Research

The Yip Research Lab at Columbia University focuses on advancing technologies and innovations to address challenges at the nexus of water, energy, and the environment. Below are our active research projects:

 

Enabling High-Salinity Desalination with COMRO

Reverse osmosis is the most energy efficient desalination technology, but is limited to treat salinities up to seawater concentrations. Although thermally-driven methods can desalinate hypersaline brines, they are very energy-intensive and costly. We developed a novel cascading osmotically mediated reverse osmosis (COMRO) technology to extend the capabilities of membrane-based processes for high-salinity and/or high-recovery desalination. The innovation utilizes the novel design of bilateral countercurrent reverse osmosis stages to achieve substantial energy savings, and simultaneously depress the hydraulic pressure needed (schematic below).

 
  Vapor-pressure driven energy production schematic

Low-grade Heat Utilization

Low-temperature heat is widely abundant from natural and anthropogenic sources (e.g., low-grade geothermal and waste heat from industrial processes, respectively). However, converting the low-temperature energy to useful work is challenging and, at present, there are no established techniques to harness the thermal energy <80 ºC. We are exploring a novel membrane-based technology, co-pioneered by the Yip Lab, that is driven by the vapor pressure of water to access low-temperature heat for sustainable power generation (schematic on the left).

 
 

IEM Conductivity-Permselectivity Constraint

Ion-exchange membranes (IEMs) are used in electrodialysis for desalination. However, a fundamental limitation is the inherently low conductivity of conventional IEMs, leading to high internal resistance in the electrodialysis circuit and consequently causing elevated ohmic losses. While membranes with lower resistivity have been developed, their permselectivity (charge discriminating ability of the IEMs) are sacrificially decreased. We are concurrently studying the underlying mechanism(s) of the conductivity-permselectivity tradeoff (graph on right) and developing new membranes with high intrinsic conductivity while preserving permselectivity.

 
 

Sustainable Nutrient Recycling

Nitrogen is fixated and phosphorus is mined at considerable costs, and energy and chemicals are further consumed for nutrient removal in wastewater effluent to prevent environmental and public health problems. These current once-through approaches of nutrients utilization is unsustainable. We are developing novel decentralized technologies for cost-effective and high-yield recovery of nitrogen and phosphorus from source-separated urine, a nutrient-rich and practically-sterile stream. The new paradigm will enable transformation to a more sustainable circular economy model, as illustrated below. 

 
  Permeability-selectivity tradeoff

Permeability-Selectivity Tradeoff of RO Membranes

Seawater desalination allows us to tap into a practically infinite reservoir to meet our water needs. However, desalting seawater with reverse osmosis – the most efficient desalination technique – is still energy intensive. To enable a more fundamental understanding of the reverse osmosis process that can then guide energy-efficiency enhancements, we are studying the intrinsic transport mechanism of reverse osmosis, specifically the water permeability-salt selectivity tradeoff that governs all salt-rejecting polymeric membranes (graph on left).

 
 

Salinity Gradient for Clean Renewable Energy

The Gibbs free energy, ΔGmix, from mixing two solutions of different concentration is an overlooked energy source that can be harnessed for useful work production. Salinity gradient energy can be derived from natural origins, such as the mixing of fresh river water with salty seawater, or from anthropogenic and engineered sources (illustration on the right). We are at the forefront of developing leading salinity gradient technologies, such as pressure retarded osmosis and reverse electrodialysis, to utilize Gmix for sustainable energy production. Read our recent review in ES&T.

Salinity gradient energy  
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