Introduction
Biological fouling is a major challenge faced in most water applications in commercial, industrial and municipal treatment plants. Biofilm formed due to the presence of bacteria in the water cause reduction in heat transfer efficiency, corrosion, increased maintenance and lost productivity to name a few. In cooling towers, biofilms cause Microbial Induced Corrosion (MIC) and equipment failures while in membrane systems it causes scaling and reduces the life of the membranes.
Aquatech has developed BioFilmProTM, an innovative method to control biological fouling in cooling towers and membrane systems. BioFilmPro is a combination of electrical deactivation of bacteria while implementing real-time sensing of biofilm potential measurement in the water. Bacteria deactivation is an electrical (thus chemical-free) process, yet BioFilmPro retains the optional use of biocide injection. Biofilm potential sensing can be used to inject biocide in a controlled manner should the electrical bacteria deactivation get overwhelmed during upset feed water conditions.
This case study focuses on a cooling tower application comparing the performance of chillers using BioFilmPro versus conventional biocide injection.
Background
Aquatech was granted a cooling water management service contract for a pharmaceutical company's facility. The customer had been plagued by frequent biofouling issues, which resulted in degraded chiller performance and the growth of severe microbial colonies in the cooling tower. Biofilm, known for its poor thermal conductivity, had been impairing the condenser approach temperature, leading to elevated power consumption and increased overall operation costs.
To combat the biofouling problem, traditional methods such as oxidizing and non-oxidizing biocides were employed in the plant. However, these conventional chemical treatment programs proved challenging as microbes often adapt to their chemical environment, continuing to grow and survive. The system required regular technician intervention and maintenance labor to maintain the desired plant performance.
Solution
BioFilmPro system was installed in a 3” metallic pipe on an outlet of a chiller condenser which returned water to a common cooling tower that supports a total of 8 chillers. Due to plant-specific production conditions typically 4 or 5 chillers run on a continuous basis. The biofilm monitoring sensor was installed 10 feet downstream of the bacteria deactivator. The sensor output was connected to Optimizer Panel for controlling the chemical dosing pumps. The signal from the biofilm sensor was also remotely monitored over an internet connection with a standard device. The chillers’ performance was monitored during the two-month trial period.
A test protocol was developed to assess and compare the performance of BioFilmPro and conventional biocides on bulk water bacteria count in the system and measurement of the biofilm sensor signal.
Performance Observations
The following figure summarizes the measurement of the biofilm potential signal through the observation period.
Sensor Acclimatization: The first 7 days of the trial period were used to allow the sensor to start building biofilm on its sensing surface. Biocide injection continued as per the existing normal operating practice. The elevated mV reading indicates the injection of biocide during that period. Note that the biofilm sensor signal temporarily increases in the presence of biocide chemicals whether oxidizing or non-oxidizing type. That is the normal behavior of the sensor. Most of the signal averages around 350 mV during this period indicating good biofouling control using biocide chemicals.
Electrical Bacteria Deactivation-1: After the acclimatization period, for the next 11 days, biocide injection was completely stopped and only the Bacteria Deactivator was used to control biofouling. As can be seen from the above signal trend, the biofilm signal was still maintained around 350 mV indicating a similar or better level of control using the BioFilmPro system.
Conventional Biocide Treatment: For the next 11 days, we returned to the normal control program using traditional biocide chemicals and without a bacteria deactivator. As shown in the previous chart, the mV signal rarely touched the baseline of 350 mV exhibiting worse performance than the prior 7 days period using electrical bacteria deactivation.
Electrical Bacteria Deactivation-2: The bacteria deactivator was resumed again and chemical dosing was completely stopped in this phase. This control methodology continues as their preferred mode of biofouling control operation. In the initial period, the sensor signal is below the 350 mV baseline but later there was a sudden spike in the signal. That spike was due to water flow being stopped due to maintenance needs and the system was stagnant for a period of time that allowed biofilm to build on the sensor. The later mV signal as shown below continues to trend downwards indicating the effect of bacteria deactivation in controlling biofilm formation.
Observations of Microbial Counts: To monitor control program performance, dip slides were used also to collect data on bulk water bacteria (free-floating) in the water after bacteria deactivation. The following chart demonstrates that BioFilmPro performed better than or equal to the traditional biocide control program in maintaining lower bacterial levels (CFU /ml).
Note: The light blue zone above indicates that electrical bacteria deactivation was active. The target CFU/ml is under 105 cfu/ml.
Chiller Condenser Approach Temperature Data
The BioFilmPro performance was evaluated in terms of chiller condenser operational parameters. The condenser approach temperature (AT) denotes the performance of chiller plants, this is mostly affected by scales and the biofilm. Since biofilm is a poor thermal conductor, it adversely impacts heat transfer and results in increased AT that leads to increased power consumption. The graph shows decreased AT compared to conventional treatment.
Conclusion
The presence of biological fouling can have a detrimental impact on plant efficiency, resulting in increased operational costs. However, with Aquatech's BioFilmPro, several benefits have been observed in chiller performance evaluation. These benefits include:
- Reduce blowdown resulting in 300 m3 of water saved per month
- Improved plant efficiency through improved chiller performance & a 3-5% reduction in power consumption
- Decreased biocide consumption - 50-100% saving in biocide chemical costs
- Reduced human intervention by 20 man-hours per month for blowdown operations & chemical injection
Contact us to learn more about BioFilmPro today:
