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Biofouling in RO Systems Biofouling is the fouling that keeps RO operators up at night. Of the four fouling types it's the hardest to prevent and the hardest to clear, and it has a habit of coming straight back after a clean. Here is what it is and how to fight it. What biofouling is Biofouling is the growth of a microbial biofilm on the membrane. Bacteria in the feed attach to the surface, mul...

Types of Membrane Fouling Membrane fouling isn't one problem, it's four, and each behaves differently. Knowing which type you're dealing with decides how you prevent it and how you clean it. Here are the four, and how to tell them apart. Particulate and colloidal fouling This is the buildup of fine suspended matter, silt, clay, colloids and metal precipitates, as a cake layer on the membrane su...

Membrane Fouling Explained Membrane fouling is the gradual accumulation of unwanted material on a membrane, and it's the main reason membrane systems lose performance over time. Every RO and UF plant faces it. The question is only how well it's managed. Here is the plain version of what fouling is and how to stay on top of it. What fouling is Fouling is anything that builds up on or in the memb...

How to Dose Antiscalants Correctly An antiscalant only works if it reaches the membrane at the right concentration, continuously. Get the dose wrong in either direction and you either invite scale or create new problems. Dosing is where a good antiscalant is made or wasted, so it's worth doing properly. Why dosing accuracy matters Underdose and you leave scale risk on the table; the reject conc...

Calcium Sulfate Scaling in RO Calcium sulfate, or gypsum, is one of the classic RO scales, and it has a nasty habit: unlike carbonate, you can't dissolve it back off with acid. That makes it a scale you prevent rather than cure. Here is how it forms and how to keep it out of your membranes. What calcium sulfate scaling is Calcium sulfate scaling is the precipitation of gypsum, calcium sulfate d...

Silica Scaling Explained Of all the scales that form in RO systems, silica is the one operators dread, because it doesn't play by the usual rules and it doesn't come off easily. If your feed water is high in silica, it often sets the ceiling on how much water you can recover. Here is why, and what to do about it. What silica scaling is Silica in water exists mostly as dissolved silicic acid. As...

What Is Antiscalant? An antiscalant is a chemical that stops scale forming on membranes. It's one of the smallest line items in running an RO plant and one of the most important, because scale is among the quickest ways to lose recovery and wreck membranes. Here is what it is and how it does its job. What an antiscalant is An antiscalant is a specialty chemical dosed continuously into the feed ...

UF Membrane Cleaning UF membranes are built to be cleaned often, and their cleaning routine is different from RO. Instead of occasional deep cleans, UF relies on frequent, light cleaning to stay ahead of fouling, with stronger chemistry held in reserve. Here is how the layers fit together. When to clean UF UF cleans on two clocks. The frequent one is automatic: backwashing runs on a timer, ever...

How UF Improves SDI If you're protecting an RO plant, SDI is the number you watch, and ultrafiltration is the most reliable way to bring it down. Here is how UF turns a marginal feed into one your RO membranes will tolerate. What SDI is SDI, the Silt Density Index, measures how quickly water plugs a fine filter, which stands in for how much colloidal and fine particulate matter it carries. It's...

UF vs RO for Pretreatment Pretreatment decides how well and how long an RO plant runs. Get it right and the membranes stay clean; get it wrong and you clean constantly and replace early. When people ask whether UF or RO is the better pretreatment, they are usually comparing two different ideas, so it's worth separating them. Why pretreatment matters RO membranes are precise and easily fouled. W...