Filter May Be a Match for Fracking Water

Superhydrophilic Membrane Cleans Fluids for Reuse

Date: September 25, 2017
Source: Rice University
Summary: A superhydrophilic filter has proven able to remove more than 90 percent of contaminants from water used in hydraulic fracturing operations at shale oil and gas wells.

A superhydrophilic filter produced at Rice University can remove more than 90 percent of contaminants from water used in hydraulic fracturing operations. In this image, 'produced' water from a Marcellus shale fracturing site is at left, the retentate (carbon removed from the feed) is at center, and filtered 'permeate' water is at right. The hydrophilic treatment keeps the filter from fouling and restricting flow while rejecting contaminants.
Credit: Barron Research Group/Rice University

A new filter produced by Rice University scientists has proven able to remove more than 90 percent of hydrocarbons, bacteria and particulates from contaminated water produced by hydraulic fracturing (fracking) operations at shale oil and gas wells.

The work by Rice chemist Andrew Barron and his colleagues turns a ceramic membrane with microscale pores into a superhydrophilic filter that "essentially eliminates" the common problem of fouling.

The researchers determined one pass through the membrane should clean contaminated water enough for reuse at a well, significantly cutting the amount that has to be stored or transported.

The work is reported in Nature's open-access Scientific Reports.

The filters keep emulsified hydrocarbons from passing through the material's ionically charged pores, which are about one-fifth of a micron wide, small enough that other contaminants cannot pass through. The charge attracts a thin layer of water that adheres to the entire surface of the filter to repel globules of oil and other hydrocarbons and keep it from clogging.

A hydraulically fractured well uses more than 5 million gallons of water on average, of which only 10 to 15 percent is recovered during the flowback stage. "This makes it very important to be able to re-use this water," Barron said.

Not every type of filter reliably removes every type of contaminant, he said.

Solubilized hydrocarbon molecules slip right through microfilters designed to remove bacteria. Natural organic matter, like sugars from guar gum used to make fracking fluids more viscous, require ultra- or nanofiltration, but those foul easily, especially from hydrocarbons that emulsify into globules. A multistage filter that could remove all the contaminants isn't practical due to cost and the energy it would consume.

"Frac water and produced waters represent a significant challenge on a technical level," Barron said. "If you use a membrane with pores small enough to separate, they foul, and this renders the membrane useless.

"In our case, the superhydrophilic treatment results in an increased flux (flow) of water through the membrane and inhibits any hydrophobic material -- such as oil -- from passing through. The difference in solubility of the contaminants thus works to allow for separation of molecules that should in theory pass through the membrane."

Barron and his colleagues used cysteic acid to modify the surface of an alumina-based ceramic membrane, making it superhydrophilic, or extremely attracted to water. The superhydrophilic surface has a contact angle of 5 degrees. (A contact angle of 0 degrees would be a puddle.)

The acid covered not only the surface but also the inside of the pores, and that kept particulates from sticking to them and fouling the filter.

In tests with fracking flowback or produced water that contained guar gum, the alumna membrane showed a slow initial decrease in flux -- a measure of the flow of mass through a material -- but it stabilized for the duration of lab tests. Untreated membranes showed a dramatic decrease within 18 hours.

The researchers theorized the initial decrease in flow through the ceramics was due to purging of air from the pores, after which the superhydrophilic pores trapped the thin layer of water that prevented fouling.

"This membrane doesn't foul, so it lasts," Barron said. "It requires lower operating pressures, so you need a smaller pump that consumes less electricity. And that's all better for the environment."

Story Source:
Rice University. "Filter may be a match for fracking water: Superhydrophilic membrane cleans fluids for reuse." ScienceDaily. ScienceDaily, 25 September 2017. https://www.sciencedaily.com/releases/2017/09/170925104714.htm.

Diverse Landscapes are More Productive and Adapt Better to Climate Change

Date: September 4, 2017
Source: University of Zurich
Summary: Ecosystems with high biodiversity are more productive and stable towards annual fluctuations in environmental conditions than those with a low diversity of species. They also adapt better to climate-driven environmental changes. These are the key findings environmental scientists made in a study of about 450 landscapes harboring 2,200 plants and animal species.

Ecosystems with high biodiversity are more productive and stable towards annual fluctuations in environmental conditions than those with a low diversity of species. They also adapt better to climate-driven environmental changes. These are the key findings environmental scientists at the University of Zurich made in a study of about 450 landscapes harbouring 2,200 plants and animal species.

The dramatic, worldwide loss of biodiversity is one of today's greatest environmental problems. The loss of species diversity affects important ecosystems on which humans depend. Previous research predominantly addressed short-term effects of biodiversity in small experimental plots planted with few randomly selected plant species. These studies have shown that species-poor plant assemblages function less well and produce less biomass than species rich systems.

Extensive Study with About 2,200 Species in 450 Landscapes

Researchers participating in the University Research Priority Programme "Global Change and Biodiversity" of the University of Zurich now demonstrate similar positive effects of biodiversity in real-world ecosystems in which mechanisms different from the ones in artificial experimental plots are at play. Using 450 different 1-km2 landscapes that spanned the entire area of Switzerland, they investigated the role of the diversity of plant, bird and butterfly species for the production of biomass, which was estimated from satellite data.

Biodiversity is Important for the Functioning of Complex, Natural Ecosystems

"Our results show that biodiversity plays an essential role for the functioning of extensive natural landscapes that consist of different ecosystem types such as forests, meadows or urban areas," study leader Pascal Niklaus from Department of Evolutionary Biology and Environmental Studies says. The analyses showed that landscapes with a greater biodiversity were more productive and that their productivity showed a lower year-to-year variation.

Biodiversity Promoted the Adaptation of Landscapes

The satellite data analysed by the scientists revealed that the annual growing period increased in length throughout the last 16 years, an effect that can be explained by climate warming. The prolongation in growing season was considerably larger in more biodiverse landscapes. These relations were robust and remained important even when a range of other drivers such as temperature, rainfall, solar irradiation, topography, of the specific composition of the landscapes were considered. "This indicates that landscapes with high biodiversity can adapt better and faster to changing environmental conditions," Niklaus concludes.

Story Source:
University of Zurich. "Diverse landscapes are more productive and adapt better to climate change." ScienceDaily. ScienceDaily, 4 September 2017. https://www.sciencedaily.com/releases/2017/09/170904165641.htm