November 2013, Vol. 25, No.11

Research Notes

Removing difficult pollutants from wastewater

Researchers at the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB (Stuttgart, Germany) have found that oxidative processes with hydrogen peroxide or ozone are effective at removing persistent pollutants from wastewater. Water resource recovery facilities’ biological treatment processes often are unable to remove such pollutants as drugs and cyanides, and additional special treatment is required, according to a Fraunhofer Institute news release.  

The institute runs a pilot facility in Stuttgart to test standard processes to determine how best to degrade many different components in wastewater. Two new methods have efficiently generated reactive species, especially hydroxyl radicals. These radicals oxidize pollutants into smaller, more degradable organic molecules or mineralize them completely to carbon dioxide.  

The first method is an electrochemical oxidative process that does not require additives and is suitable for treating extremely turbid wastewaters, the news release says. Developed within the CleanLeachate project funded by the European Union, it generates hydroxyl radicals when voltage is applied in a combined anode–cathode process. A membrane separates an electrolytic cell into two separate chemical-reaction areas. Polluted water flows past the anode, where it is oxidized and then pumped to the cathode, where the components are reduced, the news release says. A consortium of six partners from five European countries is using this process to treat highly polluted leachate from landfill sites. 

The second method is an atmospheric-pressure plasma reactor that purifies water during an oxidative process. Plasma, an ionized gas, can be ignited by applying high voltage. A stainless steel cylinder inside the reactor acts as a grounded electrode, and a copper network acts as a high-voltage electrode. The copper network sits on a glass cylinder, which acts as a dielectrical barrier, shielding the reactor to the outside. When high voltage is applied, plasma is ignited and maintained between the cylinder and copper network. Polluted water is pumped through the cylinder, and as water flows down the outer surface of the cylinder, it passes through the plasma zone, where pollutants are oxidized, the news release says. The method, funded by the European Union, is being applied by partners of a joint water plasma project. Researchers have been able to break down cyanide with this method. The method now is being tested on a larger scale, the news release says.  

Researchers also determined that an absorption stage is effective when pollutants are strongly diluted, present in low concentrations, or highly specific, the news release says. They developed a single-stage, cost-effective process for producing polymer adsorber particles. In the institute’s patented process, Nanocytes®, functional monomers are transformed into small polymeric adsorber particles with a cross-linking agent. The selectivity of the adsorber particles can be increased by adding to the mixture the target molecules to be removed from the water. Once monomers have been polymerized, target molecules can be removed from the adsorber particles. The approach offers flexibility in the design of surface chemical properties and adsorption behavior. And once the pollutants have been adsorbed, the adsorber particles can be regenerated and reused, the news release says. Researchers have been able to remove bisphenol A and penicillin G selectively from wastewater. 

  



September WER examines runoff from permeable pavement 

While runoff from newly constructed porous pavement contains fewer contaminants than other pavement, this does not always translate to improvement in the quality runoff quality over time. But stormwater treatment can improve the water quality of runoff, according to researchers from the National Institute of Water and Atmospheric Research (Newmarket, New Zealand).   

Researchers collected samples from four sites in Auckland, New Zealand; two were from impervious roads, and two from roads paved porous friction course (PFC).  

The research, reported in the September issue of Water Environment Research (WER), found that while runoff from a 1-year-old PFC highway was better than runoff from other sites, runoff from a 6-year-old PFC highway was similar in quality to that discharged from impermeable roads. The deterioration of runoff quality is consistent with the clogging of spaces in porous concrete and decrease in its permeability, the report says.  

Researchers also collected runoff samples at the outlet of a grass swale at the 1-year-old PFC highway and a wet pond at the 6-year-old PFC highway. Both showed reductions in contaminants, with the former predominantly lowering dissolved metal concentrations and the latter lowering particulate metal concentrations.  

“These results indicate that stormwater treatment can improve the quality of runoff discharged from PFCs, irrespective of their age, provided that treatment is targeted to the predominant contaminant phase present,” the report says. 

The article, “Variations in Highway Stormwater Runoff Quality and Stormwater Treatment Performance in Relation to the Age of Porous Friction Courses,” is available as an open-access document and can be downloaded free at http://goo.gl/Ao7Yqf  

 

Water Environment Research allows open access to one article per issue on a range of important technical topics such as nutrient removal, stormwater, and biosolids recycling.