The online RCAP Resources Library has a variety of resources that are useful to small, rural drinking water and wastewater systems.

Big hopes for Small Filters

At first glance, it looks like a metal box full of undercooked spaghetti. But these pasta-lookalike fibers represent the new technology of water filtration, capable of filtering material up to 30 times smaller than the current standard without things like flock ponds and sediment settling.
The new Membrane Bio-Reactor Filters are products of nanotechnology, a fancy word bandied about by engineers and computer geeks that’s rapidly finding a place in all kinds of industries, including water systems. This week’s eBulletin tells you what this is (in English!), why it’s important and whether it’s the right thing for your water system now or in the future.

Nanotechnology 101

The next generation of water systems is utilizing nanotechnology in a bid to make filtering more compact, more efficient and just plain better. Nanotechnology, in a nutshell is technology that uses objects measured in nanometers. A nanometer is one-billionth of a meter or one-millionth of a millimeter. Teeny tiny, in other words.
Nanotechnology, which really began developing in the 1980s, has been applied in a variety of fields, from medicine to computer manufacturing. It’s also being used to create better water and wastewater filtration systems.
Scientists have developed filtering material that works on the molecular level. That is, it allows the smaller water molecules to pass through its incredibly tiny holes, but it will not allow larger material, such as bacteria and solids, to pass. The result is a filter that can eliminate the need for flocculation, coagulation and sedimentation. Those filters are known as Membrane Bio-Reactor filters, or MBRs.
MBRs are popping up all over, and as prices drop and the need for more efficient systems grows, industry watchdogs expect MBR systems to take hold rapidly.

Additional Resources

Defining nanotechnology
A history of nanotechnology

MBRs – The Future Has Arrived

MBR filters eliminate several steps in the water filtration process and produce water that is often cleaner than called for by federal standards.
The standard for water filtration is 0.3 milligrams per liter. Anything bigger than that must be filtered out of the water before water can hit the tap. This includes bacteria, organic material, flock and general gunk.
MBR filters can vary in size, but they range from 0.03 milligrams to 0.01 milligrams per liter of filtration. That means they will filter 10 to 30 times smaller than standard filters today, and they do it in one step.
There are five types of membrane bioreactor filtration:

  • Reverse Osmosis (RO)
  • Nanofiltration (NF)
  • Microfiltration (MF)
  • Ultrafiltration (UF)


The main difference between each of these filters is the size of the holes within the membranes. The holes on the smallest filter, ultrafiltration, can get to less than 0.01 millimeters.
Many MBR filters are constructed of thousands of hollow tubes that look like spaghetti. Water is sucked into the tubes and flows out the ends clean, leaving the dirt, bacteria and other materials in the filter. Filter membranes also can be laid out in cone shapes or spirals, depending mainly on the manufacturer.
Most such systems are built to be self-cleaning. Backwash cycles are set up to kick on automatically after certain periods of time. The strong bursts of water flush out the filters and keep them clean and ready to work again to clean water.

Additional Resources

Microfiltration – How Does It Work?–article467

Shrinking the Steps

The MBR technology for water and wastewater is fairly new. Such systems have taken shape only within the last two decades. There are a few U.S. companies selling this technology for use in municipal wastewater treatment, and more recently for use in drinking water treatment.
As with most water and wastewater systems, MBR filtration systems can take years for a municipality to construct. However, it offers a much smaller footprint than conventional systems.
The more common, older systems use several steps and a variety of methods to filter the water. The usual methods include bringing in raw water, pretreating it chemically to help dissolved organic matter solidify, moving it into a presedimentation pool, sending it through an aeration system, pumping it into a tank and adding a coagulant, moving it to a flock pond, then to a sedimentation pond, then into filters, then to a stabilizer, then adding disinfection chemicals, moving it to a clear well and finally pumping it to the community.
MBR systems eliminate several of those steps. Raw water can be pretreated for better organic removal if needed, then it is pumped through the membrane filters, sent straight to disinfection and stored in the well until ready for distribution.
That’s it. No nasty flock ponds, no need to let the water sit in one holding tank after another. The process is shorter and faster, and the end result is cleaner water, because most solids and bacteria can’t pass through the membrane’s tiny holes. How much can get through depends on which type of filtration you use. Microfiltration may let more through than ultrafiltration, which gets close to just letting in water molecules.
All that treatment may be hard to picture, so check out our flow chart showing the basic steps most conventional systems use, and the steps that MBR systems use. A link to the flow chart is listed below.

Additional Resources

Conventional vs. MBR systems comparison

Cost Effective?

Unfortunately, the system isn’t within reach of most small, rural water systems – yet. Full installation of the system can cost several million dollars, mainly because the technology is so new. Even some of the larger systems may have trouble finding funding at the moment.
One such system serves about 14,000 customers and was looking to upgrade to meet forthcoming environmental standards on phosphorus levels. The town tested an MBR system in a pilot program and got excellent results.
One of the biggest reasons for the new system was to remove phosphorus from its wastewater. The city was trying to meet future standards of about 0.03 milligrams per liter. The MBR system, after pretreating with chemicals to precipitate dissolved solids including phosphorus, reduced the phosphorus levels to 0.025 milligrams per liter, well below their aim. It also dropped nitrate levels to less than 7 milligrams per liter, 3 milligrams below the standard; and reduced turbidity to 0.05 NTUs, far less than the standard of 0.3 NTUs.
Unfortunately, the system proved too costly for the city’s $20 million project budget. The lowest bid on an MBR system came in about $4 million over, and the city wasn’t able to find added funding in time, so they forged ahead with the more conventional biological nutrient removal system.
Funding options may be available, including bonds and grants, but it’s a good idea to have those options laid out before pursuing the MBR system.
So why bother considering such costly filters? Why would you need to exceed standard compliance?
One of the biggest factors is waterborne diseases. Current standards can eliminate most diseases, but sometimes some slip through. The most blatant example occurred in 1993 in Milwaukee County, Wisc. More than 400,000 people became sick from a Cryptosporidium outbreak caused from contaminated drinking water. However, Milwaukee’s water system, though experiencing a few operation deficiencies and high finished-water turbidities, was still in compliance with federal drinking water regulations in effect at the time. A smaller example would be in Clark County, Nev., which also experienced a Cryptosporidium outbreak in 1994. Only 78 were sickened that time, but the system was in full compliance and had no deficiencies in its filtration system.
MBR systems may be costly now, but they could save on maintenance and operational costs in the future. They also can help prevent waterborne disease outbreaks through better filtering.
Though the price isn’t right now for some, industry analysts report that competitive markets and the strong possibility of standards being lowered in the future could help drive costs down. The future may be here sooner than you think.