Part 4 of 4: Water Conditions
Challenge: Identify Critical Variations in Raw Water Conditions
The raw water coming into a plant is subject to changing conditions. For example, lakes and rivers may contain elevated levels of suspended solids or turbidity after a rainstorm. These changes must be seamlessly handled by a plant’s water treatment system to ensure the ongoing availability of purified makeup water.
Monitoring the condition of influent water and adjusting its treatment to maintain proper levels plays an important role in protecting components subject to damage or performance degradation from solids overload, such as RO membranes or plant filters. In situations of high turbidity, operators may elect to cycle highly turbid water longer through a relatively inexpensive component, such as a carbon filter, before passing it on to the RO or demineralizer. For plants with multiple demineralizer trains (parallel paths), water may be sent through a newer or older resin bed based on its condition.
Key on-line measurement parameters for raw water besides turbidity include pH, conductivity and hardness monitoring for process control. Checking chlorine may also be necessary if sourcing feedwater from rivers, wastewater treatment effluent or city water sources. Given the high sensitivity of RO membranes to chlorine and the potential for damage, measuring chlorine becomes even more important.
Water Treatment Plant RO and Demineralizer Systems
Challenge: Monitor Early Indicators of Treatment Problems
Most Reverse Osmosis (RO) systems operate under fairly steady conditions over long periods of time. However, changes in flow or RO efficiency occasionally take place, resulting from any number of causes including fouling, membrane damage or changed operating conditions. Operators strive to get at root cause quickly before more fouling takes place in membranes or the element feed path.
When anion or mixed bed demineralizers approach exhaustion, silica is the first impurity to break through into the effluent. Silica analysis provides a sensitive check of demineralizer performance given its detection by instrumentation far sooner than an increase in conductivity. On-line silica analyzers provide the added benefit of detecting increasing levels before resin exhaustion. A regeneration process can be initiated and extensive repairs for silica scale removal averted.