unit

A trial was conducted in a 50m3 recirculating cooling system servicing a dedicated computer controlled plant producing a pharmaceutical active ingredient. Prior to the trial, the treatment programme had involved regular dosing with a combined product based on nitrite, scale inhibitor and biocide. This mixture was introduced with the make-up water to maintain a level of 1000ppm nitrite in the system. With this treatment, the system contained approximately 106 c.f.u../ml aerobic bacteria and 102 -103 c.f.u. /ml anaerobic sulphate reducing bacteria (S.R.B.).

The trial treatment programme involved nitrite, again at 1000ppm, a polyacrylate scale inhibitor and Myacide AS. The biocide was shock dosed initially at 50ppm three times weekly reducing to 30ppm three times weekly after eight weeks and eventually to 30ppm twice weekly after ten weeks. The results, shown in Figure 4, clearly illustrate the dramatic effect of the Myacide AS, both on aerobic and anaerobic bacteria in the system. Throughout the trial, nitrite levels were maintained and all other parameters remained within required limits.

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