The aim of this research project was to help ensure that Micro Bio will not be limited by water supply during its capacity upgrades. It also gave an insight to water usage onsite, helping Micro Bio make the most out of each litre. This in turn should reduce pressure on the site’s feedwater supply and reduce unnecessary waste sent to the effluent, writes Pádraig Sheehan.
Introduction
In Micro Bio water is a key commodity as it is used directly in the production of caustic liquor which in turn affects HCl and sodium hypochlorite production. With pharmaceutical, food and electronics industries flourishing in Ireland the demand for caustics and acids is soaring. Naturally, Micro Bio aims to keep up with the ever-growing demand in these sectors. This increase in production will mean an increase in water usage across the site.
The aim of this research project was to help ensure that Micro Bio will not be limited by water supply during its capacity upgrades. It also, gave an insight to water usage onsite helping Micro Bio make the most out of each litre. This in turn should reduce pressure on the site’s feedwater supply and reduce unnecessary waste sent to the effluent.
Examining water usage onsite involved mapping everything including hard, soft and DI water. This helped track water from where it starts to where it ends up. Using this site level water map high-use areas can be singled out and further investigated to assess the possibility of reducing or reusing the water in these areas.
A system was designed to purify the second feedwater supply. It had to be able to treat the given feedwater to within purified water standards. This purification system has to consist of BAT treatment methods by combining various types of water purification to form one system.
A sustainability report looked at the findings from each section and ensure their sustainability as regards to economic, environmental, and social aspects. This is an essential section of the project as it ensures realistic goals are set for the company and that the research carried out can help provide a sustainable future for Micro Bio.
Water usage
A site level water map was set up. It proved to be essential for tracking high water flows back to their source. This, combined with flowrate data of wastewater entering and leaving the effluent plant, helped isolate high water users. These were prioritised in investigations to reduce their associated wastewater.
Figure 1 Micro Bio PFD
The three brine IX columns used to remove hardness from the plant feedwater were found to be one of the biggest wastewater contributors onsite. After setting up a portable flow meter, with an IBC as a control measure to ensure the flowmeter was reading correctly, the flows of the various regeneration stages were measured.
It was found that 57m3 of water was used per regeneration of each column, more than twice the required amount which was originally estimated to be aboutd 23m3. A detailed breakdown of volumes can be seen on the following two tables.
The possibility of reducing the water sent to waste was then investigated. A recycle line back into the DI tank used for regenerating these columns was considered.
Conductivity samples were taken throughout the two debrine steps to ensure high quality water would be recycled. Using an upper limit of 1000 μS/cm-1 it was found a total of 14.9m3 could be eligible for recycling.
Figure 2 Actual debrine conductivity trend
A water hardness test was carried out for a number of water samples. This further ensured the water was of high quality and minimal traces of CaCO3 were present, as it would contaminate the regeneration water.
The final test detected the presence of chlorides, as seen in Figure 3. The chlorides (Cl-) are an issue because for every 300 g/L of NaCl in brine solution there’s 6g/L of chlorates (ClO3-). If the chlorates come in contact with HCl free chlorine will form inside the column breaking down the resin, shortening its lifespan and reducing its efficiency. The acid rinse step makes the formation of free chlorine molecules inevitable therefore, making it an unsuitable option.
Figure 3 Chloride content in debrine samples overtime
Another recycle option that was assessed was to capture the debrine steps in a tank that would supply the plant feedwater make-up pit with diluted brine, helping aid the makeup of saturated brine solution to produce caustic liquor. This was a viable option.
The option implemented onsite involved connecting a VSD to the originally direct online pump. A 2kW VSD was taken from storage and installed. This helped prevent the pump from running at maximum, thereby reducing the flowrates during regeneration, and saving electricity.
Testing commenced after completion of the project before returning to college. Results were promising and it is hoped that the water used for regeneration will be reduced to the original estimate of 23m3 a reduction of 60% on current consumption.
Figure 4 2kW brine regeneration pump
Figure 5. VSD fitted
The water savings associated with the introduction of the VSD combined with the possibility of recycling back into the pit are clear throughout the different stages of increasing plant capacity when compared to the direct online pump alone, shown in Figure 6.
Figure 6 Savings in brine IX column
Secondary feedwater source and treatment
As the current feedwater supply is running at full capacity an additional water source was required. The options available were the town supply and a private well. The town supply had better quality water as it was pretreated and had greater flowrates available.
The well water was still within potable standards and would provide enough water for the planned increased production. The well would need closer monitoring to ensure no change in water quality. This could be done onsite or through an external analysis lab.
The main deciding factor was cost, the well came in much cheaper overall at only €18,500 versus at least €70,000 depending on Irish Water’s charges. The private well was, therefore, the proposed option to Micro Bio for future capacity increases.
Once the secondary feedwater source was chosen the new purification system could be designed. It was decided the best possible system, keeping BAT as a main focus, would consist of:
- Water softening using SAC IX columns;
- Chlorine removal with activated carbon, adsorption;
- Water filtration using ultrafiltration;
- An electric heater to allow faster permeate production in the RO unit;
- A membrane contractor to remove any excess gases, protecting the RO membranes;
- Water purification, the final step, consisting of a two-stage reverse osmosis system.
A UV unit was later added for sterilisation purposes to reduce biofouling problems with the RO membranes. This system can produce high-quality DIW at a much cheaper rate than the current DI system, €1.39/m3 - €1.65/m3 vs €1.91/m3. While also meeting the same high-quality standards as the current DI system.
Figure 7 New DIW purification system PFD
Conclusion
The site level mapping made identifying spikes in the wastewater and quantifying water figures more straightforward. This enabled the brine IX columns to be easily identified as high-water users. Initial results indicate that the installation of the VSD will reduce water consumption and reduce the amount of wastewater.
While the town supply had better quality and a larger capacity, the well water was the most economically sustainable choice. It had much lower capital and operating costs, saving thousands of euro each year.
The findings from a literature review were applied to produce the best system possible ensuring to comply with BAT. This resulted in multiple different methods being put in place to pretreat water before the final RO based purification step. The PFD helped visualise different stages in the system and what components were needed. The final system was one that could take well feedwater and successfully treat it to produce high quality DIW.
(This project was awarded the Best Water Conservation Opportunity when presented at Irish Water’s 2020 Certified Water Steward Programme.)
References
1.) Irish Water, 2020. Business Tariff Calculator. [Online]
Available at: https://www.water.ie/for-business/billing-explained/business-tariff-calculator/
[Accessed 26 11 2020].
2.) JHG Analytical Services, 2020. Micro Bio Water Quality Limits. [Online]
Available at: https://www.jhganalyticalservices.ie/
[Accessed 07 11 2020].
3.) ROCHE, 2018. Process Specification for Deionised Water Generation., Clarecastle: DPS Engineering.
4.) Water Technologies, 2020. Regeneration specifications in Micro Bio brine ion exchange columns, Cork: Water Tech.
Author: Pádraig Sheehan; Chemical and Biopharmaceutical Engineering, Munster Technology University. Academic supervisor: Brian Cott, Munster Technology University. Industrial supervisor: Brendan Kennedy, Micro Bio Ireland Limited.