Faculty Research Spotlight

Keisuke Ikehata, Ingram School of Engineering

Ikehata Lab Develops New Green Technology to Produce Drinking Water

“By completing this project, we will answer a critical question: what is the technical and economic feasibility of this green technology?”

Since ancient times, humans have relied on freshwater for drinking, cooking, manufacturing, agriculture, energy, and transportation. Unlike other natural resources, such as oil and gas, water does not undergo chemical reactions by itself before and after use. Water is water. Due to this unique property, water is an inherently renewable and reusable resource. However, rapid population growth and urbanization are causing major stresses on conventional water resources, including surface water and groundwater, both in terms of quality and quantity. Extreme climate events such as severe drought exacerbate water security issues in many arid and semi-arid regions, including Texas.

But there is good news—we have alternative water resources, including brackish water and reclaimed water. Brackish water is naturally saltier (>0.1%) than freshwater (0.05%) yet less salty than seawater (3.5%). Brackish water can be groundwater or surface water, and it is more abundant than freshwater. Reclaimed water is treated municipal wastewater, which is currently discharged to rivers, lakes, and seas. These are untapped local water resources. In particular, reclaimed water can be reused over and over within our community and eliminate the need for freshwater withdrawal and wastewater discharge. This process enables a fully circular economic system for water or, in other words, a system that eliminates waste and allows for continued use of resources.

For us to make these alternative waters potable, or drinkable, the salinity and other undesirable chemical and microbial contaminants must be removed by advanced treatment technologies. One such technology is reverse osmosis (RO). RO can remove more than 99% of dissolved chemicals and microorganisms and produce almost distilled water quality from lesser quality water like brackish and reclaimed water. Unfortunately, there is a downside. The RO process has limited water recovery due to the presence of silicon dioxide (silica) and calcium solubility, which results in a waste product called RO concentrate. To produce 1 million gallons of drinking water, 180,000 to 300,000 gallons of RO concentrate is generated. This resulting waste product prevents the wide-spread use of RO-based brackish water desalination and water reuse.

In our laboratory, we are developing a new green technology to enhance potable water production with the RO process using the power of diatoms and natural sunlight. Diatoms are a unique group of photosynthetic microalgae that have cells made of glass or silica. Naturally, they require silica, as well as nutrients and carbon dioxide, for growth. We have found that RO concentrate containing silica and nutrients is an excellent growth medium for diatoms. In other words, by treating RO concentrate with diatoms, we can remove silica, nutrients, and calcium. The treated water can be further desalinated by an additional RO process. This green technology requires little to no additional chemicals or energy. Instead, it produces algal biomass as a byproduct that can be harvested to produce biofuel, high-purity silica, and some specialty chemicals such as omega-3 fatty acids, while enhancing the water recovery to 95% and reducing final wastewater discharge to the environment. The applicability of this diatom-based technology has been demonstrated using RO concentrate samples from more than 10 full-scale facilities in the southwestern United States in a laboratory-scale.

Recently, I received a $250,000 award from the United States Bureau of Reclamation (USBR) through the Desalination and Water Purification Research (DWPR) Program to further develop this technology. The primary goals of this USBR-funded project are to determine long-term feasibility in a realistic, continuous-flow system and a lifecycle cost analysis. We are currently building a diatom-photobioreactor-RO system in our laboratory, which will be deployed at full-scale desalination and water purification facilities, such as San Antonio Water System (SAWS)’s H2Oaks Center and Orange County Water District (OCWD)’s Groundwater Replenishment Systems (GWRS). By completing this project, we will answer a critical question: what is the technical and economic feasibility of this green technology?

Our research has been supported by water utilities, such as SAWS, OCWD, the City of Wichita Falls, and El Paso Water. I believe that close collaboration with industry professionals, as well as federal agencies and academic researchers, is critical for successful engineering research projects like ours. Since joining Texas State in July 2019, I have received another USBR grant ($149,999) and a few external and internal grants (totaling $62,550) to investigate technological challenges in advanced water treatment and water reuse in collaboration with various industry and academic researchers. To learn more about my research, please visit my website.