INTRODUCTION

Where water is used as a heat transfer medium, from large recirculating cooling systems to smaller air conditioning/humidifier units, the problems of biofouling have been recognized for many years. Slime forming organisms, particularly bacteria, can rapidly establish themselves on pipe work and heat exchanger surfaces. The biofilms formed reduce heat exchange efficiency, cause increased flow resistance and in extreme cases, can result in pipe blockage. They also provide ideal conditions for anaerobic sulphide generating bacteria to grow under the slime, in contact with the metal surface causing subsequent corrosion problems.

In addition to the practical problems associated with microbial contamination of cooling systems, the human health factor also has to be considered. The presence of potentially pathogenic organisms, particularly in air conditioning and humidifier units, is a cause of concern. Legionella pneumophila, the bacterium implicated in the outbreaks of Legionnaires’ Disease, is only one of a number of organisms which, under the right conditions, causes human infections.

Myacide, the industrial grade of 2-bromo-nitropropane-1,3-diol (or BNPD) is a broad-spectrum bactericide which can be used as a key component in water treatment formulations to prevent these biofouling problems. Liquid formulations, such as 2K7 Solution are available for this use.

This report summarizes the relevant application data for water treatment companies to either use alone as an own-label product or as a component in a biocide formulation.

RELEVANT ANTIMICROBIAL ACTIVITY

The minimum inhibitory concentrations (m.i.c.’s) of BNPD are typically 12.5 to 25 ppm for a wide range of aerobic, water-borne bacteria including Pseudomonas spp, Staphylococcus spp, Legionella spp, Klebsiella pneumoniae and Bacillus subtilis.

Anaerobic sulphate reducing bacteria (SRB) such as Desulfovibrio vulgaris and D. desulfuricans are particularly sensitive to BNPD with m.i.c.’s of 6.25 to 12.5 ppm. Similar activity was also observed against strains of SRB found in cooling tower isolates.

In comparison, m.i.c.’s for other biocidal products as supplied, such as isothiazolones and quaternary ammonium compounds are in the 125 to 1600 ppm range for bacteria such as Pseudomonas aeruginosa and Escherichia coli.

APPLICATION INFORMATION

The following examples demonstrated the efficacy of Myacide in typical treatment conditions.

Laboratory Simulated Cooling Tower

The efficacy of Myacide at 75 ppm and another commercially available biocide, 5% methylene bisthiocyanate at 200 ppm was studied using a model recirculating water system. The systems were treated with biocide on a once weekly basis and the results below show that Myacide 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.

Comparative Biocide Activity in a Model Cooling Tower System

Cooling Tower at a Pharmaceutical Manufacturing Unit

The following trial was conducted in a 50 m3 recirculating cooling system servicing a dedicated computer controlled plant producing a pharmaceutical active ingredient. Prior to the trial, the treatment program had involved regular dosing with a combined product based on nitrite, scale inhibitor and biocide. This mixture was introduced with the makeup water to maintain a level of 1000 ppm nitrite in the system. With this treatment, bacterial numbers were running at approximately 106/ml, and sulphate reducing bacteria at 102 – 103/ml.

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

Effect of Myacide on Aerobic and Anaerobic Bacteria in a Recirculating Cooling Tower at a Pharmaceutical Manufacturing Unit

Steel Mill Application

At a site in Sweden, Myacide has been successfully used to control microbial contamination in water used in a large steel mill. The main application in this mill is the continuous casting (concast) process. A recirculating water system is used to cool the rollers and the molten iron.

In the trial Myacide was dosed at 17-20 ppm once a week. No microbial problems have occurred during two years of use as the only biocide in the system.

Air Conditioner & Humidifier Systems

At a trial conducted in a 14 m3 recirculating air conditioning unit servicing a medium sized printing works. The system was operating with 1000 ppm nitrite as the corrosion inhibitor and a chlorinated phenol as the biocide treatment at 70 ppm. In addition an antifoam was needed to combat foaming problems from the biocide. Losses in nitrite level had been observed on a fairly regular basis due to the presence of denitrifying bacteria.

In the trial chlorinated phenol was replaced by Myacide, at a rate of 25 ppm weekly. The immediate effect was a dramatic reduction in bacterial numbers. Since that trial, Myacide shock dosed at a rate of 50 ppm once weekly has been adopted as the standard treatment.

No antifoam was required and only very occasional nitrite losses have been experienced. These could be rectified by increasing the biocide dose for a short time.

Myacide is now being used successfully to treat small air conditioners servicing retail shop premises. Rates of use vary between 30 and 40 ppm shock dosed once weekly.

Air Scrubbing Units

At a pharmaceutical production site, problems were highlighted in a wet scrubbing unit linked to the dust extraction system in a tablet coating unit. The dust collected by the unit contained a high percentage of starch-based tablet binder thus providing ideal nutrients for bacteria. Despite the use of a quaternary ammonium type biocide, high bacterial populations developed rapidly with resulting slimes and foul odours. The treatment was changed to Myacide, dosed twice weekly at 40 ppm. This resulted in an immediate drop in bacterial numbers and the elimination of foul odours. Myacide has now been in regular use in this unit for over two years with continued success.

COMMERCIAL RECOMMENDATIONS

Myacide is recommended to be used once or twice weekly at 15 to 100 ppm for inhibiting the growth of slime forming and sulphate reducing bacteria in cooling towers and air conditioning systems. Shock dosing is preferred. Myacide may be dosed either as a stock solution or by adding the crystalline solid or 2K7 Bugstick directly into the sump or basin at a point where there is adequate flow or turbulence to ensure quick dissolution.

A twice weekly dose of Myacide at 100 ppm is recommended for the control of Legionella spp. A lower maintenance dose of 50 ppm used twice weekly should inhibit the growth of Legionella bacteria once contaminated systems have been treated effectively. It must be stressed that Myacide should be used as part of an integrated maintenance program involving control of scale, corrosion and regular cleaning.

Myacide in liquid formulations, should be used at the same bronopol active ingredient concentrations as for Myacide.

RELEVANT PHYSICAL CHEMICAL PROPERTIES

Compatibility

Myacide is compatible with a range of material used in general water treatment. These include commonly used corrosion inhibitors and scale control agents such as those based on nitrites, phosphonates, polyphosphates and polycarboxylates. Similarly Myacide is also compatible with biodispersants based on nonionic surfactants.

Myacide is also compatible in the presence of true oxidizing biocides such as chlorine or bromine release compounds frequently used in water treatment.

In compatibility studies, Myacide was stable in the presence of up to 5 ppm free chlorine. At normal recommended chlorine use levels of 2 ppm, Myacide should perform satisfactorily.

Myacide is also compatible with many other biocides used in water treatment including quaternary ammonium compounds, isothiazolinones, methylene bisthiocyanate and dibromonitrilopropionamide. Some synergistic activity has been observed between Myacide and some other biocides which allows a flexible approach to dealing with biofouling problems through the use of blended formulations.

However, in common with may other biocides, Myacide is inactivated by strong reducing or oxidizing agents, such as sulphites and bisulphites which are often used as oxygen scavengers. In these instances a rotational and sequential program should be adopted. Laboratory studies on dilute solutions (200 ppm) of Myacide, suggested that 25-50 ppm bisulphite had little effect on chemical stability however at 100 and 150 ppm bisulphite, the effect is fairly significant. Tests have also shown that Myacide will tolerate the presence of hydrogen peroxide at levels of 50 ppm in simple aqueous systems.

ENVIRONMENTAL SAFETY

Myacide is a well researched and safe antimicrobial product. This is also true with respect to environmental safety where test results indicate its inherent biodegradability, rapid photolysis in water, low bioaccumulation characteristics and hydrolysis at low concentrations. Myacide is therefore unlikely to cause significant, long term adverse effects in aquatic environments.

However, Myacide, like other effective biocides, is very toxic to some algal species and is therefore treated as potentially dangerous for he environment.

On the strength of this and other data, Myacide has been granted the following registrations for industrial water treatment applications.

US EPA – Registration Number 33753-5 for industrial recirculating water cooling towers, evaporative condensers, industrial and commercial air washers, air conditions, humidifying systems and industrial process waters.

Canada – Various bronopol formulations registered for cooling tower use, heat exchangers, pasteurizers, condensers and air washers for cooling towers.

UK – approved for decontamination of potable water storage tanks and associated pipework.

The information contained in this sheet is believed to be accurate but given without warranty.

MYACIDE is a Registered Trademark of BASF