New sensor detects contaminants in water in real time

Researchers from MIT and the Singapore-MIT Alliance for Research and Technology (SMART) Center for Environmental Sensing and Modeling (CENSAM) have developed a low-cost, compact, multiplatform-compatible sensor that provides a holistic solution for monitoring water resources. Harold Hemond, the William E. Leonhard Professor of Engineering at MIT, is a co-inventor of the sensor, called LEDIF (for LED-induced fluorescence).

“Having worked on this technology for the past five years, we are confident that our research will translate into a very powerful tool for industries and governments alike in safeguarding and protecting our environment and water resources,” Hemond says.

The sensor, which only needs to withdraw 10-20 ml of water, is capable of detecting, measuring, and 3-D mapping contaminants when implemented on autonomous platforms. Most water sensors currently available can only detect one substance at a time. This sensor has been able to successfully target up to six substances at a time during its trial phase.

“Beyond detection, its ability to provide a 3-D chemical mapping of the entire water body, which can be as large as two soccer fields, empowers agencies to better monitor the water situation on a large scale in the long term,” says Kelvin Chee-Loon Ng, research scientist at SMART CENSAM.

LEDIF uses three optical technologies to identify and quantify contaminants and natural substances in water: fluorescence, the emission of light by a substance that has absorbed light or other electromagnetic radiation; absorbance, expressed as a logarithmic ratio between the radiation falling upon a material and the radiation transmitted through a material; and scattering, the irregular dispersal of waves or particles.

The sensor is compatible with multiple platforms (e.g., autonomous surface vehicles, fixed platform, and portable mode of sensing) to provide both 3-D chemical mapping and long-term continuous monitoring. These applications are important in protecting water resources from industrial pollution, oil spills, and harmful algae growth.

LEDIF has also proven useful to fish farmers. The cake-sized sensor can warn farmers via SMS when chlorophyll levels spike or oxygen levels drop, and activate aeration systems to add oxygen to water. Its reduced cost ($19,800, compared to $31,600 for currently available sensors) makes the technology more affordable to fish farmers and government agencies alike.

LEDIF “has myriad applications, from detecting accidental and intentional pollution for implementing immediate counteractive action to quantifying natural occurring substances for research studies, providing a holistic solution capable of 24/7 surveillance of water resources,” says Ng.

The research is based on the paper “A multi-platform optical sensor for in situ sensing of water chemistry,” published by Hemond, Ng, and Schuyler Senft-Grupp in 2012 in the journal Limnology and Oceanography: Methods.

The AUV deployment conducted locally was done in collaboration with the Acoustic Research Laboratory of the Tropical Marine Science Institute at NUS (NUS ARL STARFISH). The research is funded by the Singapore National Research Foundation (NRF), Prime Minister’s Office, Singapore under its Campus for Research Excellence And Technological Enterprise (CREATE) program.

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