What Can Make It Difficult to Treat Feedwater

Several factors can affect the efficiency of a water treatment. The first and most obvious are undoubtedly the contaminants found in the water.

Contaminants

Indeed, the diversity of contaminants that can be found in water is very broad. These contaminants can typically be divided into two categories that branch out into several subcategories:

1. Total solids
2. Dissolved gases

Dissolved solids represent the vast majority of contaminants and are divided into two other broad categories: suspended solids and dissolved solids. Among these categories we find the following contaminants:

• Algae ;
• Fungi ;
• Bacteria
• Silt
• Rust
• Flocs
• Acid
• Tannins
• Pyrogens
• Silica
• Various ions

 Even if this list is not exhaustive, the above contaminants can cause complications if treated in the wrong way. Let's take the example of silica, which in theory can be removed by reverse osmosis treatment. If silica concentrations become too concentrated on the concentrate side, osmotic membranes can clog and increase the internal pressure of the system. When both of these events occur, an increase in the risks associated with the use of the system and an increase in operating costs can be observed.

Similarly, the presence of certain contaminants will impact water parameters. Among the parameters to be monitored during water treatment are pH, conductivity, alkalinity and turbidity. Although water has other parameters, those listed above will have an impact on the choice of a water treatment system. Let's take the example of a chlorine disinfection step consisting of the addition of 2 mg/L of chlorine. These concentrations have been suggested without taking into account seasonal changes or fluctuations. Let's imagine that the pH of your water changes from 6.8 to 8.2. This variation will have a significant impact on disinfection because when the pH of a solution increases, the disinfection capacity of chlorine decreases.

Concentrations

Contaminant concentrations can impact the effectiveness of a water treatment system in two ways.

First, it is obvious that the number of contaminants in the water will have an impact on the effectiveness of the water treatment. For example, turbidity is the concentration of suspended solids in the water. If your water needs require reverse osmosis treatment and your water has a turbidity concentration of 250 ppm, pretreatment steps would be required since to be cost-effective and efficient, the feed water for a reverse osmosis system must not exceed 50 ppm turbidity.

Changes in Concentrations

Over time, significant variations can be seen in the levels of various contaminants. These changes can be due to a number of reasons, including climate change, seasonal changes, surrounding human activities or surrounding wildlife activities.

Typically, the largest changes in concentrations are caused by snowmelt in the spring. When this occurs, the amounts of organic matter increase significantly in surface waters as runoff carries contaminants accumulated during the winter to water bodies.

The problems that can arise from these changes are varied as they can cause increased concentrations or even incorporate new contaminants.

The source of the water

Hard-to-treat water is usually from private sources. This means that the water is collected in nature. There are two types of water that can be collected in nature: surface water and groundwater.

It should be noted that water that is difficult to treat and used for industrial purposes is generally required for mining, forestry, pulp and paper and other industries that are geographically remote. This is due to the fact that industries near cities generally use municipal water supplies.

Surface water

As discussed above, surface waters are susceptible to significant changes that can be caused by seasonal changes or surrounding human and wildlife activities.

Normally, the contaminants found in surface waters are suspended solids or various microorganisms. Although dissolved matter may be present in surface waters, concentrations are generally quite low.

Groundwater

When the water supply comes from a well, the seasonal changes are generally more frivolous. Generally speaking, water drawn from a well seems to be of better quality since it is often clear and uncontaminated by materials visible to the naked eye.

Without going into detail, when water circulates through the soil to the water table, it dissolves the minerals with which it comes into contact. This is why traces of hydrogen sulphide, iron, hardness, methane and alkalinity can be found in groundwater. These examples are not exhaustive and many more than these simple contaminants can be found.

• To learn more about the impact of soils on the composition of groundwater, we invite you to read this article: Mining water supply: the impact of different contaminants

How water treatment systems can be adapted

Now that we have a better understanding of how minor or major changes can affect the effectiveness of a water treatment system, let's look at how water treatment systems can be adapted to meet the specific needs of a user.

Whether we are talking about pretreatment, primary treatment or polishing, adaptations to systems are generally related to the size of the system, the technologies used and the recommended dosages.

Dimension

As you might expect, sizing allows for the water flows required for operations to be achieved without compromise. It is important to note that installing an oversized system can have a negative impact in some cases.

In short, when adjustments are made to the size of a water treatment system, the modifications made can be an increase in the number of membranes, an increase in the quantity of media (resin, sand, carbon, etc.), or an increase in the dosage of chemicals (chlorine, sodium metabisulfite, ozone, etc.).

Technologies

Obviously, the choice of technologies will have a significant impact on the quality of the water treatment. Depending on the quality of the feed water and the quality of the water required, the stages of a treatment system generally consist of pretreatment, main treatment and polishing.

Among the choices of technologies used for pretreatment are activated carbon, ion exchange, filtration and disinfection. Each of these technologies is used to remove specific contaminants. For example, surface water with a high concentration of bacteria may require chlorine treatment. Once chlorination is complete, an activated carbon stage may be added to remove chlorine residuals that could damage downstream equipment.

Central treatment systems are usually nanofiltration or reverse osmosis. Technological adaptations that can be made to these stages can be on the membrane network, the type of membrane, the number of passes and the number of membranes. Modifications in the membrane network and the number of passes will have an impact on the quality of the treatment and the flow rate offered. The number of membranes will adjust the flow rate of the system.

As mentioned above, the type of membrane can be osmotic membranes or nanofiltration membranes. In addition to these two categories, the membranes can be of different types. The different types of membranes can offer better performance against brackish water, desalination or targeting specific cationic or anionic contaminants.

Finally, like pretreatment, the polishing step can be adjusted in technology and size. The addition of technologies such as UV irradiation, electrodeionization or ion exchange allows the removal of recalcitrant contaminants. Each of these technologies offers various advantages and disadvantages.

In summary, the pretreatment step can be adapted technologically and in size to remove contaminants that are likely to cause problems in subsequent treatments. The main treatment can be adapted in size, technology and design to achieve the required standards, regardless of the residual contaminants. Finally, polishing can be adapted in a variety of technologies and sizes.

Since the information above is brief, here are a few articles that may help you better understand the impact of different water treatment technologies:

• Understanding the treatment steps of a reverse osmosis system
• Understanding dechlorination: Definition, operation and technologies
• What is ozonation: technology, capabilities and costs
• How to reduce the conductivity of your water
• How to remove silica from water

Dozens of other articles are available on our blog, visit it to learn more.

The Importance of Pilot Testing

As we have seen, water treatment systems can be very different from one another. This allows them to provide effective and consistent treatment, regardless of the situation.

Knowing that every little variation in the feed water can affect the quality of the treated product, the optimal method for selecting a treatment system is still pilot testing.

Pilot testing is a process consisting of a series of steps to identify all treatment options in order to select the most cost-effective and efficient one. Pilot testing consists of 6 steps:

• In-depth analysis of the water in order to know its parameters.
• Identification of the user's needs (water quality to be achieved, flow rate required, etc.)
• Identification of the technologies that could be ideal according to the needs and the water parameters.
• Assembly of the test unit with the identified technologies
• Test phase to identify the best technology
• Extended test phase to take into account possible changes in the water supply.

After completing all these steps, we will be able to offer a variety of solutions with different efficiency.

Conducting a pilot test offers several advantages. These include lower operating costs (OPEX) and stability in treatment. On the other hand, acquiring a water treatment system without taking the time to perform a pilot test can lead to complications, inefficiency of the equipment or a drastic increase in operating costs.

Pilot Testing Pays Off

As in all areas of life, using the right tools pays off. The same is true in the water treatment environment. The complexity of surface and ground water demonstrates the importance of having access to a variety of water treatment technologies to allow different industries to operate their equipment safely.

This is why conducting a pilot test offers various advantages when selecting a new water treatment system. For more information about this service, please contact us.

In the meantime, if you have any questions or problems, we invite you to visit our blog and our FAQ, where you may find answers. If not, contact us and we will be happy to help you.