Development of a wireless sensor network equipped with ISFET pH measurement technology to facilitate monitoring of microalgae cultivation processes

Abstract

In response to the continuing high demand for transportation fuel in the 21st century, microalgae cultivation has emerged as one technology that could supply fuel derived from renewable sources. To ensure proper health and optimal production in a microalgae culture, several environmental parameters such as temperature, pH, dissolved oxygen, nutrient content, and other factors should be monitored continuously. In a large scale cultivation facility, the problem of developing an appropriate instrumentation and control system is compounded by the need to collect sensor information from many different locations simultaneously.In this work, a wireless sensor network is proposed and demonstrated for the measurement of pH, dissolved oxygen, and temperature in a microalgae cultivation system. ISFET (Ion-sensitive field-effect transistor) technology is selected for pH measurement in this system, due to its advantages over traditional glass pH electrodes in durability and stability. The development of this sensor network is described in three main experimental phases: preliminary experimental work, a proof of concept experiment using a single pH sensor, and a performance evaluation using three pH sensors, one temperature sensor, and one dissolved oxygen sensor. The first two phases were designed for and tested at the NASA OMEGA (Offshore Membrane Enclosures for Growing Algae) project, and the third phase, the performance evaluation, took place in the open raceway ponds used for algae cultivation at the University of Nevada, Reno. A full description of each experiment is given, and the performance of the sensor network is described in terms of system reliability and drift characteristics.