Category: August 2018

By Catherine Ortega Klett, NM WRRI Program Manager

Amanda Otieno received a master’s degree from the University of New Mexico’s Water Resources Program in December 2017. In 2017, she was awarded an NM WRRI Student Water Research Grant for a study on the effects of the 2011 Las Conchas fire on soil chemistry (see July 2017 eNews), under the advisement of Dr. Rebecca Bixby of UNM’s Department of Biology. Amanda is now working for a precious metals company in Rio Rancho as a chemist.

Amanda is a co-author on a recently published paper entitled, Metal Reactivity in Laboratory Burned Wood from a Watershed Affected by Wildfires. The paper was published in 2018 in Environmental Science and Technology (Environ. Sci. Technol. 2018, 52, 8115-8123). Authors include Asifur Rahman, Eliane El Hayek, Johanna M. Blake, Rebecca J. Bixby, Abdul-Mehdi Ali, Michael Spilde, Amanda A. Otieno, Keely Miltenberger, Cyrena Ridgeway, Kateryna Artyushkova, Viorel Atudorei, and José M. Cerrato. Both Asifur Rahman and José Cerrato also have received funding through the NM WRRI.

The paper describes how wildfires, such as the Las Conchas fire, have many lingering effects on local water quality, primarily due to the leaching of metals from burned soils and wood ash. The main objective of the reported study was to investigate the interfacial processes affecting wood ash reactions with water by integrating laboratory experiments, spectroscopy, microscopy, and aqueous chemistry methods. The release of metals and dissolved organic carbon (DOC) was assessed in batch experiments reacting laboratory burned wood ash with water. Additional experiments were conducted to investigate sorption processes that affect ash−metal interactions.

Results from the soil analysis showed that soils from different burn severities have different concentrations of major elements including iron, copper, chromium, zinc, and manganese. For example, iron was substantially higher in the high severity burned soils, compared to the unburned soils. This soil chemistry information was essential in understanding the composition of ash from different tree species. Burned soil and ash in contact will naturally exchange metallic ions, so that the determination of the concentrations of trace metals in ash as a function of temperature, which was the primary focus of this report, was supported by knowledge gained through the concurrent analysis of burned soils.

The investigation of soil chemistry changes from different burn severities help to establish the physical factors that control the metal and DOC content associated with the water leaching of ash produced by different trees, such as Pine, Spruce, and Aspen, and at different burn temperatures. An interesting qualitative result is that many metals are found to leach from the ash into water initially, but then to subsequently reassociate with the ash surface over time. For example, up to 94% of copper ions were removed from water solution over a three-hour period, by subsequent readsorption to Pine ash created at a burn temperature of 350⁰C.  This ash also produced higher DOC concentration in water compared to ash burned at higher temperatures.

Results, such as these, may provide additional insight when considering watershed management after a wildfire, specifically one with different burn severities. The detrimental effect of the transport of wood ash into nearby streams can be more properly evaluated if the effect of burn intensity of the mineralogy and reactivity of metals associated with wildfire ash is better understood. Post-fire recovery strategies might be improved by taking into account the affected types of vegetation and the burn intensities experienced. The New Mexico Environment Department and the U.S. Forest Service are examples of agencies that may benefit from such analyses.

By Catherine Ortega Klett, NM WRRI Program Manager

Galathara Lekamlage Chathurika Lakshani Bandara is a PhD graduate student in the NMSU Civil Engineering Department. In conjunction with her faculty sponsors in the same department, Drs. Nagamany Nirmalkhandan and Pei Xu, Chathurika is currently making use of an NM WRRI Student Water Research Grant to study the feasibility of recovering potable-quality water from wastewater through an innovative combination of three methodologies.

First, the energy of sunlight is used to cultivate algae in the wastewater, which entraps and removes organic contaminants and nutrients in the wastewater by processes such as adsorption and ingestion/digestion transformations. Next, the wastewater is allowed to partially diffuse through a membrane by forward osmosis (FO). This is the familiar process by which plants pump water from the ground, for example. The idea here is to separate the freshwater from the contaminated wastewater by a membrane that is permeable to water molecules. Because of the relative lack of salt, and therefore higher concentration of water molecules in the wastewater, there is a net flow of water into the provided relatively salty water (appropriately called the “draw” solution; in real-life applications this might be sea water, for example). Finally, the now water-diluted draw water is subjected to reverse osmosis (RO), wherein externally provided hydraulic pressure on the draw solution overcomes osmotic pressure and forces water in the reverse direction, across a second membrane into another reservoir of relatively salt-free “product water”. The goal of the study is to demonstrate the technical feasibility of this integrated algal-based wastewater treatment coupled with the forward and reverse (FO-RO) osmosis steps. A bench-scale FO-RO system of this type has been tested for over a year, and has produced product water meeting primary and secondary drinking water standards. Next, a pilot-scale system will be deployed to assess performance under field conditions.

This integrated process has the potential to produce potable-quality water with zero liquid discharge. This approach can reduce energy consumption of both wastewater treatment and water treatment by minimizing aeration energy, water discharge, and water pumping-related energy consumption. The proposed FO-RO process can produce drinking water of high quality, because water passes through two dense membranes that can reject almost all the contaminants in the water. In the long-term, this system has the potential to minimize freshwater withdrawals and provide a locally available renewable source of water for delivering potable water in a sustainable and environment-friendly manner.

Chathurika is from the town of Rathnapura in Sri Lanka. She received her bachelor’s degree (with Honors) from the University of Peradeniya, Sri Lanka (2014), specializing in chemical and process engineering. She also received a master’s degree from the same university in the Civil Engineering Department, specializing in water and environmental engineering (2017). She hopes to complete a PhD in civil engineering in May 2021.

Soon after beginning her graduate studies at NMSU, Chathurika participated in the Waste Management Education Research Consortium (WERC) 2018 Environmental Design Contest, along with three undergraduate students, as a team. They developed a reactor system to remove ethanol and methanol from wastewater from the International Space Station (ISS). It was an algal-based reactor system followed by an activated carbon filtering system. They received the Judges’ Choice award for that competition. She is grateful to her advisors, Dr. Khandan and Dr. Xu, who encouraged the team from the outset, and to Dr. Yanyang Zhang, who helped formulate the design model and other requirements related to the contest.

With the current WRRI grant, Chathurika says she will be able to scale up the current bench scale design to pilot scale, in order to study the feasibility and applicability in practical situations. The pilot scale testing will attempt to demonstrate the technical and economic viability of the technology such that it can overcome any industrial applicability limitations.