Ensure a Sound Basis of Design
A #highpuritywater treatment system should include technologies specifically designed to remove feed water impurities to a degree that ensures the final product water quality is constantly achieved. Since the water source is inherently dynamic and a feed water analysis only provides a snapshot of the impurities present, a worst case estimate of all critical impurities should be used as a design basis. Based on this estimate and the final product requirements, the proper treatment operations can be identified and properly designed. Incomplete knowledge of feed water source can be attributed to:
Failure to review historical data
Failure to account for seasonal fluctuations
Unknown changes in municipal treatment techniques
No review of other treatment systems operating on feed water source
Inaccuracy of subjective water chemistry tests - or incomplete feed water analysis
The feed water analysis should include not only those parameters that are included or contribute to end product specifications, but also those which may affect the treatment operations. For example, the presence of silica in the feed water can significantly impact reverse osmosis (RO), Electrodeionization (EDI), and distillation unit performance, but they may not be critical to the final product water quality for certain applications.
Process Design Considerations
#Highpuritywater systems are challenging to monitor as they contain many different unit operations. Each step is designed for a specific purpose of changing the chemistry or removing a certain impurity or several impurities. The successful operation of downstream processes often relies upon sound performance of upstream operations. The use of “pretreatment” techniques exemplifies this, as many treatment techniques are included in system design for the sole purpose of protecting expensive downstream primary deionization techniques such as RO and distillation units.
As such, the overall process design and choice of pretreatment technologies should be based not only on the final product specifications, but also with the purpose of protecting the primary deionization techniques. Inadequate pretreatment may result in scaling, fouling, oxidation, or biofouling of downstream components.
In turn, polishing treatment techniques downstream of the primary deionization steps, may be required for the following reasons:
To meet very stringent product quality specifications
For specific contaminant reduction
To maintain water quality (high-purity water is aggressive and will degrade)
To compensate for deficiencies or limitations with the primary #deionization technique
Importance of Inter-Component Monitoring
As each operation in a high purity water system is employed for a particular purpose, their performance should be measured and analyzed on a regular basis to ensure efficient and effective operation. Although the criticality of each operation may vary, over time, poor performance of any operation will have a detrimental effect on some aspect of the system. The performance of a process is ideally monitored in real time by on-line or at-line instrumentation. For example, on-line hardness analyzers for softeners and chlorine analyzers for activated carbon units provide valuable data in real time.
However, on-line instrumentation can be expensive and wet chemistry tests are a cost-effective alternative for many systems. When taking grab samples instead of using on-line analyzers, the frequency and location of sampling is critical. Daily sampling is recommended for most parameters. If microbial control is a critical attribute of your final water, periodic inter-component sampling for total viable bacteria, bacterial, endotoxin, or other specific microorganisms may be required.
Additionally, rigorous monitoring of the performance of each process helps to establish maintenance intervals that are typically arbitrarily chosen when the system is commissioned. This can be used as a tool to relax certain maintenance functions such as backwashes, regenerations, cleanings, and sanitizations, saving both money and system downtime.
However, the two most critical benefits to inter-component monitoring of unit operations in a high-purity water systems are that upsets or excursions in the system are identified before product water quality is impacted, and a comprehensive understanding of each process is realized.
Final Product Quality
The idea of monitoring each stage of the process is inherent to the concept of #QualitybyDesign and can be used as a risk reduction tool. Monitoring for specific impurities allows for the opportunity to make system adjustments in real time to ensure that final product quality is never in jeopardy. If there is an upset condition, the source of the issue may be more easily discernable.
Monitoring for specific impurities throughout a high-purity water system may ultimately reduce end product testing. With the variable nature of the feed water, it should be considered for high-purity water treatment system where reliable production of water is critical to the success of your operations.