New USGS Filter Removes Phosphorus From Waste Water

Tech may reduce water treatment plant role in Harmful Algal Blooms

A tabletop water filter demo designed to remove phosphorus from waste water has in five-years grown into a fully functional water treatment system capable of filtering more than 100-thousand gallons per day.

Designed by a small U.S. Geological Survey team, this cost-effective and environmentally friendly water filter system uses discarded mining byproducts, called mine drainage ochre, as the primary filtering agent to remove phosphorus from municipal and agricultural waste waters.

Take a quick look at a low cost phosphorus removal water filter the USGS has been working on for several years. Matthew Morgan, Leetown Science Center (Public domain.)

Even though phosphorus is a vital nutrient for humans, animals and crops, it can cause problems in watersheds. Dietary phosphorus that animals and humans consume is excreted into waste water, where it can accumulate and feed cyanobacteria, spawning harmful algal blooms.

Harmful algal blooms are an explosion in algae growth, and are fueled by excess nutrients in water like phosphorus and nitrogen. The blooms can cause thick mats to accumulate on the surface of water and can deplete water oxygen concentrations, creating hypoxic dead zones responsible for fish kills and shellfish deaths. Some species of algae can even create a variety of toxins that are harmful to humans and wildlife.

“Harmful algal blooms are a world-wide problem,” said Philip Sibrell, USGS Engineer and lead designer of the filter. “Since phosphorus is one of the main drivers for freshwater blooms, being able to remove it from waste water has some real promise for being able to reduce the ecological impacts arising from harmful algal blooms.”

Researchers have made a lot of progress on the filter system the past few years at the USGS Leetown Science Center, where it was developed. The team is now ready to take the filter out of the lab and put it into public use. 

“We are at the point now where this filter system could support a small town, maybe around 1,000 people,” Sibrell said. “Finding cooperators willing to work with us and incorporate this technology will allow the system to continue to grow in size and improve over time.”

The USGS mine drainage ochre phosphorus filter system has been in the making for a long time. While the first filter prototype was built as a demo in 2012, USGS scientists began researching mine drainage ochre as a possible agent to remove phosphorus from water in 1999. Since the early days of this research, phosphorus usage around the world has steadily increased as more nutrient filled fertilizers are being used for home gardens, lawn care, golf courses, and farm fields.

While current waste water phosphorus removal systems are effective at removing the nutrient from water, they are expensive and have some problems the USGS phosphorus filter was designed to overcome.

The USGS phosphorus filter is constructed with large tanks that each hold around six hundred pounds of granular mine drainage ochre and uses a gravity flow process where the phosphorus infused water is piped to the top of the tank, allowing it to pass through the porous ochre media, and the filtered water is released out the bottom of the tank.    

The simple design of the USGS phosphorus filter, and the fact it uses mine drainage ochre as a filtering agent, keeps the costs down for any water treatment facility that considers using this technology. 

“Every component of the water treatment system was purchased as commercial, off-the-shelf items,” Sibrell said. “Nothing was special ordered and nothing was custom fabricated, which really helped us keep the costs down.”

In addition to the simple design and economic advantages of using mine drainage ochre byproducts as the filtering agent, the USGS phosphorus filter also has the added bonus of addressing the serious problem of acid mine drainage.

Acid mine drainage occurs when certain minerals in the ground – like pyrite or other sulfide minerals – are disturbed by mining, digging and excavating, exposing these minerals to air and moisture. When this happens, it causes a chemical reaction in the sulfide minerals that creates sulfuric acid and a variety of dissolved metals. This acidic, heavy metals-laced water eventually makes it into local watersheds, altering water pH and introducing new contaminants to ecosystems.

Because of these heavy metals, not all mine drainage ochres are suitable for use as a phosphorus filtering agent because some have the potential to contaminate the treated water. Therefore, the ochres used in the USGS phosphorus filter have been sourced from coal mine drainages, which usually results in lower levels of toxic metals like copper, lead and arsenic. Water that has been treated by these coal mine drainage ochres have been laboratory tested and scientists have confirmed that heavy metals are not present in the filtered water in detectable amounts.

In addition to providing a use for the acid mine drainage byproduct, the systems also has the potential to be another source of phosphorus. During the filtering process, once the mine drainage ochre becomes saturated with phosphorus, the phosphorus can be stripped off of the ochre, regenerating the media to be reused again, and recapturing the phosphorus to be recycled.

“The world relies on high phosphorus fertilizers for food production, and many deposits of this vital mineral are becoming depleted,” Sibrell said. “Because of that, the ability to recover the phosphorus from the ochre is a big deal, allowing us to close the recycling loop by reusing both the ochre and phosphorus again.”

The team recently entered stage one of the George Barley Water Prize contest, an innovation challenge competition sponsored by the Everglades Foundation, for the development of technology to remove phosphorus from waste water and agricultural runoff. Out of over 180 initial entries from around the world, the USGS technology placed in the top five for the first stage of the competition. The team is making preparations to participate in stage two of the competition, which is a laboratory demonstration of the technology and will take place this fall.  

For more information on using mine drainage ochre byproducts to remove phosphorus from water, click here.