How are alum and ferric chloride used in water treatment?
As every water treater knows, coagulants are used in the first step of water treatment; they destabilize the water so micro flocks can begin to form. This is followed up by a polymer, which turns it into a larger flock by creating a bigger charge. Alum and ferric chloride are two widely-used “commodity chemical” coagulants that have been around for a long time.
Why are alum and ferric chloride so commonly used?
Some water treaters simply aren’t aware of alternative products. The companies that supply alum and ferric chloride aren’t advertising competing products, and the companies that do sell alternative products struggle to get the word out.
Pros and cons of alum and ferric chloride
While not an exhaustive list, here are some important positives and negatives to consider about these chemicals:
Pros of alum
- It’s inexpensive, usually widely available, and easy to use if you dial it in properly.
Cons of alum
- Alum has a demand for hydroxide and alkalinity and only works within a certain pH range.
- Large amounts are often required. The dirtier the water, the more alum you need to feed.
- Once you feed a certain amount of alum, it essentially quits working. To treat excessively dirty water, simply increasing the alum isn’t going to do anything. For example, to treat muddy water like that from the Mississippi, even 250 parts of alum isn’t going to cut it. Alum just doesn’t work in very dirty water.
- It produces a lot of sludge. Plus, the sludge it creates is not very easy to de-water because it becomes very gelatinous. For example, let’s say a small plant runs at a million gallons a day, feeding 25 parts of alum on a wet basis. That means they’re putting in 208.5 pounds of alum, but 101 of those pounds are merely wasted solids that the plant must deal with every single day. Over the course of a month, that’s 3,000 pounds. And over a year that’s almost a full truckload of extra weight due to just the alum.
Pros of ferric chloride
- There is no pH requirement; it works over a broad pH range. And it’s fairly easy to use.
Cons of ferric chloride
- It’s very, very corrosive. Special piping, storage equipment, and pumping equipment are required because it’ll eat through things like the flow meter—and basically anything but 318 stainless steel.
- The price can fluctuate. The components used to make ferric chloride, whether the iron or the hydrochloric acid, go up and down quite a bit in price, which can greatly affect the price of ferric chloride itself. Currently, ferric chloride users are facing cost increases potentially as high as 40%. Many water plants can’t afford a 40% price increase, so they’re looking for alternative products.
What are some substitutes for alum and ferric chloride?
Substitutes include other aluminum and iron salts, like sodium aluminate and ferric sulfate, but these may or may not work. Proprietary products, instead of commodities, may offer a better solution. For example, a few products from ATS Innova’s ATS 800 line are excellent substitutes for alum and ferric chloride:
ATS 835 is a great replacement for alum because it does an amazing job, but with a much, much smaller dose. For example, a water treater who feeds 25 parts of alum (or a related product) might get away with feeding just 2-3 parts of ATS 835. And because ATS 835 is completely soluble, it will hardly increase solids due to the coagulant.
Alternatively, if a water treatment plant is using ferric chloride, a recommended replacement product is ATS 806. This product is not only a successful replacement but also offers a much better quality of water for the same dollars spent. ATS 806 removes much more total organic carbon than either alum or ferric chloride. And while it may be a bit more expensive than the ferric, the amount needed is roughly only 25% of the amount of ferric required, so it’s often the same price or cheaper—with a better water quality as the outcome. Both large and small plants will see cost savings; the more ATS 806 is used to replace ferric chloride, the larger the savings.
It should be noted that both ATS 835 and 806 are potentially excellent replacements for alum or ferric chloride—it’s all dependent on the chemistry. To help you determine which replacement product to try, ATS offers free jar testing. To schedule your free jar test, call 855-215-4600.
What should water plants look for in an alternative?
Water treaters should look for settled turbidity and filtered turbidity. They also want to understand how it affects their pH and TOC removal.
How do I go about finding substitute products?
The first thing is to realize that not all chemicals are the same, and not all chemicals are commodities. Substitute products may likewise not be commodities.
Innova’s ATS 806 and 835 are examples of such products–they’re not commodities, but they can give a better outcome while using less chemical. ATS Innova’s master chemists, combined with over 30 years of experience in the water treatment industry, offer solutions beyond what commodity chemicals can achieve.
Give ATS Innova a call. We’ll arrange to come and help you with your water. If you’re not in our area, you can send us your water. We’ll test it and send you the results at no cost. If we find that a product will benefit your water, we’ll let you know. And if it’s not going to work for you, we’ll tell you that too.
As a water treater, you owe it to yourself to find out if there are better options that can save you money, improve your water quality (less TOC and fewer DBPs leftover), and make you look like a hero.
To the rare water treater who has perfect water, congrats! To the vast majority of water treaters, who struggle with meeting required levels for TOC and DBPs, there are likely better solutions for your plant than alum and ferric chloride.
