On-site But Out of Mind — Getting Extra Mileage Out of Your OSHG System

As concerns mount regarding the safety and security of using chlorine gas for water disinfection, the use of sodium hypochlorite (bleach) to create oxidants for water and wastewater treatment has quickly become considered the safer alternative.

Utilizing on-site sodium hypochlorite generation (OSHG) technology is cost-effective, safe and environmentally responsible. But, as with any piece of equipment, choosing the right technology and caring for it properly impacts both lifecycle costs and effectiveness. We talked with David McWalters, Field Service Manager-Americas, De Nora, to learn more.

Q: When specifying an on-site sodium hypochlorite generator (OSHG), what kinds of considerations can impact asset life/maintenance?

A. Understanding your project’s sizing needs makes a big difference in a successful maintenance program. In fact, system sizing is probably the most critical factor. If the system is undersized, it could be running 24/7, causing more wear and tear than the system is designed for.

Another consideration is the quality of the water. Using water that meets the system specification for hardness and other minerals will allow for the longest life of the system. 

Many OSHG manufacturers can provide ancillary equipment, such as water softeners, to resolve most problems with constituents in the water. The key is to understand and address your needs well before the project begins. 

It is also essential to implement the recommended maintenance on all of your ancillary equipment. For example, an effective water softener will extend the life of an OSHG. A poorly maintained softener, however, can result in a build-up on the cells and reduce the life of the system.

Like water, choosing a higher-quality salt can also extend the life of the OSHG system. In the way that using cheap oil in your car will affect the life of the engine, using inferior salt will affect the heart of the OSHG, your electrolytic cell. 

When salt has a high calcium content, it builds up on cells and requires more cleaning. Some OSHG systems require food-grade salt, and others do not. Always consider calcium content, system requirements and cost vs. maintenance costs when purchasing salts. 

The environment also impacts the initial OSHG system design. Some considerations include exposure to sun, heat, humidity and potential for corrosion, particularly related to the electronics of an OSHG. Cells should not be exposed to direct sunlight. That being said, part of the design for an outdoor OSHG will include a covering. These variables should all be addressed at the time of specification.

Q: How long will an electrolytic cell last?

A: We expect an average of seven years cell life, although, with proper care, I’ve seen some last as many as 12 years.

Q: Does the application of an OSHG system affect the maintenance schedule?

A: Yes. OSHG systems are used for the disinfection of produced water in oil and gas, municipal drinking water and wastewater, industrial cooling-tower water, power plant process water and aquatics, including swimming pools and large fountains. The quality of water and the harshness of the environment can significantly influence the maintenance requirements.

Q: Are OSHG systems safe? How do manufacturers ensure customer and community safety, either through design features or through maintenance recommendations?

A: OSHG is by far the safest method of disinfecting with chlorine since the raw materials are salt, water and electricity. During the electrolysis of brine, hydrogen — produced as a byproduct — is safely contained, rapidly diluted and vented into the atmosphere. 

As with any system, it is still essential to choose a unit with built-in safeguards. These include a hydrogen sensor to detect the concentration of hydrogen above certain levels, an air blower to dilute the hydrogen to a safe concentration, and associated controls to shut down the OSHG system and alert operators in case of emergency. 

To ensure customer, community, and employee safety, always choose a vendor with a proven track record for supplying systems that are designed with safety in mind.

Q: What does a typical maintenance schedule look like for an on-site sodium hypochlorite generator?

A: There are daily, weekly and monthly recommended procedures. These will vary depending on the application and use of the system. A reputable manufacturer can offer training, guidance and clear operations maintenance documentation.

The most important aspect of a maintenance plan is being proactive and performing maintenance on the manufacturer’s recommended intervals to maximize system reliability and longevity.

Q: What are the benefits of maintaining a consistent schedule, and what are the potential implications of not doing so? 

A: The benefit of performing consistent, scheduled maintenance is getting the most out of your system. On the flip side, not maintaining a consistent maintenance schedule can result in a shorter lifespan for the equipment and unplanned downtime.

Q: What kind of maintenance is required for an OSHG system?

A: Generally, the maintenance of an OSHG system is not very demanding. It includes daily or weekly reviews of the water softener, reviewing for leaks, changing filters and (the most critical part of the maintenance program) acid cleaning of the electrolytic cell. 

Acid cleaning is performed after a certain number of hours, determined by the application, the environment and water/salt quality.

Q: Are there OSHG systems on the market with features that impact maintenance?

A: Yes. Some OSHG systems come with a custom-designed acid cart. These carts are fully contained to minimize exposure to harmful chemicals, and easy connections allow for fast, clean-in-place maintenance.

Many also feature maintenance reminders via a built-in human-machine interface (HMI) display screen. These screens can be very helpful in preventing missed maintenance by notifying operators when maintenance is due for proper scheduling.

Remote monitoring allows a user to access the HMI screen from anywhere via computer, tablet, or smart device. With this remote-monitoring feature, users can view system parameters, tank levels and whether the machine is in operation or standby mode and more. 

On some OSHG systems, the electrodes are visible through either acrylic end caps or acrylic casings. This feature gives technicians the advantage of seeing the cell during maintenance checks.

Finally, some systems offer efficiency features designed to save time and money. For example, split flow technology can provide lower operating temperatures and reduced salt and electricity consumption over the lifespan of the system.

Understanding your project’s sizing needs, the quality of the water, and the harshness of the environment can significantly influence the maintenance requirements.  

Source: Q&A: On-site but out of mind... getting extra mileage out of your disinfection system with David McWalters, 1/2019