Ultrasonic Wastewater Treatment:
Application to Long-Duration Space Flight
In long term space travel, life support systems require a large level of water regeneration. Water consists of 84% of the mass required for crew supplies, which include oxygen, food, and water. In any mission, especially long term missions, the costs of the launch and storage of consumables are excessive. A major solution to storing or re-supplying fresh water is to recycle wastewater.
The goal of this project is to optimize the performance of an ultrasonic wastewater treatment system. When input in water at certain frequencies, high intensity sound waves will cause bubbles to implode violently. The violent cavitation will break down harmful chemicals in the surrounding regions, aiding in wastewater purification. To sustain long life and low costs for space travel, water recovery systems need to function with minimal power input; an important aspect of this project is to maximize the amount of cavitation with the least amount of power input.
This project is based around a test megasonic reactor, shown above. The reactor setup contains features such as an adjustable reflector piston, measurement ports and an ultrasonic collimator. The ultrasonic collimator's purpose is to produce the pressure fluctuations found in a sound wave and then focus the wave into a beam of plane sound waves. The opposite end of the reactor houses the adjustable piston (shown below) which has the ability to change the reactor geometry in length and end conditions with an array of reflectors and sound absorbing materials.
Current measurements are being made to monitor the entire reactor. This includes transducer impedance and power input as well as acoustic output with the use of a Precision Acoustics .075 mm Needle Hydrophone, shown below.
This has allowed for measurements of pressure over driving voltage at various frequencies and time. An example measurement is shown below. This information helps to determine the optimum running conditions of the transducer.
In addition to pressure measurements, theoretical modeling has been done to predict the effectiveness of changes to the transducer housing and reactor geometry. Show below is a plot showing theoretical data versus measured data.
The transducer modeling and pressure measurements have helped to tune the reactor cavity, increasing pressure with the least amount of power input.