Research Notes

Decision-support system takes nutrient management online

The U.S. Geological Survey (USGS) has created an online, interactive decision-support system that provides easy access to six newly developed regional models describing how rivers receive and transport nutrients from natural and human sources to sensitive waters, such as the Gulf of Mexico.

Each region and locality has a unique set of nutrient sources and characteristics that determine how those nutrients are transported to streams, according to a USGS press release.

“Using the decision-support system, users can evaluate combinations of source reduction scenarios that target one or multiple sources of nutrients and see the change in the amount of nutrients transported to downstream waters — a capability that has not been widely available in the past,” said Stephen Preston, USGS hydrologist and coordinator for these regional models.

For example, the decision-support system indicates that reducing wastewater discharges throughout the Neuse River Basin in North Carolina by 25% will reduce the amount of nitrogen transported to Pamlico Sound from the Neuse River Basin by 3%, whereas a 25% reduction in agricultural sources, such as fertilizer and manure, will reduce the amount of nitrogen by 12%.

The new USGS regional models were developed using the SPARROW (SPAtially Referenced Regressions On Watershed attributes) modeling framework, the press release states. Results detailing nutrient conditions in each region are published in the Journal of the American Water Resources Association and can be accessed with the decision-support system online. USGS developed the SPARROW water quality model to assist with the interpretation of available water-resource data and provide predictions of water quality in unmonitored streams.

These regional SPARROW models incorporate geospatial data on geology, soils, land use, fertilizer, manure, wastewater treatment facilities, temperature, precipitation, and other watershed characteristics from USGS, the U.S. National Oceanic and Atmospheric Administration, U.S. Department of Agriculture (USDA), and U.S. Environmental Protection Agency (EPA).

These data are then linked to measurements of streamflow from USGS stream gauges and water quality monitoring data from approximately 2700 sites operated by 73 monitoring agencies.

The model was developed by the USGS National Water Quality Assessment Program, which provides information about water quality conditions and how natural features and human activities affect those conditions. Federal, regional, and state agencies, including EPA, USDA, the U.S. Bureau of Reclamation, and others, have used the SPARROW model results to inform water quality management decisions.

Access the online decision-support system at http://cida.usgs.gov/sparrow.

 

 

Saltwater may unlock ‘inexhaustible’ source of hydrogen

A grain or two of salt may be all that microbial electrolysis cells need to produce hydrogen from wastewater or organic byproducts without adding carbon dioxide to the atmosphere or using grid electricity, according to Penn State (State College, Pa.) engineers.

“This system could produce hydrogen anyplace that there is wastewater near seawater,” said Bruce E. Logan, Kappe Professor of Environmental Engineering. “It uses no grid electricity and is completely carbon-neutral. It is an inexhaustible source of energy.”

The King Abdullah University of Science and Technology (Saudi Arabia) supported this work.

Microbial electrolysis cells that produce hydrogen are the basis of this recent work, but previously, to produce hydrogen, the fuel cells required some electrical input. Now, Logan, working with postdoctoral fellow Younggy Kim, is using the ionic difference between river water and seawater to add the extra energy needed to produce hydrogen.

The key to these microbial electrolysis cells is reverse-electrodialysis, or RED. A RED stack consists of alternating ion-exchange membranes — positive and negative — with each RED layer contributing additively to the electrical output, according to a Penn State press release.

For RED technology alone to hydrolyze water — split it into hydrogen and oxygen gases — requires 1.8 V, which in practice would require about 25 pairs of membranes and increase pumping resistance, the press release states.

Microbial fuel cells, on the other hand, require only 0.414 V to produce hydrogen. Previous research has shown microbial electrolysis cells, by themselves, produce about 0.3 V of electricity from exoelectrogenic bacteria, which consume organic material and produce an electric current. So, by adding 11 ion-exchange membranes — five RED layers, which produce about 0.5 V — to microbial cells, the combined system can produce hydrogen gas, the press release states.

“Biodegradable liquids and cellulose waste are abundant, and with no energy in and hydrogen out, we can get rid of wastewater and byproducts,” Logan said in the press release.

The results of the research, published in the Sept. 19 issue of the Proceedings of the U.S. National Academy of Sciences, “show that pure hydrogen gas can efficiently be produced from virtually limitless supplies of seawater and river water and biodegradable organic matter.”

Logan’s cells were between 58% and 64% efficient and produced between 0.8 and 1.6 m³ of hydrogen for every cubic meter of liquid passed through the cell each day, the press release states. The researchers estimated that only about 1% of the energy produced in the cell was needed to pump water through the system.

“This could be an inexhaustible source of energy,” Logan said.

 

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