Membrane filtration systems are proven effective in potable water and wastewater treatment applications, among others. However, streams high in solids can pose challenges for membranes, causing fouling that requires intensive chemical cleaning.

Koch Membrane Systems (KMS) now offers the PURON MP (formerly known as MegaPure) hollow-fiber ultrafiltration product line. It is designed for high-solids applications that include tertiary treatment for wastewater reuse, treatment of surface waters and waters high in total organic carbon (TOC) for drinking water, pretreatment for reverse osmosis (RO) and various industrial process waters.

The new line, with average continuous solids tolerance of up to 250 mg/L, is an outside-in flow system designed to simplify operations, eliminate a clarifier pretreatment step in many instances, minimize downtime and reduce chemical usage.

It includes an advanced cartridge design to enhance solids management and reinforced PVDF hollow fibers that are highly resistant to breakage. Manny Singh, senior vice president of technology with KMS, described the offering in detail in an interview with Treatment Plant Operator.

TPO: What did you observe in the marketplace that told you a membrane system of this type would be beneficial?

Singh: One challenge we saw with membrane systems was inability to handle high solids in the feedwater. For example, in a municipal wastewater treatment plant, if a clarifier is upset, that can result in a slug load of solids leaving the clarifier. If a downstream membrane cannot handle those high solids, it can clog very quickly.

Some membrane systems may apply a pretreatment process upstream to handle those high solids, or the operators may do an aggressive chemical clean whenever those upsets happen. In the case of the PURON MP system there is no need for pretreatment to handle high solids. The membrane itself will ride through those fluctuations with minimal operator intervention.

TPO: Have you observed similar performance in drinking water applications that draw from surface water sources of variable quality?

Singh: We did a pilot study in Brazil where a water utility draws from a shallow river. After a heavy rainfall, the feedwater turbidity went above 8,000 NTU. The water looked like mud; the membrane worked fine. There was no need for pretreatment or pre-clarification. The membrane was able to handle the high solids in a single-step process.

This technology also applies to waters that may be low in suspended solids and turbidity but high in total organic carbon or color. Some applications may have color at 200 to 250 TCU or higher, or TOC above 20 mg/L.

These organic-laden waters may require coagulant doses at 150 to 200 ppm of alum or ferric chloride to handle those TOC and color loadings. The ability of these membranes to handle such high levels can help in devising a single-stage system. There is no need to place a clarifier upstream of the membrane to handle those loadings.

TPO: What other market needs does this technology address?

Singh: Fiber breakage in membrane systems is a significant issue. Fiber breaks typically happen when membranes are stressed excessively, such as during aeration or intensive chemical cleaning. That requires a lot of operator intervention — the filter trains have to be taken offline to repair the fibers.

Our system has supported membranes. The PVDF membranes are cast on a polyester braid that provides structural strength — you can’t break it with your hands no matter how much force you apply. Supported membranes enable users to apply air scour at much higher rates without worrying about fiber breaks. That enhances the ability to remove solids from the fiber bundles.

TPO: What else is unique about this system?

Singh: This is the only membrane system that has a single-potted cartridge configuration. There is no header at the bottom of the cartridge — the fibers hang loosely. That makes air scour more effective. The air follows the path of least resistance, so it can channel around and between the fibers where most of the filtered solids are concentrated.

TPO: Are there any advances in the membrane fibers themselves?

Singh: We did substantial research to optimize the chemistry of the membranes. The pore size is very uniform at 0.03 micron. If the membrane pore size distribution is too wide, then the large pores can easily become plugged by foulants. In that case the transmembrane pressure rises rapidly, and it’s not easy for the filter to recover. In our pilot testing, we have observed that because of tight pore size distribution, our membranes don’t need aggressive chemical cleans. That translates into less maintenance and chemical cost savings for users.

TPO: Do higher-solids feedwater streams require more frequent backwashing?

Singh: Yes. The backwash frequency is a function of the feedwater solids content. The typical back-pulse interval ranges from 20 or 25 minutes for waters very high in solids, to 50 or 60 minutes for waters very low in solids. Backwash frequency is adjusted automatically based on transmembrane pressure.

TPO: Is this technology best suited to utilities of a particular size range?

Singh: These membrane systems are very modular. The standard, pre-engineered systems start as small as 0.1 mgd and go up 2 mgd per skid. Multiple skids can be used depending on the size of the overall system. We are pursuing jobs with flows all the way up to 50 to 70 mgd.