Five Common Problems with Raw Water Treatment and How to Avoid Them

For industrial companies treating a raw water source for its processes, there are several issues that can surface during treatment that we see on a regular basis. We’ve broken out the five most common problems with raw water treatment and how to avoid them below.

Whether you’re designing a new plant or updating existing equipment, avoiding these five common raw water treatment problems might help you operate your process more efficiently down the line, so they’re important to keep in mind and plan for ahead of time, if possible:

1. Variation in turbidity

When plants begin to experience a variation in turbidity—the cloudiness of water due to the presence of a large number of particles—it can have negative effects on the quality of the process and effluent from the plant. It’s helpful to have a consistent year’s worth of data to evaluate the turbidity levels coming into the plant from season to season prior to designing the system.

When the plant is designed around the seasonal turbidity flow without taking into consideration any of the changes it might see—if the turbidity increase without the plant being ready for this change—there are several problems that might occur.

When the turbidity is too high for the plant to remove it efficiently, it often carries over to production and can be present in your discharge, contaminating your process and causing fines when local discharge regulations are not met.

Another issue we see when turbidity levels vary, is the amount of sludge that’s generated from treating the turbidity. Oftentimes secondary sludge systems can’t handle the load, and therefore the sludge backs up in the clarifier and shuts down the pretreatment system.

The best way to combat this problem is to design a slightly oversized treatment system for turbidity, anticipating that variations will occur. It’s also beneficial to design a recycle system so if the water doesn’t meet the quality requirements as it moves through the process, it can be recycled through and retreated more thoroughly.

Another way to prepare for varying turbidity is to include variable controls on your chemical feedsystems so you can adjust chemical feed rates. You can also oversize the sludge handling system so when you pump out the sludge in the clarifiers filters, you have a sludge handling system that, if the turbidity does fluctuate, has the ability to manage it.

2. Variation in flow

Many times, industrial companies make educated guesses as to what they think their flow rates are going to be. If an industrial facility is not equipped to handle these variations, they’ll likely experience upsets to the system that will carry turbidity over and plug any downstream filters.

Understanding what peak demand is and using holding tanks to try to buffer out the peak demands is one way to prepare for flow variations. Typically, you want to design the system with an excess flow buffering/holding capacity so you can run your plant as consistently as possible and then use the holding tanks downstream to handle surges in production needs.

Another thing you can do is put variable controls on your chemical feed systems, so as your flow changes, your chemical feeders can ramp up and ramp down to handle it.

With a combination of variable flows on feed treatment equipment and storage on peak demands, you can get your system to balance out more easily and increase functionality. If you don’t have the ability to automate chemicals, you will need to test more often. You can try to run your plant at a consistent flow rate to avoid these upsets and turbidity issues.

Raw water treatment plants do not handle variations in flow well, so it’s helpful to design the system with this in mind from the start.

3. Changing feed chemistry

Many surface and well waters have seasonal variations in water chemistry. Industrial plants need to be very careful in the design of any raw water treatment systems to be large enough to handle these changes.

Let’s say, for example, you have a problem with raw water iron or silica and it changes seasonally. If you haven’t designed your clarifiers large enough to get the proper retention times and you haven’t designed your feed systems large enough to handle the increased load, you’ll get carryover with either silica and/or iron into the downstream equipment where they cause all sorts of problems such as scaling and fouling.

Secondarily, if you don’t anticipate the higher seasonal loads of iron and silica and try to precipitate it out, you may then have particulate carryover to your sludge handling systems, causing them to fail.

All in all, it’s very important to understand the variations of the contaminants feed water chemistry and design a system accordingly. Physical chemical processes to remove the iron and silica is typically an oxidation chemical (such as oxygen) and an aluminum-based coagulant such as alum that will precipitate out the iron and silica and allow them to settle so they can be removed in a clarification filtration system.

If you don’t have a chemical feeder size large enough, you may get carryover of iron and silica. Or if you’re able to precipitate higher, unanticipated volumes of iron and silica, your underflow handling systems such as your sludge thickening and filter pressing operations may not be able to handle the increased amount of sludge.

4. Being unaware of updates/changes to quality requirements

When you design a plant for a certain process and to make sure you meet stringent requirements, sometimes you might find out later you need to adapt your equipment to account for recent changes in regulations. This is a common occurrence that sometimes happens after plants have been installed for years. The plant may be running well and designed to deliver a certain kind of effluent quality, and then one day the standards of the quality requirements become more stringent and the plant no longer meets the requirements at the facility.

As an example, let’s say you are feeding water to a low-pressure boiler and you put in a bigger boiler that runs at a higher pressure. Depending on the requirements of the new boiler, the quality of the feed water to the boiler might no longer be adequate. You might need to ensure the feed water is a better quality and add ancillary equipment to the system.

For this reason, plants should be designed with some forward thinking in mind of what might be anticipated. It is also helpful to plant for expansion and quality improvement and allow space in the plant for adding additional equipment to handle changes in quality requirements.

5. Secondary waste

One of the biggest mistakes made in designing raw water treatment plants is not looking carefully at the secondary waste generated by the process.