Bardac® LF 18 — A Novel Cooling Water Algaecide

Written By: Phil Sweeny, Dean Lammering, and Luis Jimenez, Ellen Meyer, and Karlee Barton

Executive Summary

The active ingredient in Bardac® LF 18 is dioctyl dimethyl ammonium chloride. This product comes in two concentrations: -10WT (10% w/w) and -50WT (50% w/w). Several chemical properties of this product yield key benefits that set it apart from other industrial cooling water products. It is a quaternary ammonium compound (quat). Quats are typically low cost and highly effective biocides for a broad spectrum of organisms. However, quats can have a propensity to form a stable foam when agitated and can interact with polyacrylate (a scale-inhibiting additive commonly used in industrial cooling water), increasing both polyacrylate and quat usage costs. However, Bardac® LF 18 does not have these negative characteristics, making it desirable as an industrial cooling water algaecide.

Chemical Structure

The cationic surfactant nature of quats are what give them a propensity to form foam and a tendency to react with negatively charged polyacrylates.  They possess a water-soluble, positively charged nitrogen head group and a hydrophobic alkyl chain tail, See Figure 1.  

Figure 1 Structures Of Standard Water Treatment Quats
Figure 1. Structures of Standard Water Treatment Quats

In the case of Bardac® LF 18, the alkyl chain length of eight decreased the hydrophobic character of the quat, the associated foam stabilization and the likelihood it will interact with polyacrylic acid-based scale inhibitors.2

Data suggests that interaction between polyanionics and quats decrease with alkyl chain length of the quat; the decreased interaction is exponential; and the interactions decrease by a factor of 10 for each two methylene decrease of the alkyl chain length. (Sweeny 2010) In theory, Bardac® LF 18-50WT’s interaction with polyacrylate would be 100 times less than DDAC, as alkyl chain length decreases from 10 carbons to 8 carbons.

Broad-Spectrum Biocidal Efficacy

One of the most comprehensive studies on the microbiological efficacy of quaternaries is the Bacteriostatic, Fungistatic, and Algistatic Activity of Fatty Nitrogen Compounds by Hueck et al. This study determined the inhibitory concertation of 164 compounds against several common bacteria, fungi and algae. Dioctyldimethyl ammonium chloride (Bardac® LF 18) is listed in the top 24 compounds tested with good or outstanding activity towards all organisms tested. Below is a comparison of Bardac® LF 18 and two quaternaries commonly used in industrial cooling water for microbial control.1

Table 1: Inhibiting Concentrations (ppm)

Compound
Bacteria
Algae
E. coli
P. fluorescens
B. subtilis
S. aureus
Chlorella
Stigeoclonium sp.
Anabaena
Oscillatoria
Dioctyldimethyl ammonium chloride (Bardac® LF 18)
40
75
20
20
7
2
0.7
2
Benzalkonium chloride (ADBAC)
200
300
3
4
1
0.7
1
0.06
Didecyldimethyl ammonium chloride (DDAC)
225
750
< 0.7
7
2
0.7
0.2
0.7

Cost Effective

The combination of Bardac® LF 18’s cost effective product price, high algaecide efficacy and compatibility with polyacrylate scale dispersants make it a cost effective microbial solution solution.

Efficacy Comparison

To compare cost and efficacy, laboratory tests were performed on two common strains of algae found in cooling systems, Chlorella pyrenoidosa and Scenedesmus obliquus.2 Efficacy of Bardac® LF 18-50WT was compared to two competitive specialty algaecides, 6-(tertbutylamino)-4-chloro-6-(ethylamino)-S-triazine (TBA) and 4,5-dichloro-2-n-octyl-2(2H)-isothiazolone (DCOI). Tests were performed at equivalent cost dosages, comparing 13 ppm of 50% Bardac® LF, 25 ppm of 4.0% active TBA and 12 ppm of 4.25% DCOI. After 14 days, growth was scored on a 0 to 5 scale, with 0 = No Growth and 5 = Very Heavy Growth.2 Results can be seen in Figures 1 and Pictures 1 and 2.

Figure2 Algae Comparison Bar Chart
Figure 2: Algaecide Efficacy Comparison with Equivalent Cost Dosage. 0 = no growth. 5 = very heavy growth.
Contamination-Levels-Chlorella Chart
Picture 1: 14-Day Growth. Chlorella pyrenoidosa
Contamination-Levels-Scenedesmus Chart
Picture 2: 14-Day Growth. Scenedesmus obliquus.

Compatibility Comparison

When tested against standard commercial quats, ADBAC and poly(oxyethylene(dimethyliminio)-ethylene(dimethyliminio)ethylene) dichloride (WSCP), Bardac® LF 18-50WT demonstrated a significantly enhanced compatibility with polyacrylate. During these tests, Bardac® LF 18-50WT did not significantly reduce the antiscalant residual or its performance.

Reactivity Testing

Bardac® LF 18-50WT, ADBAC and WSCP were compared to see if they would react with polyacrylate. Using a recirculating water test apparatus with synthetic cooling water, each quat was tested under the following common conditions:2

  • 15 ppm active quat
  • 10 ppm active polyacrylate
  • Total Hardness (TH):600 ppm as CaCO3
  • Total Alkalinity (TA): 200 ppm as CaCO3
  • Temperature: 22 °C
  • pH: 10
  • Flow Rate: 1.5 GPM (~4 cycles/min)
  • Duration: 15 min (60 cycles)

For Bardac® LF 18-50WT, the quat recovery was ~ 80%, so some quat was lost during the test. However, complete recovery of polyacrylate was observed. Significantly less quaternary and polyacrylate wererecovered in the tests with the other quaternaries.2 These translate to extra chemical costs due to increased usage of quat and polyacrylate.

Figure 3: Quat/Polyacrylate Reactivity.
Figure 3: Quat/Polyacrylate Reactivity.

Dynamic Scale Inhibition Testing

To test the performance of the polyacrylate scale inhibitor in the presence of quats, tests utilizing a dynamic recirculating apparatus similar to the reactivity tests were performed. This test simulated “stressed” cooling water conditions by increasing the duration to one hour (240 cycles) and increasing the active concentrations. Precipitated scale was filtered out as it was formed. After exposure to the dynamic stress, the solutions were stored for one week at 50 °C. Measured changes in total hardness were used to determine scale dispersant performance in various conditions. Test conditions were as follows:2

Variable conditions:

  • 10 ppm Polyacrylate with no quaternary added
  • 10 ppm Polyacrylate with 30 ppm Bardac® LF 18-50WT
  • 10 ppm Poly acrylate with 30 ppm ADBAC
  • No polyacrylate or quaternary treatment

 

Variable conditions:

  • Temperature: 50 °C
  • Filter size 0.2 µm
  • Duration: 1 week
  • Ryznar Stability Index (RSI) = 3.5
  • Langelier Saturation Index (LSI) = +2.6
Figure 4:Dynamic Scale Inhibition Results
Figure 4:Dynamic Scale Inhibition Results

Losses of total hardness were observed in all tests, indicating that some scale was formed. Differences between the tests with polyacrylate/Bardac® LF 18-50WT and polyacrylate only were observable, but minimal. The test with polyacrylate/Bardac® LF 18-50WT lost approximately 4% more hardness than the test with polyacrylate only. However, when polyacrylate/ADBAC was used, 27% more hardness was lost than with polyacrylate only. In these tests, scale inhibition performance was ~ 35% better with Bardac® LF 18-50WT than with ADBAC. 

Low Foam

Bardac® LF 18-50WT will foam, however it creates a fast breaking foam, much more conducive to the industrial cooling water world than other quats.

Foam generation was determined in the absence of polyacrylate. The absence of polyacrylate maximizes foam potential. Testing without the antiscalant polyacrylate also necessitated reduced hardness, total alkalinity and pH to avoid CaCO3 precipitation. Foam was generated, using the dynamic recirculation apparatus described previously and foam height was measured. The following test criteria were met:

  • 30 ppm active quat
  • 0 ppm polyacrylate
  • pH: 7.3
  • Total Alkalinity: 164 ppm, as CaCO3
  • Total Hardness: 280 ppm, as CaCO3
  • Temperature: 22°C
  • Flow Rate: 1.5 GPM
  • Duration: 15 minutes
  • Cycles/turnovers: 60

 

As seen in Figure 4 comparing the foam levels generated by 30 ppm active quat of Bardac® LF 18-50WT and ADBAC, the foaming propensity of Bardac® LF 18-50WT is reduced to minimal levels

Figure 5: Foam Height
Figure 5: Foam Height

Conclusion

As shown, the properties of Bardac® LF 18 give this product the benefits of cost effectiveness, biocidal efficacy, low foam generation and low interaction with polyacrylate scale dispersants.

References

  1. Hueck et. al. “Bacteriostatic, Fungistatic, and Algistatic Activity of Fatty Nitrogen Compounds.” Applied Microbiology. Vol. 14. No. 3 pp 308-319. August 1965.
  2. Sweeny, P. et al. “Bardac® LF 18 – A Novel Cooling Water Algaecide.” Association of Water Technologies, The Analyst, 2010. Volume 17 No. 2. The Association of Water Technologies. 2010.